Pumps & Systems

How to install a pump

2012-04-02T03:32:00.001+02:00

Hoping you find it useful

KSB Amarex Cooling Jacket Submersible Pump

2012-03-31T17:02:00.002+02:00

KSB Amarex Cooling Jacket Submersible Pump

Tectnical data (1)

2012-03-10T23:32:00.000+02:00

Here is some technical data about cables and pumps (protection and measurements )

Hoping you find it useful

Cable Limitations

Problems in Pump stations

Protection in submersible pumps

Please , if you took this, put our link as source.

continued........

Useful link

2012-01-21T16:24:00.001+02:00

This is a useful website , you will find explain for all what you want in electromechanical .

Electromechanical Library

http://electronics.wisc-online.com/Category.aspx?ID=15

Types Of Electric Motors (4)

2011-10-04T17:08:00.001+02:00

Induction motor

Induction motors are the most common motors used for various equipments in industry. Their popularity is due to their simple design, they are inexpensive and easy to maintain, and can be directly connected to an AC power source.

a. Components

An induction motor has two main electrical components :

􀂃 Rotor. Induction motors use two types of rotors:

- A squirrel-cage rotor consists of thick conducting bars embedded in parallel slots. These bars are short-circuited at both ends by means of short-circuiting rings.

- A wound rotor has a three-phase, double-layer, distributed winding. It is wound for as many poles as the stator. The three phases are wired internally and the other ends are connected to slip-rings mounted on a shaft with brushes resting on them.

􀂃 Stator. The stator is made up of a number of stampings with slots to carry three-phase windings. It is wound for a definite number of poles. The windings are geometrically spaced 120 degrees apart.

An Induction Motor (Automated Buildings)

c. Classification of induction motors:

Induction motors can be classified into two main groups :
􀂃 Single-phase induction motors. These only have one stator winding, operate with a single-phase power supply, have a squirrel cage rotor, and require a device to get the
motor started. This is by far the most common type of motor used in household appliances, such as fans, washing machines and clothes dryers, and for applications for
up to 3 to 4 horsepower.

􀂃 Three-phase induction motors. The rotating magnetic field is produced by the balanced three-phase supply. These motors have high power capabilities, can have squirrel cage or wound rotors (although 90% have a squirrel cage rotor), and are self-starting. It is estimated that about 70% of motors in industry are of this type, are used in, for example,pumps, compressors, conveyor belts, heavy-duty electrical networks, and grinders. They are available in 1/3 to hundreds of horsepower ratings.

d. Speed of induction motor

Induction motors work as follows. Electricity is supplied to the stator, which generates a magnetic field. This magnetic field moves at synchronous speed around the rotor, which in
turn induces a current in the rotor. The rotor current produces a second magnetic field, which tries to oppose the stator magnetic field, and this causes the rotor to rotate.
In practice however, the motor never runs at synchronous speed but at a lower “base speed”.
The difference between these two speeds is the “slip”, which increases with higher loads. Slip only occurs in all induction motors. To avoid slip, a slip ring can be installed, and these
motors are called “slip ring motors”. The following equation can be used to calculate the percentage slip :

% Slip =(Ns – Nb x 100)/( Ns)

Where:
Ns = synchronous speed in RPM
Nb = base speed in RPM

e. Relationship between load, speed and torque:

When the motor :
􀂃 Starts there is a high starting current and low torque (“pull-up torque”).
􀂃 Reaches 80% of the full speed, the torque is at its highest level (“pull-out torque”) and the current begins to drop.
􀂃 Is at full speed, or synchronous speed, the torque and stator current drop to zero.

Typical Torque-Speed Curve of 3-Phase AC
Induction Motors

Types Of Electric Motors (3)

2011-10-03T01:53:00.002+02:00

*AC Motors:

Alternating current (AC) motors use an electrical current, which reverses its direction at regular intervals. An AC motor has two basic electrical parts: a "stator" and a "rotor" . The stator is in the stationary electrical component. The rotor is the rotating electrical component
, which in turn rotates the motor shaft. The main advantage of DC motors over AC motors is that speed is more difficult to control for AC motors. To compensate for this, AC motors can be equipped with variable frequency drives but the improved speed control comes together with a reduced power quality. Induction motors are the most popular motors in industry because of their ruggedness and

lower maintenance requirements. AC induction motors are inexpensive (half or less of the cost of a DC motor) and also provide a high power to weight ratio (about twice that of a DC motor).

* Synchronous motor:

A synchronous motor is an AC motor, which runs at constant speed fixed by frequency of the

system. It requires direct current (DC) for excitation and has low starting torque, and synchronous motors are therefore suited for applications that start with a low load, such as air compressors, frequency changes and motor generators. Synchronous motors are able to improve the power factor of a system, which is why they are often used in systems that use a lot of electricity.

A Synchronous Motor

The main components of a synchronous motor are :

􀂃 Rotor.

The main difference between the synchronous motor and the induction motor is
that the rotor of the synchronous motor travels at the same speed as the rotating magnetic
field. This is possible because the magnetic field of the rotor is no longer induced. The
rotor either has permanent magnets or DC-excited currents, which are forced to lock into
a certain position when confronted with another magnetic field.

􀂃 Stator.

The stator produces a rotating magnetic field that is proportional to the frequency
supplied.
This motor rotates at a synchronous speed, which is given by the following equation:

Ns = 120 f / P
Where:
f = frequency of the supply frequency
P= number of poles

continued..............

Types Of Electric Motors (2)

2011-10-01T23:19:00.002+02:00

* Separately excited DC motor:

If the field current is supplied from a separate source it is a separately excited DC motor.

* Self excited DC motor: shunt motor:

In a shunt motor, the field winding (shunt field) is connected in parallel with the armature
winding (A) . The total line current is therefore the sum of field current and armature current.

Characteristics of a DC Shunt Motor

The following can be said about the speed of shunt motors:

􀂃 The speed is practically constant independent of the load (up to a certain torque after which speed decreases)

and therefore suitable for commercial applications with

a low starting load, such as machine tools
􀂃 Speed can be controlled by either inserting a resistance in series with the armature (decreasing speed) or by inserting resistance in the field current (increasing speed).

* Self excited DC motor: series motor:

In a series motor, the field winding (shunt field) is connected in series with the armature winding (A).The field current is therefore equal to the armature current.

The following can be said about the speed of a series motor:

􀂃 Speed is restricted to 5000 RPM
􀂃 It must be avoided to run a series motor with no load because the motor will accelerate uncontrollably
Series motors are suited for applications requiring a high starting torque, such as cranes and hoists . Characteristics of a DC Series Motor
* DC Compound Motor:

A DC compound motor is a combination of shunt and series motor. In a compound motor, the field winding (shunt field) is connected in parallel and in series with the armature winding (A) . For this reason this motor has a good starting torque and a stable speed. The higher the percentage of compounding (i.e. percentage of field winding connected in series), the higher the starting torque this motor can handle. For example, compounding of 40-50% makes the motor suitable for hoists and cranes, but standard compound motors (12%) are not .

Characteristics of a DC Compound Motor

Types Of Electric Motors (1)

2011-09-29T01:11:00.002+02:00

DC motors:

Direct-current motors, as the name implies, use direct-unidirectional current. DC motors are used in special applications where high torque starting or smooth acceleration over
a broad speed range is required.

A DC motor is shown has three main components:

�� Field pole. Simply put, the interaction of two magnetic fields causes the rotation in a DC
motor. The DC motor has field poles that are
stationary and an armature that turns on
bearings in the space between the field poles. A simple DC motor has two field poles: a
north pole and a south pole. The magnetic lines of force extend across the opening
between the poles from north to south. For larger or more complex motors there are one
or more electromagnets. These electromagnets receive electricity from an outside power
source and serve as the field structure.

�� Armature. When current goes through the armature, it becomes an electromagnet. The
armature, cylindrical in shape, is linked to a drive shaft in order to drive the load. For the
case of a small DC motor, the armature rotates in the magnetic field established by the
poles, until the north and south poles of the magnets change location with respect to the
armature. Once this happens, the current is reversed to switch the south and north poles
of the armature.

�� Commutator. This component is found mainly in DC motors. Its purpose is to overturn
the direction of the electric current in the armature. The commutator also aids in the
transmission of current between the armature and the power source.
power supply. It can be controlled by adjusting:

�� the armature voltage – increasing the armature voltage will increase the speed
�� the field current – reducing the field current will increase the speed.

DC motors are available in a wide range of sizes, but their use is generally restricted to a few
low speed, low-to-medium power applications like machine tools and rolling mills because of
problems with mechanical commutation at large sizes. Also, they are restricted for use only in
clean, non-hazardous areas because of the risk of sparking at the brushes. DC motors are also
expensive relative to AC motors.

The relationship between speed, field flux and armature voltage is shown in the following
equation:

Back electromagnetic force: E = KΦN
Torque: T = KΦIa

Where:

E = electromagnetic force developed at armature terminal (volt)
Φ = field flux which is directly proportional to field current
N = speed in RPM (revolutions per minute)
T = electromagnetic torque
Ia = armature current
K = an equation constant

continued..............

Different Types of Pumps

2011-09-25T00:30:00.006+02:00

Pumps are employed in numerous applications due to its efficient design and increased lifespan. However, frequent maintenance is required to maintain the performance and lifespan of the pumps. There are different types of pumps available that varies mainly in its working principle.

Some important pump types that are popular presently are listed below:

Centrifugal pumps:

These pumps are used most often in industries to transfer liquids through a piping system. These types of pumps are used for low pressure, high volume flow applications in the industry. The output of this pump mainly depends on the rotational speed of the driving source. It uses a rotating impeller to increase the pressure and flow rate of the liquid. Industrial pumps such as centrifugal pumps should be selected properly after analyzing the design and fabrication of the pump because small defects may prove to be very expensive in the future.

Rotary-gear pumps:

It is the simplest form of rotary pumps that consists of two gears laid out side-by-side with their teeth enmeshed. There are different types of rotary gear pumps that vary slightly in the mode of operation. To maintain a constant flow of water it is important to have many small teeth, while the large teeth make the pump to discharge water in an inconsistent basis.

Reciprocating-type pumps:

It is a type of Industrial pump that is used commonly in both air compressor and hydraulic applications operate on the reciprocating principle. To move the liquid in positive direction this pump requires a system of suction and discharge valves. These types of pumps were used for steam propulsion in the earlier days. There are many more benefits offered by this type of pump due to its effective design.

Hydromantic pumps:

This pump is used for water treatment system. It is also employed in industries to treat the waste waters that are produced as the byproduct during cleaning processes. This type of water pump needs proper maintenance, because problems such as contamination, rusting will occur if not frequently maintained.

Velocity pumps:

This type of pump is mainly used, when there is a need of high intensity flow of liquid. It uses kinetic energy to enhance the flow velocity. These types of pumps are found in industries, agricultural field and in large scale applications.

Valveless pumps:

As the name implies there are no valves in this pump to regulate the flow direction. It is used most often in engineering and biomedical sectors.

Due to continuous execution, industrial pumps are prone to frequent repairs. However, Industrial pump repair should be performed only by a well trained person, because repairing is not just resolving the present problem, but it also involves inspecting the entire pump to prevent frequent repairs. Moreover, leakage problems might occur in the water pumps. This leakage problem can be resolved by using mechanical seals or mechanical packing. Remember, you must choose the pumps after several considerations, because low quality pumps might not be reliable and its maintenance will be very expensive.

Industrial pump repair performed by expert professionals will increase the lifespan of the pump. The author has written numerous articles regarding industrial pumps and mechanical seals in the past.

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Electric Motors

2011-09-24T00:47:00.000+02:00

Electric motors are a kind of machine that serves the purpose of converting electrical energy into mechanical energy (such that can be used in a mechanical machine to turn cogs or levers etc). Electric motors normally operate through the interaction of
magnetic fields and conductors carrying currents in order to generate force, while some others use alternate methods of action such as electrostatic forces. The opposite use - of creating electrical energy from mechanical energy, is conversely caused by an alternator, a generator or a dynamo. Lots of types of electric motors can run as generators however and vice versa - for instance a starter/generator used in a gas turbine or traction motor in vehicles often perform both of these tasks through a single unit.

Electrical motors are found in a huge range of applications and are a crucial component of almost any mechanical device that it powered electrically as well as many smaller appliances for use around the home. These include industrial fans, pumps, blowers, hair dryers, computers, power tools, motors, cars, even wristwatches. With something like a computer you might not at first see how they are required to use electric motors - however when you think of how a disk drive works; by rapidly rotating the disk and reading the data off of it as this happens, it becomes apparent. The largest electrical motors are used for the propulsion of large ships and sometimes the rotor blades of air-born vehicles. They are also often used as pipeline compressors and these huge electric motors have ratings of millions of watts. Electrical motors can be classified in a number of different ways - through the source of their power, through their design and construction, through their use within a mechanism, or by the type of motion they give (normally rotary).

The principles of how mechanical force could be created by the interactions of magnetic files and electric current has been known as early as 1821 which allowed for the construction of the first such motors. Following this, electric motors of increasing efficiency were constructed through the 19th century. In order to keep up with this demand it was necessary for larger electrical generators and electrical distribution methods - so that the motor has thereby contributed so much of industry and development.

Some devices are similar to electric motors but are not referred to as such, for instance magnetic solenoids and loudspeakers. A loudspeaker fits the criteria of using electrical energy in order to generate some mechanical movement, but this is normally referred to as a transducer. Here the mechanical movement is not the end result of that particular unit - but rather the sound generated as a result.

It is possible also to power motors by other means - for example by using steam as was used in old steam trains, or by using petroleum or other fossil fuels. These types of motor however are not as desirable as electrical motors as they are more expensive to run, and as they create fuel emissions as a by-product that is harmful to our health and to the atmosphere.

Looking for cutting edge tools for a more durable, long lasting Electric Motors? Visit our website now to see our wide range of electirc motors that will enhance the performance of your energy production.

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Piston Pumps And Their Essential Facts

2011-09-22T22:25:00.005+02:00

For high pressure applications, there are a variety of pumps that are used and installed to manage the work for different set of industries. The pumps are widely used around the world and they are manufactured with unique skills of designing and engineering.

Finding their way in the most significant work sites, the pumps have proved its worth and are hugely accepted by all the industries. The quality thus plays a pivotal role while manufacturing and delivering them to clients and customers.

There are different types and models of pumps available that include Piston Pumps, Pressure Washer Pumps, Car Wash Pumps, Plunger Pumps, Triplex Piston Pumps and many more. With each serving various segments of industries, their unique features and functioning separates them. The pricing also varies as per usability.

While choosing your option, always go for renowned manufacturers and dealers. Never compromise on the efficiency and performance of pumps. The long lasting ad durable ones will always prove beneficial in the long run as they perform in the best possible manner at any given point.

Piston Pumps creates a reciprocating motion that tends to create pressure in the cylinder or barrel used. Piston Pumps utilizes a variety of data that comprises of different materials that may be stainless steel, metal, brass, bronze, iron and many others. The inner cylinder materials vary as per its usage and it can be customized to offer the best of results.

These pumps are very powerful and have wonderful capacity to complete the task and functions. Plunger Pumps are another form of reciprocating pumps and are also termed as pressure pumps. The main difference between Piston and Plunger Pumps lies in their mechanism used to transfer fluids.

For all your industrial cleaning purpose, Pressure Washer Pumps are used. They are highly effective and eliminate the usage of man power and waste of time as well. They are excellent when it comes to cleaning stubborn dirt, grit, grease etc. Various industries utilize these pumps for all types of cleaning. It directs a high pressure stream or jet of water that lets the dirt wash away instantly. Apart from this there are separate pumps available for car wash. They are known as Car Wash Pumps and also have the ability to clean dirt from the areas that are otherwise hard to access.

A.R. North America provide many industrial products with best quality like piston pumps, high pressure pumps, tri-plex plunger pumps, misting pumps, plunger pumps, car wash pumps, pressure washer pumps .

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An Overview on Plunger Pumps

2011-09-22T22:23:00.005+02:00

With state-of-the-art techniques and advanced mechanism, numerous kinds of pumps have revolutionized the functioning of specific industries. With the best of raw materials and methodologies, the pumps facilitate effective performance and production of products.

The types determine the particular tasks they perform for various industries. Be it chemical, mechanical, automobiles, manufacturing, pharmaceuticals and others, pumps are used everywhere to ease the work load and increase efficiency.

Amongst the variety of pumps, there are Piston Pumps, Pressure Washer Pumps. Car Wash Pumps and many more types that are available and can be used for varied purposes. Every type has specific models and they are utilized for the carrying forward the work for industrial sector. As the implementation is likely in industrial conditions, the manufacturing needs to be up to the mark. The pumps perform the best when they are robust, highly effective and sturdy enough to handle the circumstances and conditions.

When it comes to Plunger Pumps, they are basically known for their reciprocating motion. They are high pressure pumps that utilize cylindrical mechanism for creating the desired effect. The entire mechanism is safe and excellent for usage and follows a pattern for functioning.

The types of Plunger Pumps include Industrial Triplex Plunger Pumps, Car Wash Triplex Plunger Pumps, Medium Duty Triplex Plunger Pumps, Stainless Steel Triplex Plunger Pumps and many more. The models may vary from one manufacturer to the other.

Other than Plunger Pumps, Piston Pumps are also high pressure pumps that effectively involve itself in performing at its level best. Pressure Washer Pumps and Car Wash Pumps, as the name suggests are used for cleaning and maintaining Cars and their parts. The high pressure helps in cleaning every bit of dirt, debris and other hazardous elements.

While selecting any type of pump, always look for certification and authentication from the manufacturer. When you are investing on any of the pumps, it is a must to check the return on your investment.

A.R. North America provide many industrial products with best quality like plunger pumps, high pressure pumps, tri-plex plunger pumps, piston pumps, misting pumps, car wash pumps, pressure washer pumps.

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PD Pump Fundamentals, Design and Applications (Part Two)

2011-09-20T19:28:00.007+02:00

Editor's Note: This is the second in a series of five articles based on the Hydraulic Institute's new Positive Displacement (PD) Pumps: Fundamentals, Design and Applications e-Learning course.

Positive displacement (PD) pumps are used in a myriad of applications across multiple industries. Users have found them to be the solution to many specific pumping challenges; however, due to their size, simplicity and ruggedness, they often are not as well understood as other pump types.

Technologies within the extensive positive displacement family cover a broad range of horsepower, fluid and pressure applications. These products merit increased consideration in a user's pump selection process. To assist pump users with a proper understanding of definitions, applications, installation, operation, maintenance and testing procedures, the Hydraulic Institute publishes ten ANSI/HI Standards covering PD pumps including: Air Operated, Controlled Volume Metering, Reciprocating and Rotary.

ANSI/HI standards perform a vital function in pump industry commerce and serve important roles in minimizing misunderstandings in the marketplace. The Hydraulic Institute has extended its mission to include the development of a pump knowledge and education portfolio in response to member and pump user needs. Among the first key elements are a re-launch of the Centrifugal Pump e-Learning course and the development of a new Positive Displacement Pump course covering fundamentals, design and applications.

Last month, we provided an overview of the curriculum and an overview of positive displacement pumps, as well as the 12 benefits of PD pumps.

This installment will focus on "Positive Displacement Pump Hydraulics," which introduces the fundamental physical concepts and fluid properties that affect positive displacement pump selection and operation.

Since many of these properties affect positive displacement pumps differently than centrifugal pumps, it is critical to understand the interaction between the pump and the fluid, and how the operation of positive displacement pumps differs from centrifugal pumps. Without this foundation of fundamental principles, it would be difficult to effectively learn about the myriad of positive displacement pumps (to be presented in the next three articles).

On the most basic level, pumps are used to provide pressure and/or flow so that the pump user can accomplish a specified task. With this premise in mind, note that positive displacement pumps create flow, not pressure. The pressure on the pump is a function of the system's reaction to the delivered flow due to pipe losses, restrictions and elevation changes. See Figure 1 for an explanation of gauge versus absolute pressure; these two different reference points have caused confusion through the years.

Figure 1. Gauge versus Absolute Pressure

Since positive displacement pumps theoretically generate flow independent of discharge pressure, Figures 2 and 3 show how the delivered flow rate is affected by the differential pressure and speed. This is a fundamental difference between positive displacement pumps and centrifugal pumps. The delivered flow rate is the theoretical flow rate minus the internal slip of the pump. The slip is the internal leakage that occurs in the pump due to clearances, viscosity and differential pressure, and will vary between pump types and applications.

Figures 2 and 3.

Of course, nothing comes for free, and every pump requires a certain amount of power to perform work. The pump input power is comprised of the theoretical liquid horsepower and the internal power losses at the operating point. The theoretical liquid horsepower is the work done to move the theoretical volume of fluid from inlet to outlet pressure and is solely based on the physical dimensions of the pumping elements, the operating speed and the differential pressure. On the other hand, the internal power losses account for the mechanical and viscous losses that occur as the pump operates. It is typical that the mechanical loss is the major component when operating at low viscosities, while the viscous loss is larger at high viscosities. These losses in turn affect the overall efficiency of the pump.

Fluid characteristics play a major role with positive displacement pumps since most of these pumps are used to handle products other than water. The most important fluid property is viscosity, which is the fluid's ability to resist a shearing force, or how easily the fluid will flow. Viscosity affects pump selections due to its impact on operating speed, allowable differential pressure, suction capability and input power. Since viscosity is typically temperature dependent, it is important to know what the viscosity values will be over the entire operating temperature range, from cold start-up to maximum upset condition. Viscosity can be expressed in many different units, the most common being SSU, SSF, centipoises (cP) and centistokes (cSt). Units depend on which viscometer instrument was used to evaluate the different fluids. These values are tabulated in many texts, and several examples are provided in the module (see sidebar for more information).

Along with viscosity, it is essential to understand how a fluid reacts to being pumped. A fluid can have a constant viscosity (at a particular temperature and pressure) regardless of the rate of shear (known as a Newtonian fluid), or the viscosity can vary with the shear rate and shear stress (known as a Non-Newtonian fluid). Non-Newtonian fluids are divided into five types: plastic, pseudo-plastic, dilatant, thixotropic and rheopectic. The first three are time independent since the viscosity is simply a function of the shear stress, while the last two are dependent on both time and shear stress. To accurately determine the viscosity of non-Newtonian fluids, it is usually necessary to take measurements at several points. If the apparent viscosity is not accurate, it can result in an improper pump selection.

Beyond viscosity, several other fluid characteristics relate to positive displacement pump selection and operation. One of these characteristics is vapor pressure. The vapor pressure is the absolute pressure at which a liquid changes to a gas (see Figure 4). The primary influence of vapor pressure is on the Net Positive Inlet Pressure (NPIP) required for the pump. The NPIP is the absolute pressure above vapor pressure required to get the fluid into the pumping elements. As can be seen with a fixed inlet pressure, the higher the vapor pressure, the less pressure available to get the fluid into the pump.

Figure 4. Vapor pressure at 60-deg F in PSI absolute

Net Positive Inlet Pressure plays a key role in pump selection and system design. Since pumps cannot pull fluid into them, they rely on the difference in pressure between the liquid source and the pump inlet to get the product into the pump. Sufficient pressure must be available at the pump inlet to fill the pumping chambers and prevent gas from being released from the fluid. Therefore, the inlet pressure available must always be greater than the inlet pressure required.

The inlet pressure available is a system characteristic that is determined from the following factors: atmospheric pressure, elevation of the fluid level (above or below the pump inlet), inlet line friction losses, vapor pressure, and in the case of reciprocating pumps, acceleration head. Acceleration head, a unique factor for reciprocating pumps, is the pressure required to accelerate the liquid column at the beginning of each stroke. Depending on the suction line length, average line velocity, pump rotational speed, number of pistons and liquid elasticity, the acceleration head can easily be the largest factor of the available inlet pressure calculation.

The inlet pressure required is a pump characteristic that the manufacturer calculates. It is affected by such factors as pump design, viscosity and speed. Once the available inlet pressure is known, it can be compared to the inlet pressure required by the pump to determine if the pump will operate properly. Sometimes several iterations between the user and supplier are required to select the correct pump.

Once all of the important factors affecting pump selection are understood, hydraulic selection becomes easier. However, other factors external to the pump need to be evaluated to ensure that the entire pump system is properly selected. These factors include environmental conditions such as installation location and electrical requirements, the control philosophy of how the pump will operate, the utilities available and the operating energy requirements.

All of these factors flow into the life cycle costs of a pumping system, which nearly always exceed the initial cost of the machine. The life cycle costs, which can be fully explored in the Hydraulic Institute publication, Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping Systems, are explained in detail and consist of the initial cost plus such items as installation, power, operation, maintenance, downtime and environmental considerations.

This information on PD hydraulics forms the knowledge base for PD pumps (and the HI e-Learning course), so users can properly evaluate any pumping system and select the best technological solution based on the entire spectrum of process conditions and system limitations.

In future issues, look for articles devoted to specific positive displacement pump technologies:

Rotary Pumps, including: Vane, Rotary Piston, Flexible Member, Lobe, Gear, Circumferential, Piston, Progressing Cavity, Timed Screw, Untimed Screw
Reciprocating Pumps, including: Power, Direct Acting, Power Diaphragm, Air Operated Double Diaphragm, Air Operated Piston
Metering Pumps, including: Torque Sources, Drive Mechanisms, Capacity Control, Liquid End Reviews

With the development of the new e-Learning course, Positive Displacement Pumps: Fundamentals, Design and Applications, HI has again reached a new level in its role of serving member companies and pump professionals. Recently debuted by Hydraulic Institute, PumpLearning.org was created to serve as the ultimate "go to" center for information on pumps and pumping technologies, and provides knowledge seekers with a panoply of sources and opportunities to gain state-of-the-art intelligence. Offerings presented on the new user-focused website include: e-Learning Courses (now featuring HI's latest course, Positive Displacement Pumps: Fundamentals, Design and Applications, and the updated and soon-to-be released course, Rotodynamic [Centrifugal] Pumps: Fundamentals, Design and Applications), webcasts, conferences and special programs jointly sponsored by renowned industry experts. The site is constantly updated to present users with the latest news, activities and connections to the industry.

The Hydraulic Institute is the largest association of pump producers in North America and the "value-add" standard-setting resource for member companies and pump users worldwide.

This course has been created by renowned industry experts from the following HI Sponsor companies:

ARO/Ingersoll Rand

Colfax-IMO & Warren Pump

CLYDEUNION

Flowserve Pump Division

Grundfos Pumps Corporation

Iwaki America Incorporated

Leistritz Corporation

LEWA Inc.

Milton Roy Americas

Moyno, Inc.

Roper Pump Company

Siemens Water Technologies

Written by Hydraulic Institute Positive Displacement Pump Sponsors

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PD Pump Fundamentals, Design and Applications (Part One)

2011-09-20T02:39:00.001+02:00

Editor's Note: This is the first in a series of five articles based on the Hydraulic Institute's new Positive Displacement (PD) Pumps: Fundamentals, Design and Applications e-Learning course.

Positive displacement pumps are used in a myriad of applications across multiple industries. Users have found them to be the solution to many specific pumping challenges; however, due to their size, simplicity and ruggedness, they often are not as well understood as other pump types.

Technologies within the extensive positive displacement family enable coverage of a broad range of horsepower, fluid and pressure applications. These products, therefore, merit increased consideration in a user's pump selection process. To assist pump users with a proper understanding of definitions, applications, installation, operation, maintenance and testing procedures the Hydraulic Institute publishes ten ANSI/HI Standards covering PD pumps including: Air Operated, Controlled Volume Metering, Reciprocating and Rotary.

Figure 1. Positive Displacement Pump Family Tree.

ANSI/HI standards perform a vital function in pump industry commerce and serve important roles in minimizing misunderstandings in the marketplace. The Hydraulic Institute, however, has extended its mission to include the development of a pump knowledge and education portfolio in response to member and pump user needs. Among the first key elements are a re-launch of the Centrifugal Pump e-Learning course and the development of a new Positive Displacement Pump course covering fundamentals, design and applications. These, and future courses, will be hosted within HI's new educational portal, http://www.pumplearning.org/.

Curriculum Overview

The PD pump e-Learning course is a five module internet-delivered learning program designed to provide users with broad and comprehensive knowledge of positive displacement pumping technologies. Material is highly visual and interactive, designed to allow students to take full advantage of the latest internet technology.

Content is arranged in independent modules with each one focusing on markets and applications, as well as providing basic recommended technical terms and fundamentals for an understanding of positive displacement pump hydraulics. The first two modules in the series are:

Why Positive Displacement Pumps
Positive Displacement Pump Hydraulics

Three other modules are each devoted to a specific positive displacement pump technology. To enhance the users learning experience, these modules rely heavily on color photographs of pumps and pumping installations.

Rotary Pumps, including: Vane, Rotary Piston, Flexible Member, Lobe, Gear, Circumferential, Piston, Progressing Cavity, Timed Screw, Untimed Screw
Reciprocating Pumps, including: Power, Direct Acting, Power Diaphragm, Air Operated Double Diaphragm, Air Operated Piston
Metering Pumps, including: Torque Sources, Drive Mechanisms, Capacity Control, Liquid End Reviews

Multiple 1500-hp Rotary Pump Heavy Crude Loading Station.

Modules are designed for either self-instruction, instructor lead courses by the twelve PD pump company sponsors or as HI sponsored webinars. Each module, designed to stand alone or combined with others, includes an examination and completion certificates suitable for submittal for PDH or CE credit. [af1]

Pump education courses typically highlight rotodynamic (centrifugal and vertical) pumps, and a good knowledge of that technology is helpful in understanding positive displacement pumps. Many subjects are common, but certain terms and concepts are unique because PD pumps involve an entirely different technology.

Centrifugal vs. PD Pumps

In simple terms, a centrifugal pump impeller moves a stream of liquid from the pump suction to a discharge cone where velocity is gradually decreased and converted to pressure energy. A positive displacement pump, however, moves a set volume of liquid. Pressure is obtained as liquid is forced through the pump discharge into the system, thereby converting energy to pressure.

One example of this principle is demonstrated by reciprocating motion where the movement of a piston forces liquid out of a closed cylinder, which has (inlet) suction and discharge valves to control flow. This forms one of the major PD technologies, reciprocating pumps. In portions of their operating range, reciprocating pumps are the single technology that can successfully provide the necessary pumping solution.

Rotary pumps constitute the second major positive displacement category in which a pumping chamber and a pumping element are actuated by the relative rotation of the drive shaft to the casing. This family is distinguished by having no valves on the inlet or discharge. These types of pumps are available in a number of different pumping principles, each with its own features and benefits that provide specific pumping solutions.

The third major category is controlled volume metering pump (CVMP). These types of pumps are often known as chemical injection feed pumps or dosing pumps. Essentially, these are reciprocating positive displacement pumps configured to accurately dispense a set volume of liquid in a specified time period. They may include one of several types of mechanisms for varying the effective displacement. These types of pumps are used in applications requiring highly accurate, repeatable and adjustable rates of flow.

Pumping Solution Products

Technologies within PD pumps are often called "pumping solution products," as they perform that function for applications across a broad range of process conditions. For example, rotary PD pumps can handle highly viscous product (3,000,000 SSU) while reciprocating pumps handle water thin liquids. PD pumps handle flow rates from less than 1-gpm to 15,000-gpm, and pressures from a few psi to 70,000-psi and higher. PD pumps, at constant speed, are constant flow rate devices, but centrifugal pumps are variable flow rate devices. Generally, PD pumps require some type of pressure protection, and certain designs will require pulsation control. System design requirements are different from centrifugal pumps.

PD pumps may be found almost anywhere, but a generally accepted view is that 90+ percent go into applications within these top six industrial market segments:

Oil and Gas
Water and Wastewater Treatment
Chemical
Food, Beverage and Pharmaceutical
Power
General Industrial (Marine/Medical/OEM)

Many of these industries represent multiple markets. Oil and gas, for example, has distinctly different applications for PD pumps across its segments: exploration, production, pipeline, processing and distribution marketing.

The food and beverage market is another key positive displacement market with multiple segments such as beverage, bakery, confectionary, dairy and meat packaging.

Selection Consideration: Twelve Benefits of PD Pumps

In many markets, there are applications that clearly should be positive displacement and applications that are clearly centrifugal. It is important for the user or specifying engineer to recognize, however, that there are also a broad range of applications where both types should be considered and selection should be based on the results that the user desires.

In such consideration, there are reasons why positive displacement pumps make an ideal solution to specific pumping requirements. Twelve suggested reasons to use PD pumps are summarized below, grouped by fluid characteristics, process conditions, environmental system requirements and flow control. Additionally, Figure 3 provides a matrix of these 12 reasons compared to the primary markets of PD pumps. Some may surprise you.

Figure 3. Matrix Market Application vs. Desired Pump Characteristics

Fluid Characteristics

High Viscosity

Selected rotary technologies and air operated piston pumps easily handle highly viscous fluids. Due to high friction losses in centrifugal pumps, their flow rate and efficiency start to drop above 500 SSU. Flow and efficiency in a rotary pump, however, typically increase with viscosity. PD pumps can handle fluids with viscosities of several million SSU.

Low and Variable Viscosity

PD pumps, such as vane or air operated double diaphragm (AODD), are often applied on very thin fluids. Other liquids, such as oil, have viscosities that vary with temperature. With variable viscosity liquids, a moderately small change in viscosity may have a large effect on centrifugal efficiency but little effect on PD pump efficiency.

Low Shear Pumping Required

In many fluid applications, liquid shear is not a problem; however, it is critical in some applications. PD pumps excel in the handling of shear sensitive fluids.

Solids Handling Capability

Progressing cavity pumps handling high solids content sludge in a waste treatment plant and reciprocating pumps are applied on coal slurry pipeline with solids contents as high as 40 percent by weight. This is sometimes a surprising PD pump characteristic, but widely varied applications serve as examples.

Multi-Phase Flow

A constant source of liquid is a centrifugal pump requirement, but unfortunately all processes do not provide such constant sources. If there is insufficient liquid, a gas bubble forms in the suction and causes loss of prime (the pump stops pumping). PD pumps, on the other hand, are capable of handling a high percentage of air or gas entrainment.

Process Condition

High Pressure

Beyond the range of centrifugal pumps are many chemical, sandblasting and high-pressure water-cutting applications where PD pump technology dominates. Figure 4 provides an overview of the pressure and capabilities among pump technologies.

Figure 4. Technology Flow Pressure Range Chart.

Low Flow

Flow below 100-gpm and above 200-psi provides excellent application opportunities for PD pump technology.

Efficiency

For viscous fluids where both PD and centrifugal pumps can operate, PD pumps can often be 10 to 40 points more efficient than centrifugal pumps.

Combination of High Pressure/Low Flow-Efficiency Demand

Any of the previous three characteristics individually are a reason to use PD pumps; however, in applications where all of these conditions occur simultaneously, a PD pump solution is ideal.

Figure 4 provides an overview of the pressure and capabilities among pump technologies.

Environmental System Requirements

Sealless Pumping (No Shaft Seal)

Magnetic drives and canned motor pumps are available in PD pump designs. The requirement is also met by designs where the pumping environment does not have a shaft penetration, such as peristaltic or diaphragm pumps.

Self-Priming and Inlet Conditions

The ability to self-prime is a useful feature for PD pumps as it allows substantial flexibility in system layout and eliminates the need for suction priming systems. PD pumps are self-priming, have excellent suction lift capabilities (raising liquids on the suction side) and are capable of drawing down to near vacuum.

Flow Control

Constant Flow Against Variable System Pressure

At a constant speed, PD pumps deliver practically constant flow. Flow is constant even if the system pressure varies, which is a desirable condition in certain systems.

Accurate Repeatable Measurement

Since a PD pump is a constant flow device, certain designs that limit slip are ideal for metering fluids in or out of systems. This application, of course, requires accuracy and repeatability. It also may need flow variation, which is typically obtained mechanically or electronically by speed variation.

There is a universe of standard PD solutions in addition to the bakers dozen described here. As these pumps also must meet many other requirements, manufacturers provide products with special options such as jacketing, non-corrosive materials and built-in pressure relief valves.

Some PD units have duty cycle limits that users are advised to investigate. It is important to note PD pumps are constant torque devices. In variable speed applications, VFD drives must be rated with that understanding.

Fundamentals of PD Pumps: Online Learning

Extensive material is provided in the HI PD pump e-Learning modules to allow for expanded and detailed understanding of these items and applications. The course contains more than 500 screens of information in five separate modules for 10 hours of credit work for those seeking PDH or CE credit.

With the development of Positive Displacement Pumps: Fundamentals, Design and Applications, HI has again reached a new level in its role of serving member companies and pump professionals. The entire five-module course is now available at its website. Recently debuted by Hydraulic Institute, PumpLearning.org was created to serve as the ultimate "go to" center for information on pumps and pumping technologies, and provides knowledge seekers with a panoply of sources and opportunities to gain state-of-the-art intelligence. Offerings presented on the new user-focused website include: e-Learning Courses (now featuring HI's latest course, Positive Displacement Pumps: Fundamentals, Design and Applications, and the updated and soon-to-be released course, Rotodynamic [Centrifugal] Pumps: Fundamentals, Design and Applications), webcasts, conferences and special programs jointly sponsored by renowned industry experts. The site is constantly updated to present users with the latest news, activities and connections to the industry.

Hydraulic Institute is the largest association of pump producers in North America and the "value-add" standard-setting resource for member companies and pump users worldwide.

This course has been created by Positive Displacement Pump experts and HI Sponsors:

ARO/Ingersoll Rand
Colfax-IMO & Warren Pump
Flowserve Pump Division
Grundfos Pumps Corporation
Iwaki American Corporation
Leistritz Corporation
Milton Roy Company
Moyno, Inc.
Roper Pump
Siemens Water Technologies
Union Pump
http://www.pump-zone.com/pumps/rotary-pumps/pd-pump-fundamentals-design-and-applications-part-one.html

Dry Split Seal a Solution for High-Temperature Mixing Tanks

2011-09-19T20:33:00.000+02:00

Use of bearing sleeve material helps the long shaft run true.

Chemical attack is a destructive force in any high-tech manufacturing process. For TIMET’s Las Vegas, Nev., plant, the force was presenting itself during the high temperature mixing of titanium tetrachloride (TiCl4), known in the industry as TiCL.

TIMET is a supplier of high-quality titanium metal products. With its unique combination of strength, light weight, corrosion resistance and other metallurgical properties, the company’s titanium is used in hundreds of diverse aerospace, industrial and emerging applications.

TIMET searched for a consulting company to determine the best way to seal the shaft entry point in its high-temperature mixing tanks where the TiCL was batched. The aggressive chemical has a tendency to flash off and form a potentially noxious vapor and toxic white cloud, making worker safety an issue. In addition, when the chemical contacts water, it can become hazardous.

The Timet Mixer

A mechanical seal installed on one of the Philly mixers

The Challenge

How could TIMET develop a more effective way to seal each tank? Two major challenges loomed. The first was to determine how to maintain a strong, positive seal. The seal design was of paramount importance, and critical metallurgy issues existed as well.

Previously, the system employed a double mechanical seal with a mineral oil barrier fluid that provided lubrication between the inboard and outboard faces. The customer had planned to use a split mechanical seal because it offered a quick replacement time.

However to enhance the operation, a dry seal was needed. The problem? No one made a dry running seal.

The second obstacle was the length of the shaft. The mixing operation used a long, unsupported shaft, which created excessive run out at the mechanical seal.

The Solution

The company recommended that DuPont Vespel CR6100 be installed as the bearing sleeve material. The additional sleeve would help the long shaft run true and minimize shaft run out at the mechanical seal.

The typical clearance for a steady bearing for a shaft of this diameter is 0.0020 side to side for a total of 0.040-inch clearance. The Vespel sleeve bearing that was used had been machined for a total clearance of 0.007 inch to 0.010 inch. This reduction in clearance between the bearing and shaft was so dramatic, the Vespel sleeve bearing acted as a primary seal and minimized shaft run out well below acceptable levels.

The reason that the clearances could be reduced to this level had to do with the coefficient of thermal expansion (CTE). Dupont Vespel 6100’s thermal growth is confined to the Z direction (along the shaft) while keeping the growth in the X and the Y directions extremely low. In addition to the unique CTE properties of the material, Vespel is chemically inert to the TiCL and can operate without lubrication because of the very low coefficient of friction of this material.

The consulting company redesigned the mixer stuffing box to accommodate a John Crane Type 3740D using the Vespel sleeve bearing, one of the first dry running beta split seals installed by John Crane.

Final Analysis

During the final assembly of the bearing and split seal system, the engineering team experienced a slight dimensional issue that initially prevented them from installing the seal. As a result, time was short and the mixer had to be placed back into service. Both TIMET and the engineering team were pleased to see that the Vespel sleeve bearing alone was sealing nearly 100 percent of the vapor.

The engineering team and plant officials decided to leave the unit in operation without the split seal while the minor dimensional issue was addressed. At the first opportunity, the dry running split seals were installed on the mixers to ensure that the vapor leakage would be completely contained.

The Vespel sleeve bearing demonstrated reduced run out as a temporary seal. The team made the dimensional modifications to the system and standardized all the components.

The adjustments made to the mixer stuffing box.

Conclusion

Several vessels within the plant that were experiencing problems similar to the first vessel were fitted with a dry running split seal in their mixers as well as Dupont Vespel 6100 sleeve bearings, resulting in the containment of all TiCl vapor. The split seal, which was installed during a very brief outage, operated without a hitch (a double seal would have required days versus hours to install).

The cost of running the enhancements to the TIMET system reduced downtime and the requirements for complex seal support systems. The fact that mineral oil barrier fluid was not required with the split seal, as it is with a double mechanical seal, was a major enhancement.

This saved money, specialized seal support equipment to regulate flow and pressure to the seal and reduced the amount of time required to replace mechanical seals in the future.

For all the tanks, the combination of the dry running split seal and the Dupont Vespel sleeve, along with other modifications, resulted in total success. As a result of the work completed to date, the engineering team members are incorporating all the new modifications as standard offerings for new mixers that the company purchases for its plant. The assessment of the mixers’ needs began in late 2010, and final installation on both tanks will be completed by the end of 2011.

Written by Vic Lundberg, Quadna, a DXP Company

http://www.pump-zone.com/seals/mechanical-seals/dry-split-seal-a-solution-for-high-temperature-mixing-tanks.html

The Vital Role of Valve Springs in Power Pumps

2011-09-18T15:24:00.001+02:00

When calculating maximum speed, power pump valve springs are an under-valued factor.

History tells us that a fellow named Ctesbius built a reciprocating power pump in about 150 B.C. on the Nile1. It sat near the surface of the river, was driven by an undershoot waterwheel and pushed river water into an irrigation system. During the more than 2,000 years since, it seems we have struggled to analyze the valve dynamics of this basic machine.

I have often wondered why reciprocating power pumps cannot run as fast as reciprocating compressors. The power ends look the same and are similar to internal combustion engines, which also run much faster. It, therefore, must be a fluid end limitation.

Could it be only the difference in the densities of the different fluids, and if so, what is the mathematical relationship between the fluid density and the maximum acceptable running speed?

Figure 1. (left) A three-inch stroke, triplex power pump showing the springs on both valves.

Early in my exposure to power pumps, I learned that some experienced users had established maximum allowable speeds for power pumps, based on stroke length. After a few years of wrestling field problems with power pumps running at high speeds, I established my own set of maximum speeds, based strictly on field observations. My standards were also based on stroke length.

These standards were published in References 10 and 11. I’ve never been totally comfortable with these standards, wondering if there could be an engineering basis for establishing maximum speeds.

The Role of Valve Springs

After observing a number of pumps, in operation on test stands and in the field, I concluded that the seemingly-innocuous valve spring plays a major role in establishing the maximum speed and is, in fact, the most important part of a power pump. Strong springs push the valves onto the seats near the ends of both the suction and discharge strokes, resulting in a smooth, quiet pump which produces acceptable pulsations.

On the other hand, weak valve springs allow the valves to be off the seats so far that, as the plunger reverses, the valves are slammed, by the reverse flow of pumpage, onto the seats. This results in a noisy, excessively-pulsing pump. The resulting hydraulic shocks shake pipe, damage instruments, damage drive components (such as gears and couplings) and damage pump components (such as valves and packing). The excessive pulsations can also cause cavitation. I have solved a number of field problems caused by excessive pulsations by installing semi-arbitrarilly-selected stronger valve springs in the pumps.

For years, I searched, numerous technical documents for equations that would provide the requirements for valve springs that would result in a smooth-running pump. The Worthington group (References 2, 3, and 4) provided significant information on valve characteristics, but their equations yielded inconsistent results.

Finally, after searching for more than 40 years and after many calculations and analyses, I discovered the mathematical models (equations) which seem to accurately describe power pump valve dynamics. Those models were presented in a technical paper at the 2009 International Pump Users Symposium (Reference 13) and in an article that appeared in the COMPRESSOR Tech Two magazine in July 2010 (reference 14). The models are verified by test results, as shown by the examples in the article.

Figure 3. (left) A bevel-face, wing guided valve
The above documents explain how to calculate the required spring force for a particular set of physical and operating parameters or how to calculate the actual valve lift for a valve assembly in a particular application.

After writing these documents, I began to wonder…rather than calculate the spring force required (which is based partially on pump speed), can I use the equations to calculate the maximum speed of a power pump, based partially on the maximum available spring force? The maximum available spring force is a function of the maximum allowable shear stress in the spring and the spring dimensions. Equation 6 (detailed later in the article), is the resultant which ties it all together.

Equation 6 combines the equation that calculates the spring force required to obtain smooth pump operation with the equation that relates spring force to spring stress, wire diameter and spring mean diameter. Using a number of half-reasonable approximations for spring dimensions and stress, an equation was also obtained which enables the calculation of the maximum speed for a “typical” power pump. Examples are shown.

Types of Valves

The equations in this article apply to the more common pump valves as shown in Figures 2 & 3. The pumpage flows radially outward between the valve (disc) and seat seating surfaces. Both the flat face disc valve and the bevel face, wing guided valve are covered. Different equations are required for a valve if the flow is radially inward, or if the valve is double ported.

Figure 2. (right) A flat-faced, single-port, outward flow disc valve

The Preferred Valve Lift at a 90-Degree Crank Angle (L90)

Previous attempts at analyzing power pump valve dynamics, as seen in References 2, 3, and 4, were based on the maximum acceptable valve lift being proportional to the diameter of the valve. (The larger the valve, the higher it could be allowed to lift.) Such a relationship resulted in large valves that slammed onto seats and small valves that were unnecessarily limited in their lifts. My discovery was that the maximum acceptable valve lift, for smooth operation, is entirely a function of the pump speed (rpm of the crankshaft). It is independent of valve size. That simple concept formed the basis for all the analyses that followed.

Nomenclature

As   Flow area through valve seat (wings & webs are ignored), ft² (m²) = (π/4)(D₃² – D₂²)

A₂   Valve area acted upon by P₂, ft² (m²) = (π/4)(D₃² – D₁²) = A₄ - A₃A₃   Seating surface area exposed to P₃, ft² (m²) = (π /4)(D₄² – D₃²)

A₄   Area of top of valve (that exposed to P4), ft² (m²) = (π /4)(D₄² – D₁²)

c   Orifice coefficient of valve “escape” area
d   Diameter of wire in the helical valve spring, ft (m)
D_m   Mean diameter of the helical spring, ft (m)
D_P Diameter of plunger or piston, ft (m)
D₁   Diameter of hole in center of valve disc, feet (m)
D₂ OD of inner seating surface, feet (m) (ID of port opening in seat)
D₃   ID of outer seating surface, feet (m) (OD of port opening in seat)
D₄ OD of valve outer seating surface, ft (m)
F_S90   Spring force on valve when crank angle, θ, = 90 degrees, lb (N)
g   Acceleration of gravity, 32.2 ft/sec² (9.8 m/s²)
K   Whal stress correction factor for a helical spring made of round wire
K_c    Clinging coefficient 
       for an OD-flow valve = ((₄/D₃)² + (D₃/D₄)² - 2)/8π(sinα)² 
      for an ID-flow valve = (2 - (₂/D₁)² - (D₁/D₂)²)/8π(sinα)²K_i Coefficient of inertial impact of pumpage on upstream side of valve
L_s Stroke length of plunger, feet (m)
L₉₀   The lift of the valve at about 90 degrees of crank rotation, ft (m)
N   Rotative speed of pump crankshaft, rev/min
P₁   Stagnation pressure upstream of valve assembly, lb/ft² (Pa)
P₂   Static pressure acting on upstream disc area A², Ib/ft² (Pa) = P₁ - ρ(V_S)²/2
P₃   Static pressure in lift flow area between valve and seat, lb/ft²(Pa)
P₄   Stagnation pressure downstream of valve assembly, lb/ft² (Pa)
Q₁   Flow rate created by plunger at mid-stroke (the peak) = Q₉₀, assuming pure sinusoidal movement of plunger, ft³/sec (m³/s) = π²NL_sD_P²/240
Q₂   Instantaneous flow rate created by the plunger (plunger volume displacement), ft³/sec (m³/s) = (Q₁)(sin θ)
S_S   Shear stress in the wire of the helical spring, lb/ft² (Pa)
t   Time increment, sec = 30θ/πN (for θ in radians) = θ/6N (for θ in degrees)
V_S   Velocity of pumpage moving through seat, ft/sec (m/s) = (Q₂)/(A_S)
V_V   Velocity of valve, ft/sec (m/s)
W₁   Weight of valve (in air), lb (N)
W₂   Weight of valve if axis is vertical, less the bouyant effect of the pumpage, lb (N) = W₁(1 - W₃/W₄)  (if axis is horizontal, W₂ = 0)
W₃   Specific weight of pumpage, lb/ft³ (N/m³) = ρg
W₄   Specific weight of valve, lb/ft³ (N/m³)
α   Angle between valve seating surface and valve axis, degrees
θ   Angle of crank rotation from start of stroke of plunger, radians = ωt = πNt/30
ρ   Density of pumpage, slugs/ft³ (lb-s²/ft⁴) (kg/m³) = W₃/g

ω   Angular velocity of pump crankshaft, radians/sec = πN/30

Although the maximum valve lift (except for the case when a late opening valve overshoots upon opening) occurs at angles only near 90 degrees of crankshaft rotation, the symbol L90 is used here to represent this value. For smooth valve action and minimal hydraulic shock, the following has been established, from field experience, and gleaned from References 3, 6, and 7, as the maximum plunger-mid stroke lift of the valve:

Equation 1
L₉₀ = 6/N feet (72/N inches) (1800/N mm)

This equation results from the need for the valve to impact the seat, upon closing, at a velocity low enough to prevent damage to the valve and seat, and to minimize hydraulic shock. This limit applies to both the suction and discharge valves. (The suction valve should not lift higher than the discharge valve.)

The Spring Force Required at 90-Degree Crank Angle
As shown in Reference 13, the following spring force is required, when the valve is at L₉₀:

Equation 2
F_S90 = ρA₂(Q₁/cπD₃ L₉₀sin_α)²/2 – ρ(Q₁/A_S)²A2/2 – K_CρQ₁²/ L₉₀²+ K_iρQ₁²/A_S– W₂ + W₁L₉₀(πN/30)²/g

On the right side of the equation, the first term represents the pressure drop through the lift area and is the predominant term at higher pump speeds. The second term represents the pressure drop within the valve seat caused by the velocity head. The third term is the “clinging” effect. The fourth is the pumpage impact effect. The fifth is valve weight (if the valve axis is vertical), and the sixth is the valve acceleration (inertial) effect.

In the case of a wing guided valve or a disc valve guided by wings on the O.D., D₁ = 0 and D₂ = 0, the above equation reduces to:

Equation 3
F_S90 = ρ(Q₁/cL₉₀sin_α)²/8π + ρ(Q₁²/A_S)(K_i– ½) – K_CρQ₁²/ L₉₀² – W₂ + W₁L⁹⁰(πN/30)²/g

Surprisingly, the valve size drops from the first term, and as stated above, the first term is the predominant term at higher pump speeds. Therefore at higher speeds, a close approximation of the required F_S90spring force can be calculated with the first term only, and without knowing the size of the valve. To simplify the analysis presented, only the first term will be used to represent the spring force required for smooth operation. With L₉₀ = 6/N, the first term can be rewritten as follows:

Equation 4
FS90 =   ρ/8π [ π²N²L_SD_P²(240)(6)csin_α]²

Spring Stress and Size Parameters

The equation that relates the stress and spring dimensions to the force in a helical spring, made of round wire, is:

Equation 5
F =  πd³S_S/8KD_m
Equating 4 and 5 and solving for pump speed, N, yields the following:

Equation 6
N_max=  21.4/DP[ csin_αL_S ]^1/2[ d³S_SρKD_m ]^1/4

To obtain an approximate solution, we can substitute the approximate value of 0.6 for c sin α, which yields:

Equation 7
N_max = 16.6/D_P[ 1/L_S ]^1/2[ d³S_SρKD_m ]^1/4

This equation can be used to calculate the maximum speed for a pump with a single-spring, single-ported, outward-flow valve with the optimum valve lift. For the popular 302 stainless steel valve spring material, the approximate maximum shear stress is 40,000 psi (5.76 x 10⁶ lb/ ft²), and with a Whal spring stress correction factor of K = 1.2, the following is obtained:

Equation 8
N_max = 776/D_P[ 1/L_S ]^1/2[ d3/ρD_m ]^1/4

To be able to calculate the approximate maximum speed for a “typical” power pump, we can substitute approximate spring dimension ratios as follows:

Equation 9
Dm = _P/2         d = D_m/8 = D_P/16

which results in:
N_max = 116 [1/L_sD_p ]^1/2[ 1/ρ]^1/4For cool water, ρ=1.94 lb-s²/ft⁴, and the equation reduces to:

Equation 10
N_max =  98(L_SD_P)^1/2where the stroke length, L_S, and the plunger diameter, D_P, are both in feet. To substitute inches directly, change the numerator from 98 to 1180.

Examples
D_P = 1 in., L_S = 2 in.   N_max = 1180/(2)^1/2 = 834 RPM

D_P = 2 in., L_S= 5 in.   N_max = 1180/(10)^1/2 = 373 RPM

D_P = 4 in., L_S= 6 in.   N_max = 1180/(24)^1/2 = 241 RPM

D_P = 6 in., L_S = 12 in.   N_max = 1180/(72)^1/2 = 139 RPM

Figure 4 is a plot of N_max = 1180/(L_S _P)^1/2 with L_S and D_P expressed in inches.

The Unexpected Results

Equations 6 and 9 reveal some of the following unexpected results:

The maximum allowable speed varies inversely as the square root of the product of the plunger stroke and diameter.
The density of the pumpage affects the maximum speed only to the one-fourth power, a small amount.
The maximum allowable spring shear stress affects speed only to the one-fourth power, a small amount. Doubling the allowable stress (to 80,000 psi) increases the maximum speed by only 19 percent. Doubling the spring force with two springs in parallel also increases the maximum speed by only 19 percent.

Increasing the spring wire diameter, d, increases the maximum allowable speed to the three-quarter power.

Increasing the spring mean diameter, D_m, increases the maximum allowable speed to the one-half power (square root).

Figure 4 (above). Plot of the approximate maximum power pump speed, on water, for a single-spring, outward-flow valve.

About That Compressor Speed

The density of air at standard conditions is approximately 1/800th that of cool water. Therefore, an air compressor with a single-ported, single-spring valve would be limited to an approximate maximum speed that is about (800)^1/4 = 5.3 times that of the same size pump on water, and that looks about right. Because compressors are typically made with multi-port, multi-spring valves, the multiplier is higher than 5.3. That seems to provide a reasonable answer to the question: why can’t reciprocating power pumps run as fast as reciprocating compressors.

Another Unexpected Result

Plugging Equation 9 into Equation 4 produces another surprising result:

Equation 11
F_S90 = ρ8π[ π²N²L_SD_P²/(240)(6)csinα]²= ρ[ N²L_SD_P²/439]²= ρ[ 13460L_SD_P² L_SD_Pρ^1/2 439 ]²= 940D_P²
This equation says that the approximate spring force (in pounds) required for any power pump—with the general design parameters stated above, with any density pumpage, to achieve the optimum valve lift—can be obtained by the simple calculation of 940 times the plunger diameter (in feet) squared. For the plunger diameter in inches, change the 940 coefficient to 6.52.

For example, a 4-inch diameter plunger in a 5-inch stroke pump—running on cool water, at the maximum allowable speed of 264 rpm, with the optimum valve lift of 0.273 inches—will require a spring force, at that valve lift, of about 104 pounds. This same spring would be selected for a 4-inch diameter plunger in a 10-inch stroke pump—running, on cool water, at the maximum allowable speed of 187 rpm, with the optimum valve lift of 0.386 inches. A more accurate value of FS90 can be obtained with Equation 2 or 3.

Can it be so simple? So it seems.

High-Speed Warning

Although the above equations allow us to determine the approximate maximum speed allowed by adequate valve springs, many factors may dictate a lower speed. Some of those conditions are:

Weak valve springs
Valve springs that have a stiffness that is less than calculated (not uncommon)
Special valves (such as balls)
Limited NPSH available from the system
Air or other gas dissolved in the pumpage
Air or other gas entrained in the pumpage
Long, and/or undersized, and/or complex, suction pipe
Absent or inadequate pulsation-dampening equipment
High temperature of pumpage
Solids in pumpage (slurry)
Compressible pumpage
Viscous pumpage
High ambient temperature
Desire for less pulsation in suction and/or discharge piping
A high spring force, as required by large pumps, which may be difficult or unsafe to assemble or disassemble
Desire for extended life of packing, plungers, valves, springs and other pump and system components (reduced maintenance requirements)

Therefore, the above equations simply indicate the approximate maximum speed as determined by the valve spring, which usually must be reduced to meet specific application conditions.

Did it really take us 2,000 years to establish the more significant characteristics of the power pump? So it seems.

Reference:
1. Ingenious Mechanisms, New York: Ingersoll-Rand, Hydraulic Division, 1960

2. Worthington Pump and Machinery Corp., formulas and derivations for reciprocating pump valve lift and valve springs, 1949 1953

3. Wright, Elliott F., “New Developments in Reciprocating Power Pumps,” A paper presented to the 6th meeting of the National Conference on Industrial Hydraulics, about 1955

4. Wright, E. F., Marks’ Mechanical Engineers’ Handbook, 6th Edition, Section 14 - Reciprocating Power Pumps, 1958

5. Collier, Samuel L., “Knocking From Valve Hammer in Triplex Pumps,” ASME Paper 83 PET 29, 1983

6. Collier, Samuel L., Mud Pump Handbook, Gulf Publishing Co., 1983

7. Worster, A. R., “Importance of Maintaining Proper Valve Lift on Compressor Valves,” a paper presented to the N.G.A.A. regional meeting in Odessa, Texas, February 26, 1954.

8. White, K. H., “Prediction and Measurement of Compressor Valve Losses,” ASME Paper 72 Pet 4, 1972

9. Vetter, Gerhard and Schweinfurter, Friedrich, “Pressure Pulsations in the Piping of Reciprocating Pumps,” Chem. Eng. Technol. 10, 1987

10. Henshaw, Terry L., Reciprocating Pumps, Van Nostrand Reinhold Co. Inc., New York, 1987

11. Positive Displacement Pumps – Reciprocating, API STANDARD 674, American Petroleum Institute, Washington. D.C., June 1995

12. Price, Stephen M., Smith, Donald R., and Tison, James D., “The Effects of Valve Dynamics on Reciprocating Pump Reliability,” a tutorial presented at the 12th International Pump Users Symposium, Houston, Texas, 1995

13. Henshaw, Terry, “Power Pump Valve Dynamics – A Study of the Velocity and Pressure Distribution in Outward-Flow Bevel-Face and Flat-Face Power Pump Valves,” a technical paper presented at the 25th International Pump Users Symposium, Houston, Texas, 2009

14. Henshaw, Terry, “Improve Power Pump Performance With Stronger Valve Springs,” COMPRESSOR Tech Two, July 2010

Written by Terry Henshaw

http://www.pump-zone.com/valves/valves/the-vital-role-of-valve-springs-in-power-pumps.html

The Evolution of Pump Control

2011-09-16T20:10:00.001+02:00

Advanced motor protective relays provide superior protection for motors and pumps.

For years, motor overload relays have been used to protect pumping systems. Traditionally, they monitored current to protect the motor and relied on separate electromechanical sensors, such as flow meters or pressure gauges to protect the pump.

Today, advanced motor protective relays are able to provide superior protection for not only the motor but the pump as well by monitoring under-power conditions, which are a direct linear interpretation of pump performance.

The increasing intelligence of electrical controls is shifting knowledge from mechanical systems to electrical controls, essentially following the flow of data.
In pumping applications, today’s advanced motor protective relays provide a spectrum of real-time performance data and diagnostics, helping facilities save energy, optimize maintenance and extend equipment life.

Further, they have such a degree of flexibility that the user is able to customize the level and type of protection depending on how critical the equipment is to the process.

Every motor of any value needs an overload relay. Today’s overload relays have evolved significantly from traditional overload protection. Advanced overload relays provide continuous data on motors and pumps.

Since they reside in the motor control center or in pump houses, they are able to communicate on standard industrial protocols and tie into SCADA, PLC and DCS systems.

Using the data provided by the relay, maintenance teams can be scheduled when changes are detected and before downtime occurs, enabling optimized use of personnel time.

With real-time, remote, continuous information, end users are able to identify a potential issue before it causes downtime or wasted energy, and maintenance can be targeted at real or detected variations.

Extend Life & Avoid Deadhead

Advanced overload relays provide remote data monitoring of a host of parameters. The goal of this information is to prevent the failure of a motor or pump asset. Overload relays can act on their down data with a host of flexible protection settings.

Specifically, the low-power protection configuration is designed to protect the load or (centrifugal and submersible) pumps from starved and deadhead conditions, which are common causes of pump and pump seal failure. In such a situation, overload relays, performing as pump-off relays, can shut down the pump, extending equipment life and reducing downtime and maintenance expenditures.

This low-power condition occurs when real power provided to the motor or pump falls below the normal operating conditions, which is caused by a deadhead or starved pump.

A dead-head situation occurs when a pump continues to run against a mostly closed valve.

A starved condition occurs when a blockage occurs upstream of the pump or if a submersible pump runs dry. These situations can cause mechanical failure by excessively heat aging expensive pump seals, which in-turn fail and cause leakage.

Without an advanced overload relay with low-power detection, the pump would continue to run, because a float limit switch would not drop because the water level would not decrease. A second pump would likely be turned on to compensate. In other words, two pumps would be running and performing the work of a single pump. Meanwhile, the seal of the first pump would be heat aging, shortening its life.

Today, this situation can be monitored, detected and avoided. Wasted run-time hours can be prevented, with the protective fault, under-power feature. The overload relay would take the first motor offline, and the second pump would come online and complete the pumping activity.

Additionally, the wear and tear on components would be reduced, as the overload relay would have taken the first pump offline, avoiding the heat aging of the seal. Maintenance and energy consumption would also be reduced by avoiding a total failure of the first pump and running two pumps to do the work of one.

Optimize Maintenance

Tapping the monitoring capabilities of today’s overload relays, maintenance can be optimized. This means scheduled downtime, unnecessary inspections eliminated, labor skill sets optimized, reduced service time.With a remote view of the performance of a motor or pump, maintenance can be optimized and costs can be reduced.

Advanced overload relays enable personnel to check motor or pump operation from any computer in a plant or facility and even from home. Trending data collection allows for the detection or prediction of potential failure conditions. Further, when conditions indicate an imminent failure, operators can switch to spare or secondary motors or pumps to avoid downtime.

Intelligent pump, motor and line quality monitoring arms operators with the information that they need to only send personnel when data indicates an issue, which eliminates unnecessary inspections. With an understanding of the fault type or pending fault type, individuals are sent who have the appropriate experience and expertise to address the defined issues. Additionally, an understanding of fault type enables personnel to come equipped with the appropriate tools, which can reduce service time.

Improve Energy Efficiency

Overload relays that monitor power factor and energy can help:

Avoid peak demand charges
Shed non-vital loads
Identify and rectify increased consumption over time
Identify a discrepancy between equal loads
Identify power factor line items

Today’s advanced overload relays allow for the staggered and deliberate starting of motors and pumps after power loss.

This prevents numerous loads from coming on simultaneously, facilitates successful startup and avoids peak demand charges. Overload relays with advanced power monitoring and flexible communications capabilities allow for the observation of abnormal and inefficient operation in real time.

For across-the-line loads, they are able to do more than protect the motor. They let end users see consumption at the specific load—something that used to be reserved to expensive meters on groups of motors.

With an individual look into each motor, operators can catch increased consumption in real time, control it and prevent it.

Using a power-monitoring-equip-ped overload relay, system inefficiencies can be monitored with side-by-side comparisons of similarly-sized assets as well as comparisons on a single asset made over time.

Such situations prior to the use of a power monitoring overload relay would often go unnoticed and result in higher utility bills. Further, commands over numerous fieldbus networks allow remote or programmed shutdown of non-vital assets.

Many facilities must run continuously, and all operations want to run efficiently. So, being able to prevent equipment failure and schedule downtime to address detected problems is critical.

Continuously monitoring key failure indicators with remote monitoring solutions helps maintenance and operation teams respond to equipment problems sooner. The early detection of system degradation is crucial to productivity and the bottom line.

Overload relays with advanced remote monitoring and power capabilities can yield significant energy and cost savings while improving system reliability and reducing maintenance.

Written by Paul Twaddell and Adam Krug

http://www.pump-zone.com/motors/motors/the-evolution-of-pump-control.html

What Are the Basics of Gas Lubricated Seals? (Part Two)

2011-09-02T10:23:00.000+02:00

Last month's Sealing Sense provided an overview of pump gas seal benefits and general design issues. This article will discuss some application conditions that must be considered when applying gas seals to pumps.

As noted in Part One, gas seal technology for pump applications offers a number of benefits, including zero emissions, high reliability and low power consumption. Gas seal support systems are also simpler and require less maintenance than the buffer or barrier systems required for dual wet seals.

However, some application conditions require special consideration when choosing gas seals for rotating equipment. Considerations include selecting the optimal topographical seal face features to create face separation and finding the seal types and arrangements best suited for the process fluids being pumped.

Rotational Speeds

Gas seal faces are designed to generate hydrodynamic forces that separate the seal faces during operation of the rotating equipment. These forces are proportional to the rotational speed of the shaft. Seal face topographies are designed for optimal performance within a specified range of rotational speeds. The gas film stiffness can be significantly reduced if the seal is operated at rotational speeds below the lower limits of the design.

Normal operating speeds of the equipment may be within the gas seal's design range. However, transient slow roll conditions can occur as the equipment shuts down, especially in applications where a variable frequency drive with an extended soft start or shutdown is applied. High temperature applications may also implement slow roll conditions to avoid shaft droop during periods of non-operation, and pumps with steam turbine drivers are typically slow rolled for long periods.

Gas seals can be successfully applied under these conditions so long as they are recognized at the time the gas seal is specified. The face topography can be modified to rely more on hydrostatic forces and less on hydrodynamic forces to create face separation. This can be effective even under slow rotational speeds, but the possibility of increased barrier gas consumption must then be considered.

Another option is to apply a coating to the hard face (typically silicon carbide) that will minimize the potential for scuffing of the seal faces if contact occurs during the slow roll condition. Diamond-like coatings (DLC) and true diamond coatings can be applied for this purpose.

Rotational Direction

Many topographical seal face patterns are designed to create hydrodynamic load support and seal face separation when the seal faces rotate in a specific direction, but act to draw the seal faces into contact when the direction of rotation is reversed. These seal face patterns are called unidirectional.

For most pump applications, a unidirectional seal face does not present problems because the pump shaft only rotates in one direction. However, this may not be the case for some pump system designs with a significant length of vertical discharge and a piping configuration that allows the fluid in the discharge line to drain back through the pump when the pump is shut down. The draining of the discharge line can cause the impeller to rotate in a reverse direction, resulting in reverse rotation of the pump shaft and seal faces.

Most gas seals readily tolerate short duration reverse rotation without damage to the seal. However, if the pumping system design allows reverse flow through the idle pump for long periods, it becomes imperative to recognize that this condition can result in reverse rotation of the seal. Make sure to advise the seal manufacturer of this pumping system design situation during the selection process.

As with rotational speeds, the face topography for unidirectional seal faces can be modified to rely more on hydrostatic and less on hydrodynamic forces to provide face separation for successful performance. In this case as well, some application conditions and seal designs may lead to increased seal face separation with a corresponding increase in barrier gas consumption.

Bidirectional seal face topography can also be employed. While bidirectional topographies are able to generate hydrodynamic separating forces regardless of the rotational direction, they typically generate lower gas film stiffness. This can potentially allow seal face contact when axial perturbations of the seal rings occur.

Solids in Process Fluid

Solids are a common cause of mechanical seal failure in pump applications, but can be particularly problematic in some gas seal designs. Solids may be dispersed throughout the process stream or may be dissolved and crystallize out of solution between the inboard and outboard seals. In either situation, the solids cause two significant problems for gas seal performance.

First, gas seal faces are designed to operate with a gap between the mating faces on the order of 0.0001 in (2.54 µm). The solids can migrate into the seal face gap as shown in Figure 1 and cause third body erosion, degrading the seal face topography and diminishing its effect. For gas seal configurations where the process fluid is at the I.D. of the inboard seal faces, centrifugal forces will act to aid the migration of solids into the gap between the seal faces.

Figure 1. Solids migration into seal face gap

Spring Loads

Second, the spring loads that provide the closing force of the seal faces in pusher type seals are typically about 50 percent lower for pump gas seals than for liquid lubricated seals. These lower spring loads are employed to avoid overcoming the gas film stiffness created by the hydrodynamic opening forces (Fo) and minimize the risk of seal face contact.

Figure 2. Forces on gas seal faces

Due to these low spring loads, pusher type gas seals can be susceptible to secondary seal hang-up, which occurs when the dynamic secondary seal cannot move axially to allow the flexibly mounted seal ring to track the mating ring. Hang-up can occur when the seal ring is displaced axially from the mating ring, resulting in excessive barrier gas consumption, or when the seal ring is displaced axially toward the mating ring, resulting in excessive closing forces and possible seal face contact.

Design Solutions

Several design features can be incorporated into pump gas seal systems when solids are known to exist in the process fluid. One approach is to prevent the solids from entering the seal chamber area. This can be achieved using solids exclusion devices that are mounted at the impeller end of the seal chamber. These devices may include volute-like geometries that convert the rotational velocity of the process fluid in the seal chamber into axial velocity, directing the fluid and its solids out of the seal chamber.

Seal configurations with process fluid at the O.D. of the inboard faces also help to reduce the migration of solids into the seal face gap.

Other designs may use a restriction at the seal chamber throat such as a labyrinth seal (see Figure 3). API Plan 32 can also be used to prevent the ingress of process fluid and solids into the seal chamber with a close clearance bushing and injection of a clean fluid into the seal chamber.

Special dynamic secondary seal designs can be employed to minimize the chance of hang-up. These designs typically minimize the amount of drag that the secondary seal creates when it moves axially. They may also prevent solids from collecting at the process side and restrict axial movement of the secondary seal. The designs often control the secondary seal squeeze in the radial direction by using a canted coil or leaf spring to energize the secondary sealing surfaces against the axial sealing surfaces.

Gas seal designs incorporating metal bellows seals are also available. The use of a metal bellows seal instead of a pusher type seal completely eliminates O-ring secondary seal hang-up.

Conclusion

The conditions described in this article are some of the most common causes of failure when gas seals are applied to pumps. However, with clear identification of these conditions during seal specification, gas seal designs can be applied that mitigate these application challenges. With proper engineering and application, gas seals provide a highly reliable, energy efficient method for providing zero emissions sealing solutions for pump applications. Contacting a seal manufacturer with complete application details first can ensure optimum results.

Pumps & Systems, December 2009

Next Month: How do I prevent gasket blow out?

We invite your questions on sealing issues and will provide best efforts answers based on FSA publications. Please direct your questions to: sealingsensequestions@fluidsealing.com

Fluid Sealing Association

Sealing Sense is produced by the Fluid Sealing Association as part of our commitment to industry consensus technical education for pump users, contractors, distributors, OEMs and reps. As a source of technical information on sealing systems and devices, and in cooperation with the European Sealing Association, the FSA also supports development of harmonized standards in all areas of fluid sealing technology. The education is provided in the public interest to enable a balanced assessment of the most effective solutions to pump technology issues on rational Total Life Cycle Cost (LCC) principles.

The Mechanical Seal Division of the FSA is one of six with a specific product technology focus. As part of their educational mission they develop publications such as the Mechanical Seal Handbook, a primer intended to complement the more detailed manufacturer's documents produced by the member companies. This document served as the basis for joint development of the more comprehensive Hydraulic Institute publication: Mechanical Seals for Pumps: Application Guidelines. Joint FSA/ESA publications such as the Seal Forum, a series of case studies in pump performance, are another example as is the Life Cycle Cost Estimator, a web-based software tool for determination of pump seal total Life Cycle Costs. The Sealing Systems Matter initiative was also launched to support the case for choosing mechanical seals that optimize life cycle cost, reliability, safety and environmental compliance.

The following members of the Mechanical Seal Division sponsor this Sealing Sense series:

Advanced Sealing International (ASI)
Ashbridge & Roseburgh Inc.
A.W. Chesterton Co.
Daikin America, Inc.
DuPont Performance Elastomers LLC
EagleBurgmann
Flex-A-Seal, Inc.
Flowserve Flow Solutions Div. - Seal Group
Garlock Sealing Technologies
Greene, Tweed & Co./Palmetto, Inc.
Industrias Vago de Mexico SA de CV
John Crane
Latty International S.A.
Metallized Carbon Corp.
Morgan AM&T
Nippon Pillar Corp. of America
PPC Mechanical Seals
Scenic Precise Element Inc.
SEPCO - Sealing Equipment Products Co.
SGL Technic Polycarbon Division

Written by Fluid Sealing Association Member Rob Phillips

http://www.pump-zone.com/seals/mechanical-seals/what-are-the-basics-of-gas-lubricated-seals-part-two.html

AC Motor Torque

2011-09-01T02:03:00.001+02:00

As a follow up on my AC Motors series, I thought it would be a good idea to provide a short overview of work, power and torque as it applies to the AC motor. I will provide a reference to a more in depth study at the end of this article.

Work

The AC motor is a machine designed to transform electrical energy into mechanical energy so that work can be performed.

Work (w), in a translational (linear) system, is defined as the force (f) applied to some object multiplied by the distance (d) that it travels. In the English system force is measured in pounds and distance is measured in feet.

The equation for work, which is quite straight forward (no pun intended), is:

w = fd

If you lift 100 pounds to a height of 10 feet, you perform 1,000 lb-ft of work.

The same amount of work is performed if you lift a 200 pound object to a height of 5 feet or, for that matter, a 50 pound object 20 feet.

Work is a somewhat unfortunate term because for work to be performed, we must actually move an object in a direction that is opposite the force acting upon it.

For example, if you lift a suitcase off the floor you have performed work because the force you applied overcame the force of gravity that was holding it to the floor.

Carrying it across the room, however, is not work because you do not move in a direction that opposes the force acting upon it. However, try telling that to someone with a thirty pound suitcase in each hand. He or she will expend energy but will perform no work.

The equation for work tells us how much work is done, but it says nothing about how quickly it gets done. If you carry a 50 pound object up a flight of stairs that are 10 feet high, you will perform 500 lb-ft of work. It makes no difference if you do it in five seconds or five days, the same amount of work is performed.

Power

The rate at which work is done is power. Power (p) is equal to work (w) divided by the time (t) it takes to perform it. The equation, also very straight forward, is:

p = w / t

In the late eighteenth century, James Watt made some major improvements to the steam engine—improvements that made it a viable alternative to other sources of power.

One of the power hungry applications in Scotland at the time was pumping water from coal mines.

The pumps were powered by horses, and Watt needed a way to relate the power of his engine to that of a team of horses.

Through experimentation, he reportedly determined that the average horse could lift 150 pounds to a height of 220 feet in one minute. The work performed then, is 33,000 lb-ft (w = fd). Power, or in this case horsepower, is 33,000 lb-ft/min. This rather cumbersome number is equal to 745.7 joules/sec in the MKS system.

One joule/sec was called a watt in his honor. Therefore, one horsepower is equal to approximately 746 watts. In the United States we rate a motor's power in horsepower. In most other countries, it is the kilowatt (KW).

Torque

Torque is defined as the force that gives rise to rotational motion. It is also the result of rotational motion. Torque (t) is equal to force (f) times the radius (r) through which it acts and the angle (Ø) at which the force is applied. The equation used to calculate torque is:

T = f (r sin Ø)

Torque in a rotational system is analogous to force in a translational system. The straight line distance of the translational system, however, is replaced with an angular quantity.

For any given horsepower, torque varies inversely with rotational speed.

For example, a 100 horsepower motor operating at 3,600 rpm produces a torque of approximately 150 lb-ft. At 1,800 rpm, torque would be about 300 lb-ft and at 1,200 rpm about 450 lb-ft. This is exactly what one would expect since horsepower (power) is the rate at which work is done.

If a 1,800-rpm motor is to accomplish the same amount of work in the same amount of time as one rotating at 3,600 rpm, it must do twice the work per rotation.

It is for this reason that the shaft diameter of a 900-rpm motor is larger than that of the 3,600 rpm model even though they produce the same horsepower.

Lower rpm motors use larger diameter shafts to accommodate the higher torque required to do the same amount of work in fewer rotations.

Earlier, horsepower was defined as w / t and expressed in lb-ft or watts. It can also be defined in terms of torque (t) and speed (rpm).

HP = (t x rpm) / 5,250

Torque can also be expressed in terms other than force and the radius through which it travels.

Rearranging the previous equation we get:

t = (HP x 5,250) / rpm

These two equations are probably more useful in daily work than the previous ones.

Written by Joe Evans, Ph.D.

http://www.pump-zone.com/motors/motors/ac-motor-torque/all-pages.html

What are the basics of gas lubricated seals? (Part One)

2011-09-01T01:53:00.001+02:00

The use of gas lubricated mechanical seals in pumps has increased for a variety of reasons. This two part article will address the principles of gas seals, some basic application questions, what to expect from seal performance and the environmental factors that may affect performance.

What Are Gas Lubricated Mechanical Seals?

Gas seals run in a clean, controlled fluid environment and are designed to remain non-contacting and non-wearing for the expected operating conditions. Seal faces operate on a barrier fluid film, typically in pressurized dual seal arrangements like in Figure 1.

Typical barrier fluids used in gas seals include nitrogen, steam, purified air or other inert gases. Each of the sealing end faces have some macro-topographic design pattern, are wider than plain face seals and are loaded with lighter spring force. These features enable generation of the hydrodynamic pressures that prevent contact of the seal faces.

Since they are non-contacting and do not wear, gas lubricated mechanical seals produce consistent seal performance, even in a widely varying duty cycle, and reduce power consumption at the seal faces. The seal generates little heat, and any gas leakage absorbs heat away through gas expansion. It is imperative that the seal faces are separated with a gas barrier film. If the faces contact, the seal will not last long running dry at typical pump speeds.

Figure 1. Typical dual gas seal for pumps

Why Gas?

Since gas has poor lubricity, why rely on it to "lubricate" the seal faces? The reason is that in some pump applications, the process fluid to be sealed can be volatile, non-lubricating and sensitive to heat. It can also polymerize to foul the seal face, corrode the seal parts or be hazardous to the environment.

Dual seal arrangements with liquid barrier fluid are commonly used to overcome the above problems. In situations where the liquid barrier fluid can contaminate the process, or it is cost prohibitive to add the circulating cooled barrier system, the gas barrier fluid can become a viable choice.

A seal support system (example in Figure 2) is usually installed, including a gas control panel with coalescing filter to minimize liquid contamination, ensure cleanness of the gas and monitor leakage flow rate.

Figure 2. Typical gas seal support system

What Keeps the Seal Faces Separated?

There are many methods for generating the gas barrier film. The underlying principle uses a shallow step height change on the face to squeeze the film and generate fluid pressure (see Figure 3). Design variations like those shown in Figure 4 include Rayleigh pad, spiral groove, wavy face and others. All demonstrate various capabilities to control the gas flow and generate the face separating pressure.

If the gas pressure generated depends on the relative sliding of the seal faces, it is called hydrodynamic pressure. If it depends only on the pressure differential and is effective even at standstill, it is called hydrostatic pressure. Depending on the operational requirements, typical gas lubricated mechanical seals use varying degrees of combinations of both hydrodynamic and hydrostatic effects to maximize protection for the seal faces. They use carbon-graphite as the primary ring material to run against a silicon carbide or tungsten carbide mating ring, which helps the seal survive short durations of face contact in transient or emergency conditions. For higher pressure applications, carbide primary rings are used to take advantage of higher Young's Modulus and strength.

Figure 3. Hydrodynamic pressure generation in a step bearing

Figure 4. Typical gas seal face patterns

What Are Acceptable Leak Rates?

Gas leak rates are typically small, in the order of SCFH (standard cubic feet per hour). Predicting the actual leak rate from the theoretical rate is difficult since the leakage is sensitive to manufacturing variations and deviates from the idealized theoretical model. It is better to use the initial leak rate for any specific new seal installation as the baseline for future reference. If the operating leak rate exceeds 10 times the initial, contact the seal manufacturer to see if the seal needs to be repaired.

Barrier gas pressure is typically set at about 30 psi higher than the process pressure. As a rule of thumb, only about one-third of the total barrier gas flow leaks through the inboard seal into the process. Gas ingestion into the process is typically not an issue. The process fluid carries it through the system and vents it out at some stage. However, for a closed loop system, the user and seal manufacturer need to determine if the gas will accumulate and cause operational problem such as cavitation or vapor (gas) lock, which may starve the pump.

What Are the Other Performance Characteristics?

Gas film thickness will vary with the operating conditions. Users need to provide the details of expected duty cycles, not just the maximum pressure and speed conditions, so that seal engineers can ensure reliable seal operation through all phases. Since the seal does not wear, it will not have hysteresis behavior, i.e., the leak rate depends only on the current operating conditions and not on the operation history.

When the seal contacts and runs in dry condition, it generates carbon dust, which may be noticeable along the leakage path such as the gland bore area. High gland temperature may also indicate face contacting the outboard seal. If both signs show up, the pump most likely needs to be shut down and the seal repaired soon.

In an upset condition from too high process pressure or lost barrier gas pressure, most seals are designed to withstand the reversed pressure, but the seal face will contact to prevent the process fluid from leaking into the barrier and the atmosphere thereafter. After the cause of the upset is corrected, depending on the actual scenario, the seal may be able to resume normal operation. Consult with the seal manufacturer to see if the seal needs to be removed for refurbishment. Static leakage measurement can be helpful in assessing the severity of face damage, if any.

Watch For These Potential Problems

A common problem encountered is loss of barrier gas pressure. This can occur when the barrier pressure drops below the set point or the process pressure becomes higher than projected.

Since the seal is lightly loaded by a spring, too much drag on the primary ring may hang it up. The dynamic O-ring is critical to the seal reliability and has been carefully sized to ensure reliable performance. If it stays in a dirty fluid environment, the dirt accumulation will cause extra friction drag and cause the seal to fail. Solid exclusion devices should be incorporated to prevent the dirt from entering the dynamic O-ring area.

Elastomeric O-rings have relatively low temperature limits. Outside these temperature limits, other secondary seal materials and designs, such as metal bellows seal, should be considered.

Sometimes the metal bellows is used to avoid the seal hang up problem. Liquid contamination in the barrier gas, as can occur with steam, may cause a larger face separation than the seal was designed to handle. This will lead to a higher leak rate but should not damage the seal. After the liquid passes through the seal face, the seal should return to normal performance if the liquid does not leave any deposit on the face.

Conclusion

Gas lubricated seals are relatively recent developments in pump seal technology. They provide a new approach to double seals for controlling pump emissions, minimizing heat generation and reducing power consumption. A number of design combinations are available specific to application requirements. This Sealing Sense provided some design and functional principles, and Part Two will further address application issues and guidance.

Technology improvements are ongoing, so it is important to consult with a seal manufacturer to take advantage of the latest designs and application information.

Written by Fluid Sealing Association Member Tom Lai

http://www.pump-zone.com/seals/mechanical-seals/what-are-the-basics-of-gas-lubricated-seals-part-one.html

Happy Feast

2011-08-31T06:46:00.003+02:00

The Submersible Pumps Market in North America

2011-08-31T04:48:00.002+02:00

The North American submersible pumps market is a mature market in an uncertain economic climate, especially in the United States. Suppliers face a number of key challenges: general economic malaise, a housing industry downturn that has dramatically affected various markets including construction, and the threat of eroded funding (which affects the largest user industry: water/wastewater) from federal, state and local budgets.

However, while the short term picture appears somewhat bleak, we expect the market to eke out moderate growth during the next seven years. As presented in the recently published "North American Submersible Pumps Markets" report, the submersible pumps market is expected to experience a compound annual growth rate fewer than 4 percent (2008-2014), on 2007 base year revenues of approximately $175 million.

Key Growth Factors

While there are a number of challenges for revenue growth in North America, there are also several compelling factors expected to support growth:

• Environmental legislation encouraging manufacturers to produce

energy-efficient pumps

• Increased focus on services and solutions from an end-user

perspective driving sales revenues

• Upgrading aging and existing treatment plants boosting sales

revenues

Environmental legislation and enforcement has historically been a key market driver in the submersible pumps space. The Safe Water Drinking Act, reauthorized in 1996, facilitated the emergence of a more advanced water and wastewater industry in the United States, creating a demand for products such a membrane-based filtration, as opposed to traditional gravel and sand techniques. Compliance with regulatory issues is a critical aspect of the market, particularly in the huge water constituency. Aging systems and population growth create challenges for water operators to remain in compliance and provide adequate services levels to customers.

As water is increasingly viewed as a precious resource, there will be continued pressure-in spite of economic trends-for water system operators to adequately maintain and expand their systems. These converging factors are expected to support continued spend in critical components such as submersible pumps.

Another avenue supporting submersible suppliers' revenues is the provision of services and solutions (as opposed to simply providing a piece of hardware). A variety of end-user industries face key constraints or trends that have helped the service sector blossom for pump suppliers in general, including:

• A lack of qualified engineers on staff to specify and/or maintain

equipment

• Downsizing of organizations, which exacerbates the problem of

availability of personnel to attend to equipment

• An increased trend towards outsourcing all but core value-add

functions in process and manufacturing plants

These factors, among others, have contributed to an environment where pump suppliers have been able to enhance incoming revenue streams by basically becoming an extension of their customers' operating personnel. Pump suppliers now provide design and specification consulting, help properly size pump and system components for specific applications and provide various services from installation/commissioning to maintenance and life cycle cost analysis, even on units not of their own manufacture. Even in a strained market, opportunities for revenue enhancement have come from an expansion of the role of pump suppliers in their customers' operations.

The Water/Wastewater Industry

As Figure 1 shows, the water and wastewater industry is estimated to be a sizeable portion of the North American market for submersible pumps.

More than 50,000 municipal drinking water systems are in the U.S. water infrastructure. As a whole, U.S. communities have spent in excess of $1 trillion throughout the last twenty years on water/wastewater infrastructure, operations and maintenance. Much of this infrastructure dates from the World War II era, which means that, considering an approximately 30 to 40 year life expectancy, many systems can currently expect extensive refurbishment. Estimates of needs for infrastructure investment for potable water over the next 20 years top $150 billion. This includes upgrades and also expansion for significant population growth expected by the U.S. Census Bureau through 2020.

Regarding U.S. municipal wastewater infrastructure, the Environmental Protection Agency (EPA) recently released a report that concluded that U.S. investment in wastewater infrastructure could exceed $200 billion, based on the trends of aging systems, rising water quality standards and population growth. The bulk of this estimate (65 percent) will be needed for waste treatment systems, with the remainder going to sewer overflows (25 percent) and stormwater management (10 percent).

Despite this huge need for spending in the near and mid-term future, municipal spending is largely dependent on local, state and federal budgets. The magnitude of the need is not at issue-it is how these needs will be funded over the next few decades. While water providers struggle with budgets and funding, the bottom line is the health and welfare of communities. Deteriorating pipelines that inappropriately release water can have major economic, environmental and human health ramifications. The U.S. EPA is also looking with greater interest at water quality issues in the distribution segment (as opposed to in-plant), realizing that, as systems age, more data and tracking are needed to ensure water quality throughout the system. Although the price tag is high, the industry must modernize water systems.

Figure 2 shows the forecast for submersible pumps in the North American water and wastewater industry.

Regarding other North American countries, Canada has spent approximately $14 billion on water/wastewater infrastructure from 2000 to 2007. On the wastewater side, Canadian laws requiring strict performance standards for water purity (based on concentrations of suspended solids, etc.) will mandate equipment upgrades for many municipal facilities. This is expected to be a significant portion of Canada's $33 billion 2007 Infrastructure Plan (2007-2014).

Mexico has recently (late 1990s) begun addressing the difficult state of water infrastructure in the country, particularly in large cities like Mexico City. Erratic billing practices (or no billing at all), aged infrastructure, competing factions for water control, social resistance to the "commoditization" of water and a lack of consensus on advancements have kept the country's water/wastewater services at less than state-of-the-art conditions. Plans put in place to address the vast need there are promising, but much of the funding is sought from world agencies (such as The World Bank), where funding can be unpredictable..

There is significant opportunity overall for growth in the submersibles pumps market in North America given the general state of infrastructure in all North American nations. Growth will be tempered by the reality of government funding levels, and the length of time key economies are in no-growth or low-growth economic scenarios.

Written by Laurel Donoho and Prasanna Mohan, Frost & Sullivan

http://www.pump-zone.com/pumps/pumps/the-submersible-pumps-market-in-north-america.html

Newtonian and Non-Newtonian Fluids

2011-08-30T20:44:00.001+02:00

How viscosity affects centrifugal pumps

The Hydraulic Institute published a standard to account for the effects of viscosity of centrifugal pump performance. Effects of Liquid Viscosity on Rotodynamic Centrifugal and Vertical Pump Performance—available at www.estore.pumps.org—was revised in 2010. Before this publication, viscosity corrections were done using viscosity correction charts.

The new method is much easier to use because it calculates the viscosity corrections automatically by using the formulas provided. The need to "eyeball" from charts has been removed, so the new method is more accurate. The standard also provides a nice background description of the method as well as its limitations and the pump types and pump design characteristics for which the procedure is applicable. The following came as a result of a discussion between several of our readers.

What Are Newtonian Fluids?

Can we assume that crude oil or refined products behave as Newtonian fluids? A key statement is "The viscosity is a function only of the condition of the fluid, particularly its temperature." Water, oil, gasoline, alcohol and even glycerin are examples of Newtonian fluids.

Examples of non-Newtonian fluids are slurries, suspensions, gels and colloids. Perhaps one would feel comfortable with this assumption for crude oil and refined products. But does heavy crude at some point (low temperature) stop behaving as a Newtonian fluid?

Most of the fluids are Newtonian with the basic definition being that viscosity is constant with the shear rate. What is shear rate? It is the relative stress imposed on the fluid by the moving fluid. Consider, for example, a 10–inch, outside diameter (OD) closed impeller, with 0.010-inch radial clearance between the wear rings, which are at a 5-inch diameter. If it rotates at 3,600 rpm, then the metal peripheral velocity is 78 feet per second. The fluid in direct contact with the ring is spinning at the same velocity, according to a no-slip condition. The stationary ring is 0.010 inch away from the motion, so the gradient of velocity is:

(78 – 0) / (0.010/12) = 94,300 ft/sec / ft = 94,300 1/sec

That is the shear rate.

For an open impeller, the distance is between the spinning impeller's open vane and the casing wall. Now the peripheral velocity changes along the radial position of the vane (it is at a little less than 5 inches as compared to the OD of, say, 10 inches). An average value can be estimated (the calculation is similar to the one above), and the shear rate will be similar.

Shear-Sensitive, Non-Newtonian Fluids

Shear-sensitive fluids do not like such shearing action. Glue, for example, gets sticky. Glue, however, is not pumped by centrifugal pumps but more typically by gear pumps. Shear rate, however, still works there as well: in a clearance between the spinning gear and the wall, and such clearance is also typically in the range of 0.005 inch.

Such a shear rate, however, is usually not an issue, as the amount of product in the clearance is small and the overall "dilution" by the sticky, damaged fluid is negligible. In certain cases, though, it does matter. For example, if the fluid pumped by a gear pump is an emulsion deposited on photography film, then even minor imperfections may cause specks and blemishes, and the film ends up defective.

Pumping food—such as cherries, applies, etc.—in the canned food industry raises similar concerns. The pump requirement is gentle pumping with low shear. Progressing cavity pumps work best for these cases.

In a centrifugal pump with clearance between the impeller wall and casing of 0.5 inch, the shear rate is:

(78 – 0) / (0.5/12) = 1,870 1/sec

Newtonian & Non-Newtonian Fluids and Viscosity

With Newtonian fluids, viscosity does not depend on the shear rate. If pumped oil has a 300-cSt viscosity, for example, it stays so at 3,600 rpm or 1,800 rpm. The shear rate changes, but the viscosity is still 300 cSt.

However for some fluids (non-Newtonian), viscosity does change—either up or down, as shown in Figure 1. These fluids are dilatent or thixotropic. This has an effect on the power required and also may cause fluid degradation, in addition to having an effect (and usually does) on power. Power is force times speed. Force is stress times area. Stress is viscosity times shear rate.

For dilatent fluids shear stress goes up always, as both viscosity and shear rate increase, but for thixotropic fluids it can go either way. Shear rate may not increase as fast as the decrease in viscosity, and the product (stress) can increase, decrease or stay about the same. It all depends on the fluid being pumped. Usually, however, shear stress decreases. That means that power to the pump also decreases with the shear rate. In other words, fluid is first viscous, but once it begins moving, it becomes less viscous, which means less power is required to pump it.

Neglecting the driver rating (motor selected too small) is common. It gets sized for the viscosity of the fluid in motion, but then a motor keeps tripping upon start-up because more power is needed to get things going. Ketchup is one example, and this is why you must shake the bottle like crazy at a restaurant to get it flowing. However once it flows, it does so quickly.

Written by Dr. Lev Nelik, P.E., P&S Editorial Advisory Board

http://www.pump-zone.com/pumps/centrifugal-pumps/newtonian-and-non-newtonian-fluids/all-pages.html

Testing Centrifugal Pumps in the Field

2011-08-29T12:46:00.001+02:00

The performance curves generated by many pump manufacturers are based on results obtained in their test facilities under tightly controlled conditions. The testing techniques used in the field can vary substantially and may or may not provide accurate results.

The Field Test Calculator

Last year, one of my associates asked me to develop a single field test procedure that could be used company-wide for water-pumping applications. After a little research, I found that we were using several different procedures, and although similar, the measured results could differ depending upon the system conditions. I put together several versions and received feedback from our field personnel. I also received some excellent feedback from Lee Ruiz, one of our faithful Pumps & Systems readers and commentators.

The final result is an Excel spreadsheet, Field Test Calculator (FTC), that standardizes the testing of three of our most common water pumping configurations. It is used for both startup and post-installation testing. To date, it has met or exceeded the testing requirements of our major pump manufacturers and the specifying engineering community.

We still use some special procedures for testing pumps in the chemical, petroleum and food processing industries. The design and content is not earth-shattering. Its purpose is to ensure that we use consistent methods when testing pumps. You can take advantage of this tool, or use it as a template for developing your own version. It can be downloaded from the “Pump Sizing, Selection & Testing Tools” page on www.PumpEd101.com.

Figure 1. Screen shot of the End Suction and Split-Case Tab

How It Works

The FTC is designed for three basic pumping configurations—end suction and split-case pumps, submersible well and wastewater pumps and line-shaft turbines. The first uses both suction and discharge gauge measurements, while the latter two use discharge gauge measurement only. Figure 1 is a screenshot of the end suction and split-case tab. The other tabs are similar in design but require different input based on the system design.

The gray cells are for data entry and the yellow cells are calculated results. With the exception of specific gravity, the data entered into the upper block is for reference only and is not used in the calculations. The equations to the right show how each of the results was calculated, and all the variables are defined below the equation.

Each tab allows for the testing of multiple points or one or two points multiple times. Testing multiple points will automatically plot the performance curve on Page 3 of the sheet. Page 2 is for comments, additional information and witness signatures.

The Instructions Tab includes instructions for each test procedure and explains some of the data that may or may not be required. For example, you will note that suction piping friction is included in the calculation for total discharge head (TDH). Normally, the suction gauge reading will take friction into account. However, if the gauge is located some distance from the pump’s suction, the friction that arises from the gauge location to the suction must be included.

There are also instructions for modifying the equation used to compute the brake horsepower (BHP) if your measurement device is a kW meter. The default computation for BHP is average voltage and current.

Written by Joe Evans, Ph.D.
http://www.pump-zone.com/pumps/centrifugal-pumps/testing-centrifugal-pumps-in-the-field.html

Solar Water Pump FAQ

2011-06-06T18:05:00.000+02:00

How much water do I need?
How much will a solar pumping system cost to water 100 head of cattle?
How many different types of solar pumps are there? Which pump should I use?
What is total dynamic head (TDH)?
Can I "pull" water out of a well with a surface pump?
Can I install a solar pumping system in my 2″ cased well?
Should I use a tracker or fixed mount for my solar modules?
Should I use batteries in my pumping system or go solar direct?
Can I use a solar pump to pressurize a tank for domestic use?
Can I use a wind turbine to pump water?
What size wire and discharge pipe should I use?
Can I use solar or wind power to keep my stock tank from freezing?
Will a solar pump s pumping once the tank is full?

How much water do I need?
That depends on how many people or head of livestock you want to provide water for. The chart below lists some averages that you can use to estimate your daily water demand.

Person (drinking, bathing, toilet, etc.) 75 gal/day
Cow/calf pair 20-30 gal/day
Horse or dry cow 20 gal/day
Milking cow 35 gal/day
Sheep 2 gal/day
Hog or 100 chickens 4 gal/day

How much will a solar pumping system cost to water 100 head of cattle?That depends on your location, water source and time of year usage. One hundred cattle can drink 2,000+ gallons of water per day which can be very cost effective to provide from a shallow source of water (£100′) in the summer months. Please fill out our water pumping questionnaire and send it to us and we can put together an itemized system quote for you.
How many different types of solar pumps are there?
There are really only two basic types of solar pumps; positive displacement and centrifugal and these can both be subdivided into surface mount and submersible categories. Your water source will dictate whether you need to use a surface mount or submersible pump while your daily volume requirement and total dynamic head (TDH) will determine if you need a positive displacement pump or centrifugal pump. In general, positive displacement pumps (diaphragm, piston, helical rotor, etc.) are best used where the TDH is high and the daily volume requirement is low. Positive displacement pumps usually require less power to operate than a centrifugal pump and they will produce some water even in cloudy conditions where a centrifugal pump might not. Centrifugal pumps are good in situations where the TDH is low and the daily volume requirement is high. One of the disadvantages of a centrifugal pump is that it has to operate at a high enough rpm to push the water all the way out of the well. If it is cloudy and the solar array is not producing enough power, the pump/motor may be turning but not fast enough to do this. Using a tracker is highly recommended with a centrifugal pump since it increases the solar array's power output over a longer period of time which increases your daily volume of water delivered. We carry pumps from the following manufacturers: Lorentz, Dankoff, Grundfos, Shurflo, Sunmotor and Sun Pumps. Click on each name for information about the different models that they have to offer.

Which pump should I use?
That depends on many factors all of which are addressed in our "Water Pumping Questionnaire". Please fill it out as best you can and fax/e-mail it to us and we will gladly recommend which pumping system will best suit your needs.
What is total dynamic head (TDH)?
Head is measured in feet/meters or psi and it is a term for the distance that a pump has to push the water from your source to your tank. It may seem odd to be able to list head in terms of pressure or distance, but keep in mind that a column of water 2.31′ tall produces 1 psi at the bottom of that column so there is a correlation between distance and pressure. The greater the vertical distance is in between the water source and the tank, the harder the pump has to work to get the water there. Static head is the simple measurement from the surface of the water (when the pump is not running) to the tank. Dynamic head takes into account the amount the water level in the well drops when the pump is running plus the friction loss in the discharge pipe run. Total Dynamic Head is the sum of the static head and dynamic head.

Can I "pull" water out of a well with a surface pump?
Yes, but you are limited as to how far you can pull water up. The theoretical maximum is 33′ if you were able to pull a perfect vacuum at sea level. However, few pumping systems are setup at sea level and no pump on the market is able to develop a perfect vacuum on its inlet side. A good rule-of-thumb to go by is don't assume that you can reliably pull water out a well where the static water level is lower than 10′.

Can I install a solar pumping system in my 2″ cased well?
The smallest submersible solar pump that we have is the 3″ diameter Grundfos SQFlex so a 2″ casing presents a bit of a challenge. If the water is within 10′ of the surface, we may be able to pull the water out with a surface pump. Otherwise you would have to consider using a jack pump which looks and works just like an oil well you see in various parts of the country. These systems are fairly expensive and complex with their sucker rods, cylinders stroke length so give us a call and we can help you design this type of system.

Should I use a tracker or fixed mount for my solar modules?
The answer to this question depends on your application (domestic use or stock watering), the daily volume of water that you need and what time of year you plan to use the pumping system. For most livestock water pumping applications where the highest daily volume of water is usually needed during the summer, a tracker is highly recommended since it can increase your daily water production by as much as 40% as compared to the same array on a fixed mount. In the winter time, a tracker only increases your daily water production by 5-10%. If your daily water volume requirement is low or you are setting a solar pumping system up for winter time use, then a fixed mount structure is probably the best choice. There are several manufacturers of tracking mount structures, but they can all be divided into two categories: active and passive. Active trackers use sensors, actuators and motors to follow the sun from east-to-west while passive trackers use the heat of the sun on two sealed freon containers (one on each side of the tracker connected with a tube) to do the same thing. Passive trackers are simple and reliable, but they aren't as accurate in aiming at the sun as active trackers and they can be blown off course in high winds. On the other hand, active trackers are more trouble prone and more expensive than their passive counterparts. Give us a call if you want to look into trackers in more detail.

Should I use batteries in my pumping system or go solar direct?DON'T USE BATTERIES! The only reason I would ever consider using batteries in a solar pumping system is if you have a very low volume producing water source (well/spring) and you need to pump as much water out of it as you can each day. Otherwise, there are several reasons to avoid batteries in a pumping system:

Using batteries in a solar pumping system lowers the efficiency as compared to going solar direct since it usually lowers the operating voltage of the pump which lowers the operating speed and flow rate of the pump.
Adding batteries to a pumping system costs more money for the batteries themselves plus a required charge controller, battery enclosure and additional disconnects and wiring.
Batteries require care and maintenance that isn't always possible in a remote location.
Batteries performance level and expected lifetime are closely connected with the temperatures that they are subjected to. If batteries are undercharged and subjected tofreezing temperatures they could be damaged. If batteries are overcharged and subjected to high temperatures their lifetime will be shortened dramatically. Care must be taken to shield batteries in a remote location from temperature extremes.
You're better off all the way around if you simply go with a solar pumping system that is designed to give you all the water you need during the daylight hours without having to resort to using batteries. Store water in a tank instead of energy in a battery! For a livestock watering system or gravity fed domestic application, we recommend that you use a storage tank that can hold a minimum of 3 days worth of water.

Can I use a solar pump to pressurize a tank for domestic use?
Maybe. Keep in mind that 1 psi = 2.31 feet of head so pressurizing a tank up to 50 psi adds about 115′ of head that the pump must push against so be sure that your pump can handle it. I would not recommend using a diaphragm pump for this application because you run the risk of rupturing the diaphragm if your pressure switch malfunctions. Another reason not to use a solar direct pump to pressurize a tank is that your tank might get low in the early morning or late evening when there isn't enough sunlight for the pump to operate. Pressurizing a tank is best left to a separate booster pump or an AC centrifugal submersible pump running off of your inverter/battery bank, generator or utility power. Better yet, pump to an elevated tank and gravity feed down to your home or wherever you need the water.
Can I use a wind turbine to pump water?
Yes, but how cost effective this will be depends on your location (i.e. average wind speed), the daily volume of water you need and what season(s) of the year you need the water. If you have a very windy site and you are looking to provide water for a winter pasture, then a wind powered pumping system makes sense. In general the available wind power is highest in the winter and a solar array's power output is highest in summer. The two power sources compliment each other very well seasonally so for the best year round pumping system it could very cost effective to setup a hybrid solar/wind pumping system using one of the new Grundfos SQFlex pumps with a Whisper H80 wind turbine. Keep in mind that wind turbines have moving parts which are subject to wear and tear and require maintenance so a wind powered pumping system may not be as reliable as solar.
What size wire and discharge pipe should I use?
The proper size wire to use in between your solar array and/or wind turbine and the pump depends on the voltage and amperage of your power source and the distance you need to run the wire. The size of the pump's discharge pipe depends on what type of pipe you plan to use (steel or PVC), the distance from pump to tank and the gpm flowrate that the pump will produce. The smaller the pipe is the higher the friction loss which makes your pump work harder to produce less water. We have several charts available to determine the best wire and pipe sizes to use for your pumping application so just give us a call and we'll design it for you.
Can I use solar or wind power to keep my stock tank from freezing?That depends on how cold it gets at your site, if your tank is insulated/bermed and how you plan to keep your tank from freezing. Heating elements consume a lot of power to keep water from freezing which would require a large and expensive solar array to operate. There are bubbler system on the market that simply circulate the warmer water from the bottom to the of the tank and those are much more efficient than a heating element. In very cold climates it is best to install a cover on your tank that leaves only a small portion of the water exposed and then berm your tank all the way around and on of the cover. There are other more expensive and complicated methods of taping into the warm earth temperatures below the tank as well as insulating the tank and only providing water to the livestock when they come to the tank to drink so give us a call and we can direct you to companies that provide those products .
Will a solar pump s pumping once the tank is full?
Yes if you design it that way. Most solar pumping systems utilize a controller that among other things will accept the input from a float switch in your tank which tells the pump when to start and s. Some of the other functions of pump controllers are low water cut-off, lightning protection and load matching through the use of maximum power point tracking from the solar array.

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