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What Are The Cylinder Liner Checks During Scavenge Inspection?

2023-05-23T20:19:00.000+05:30

Visual Inspection: Start by visually inspecting the cylinder liners for any signs of damage, such as cracks, scoring, or excessive wear. Look for indications of overheating or corrosion as well. Pay close attention to the liner surfaces, flanges, and cooling water passages.

Scuffing and Scoring Analysis: Check for scuffing or scoring marks on the liner surface. These marks may indicate issues with lubrication, fuel quality, or abnormal operating conditions. Assess the severity of the marks and determine if corrective action is required.

Piston Ring Grooves: Examine the piston ring grooves in the liner for wear, deposits, or damage. Excessive wear can lead to poor sealing and reduced engine performance. If required, clean the ring grooves and inspect or replace the piston rings. Use a feeler gauge to measure the clearances.

Lubrication Assessment: Evaluate the lubrication system and its effectiveness in providing adequate lubrication to the liner surfaces. Ensure that the lubricating oil is of the correct grade and viscosity for the engine operating conditions.

Corrosion Inspection: Check for signs of corrosion on the liner surfaces. Corrosion can be caused by the ingress of acidic combustion by-products or improper cooling water quality. Take necessary measures to prevent or mitigate corrosion, such as adjusting the cooling water treatment or addressing fuel quality issues.

Documentation: Maintain a record of the inspection findings for each cylinder liner. Document measurements, observations, and any necessary maintenance or corrective actions taken. This record will help track the condition of the liners over time and aid in future inspections.

Why Does a Piston Seize? What Action will You Take if Main Engine Piston is About to Seize?

2023-05-23T20:06:00.002+05:30

A piston can seize in a marine engine due to various reasons, including:

Insufficient Lubrication: If the piston does not receive an adequate supply of lubricating oil, the friction between the piston and cylinder wall increases, leading to overheating and potential seizure.

Overheating: Excessive heat within the combustion chamber can cause the piston to expand beyond its designed tolerances. This can result from factors such as coolant system failure, incorrect fuel-air mixture, or prolonged high-load operation.

Contaminants: The presence of foreign particles or contaminants in the engine oil can cause abrasive wear on the piston and cylinder wall, leading to increased friction and the potential for seizure.

Improper Clearances: If the piston-to-cylinder clearance is not within the specified limits, either too tight or too loose, it can affect proper lubrication and thermal expansion, increasing the risk of seizure.

What Action will You Take if Main Engine Piston is About to Seize?

Shut down the engine: If you think your piston is about to seize, the first thing you should do is shut down the engine. This will help to prevent further damage.

Check the oil level: Once the engine is shut down, check the oil level. If the oil level is low, add oil until it reaches the correct level.

Inspect the piston: If you can, inspect the piston for damage. If the piston is damaged, it will need to be replaced.

Change the oil: Once you have inspected the piston, change the oil. This will help to remove any contaminants that may have caused the piston to seize.

What are The Forces Acting On Tie Rods?

2023-05-23T19:46:00.001+05:30

Tensile force: The tensile force is the force that pulls the tie rod apart. It is caused by the firing pressure of the cylinders. The firing pressure is the force that is generated when the fuel ignites in the cylinder. This force pushes down on the piston, which in turn pushes down on the connecting rod, which in turn pushes down on the crankshaft. The crankshaft then transmits this force to the tie rods. The tie rods must be strong enough to withstand this force without bending or breaking.

Compressive force: The compressive force is the force that pushes the tie rod together. It is caused by the weight of the engine and the forces generated when the engine is running. The weight of the engine is the force that pulls down on the engine block. The forces generated when the engine is running are the forces that are created by the pistons moving up and down in the cylinders. These forces push up on the engine block. The tie rods must be strong enough to withstand these forces without bending or breaking.

Torsional force: The torsional force is the force that twists the tie rod. It is caused by the forces generated when the engine is running. The forces generated when the engine is running are the forces that are created by the pistons moving up and down in the cylinders. These forces cause the engine to rotate. The tie rods must be strong enough to withstand these forces without bending or breaking.

Bending force: The bending force is the force that bends the tie rod. It is caused by the forces generated when the engine is running. The forces generated when the engine is running are the forces that are created by the pistons moving up and down in the cylinders. These forces cause the engine to bend. The tie rods must be strong enough to withstand these forces without bending or breaking.

How does low sea water temperature effect fresh water generation?

2023-01-29T13:08:00.001+05:30

Low sea water temperature can affect the efficiency of fresh water generation through distillation, a process that uses heat to vaporize seawater and then condense the resulting steam into fresh water. The effects of low sea water temperature on distillation include:

Reduced efficiency: Lower temperature seawater has less thermal energy, making it more difficult to vaporize. This can lead to a decrease in the amount of fresh water produced, longer distillation times, and increased energy consumption.

Increased scaling: Cold seawater can cause mineral scaling on the heat transfer surfaces, reducing the efficiency of heat transfer and making it more difficult to vaporize the seawater.

Increased fouling: Cold seawater can also cause fouling of the heat transfer surfaces, reducing the efficiency of heat transfer and the performance of the distillation system.

To mitigate these effects, ship operators may need to take steps to warm the seawater before it enters the distillation system, such as using a heat exchanger, or install additional pre-treatment systems to prevent fouling. These measures can help maintain the efficiency of fresh water generation and reduce operating costs

What is Water Hammering and How Will You Prevent it?

2021-09-05T18:53:00.004+05:30

What is Water Hammering?

When steam contact with cold area of the pipeline or in contact with water, it condenses and create vaccum, Which forces the water towards opened valve at high velocity and hit the valve with high speed make hammering sound.

How to Prevent Water Hammering?

> Drain the line before allowingsteam to the pipeline

> Slowly allow the steam by opening steam valve sowly

> Install steam trap in the line.

Oil In Cascade Tank (Hot well) Cause And Action

2021-08-26T09:30:00.002+05:30

Cause

> Most probable cause is leaky fuel oil heaters. Any leaks in oil heaters leads oil in cascade tank.

> Deck cargo tank steam line leak

Action

> Reduce load on boiler

> Keep a watch on Observation tank oil level

> With proper PPE Open top cover of Cascade tank.

> If less oil, drain it from top or add a chemical that breaks the oil infine particles.

> If more oil, manually remove it by absorband pads or remove it by weldon pump from top.

> In no case emulsified water to go in boiler.

> Once leak identified shut down boiler if necessary.

> Shut the I/L valve to Atm. Condensor.

> Check Atm.Condensor drain for oil traces in atm. Condensor. If yes flush it completely.

> Check boiler water condition from sampling line. Find out if any oil present in boiler.If yes Do a Scum blow down.

> Take a sample again, if oil traces that means boiler too much contaminated, then completely blow down the boiler.

> Make sure Of MARPOL ANNEX 1 in this case.

> Oil content to be <15 ppm Or We would have to drain in Bilges or Collect it in a seperate drum then give it to Port reception.

> Flush clascade tank after cleaning

> Flush Boiler with FW

> Check cascade water samples

> Once all samples ok Take water in cascade tank

> Take water in boiler

> Do Cold firing

> Increase the load slowly

> See how much time it takes for the steam to rise.

> If it takes more time, that means oil is still present and will take more time to raise steam.

> Proceed further according to action req.

How to Find Out Leaks

> If ER leak check heaters= open heater drains and confirm.

> If ER tanks heaters leak = open the steam trap drain and confirm.

> If Deck cargo tank steam lines leak = open return lines and check on deck.

> If a Observation tank is given on deck, then check there.

Basic Terms In Marine Refrigeration System

2021-07-06T20:13:00.002+05:30

Which Refrigerants Used Nowadays?

Freon 11&12 are CFC and are banned now; Freon 22 are HCFC and can be utilized by 1 st Jan 2020; and only HFC-133, HFC-134, HFC-404 will be in use later

What is relative humidity ?

> Ratio of amount of water vapour in given volume of air, to maximum amount of water vapour that can be present before precipitation occurs.

> It is the mass of water vapour per unit volume of air compared to the mass of water vapour per unit volume of saturated air at the same temperature.

What is critical temperature ?

> Critical temperature is the temperature above which it is impossible to liquefy the refrigerant regardless of pressure.

> It should be as high as possible and certainly above the maximum expected condenser temperature.

What is saturated air ?

The air contains maximum weight of water vapour at the particular temperature.

What is superheating ?

Keeping refrigerant at a temperature above the saturated temperature.

Procedure for Starting and Stopping of Refrigeration Plant?

2021-07-06T20:10:00.001+05:30

Starting

> Check oil level in the compressor.

> Open the condenser cooling valves, close the drain cock and start cooling water pump

> Open all the refrigeration system valves except the compressor suction valve. ensure that compressor discharge is open .

> Start Blower and put the solenoid valve in auto

> check power supply to the compressor and solenoid valves.

> Now open the suction valve of the compressor and start the compressor.

> observe the system for any abnormal operation for ten minutes before putting it in “auto-mode”

> The system generally operates automatically once started. If the temp., in the room rises, solenoid valve opens and the refrigerant then flows through the evaporator through the expansion valve. As the refrigerant flows through the evaporator, compressor suction pressure begins to rise. This suction pressure is sensed by the “lpco” which cuts-in at it’s high pressure setting and starts the compressor.

> When the intended cold temp., is reached, the thermostat closes the solenoid valve.

> Compressor continue running, unloading the cylinders until the suction pressure is low enough to actuate low pressure cut off (LPCO). When set pressure is reached the “lpco” switch stops the compressor.

Stopping

> Refrigeration plan cut in and cut off automatically here below the procedure for manual stopping

> Close the discharge valve of the condenser.

> When the compressor suction pressure below set point compressor will be cut off by low pressure cut off

> When the compressor suction side pressure come up it will run for some time and cut off let it do the same process 2 time and allow whole refrigerant in condenser

> Close the suction and discharge valve of compressor

> Switch off the breaker.

How to Charge Refrigeration Plant on Ships?

2021-07-06T20:06:00.001+05:30

Charging can be done by two method,

> Vapour charging

> Liquid Charging

Vapour charging

In vapour charging vapour refrigerant introduced in the suction side of the compressor

Liquid Charging

In Liquid charging liquid refrigerant charge through the charging point provided near the receiver.

Procedure

> Kept the charging Bottle on weighing machine note down the weight

> Connect the bottle to charging valve with connection pipe

> Before connecting to the charging valve remove air by crack open the bottle

> Tighten the cap and open bottle valve fully, charging valve is still closed

> Change compressor to manual running and start it

> Close the condenser outlet valve

> Open the charging valve slowly when suction pressure is just above zero.

> Control the valve opening slowly

> Monitor the level through condenser sight glass

> Close the charging valve

> pumping down the entire charge until suction pressure just above zero

> Stop the compressor and close the discharge valve.

> Cooling water kept running for an hour.

> Purge air through the purging valve provided on condenser top

> Calculate the amount of refrigerant by weighing the cylinder.

What are The Symptoms And Remedies of Over Charging And Under Charging

2021-07-06T19:59:00.009+05:30

Over Charging

Symptoms

> Compressor runs cold.

> High compressor discharge pressure.

> Excess frost on compressor suction line after evaporator.

> Sight glass shows full of refrigerant

Remedies

> Collect excess refrigerant gas to collecting bottle

Under Charging

> Low discharge pressure

> Large bubbles in the liquid sight glass

> Compressor delivery temperature high.

> Compressor continuously run without cut off or the cutoff interval will be too long

Remedies

> To charge the refrigerant until the bubbles disappear in the liquid sight glass and charging will correct the pressure gauge reading.

> To find out the leaky points by halide torch or soap solution or electronic leak detector.

Explain Marine Refrigeration System With simple Diagram

2021-07-06T19:39:00.003+05:30

Components

> Compressor: Reciprocating single or two stage compressor is commonly used for compressing and supplying the refrigerant to the system.

> Condenser: Shell and tube type condenser is used to cool down the refrigerant in the system.

> Receiver: The cooled refrigerant is supplied to the receiver, which is also used to drain out the refrigerant from the system for maintenance purposes.

> Drier: The drier connected in the system consists of silica gel to remove any moisture from the refrigerant

> Solenoids: Different solenoid valves are used to control the flow of refrigerant into the hold or room. Master solenoid is provided in the main line and other solenoids are present in all individual cargo holds or rooms.

> Expansion valve: An Expansion valve regulates the refrigerants to maintain the correct hold or room temperature.

> Evaporator unit: The evaporator unit acts as a heat exchanger to cool down the hold or room area by transferring heat to the refrigerant.

> HP and LP cut out: LP cut out is controlled automatically i.e. when the suction pressure drops, the compressor stops and when the suction pressure rises again, the control system starts the compressor. HP or high pressure cut out is provided with manually reset

> Oil Differential Pressure switch compares the measured lubricating oil pressure to the Suction (crankcase) pressure. Should the differential pressure fall below a pre-set minimum (about 1.2 bar) then the compressor will trip and require a manual reset to restart. A time delay is built into the circuit to allow sufficient time for the lubricating oil pressure to build up when starting before arming the circuit.

Simple Notes For Marine Refrigeration System | Guide

2021-07-01T20:26:00.001+05:30

It is a complete guide for Marine Refrigeration System on ship. This is a good collection of notes prepared in the purview of Marine exams in a simple and easy understandable language with bullet points.

As it is impossible to answer all questions at a time it is done on timely basis. please comment below or contact on admin@marinesite.info, once you find any important area, missed out. Also contact us, if you wish to answer any of the questions listed.

Refrigeration

Basics

> Basic Terms In Marine Refrigeration System

> Principle Of refrigeration With Simple Diagram

> Explain Marine Refrigeration System With simple Diagram

> Thermostatic Expansion Explain with Simple Diagram

> Use Of Back pressure valve In Refrigeration System

> Refrigerator LO properties

> Properties of Refrigerant

> What is super heating in refrigeration system

> PH diagram of refrigeration cycle

Procedures

> Procedure for Starting and Stopping of Refrigeration Plant?

> How to Charge Refrigeration Plant on Ships?

> Air in refrigeration system indication and procedure to remove
> Leak detection methods in refrigeration and A/c System

Alarm And Safeties

> Safeties in Refrigeration system

Troubleshooting
> Short Cycling in refrigeration and A/C

> What are The Symptoms And Remedies of Over Charging And Under Charging

Marine Refrigeration Important MEO Class 4 Topics

2021-07-01T09:08:00.003+05:30

Here I have tried my level best to list almost all possible questions from Marine Refrigeration System And Air-conditioning. As it is impossible to answer all questions at a time I am doing it on timely basis. If you find that I have missed out any questions, please hint me by commenting below or mail at admin@marinesite.info. Repeatedly asked questions marked as V.imp and Imp so please do give special attention for those questions

If interested in answering unanswered questions please do mail us admin@marinesite.info. Your small contribution can make a big change in someone’s life

Refrigeration

Basics

> Basic Terms In Marine Refrigeration System

> Principle Of refrigeration With Simple Diagram (Imp)

> Explain Marine Refrigeration System With simple Diagram

> Thermostatic Expansion Explain with Simple Diagram (Imp)

> Use Of Back pressure valve In Refrigeration System (Imp)

> Refrigerator LO properties (Imp)

> Properties of Refrigerant (Imp)

> What is super heating in refrigeration system (V.Imp)

> PH diagram of refrigeration cycle

Procedures

> Procedure for Starting and Stopping of Refrigeration Plant?

> How to Charge Refrigeration Plant on Ships? (Imp)

> Air in refrigeration system indication and procedure to remove (Imp)
> Leak detection methods in refrigeration and A/c System

Alarm And Safeties

> Safeties in Refrigeration system

Troubleshooting
> Short Cycling in refrigeration and A/C (imp)

> What are The Symptoms And Remedies of Over Charging And Under Charging (V.imp)

Marine Sewage Treatment Plant (STP) Simple Guide | Notes

2021-06-30T10:20:00.007+05:30

It is a complete guide for Sewage Treatment Plant (STP) onboard ship. This is a good collection of notes prepared in the purview of Marine exams in a simple and easy understandable language with bullet points.

Basics

> Explain Working Principle of STP with the help of diagram
> What is BOD ( Biological Oxygen Demand)?
> Why anaerobic bacteria is not used in STP?
> Why there is a vented loop or Anti-siphon tube after STP and before overboard Valve?

> What are the tests in STP

Maintenance

> Sewage Treatment Plant Maintenance Routines

Troubleshooting

> Reason for STP blower failure and Action taken
> Reason for grey colour discharge from STP?

Marine Sewage Treatment Plant Maintenance

2021-06-30T10:17:00.003+05:30

Regular maintenance is required to ensure biological treatment process is running smoothly and there is no malfunctions with the risk of anaerobic process resulting formation of methane gas and toxic fumes

Daily

> Check for any abnormal alarms

> Check smell and abnormal noise from blower and pump

> Check the sludge return flow from settling tank to aeration chamber

> Check the chemical dosing tank

Weekly

> Take a sludge content test

> check chlorine content of effluent

Monthly

> Check aeration lines are clear. If solenoid valves are present check the working of the same.

> Do backwash if the sludge content is high

> Check that there is no obstruction in the venting line

> Inspect the tank’s external and internal coatings for corrosion

> Try out all the external valves

> Try out high level alarms

Yearly

> Empty whole system and clean thoroughly

> Clean the floats for pump cut in and cut of as well as high level alarm

> Replace the gaskets if required

> Replace the non return valve in case of vacuum STP

Marine Sewage Treatment Plant On Ship Principle and Working

2021-06-30T09:58:00.002+05:30

There are two methods used onboard to treat the sewage, chemical or biological methods. The chemical method is basically a storage tank which collects solid material for disposal in permitted areas or to a shore collection facility. The biological method treats the sewage so that it is acceptable for discharge inshore.

The most preferred sewage treatment in ship is biological sewage treatment i.e., using aerobic bacteria. So we will discuss only biological treatment plants here.

Principle

The basic principle of a biological sewage treatment plant is decomposition of raw sewage with the help of aerobic bacteria. This is done by aerating the chamber with fresh air. The extended aeration process provides a climate in which oxygen-loving bacteria multiply and digest the sewage, converting it into a sludge. These oxygen-loving bacteria are known as aerobic bacteria.

Working

A typical ship STP is having 4 chambers

> Primary Chamber

> Aeration Chamber

> Settling Chamber

> Chlorination Chamber

Primary Chamber

The row sewage enters the primary chamber via a coarse mesh filter where large solids are broken down. The advantage of breaking sewage in small particles is that it increases the area and a high number of bacteria can attack simultaneously to decompose the sewage.

Aeration Chamber

The sewage enters the aeration compartment where it is digested by aerobic bacteria and microorganisms. The aeration chamber is where the main biological action takes place. Here air blowers mounted on the outside of the unit oxygenate and stir the effluent and bacteria mix via a series of pipes and nozzles. The sewage remains in this aeration tank for some time.

The sewage is decomposed into carbon dioxide, water, and inorganic sewage

Settling Chamber

The sewage then flows into the settling compartment where the activated sludge is settled out. Any solids that settle out are returned via an air lift to the aeration chamber which ensures that they are fully broken down. This returned sludge contains the bacteria to digest the incoming sewage.

Chlorination Chamber

The clear liquid then overflows from the settling tank to the chlorination chamber, and the chlorinator disinfects the liquid. The chamber has float switches, which control the discharge pump, and a high level alarm.

Starting and Stopping Procedure of Oily Water Separator (OWS)

2021-06-29T20:35:00.008+05:30

STARTING

> Get the permission from bridge (duty officer should know if OWS is running new ships having OWS master breaker on bride)

> OWS overboard manual discharge valve is to be kept locked and keys are to be kept with the chief engineer or master.

> Open the lock and overboard valve

> Open all required valves for the operation

> Open the desired bilge tank valve from which the oily water mixture is to be discharged from OWS

> Open air if the control valves are air operated

> Switch on the power supply of the control panel and OCM unit

> Fill the separator and filter unit with fresh or sea water to clean up and prime the system until the water comes out from the vent of the second stage

> Close the vents

> Start the OWS supply pump

> Monitor the OCM for ppm value and keep checking sounding of bilge tank from where the OWS is taking suction

> Also check the sounding of the OWS sludge tank

> A skin valve / sample valve is provided just before the overboard valve and after the 3-way valve. Keep a check on the sample for any effluent and clarity

> Keep a watch on the ship side at the overboard discharge valve

> Monitor the sounding at frequent intervals.

STOPPING

> When the operation of bilge water overboard is finished, flush the OWS with sea / fresh water for at least 10 minutes

> This is done to ensure that the oil mixture which resides in the separator may be prevented from getting decomposed

> Open the oil drain valve manually and discharge the separated oil from the separator as much as possible

> Turn off the electric / pneumatic supply for 3 ways and also of the drain valves

> Turn off the power supply of oil content monitor

> Flush the oil content monitor with fresh water and clean the same

> Turn off the electrical supply to the bilge pump and shut its valves

> Shut all the valves in the bilge pipeline going to the OWS

> Lock the overboard valve

> Inform bridge and Switch off the breaker from bridge

> Keys should be handed over to the chief engineer

> Entry is to be made by the chief engineer in the oil record book, along with the signature of the operating Engineer, the chief engineer and the master

You Can Answer Following Procedure

> Describe the operating procedure of an oily water separator?

Different Types Of Filters Used In OWS

2021-06-29T20:32:00.006+05:30

Type of Filters used in OWS

Coalescence type:

Hydrophilic material i.e. glass wool.
Absorbs water rather than oil.
Has to be renewed after certain periods.

Absorption type:

Oleophilic material
Absorbs oil rather than water.
Frequent replacement is not required.

High rate of separation is favored by:

> Large size of oil globule.

> Elevated temperature of the system ( i.e. lowers viscosity of oil, density of oil-water but oil is higher).

> Residence time.

> Avoidance of turbulence or agitation.

> Laminar or stream line flow.

> Low viscosity of oil globule.

What is Under Charge and Over Charge Condition in Hydrophore

2021-06-28T14:46:00.007+05:30

Under Charge

The pressure inside the hydrophore is below the rated pressure range and is called under charged condition. This condition is the result of air leaking from either; relief valve, isolation valve, air supply valve, vent valve or the gauge glass itself. The situation can be found with no water supply at the accommodation top.

Over Charge

The pressure inside the hydrophore above the rated pressure is called overcharged condition. This condition is because of a leak in the air supply valve. The situation can result in no water in the hydrophore tank in some cases and thus be reacted quickly with care.

Reasons For Continous running or Frequent Cut-in & Cut-off Hydrophore Pump

2021-06-28T14:35:00.009+05:30

Continuous running of the hydrophore pump

> Mainly continuous running of pump is due to the insufficient air pressure, so charge air as per manufacturer's instructions

> Due to wrong setting of pressure switches or faulty pressure switch.

> Problems with pumps, such as loose suction, insufficient capacity, high water consumption rates etc.

> Under Charge

Frequently cut-in and cut-out of hydrophore

> Cut in and cut off the differential set too narrow

> Faulty pressure switch

> Vent is leaking

> Gauge is leaking

> Air is leaking from any damaged joint in the shell

> Under Charge

What is Priming In Freshwater Generator? Reasons

2021-06-28T11:26:00.004+05:30

What is Priming In Freshwater Generator?

Salt water carried over in large quantities during operation of the fresh water generator is called priming.

General reasons of the priming are:

> Level of salt water inside the shell is high. When the water level is high agitation due to boiling occurs and salt water may carry over along with the vapours.

> When the salt water brine density is too high, agitation of salt water occurs which results in priming.

> Increased evaporation rate.

Fresh Water Generator Troubleshooting

2021-06-28T11:15:00.001+05:30

Low fresh water production

> sea water pressure low because of Ships draft, choked filters, fault in pump etc.

> Level of brine is too high

> Faulty Ejector nozzle/ nozzle choked

> Incorrect feed

> scale formation in evaporator or condenser

> shell temperature is too high

> condenser cooling water flow is reduced

> Condenser cooling water temp. too high

> Incorrect assembly of plates

> improper vacuum dueto the leakage in plants like from pressure gauge, vent, distillate pump seal etc.

Vacuum is not maintaining

> Air leaks into the evaporator shell in large quantities and the air ejector cannot cope.

> The cooling water flow through the condenser is reduced or the cooling water temperature is high. This causes saturation temperature and hence saturation pressure within the condenser to rise.

> Malfunctioning of the air ejector.

> The flow rate of the heating medium increased and excess water vapour produced. Since this excess vapours cannot be condensed, shell pressure increases or vacuum falls.

Increase in Salinity of Freshwater

> Brine level inside the shell too high.

> Leaking condenser tubes or plates.

> Operation of evaporator near shore with contaminated feed water.

> Shell temperature and pressure are too low.

> Increased solubility of CO2 generated from the salt water due to reduced seawater temperature. This dissolved CO2 makes water acidic and conductivity of water increases. Hence salinometer shows increased salinity, which is a measure of conductivity and not the presence of salt.

Starting And Stopping Procedure Of FreshwaterGenerator

2021-06-28T11:01:00.008+05:30

Starting

> Open seawater ejector pump suction, discharge and overboard valves.

> Start the ejector pump, discharge pressure must be more than 3bar.

> Wait for the vacuum to build up inside the fresh water generator shell. (About 92 % vacuum).

> Open the feed water valve to feed seawater to the evaporator. Adjust the feed water pressure. Normally marking is provided on the pressure gauge for desired feed water pressure.

> Open main engine jacket cooling water inlet and outlet to the evaporator gradually.

> Open the air vent clock at the top of the evaporator to make sure the evaporator is filled with jacket cooling water. Air must be purged out if any.

> Throttle the jacket cooling water by-pass valve

> Switch on the salinity alarm panel for measuring the purity of the freshwater produced.

> There will be a sight glass provided at the suction line for the distillate pump. Make sure condensed water is coming to the suction line.

> Start the distillate pump and open discharge valve to lead generated water to specified storage tanks.

Checks during running

> Through the sight glass provided in the evaporator shell, observe flashing of water.

> Also, check for the brine level inside. It should not be too high or too low.

> Shell temperature must be around 50 deg cel.

> Make sure the shell vacuum is more than 90% from the vacuum gauge.

> Check seawater inlet and outlet temperature to the condenser.

> Ensure seawater pressure at air ejector inlet more than 3 bars.

> Check for distillate pump pressure and water flow meter.

> Check salinity of fresh water produced.

> Check level and flow of dosing chemicals.

> Check ampere of ejector pump and distillate pump motor.

Stopping

> Slowly open bypass valve for main engine jacket cooling water.

> Ensure that main engine jacket cooling water temperature is within normal limits.

> Close jacket cooling water inlet and outlet valves for the freshwater generator respectively.

> Close the feed water chemical dosing valve.

> Stop the distillate pump and shut discharge valve.

> Switch off the salinity meter.

> Close the filling valve to the freshwater tanks.

> Wait for evaporator shell temperature to drop below 50 deg cel.

> Close the feed water valve to the evaporator.

> Stop ejector pump. Shut the fresh water generator overboard valve.

> Open the vacuum breaker valve to make shell side pressure equal to atmospheric pressure.

> Open the drain valve of the evaporator to drain all the seawater from the fresh water generator.

Overhauling of Centrifugal Pump And Checks

2021-06-23T16:28:00.001+05:30

Overhauling Procedure

> Put off breaker and remove fuse from motor starter box and issue isolation certificate

> Close suction and discharge valve

> Remove suction and discharge pipe flange bolt & nut, coupling bolt of motor coupling

> Remove pump foundation bolts & take out pump from motor

> Remove impeller lock & nut & take out the impeller

> Remove mechanical seal

> Remove bearing cover from other side & take out shaft with ball bearing

> Renew mechanical seal and bearings if required.

> Clean, replace and inspect all parts and assemble.

Important Check points

> Impeller

> Wear ring

> Neck bush

> Ball bearing

> Shaft.

> Mechanical seal

What is Cavitation, Causes and Remedies

2021-06-23T16:24:00.002+05:30

Cavitation can occur when the pump suction contains air or when the pump is running faster than the designed speed

Cavitation is the formation and accumulation of bubbles around a pump impeller. This tends to form in liquids of any viscosity as they are being transported through and around a pump system. When each of these tiny bubbles collapses or bursts, it creates a high energy shock wave inside the liquid. These shock waves hit the impeller and other pump components which cause erosion over time.

Causes

> Air leakage to suction side

> Pressure in the suction side is less than the vapour pressure of that pumping liquid

> High temperature

> Throttled suction valve

> Pump running faster than the designed

> Pump taking suction lower than designed

Indication

> Decreased Flow or Pressure

> Erratic Power Consumption

> Pitting

> Noise

> Vibration

> Decrease in the pump efficiency.

How to Prevent Cavitation

> Reduce motor speed (RPMs). Note: Slowing the pump down will reduce flow rate and head pressure.

> Incorporate a booster pump into your pump system. This will take some of the stress off of your primary pump.

> If possible, reduce the temperature of your pump, liquid, and/or other components.

> Increase liquid level around the suction area.

> Always keep NPSHA greater than NPSHR