Pumps/Injectors/Ejectors Flashcards
List eight reasons why a bilge pump may not be able to remove water from an engine room bilge.
- Choked strum box Broken seals on strum box or Pump suction filter is dirty
- Another valve has accidentally been left open so pump sucking from an empty bilge well
- Failure of pump priming system and or Discharge valve has been left closed
4 pipeline is damaged, so air is leaking or holes on pipe allowing air in
- Pump is mechanically worn/damaged or obstructed
- Coupling between motor and pump is broken.
- insufficient level in bilge well to maintain suction
- bilge suction or delivery valve is damaged
With reference to of a gear pump suitable for use with fuel or lubricating oil:
a) Sketch a cross-section indicating flow of fluid (8)
b.) Explain the working principle of a gear pump
a.) see EOOW ORAL sketch pack
b.) Fluid enters external gear pump at suction side and flows around the drive gear and the other inner casing part and flows towards the discharge side as the gears become interlocked, volume is reduced and fluid is forced out under pressure. fluid isn’t transferred through the centre because gears are interlocked. due to the small gap between the gears and casing this prevents fluid leaking back from the discharge side (depends on viscosity) if low there is more leakage.
These pumps supply a constant volume at the correct pressure and are self regulating and so wont need controlling. theyre always full of liquid so theres no suction or delivery valves. however if control is required this can be achieved by using a bypass valve for single speed AC drives or with the use of electronically controlled variable AC or DC motors.
Advantage of these pumps is the constant volume output. the pump is ideal for situations like the LO pressure feed to diesel engine bearings where slightest hesitation in flow can cause LO starvation to bearings and therefore lead to bearing failure.
With reference to centrifugal pumps:
a) State why the pump can be started with the discharge valve closed; (8)
The pump works on principle of changing the momentum of the liquid. As the impeller of the pump rotates at high speed, a centrifugal force is created. The force gives kinetic energy to the fluid as its thrown from the eye of the impeller to the outer part. The impeller rotates inside a volute casing; whose cross-sectional area increases as it nears the pump outlet. This acts as a diverging nozzle that converts the kinetic energy in the fluid to pressure energy. the increase in pressure energy is proportional to the fluids velocity. Fluid velocity is also proportional to momentum of fluid due to discharge valve closed there can’t be any momentum.
Addtionaly when discharge valve is closed pressure in discharge side will increase, which will lead to water coming back to pump impeller section and there is no discharge because discharge valve is closed so nowhere for the fluid to go and so same amount of water keeps on rotating within pump body (churning). in due time water temperature increases but it takes time to reach vaporisation temperature of water (cavitation) and for the amount of time temperature is increasing to vaporisation temperature there will not be any direct damage on pump or associated equipment.
Therefore, it is perfectly safe to start the centrfugal pump with the discharge valve closed, without causing over pressurization or any damage to pump equipment.
However should the length of time exceed and water reach vapourisation temp then this results in cavitation and the churning will raise the internal temperature of the pump leading to overheating this is dependant on the length of time outlet discharge is closed. therefore its not possible to run the centrifugal pump with the discharge valve closed
State possible reasons for the pump failing to achieve suction from a double bottom tank. (8)
- pump suction line is is blocked it must first be cleaned of any debris. When suction line is blocked the pump can’t crate enough suction and therefore it can’t transfer anything out of double bottom tank.
- Pump wear ring wear plate is damaged and or vanes for impeller. If the vanes on the impeller are worn, the hydraulic capacity of the pump is reduced. Same with the wear ring and wear plate. This is because clearances open up due to wear, so more recirculation occurs inside the pump and reduces the pump’s flow.
- Excessive Clearances
If clearances are too wide for the type of fluid pumped, excessive slip will occur. Fluid will continue to recirculate inside the pump, causing lower flow output for the pump. - Debris in the impeller
If the eye of the impeller is plugged with debris, it removes the hydraulic capacity of the impeller to create an area of low pressure. - Running Dry:Operating the pump without proper fluid flow (running dry) can cause excessive heat, seal damage, and accelerated wear on pump parts. Adequate training and awareness among the vessel engine crew regarding the importance of maintaining sufficient fluid levels are crucial for preventing such issues.
What is meant by Eductor ?
Eductor is a simple type of pump which works on the ‘venturi effect’ to pump out air, gas or liquid from a specified area. Eductor require only a motive fluid or driving fluid for its operation. When the driving fluid is passed through the eductor at the required capacity (which depends on the design of the eductor), a low pressure is created inside it. This low pressure or vacuum enables the eductor to suck liquid or gas from a certain area. This liquid or gas is pumped out through the driving fluid discharge. Eductor works on Bernoulli’s principle. It states that an increase in the speed of a fluid occurs simultaneously with a reduction in pressure
Draw an eductor to help explain the working principle
see EOOW ORAL/IAMI Sketch pack
The driving fluid (normally seawater or air on ships) is allowed to pass through the nozzle(3) and diffuser(2) as shown in the drawing. When the driving fluid achieves desired pressure and capacity, it starts taking suction through the suction side. Normally valves will be connected to driving fluid inlet, discharge side and suction side of the eductor.
state the procedure for operating an eductor
To operate the eductor follow the procedure below.
Open driving fluid inlet valve and discharge valve of the eductor.
Start the driving fluid pump (normally fire pump) and regulate the pressure to obtain necessary capacity for the operation of the eductor.
Driving pressure varies with the discharge head.
Now open suction the valve for enabling eductor to take suction from the desired compartment.
Never open suction valve before achieving desired capacity of driving fluid. It may cause back flow of driving fluid through suction.
Similarly, before stopping, first close the suction valve before stopping driving fluid. (For the same reason stated above).
what are parameters of a standard bilge eductor used on ships.
The design parameters of a normal bilge eductor used on ships are the following:
Driving Fluid Pressure: 7 kg/cm2
Driving Capacity: 20 m3/hr
Suction Head: -7 mAq
Suction Capacity: 5 m3/hr
Discharge Head: 6 mAq
Weight: 20 kg
draw a performance curves for an eductor and explain what can be seen from these
From the suction flow capacity curve shown above it can be seen that, for the same discharge head, suction capacity varies with a change in driving fluid pressure. For example, keeping discharge head as 6 mAq, suction capacity is 3 m3/hr and 5 m3/hr for driving pressures of 5 kg/cm2 and 7 kg/cm2 respectively. Increasing driving fluid pressure above designed pressure will not increase the design suction capacity. On the other hand, reduction of driving pressure below design pressure leads to reduction in suction capacity. higher discharge head (or back pressure) results in reduced suction capacity. Also, driving flow capacity curve shown below gives us the driving capacity for a particular driving pressure.
what are examples of where a eductor would be used on a ship?
For creating vacuum in freshwater generator
In vacuum toilet systems
As self-priming system for centrifugal pumps
Foam applicator in fire extinguishing system
For pumping out water from bosun store, chain locker, etc.
what are examples of common problems that can occur with eductor
Clogged Nozzle or Throat
The most common cause of trouble in the eductor is restriction of fluid flow in the nozzle or throat with foreign particles. Particles lodged in the nozzle or throat can be removed with a soft material such as wood. Do not use hard or sharp materials as these can cause permanent damage to the eductor.
Low Driving Pressure
Driving fluid pressure below specified may result in loss of suction capacity or even back flow of fluid to the suction side.
High Back Pressure
Suction capacity will reduce drastically when the back pressure of driving fluid increases. This effect can be reduced by increasing the driving fluid capacity or pressure. So back pressure always to be monitored during operation of eductor.
What is cavitation ?
Cavitation occurs when the pump suction line contains air or when the pump is running faster than the designed speed. If the pump is allowed to run with air or faster than designed speed than low pressure regions occur in the flow at points where high local velocities exist. Also vaporisation occurs due to these low pressure areas and then bubbles form, these expand as they move with the flow and collapse when they reach a high pressure region. Such formation and collapse of bubbles is very rapid and collapse near a surface will generate very high pressure hammer blows which results in pitting, noise, vibration, and fall in the pump efficiency. Therefore to avoid damage to the pump by cavitation the pump should be run at designed speed, the throttiling of the suction should be avoided and to avoid air in the pump suction line when the pump is being started the priming system should be used to prime the pump and remove any air, except of course for pumps which are self priming like positive displacement pumps.
Cavitation can occur due, generally to the following factors:
increase of the temperature of the pumped liquid
a reduction or frequent oscillation in suction pressure
increase or reduction in the velocity or flow of the fluid due change in the fluid viscosity
undesirable flow conditions caused by obstructions or sharp elbows in the suction piping
If the pump operates under cavitation conditions for long period of time, the following can occur:
premature bearing failure
pitting or erosion marks on the impeller and casing wall of the pump
premature mechanical seal failure
failure of the pump shaft and other fatigue failures in the pump components.
What are the reasons for ballast pump not delivering water ?
Incomplete priming
Too high suction lift
Low net positive suction head
Air leaks in suction line
Gas or air lock
Suction filter choke
what is the procedure for a Screw pump overhaul ?
Put off breaker and remove fuse from motor starter box
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 cover both side & remove driver screw & driven screw with bearing and mechanical seal
Inspect mechanical seal, bearing and renew if required.
Clean all parts and assemble back.
after screw pump is assembled what parts should you pay attention to make sure everything is correct before you put pump back into operation
Mechanical seal
Bearing
Driver screw and driven screw wear & tear
Pump casing internal surface wear
Clearance between driver and driven screw
Clearance between driver and casing.
What is the centrifugal pump overhaul procedure ?
Put off breaker and remove fuse from motor starter box
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 and inspect all parts and assemble.
after centrifugal pump is assembled what parts should you pay attention to make sure everything is correct before you put pump back into operation?
Impeller
Wear ring
Neck bush
Ball bearing
Shaft.
Mechanical seal.
describe the procedure for Starting up a Screw Pump
The complete pipe line system must be flushed and pressure tested before installing and operating the pump.
If any corrosive liquid is used, then complete system to be properly drained and dried for protection.
Before starting the pump for the first time, it must be completely filled with working liquid to prime the pump.
Line up all the valves in the pumping system to avoid liquid pressure build up as well as pump losing suction.
Make sure the prime mover motor is isolated electrically and turn the pump-motor coupling by hand to check it is turning smoothly.
When pump is ready to be started, first briefly switch on and off the motor and check the direction of rotation is as per the marking on the pump.
Start the pump and keep checking suction and discharge pressure gauges for rated pressure.
Check prime mover motor ampere and compare with rated current.
Check for any leakages from mechanical seal or other joints of the pump, flanges, etc.
Air in the pumping liquid causes abnormal vibration, noise and over heating of the pump and liquid which may result in a fire hazard.
Periodically inspect foundation bolts, coupling pads, leakages and performance of the pump as condition monitoring to avoid breakdown maintenance.
describe the Maintenance carried out on Screw Pumps
Pump to be overhauled at regular intervals, not exceeding 3 years.
Wear of spare parts greatly depends on the pumping medium.
Pump screws, liner, etc. are lubricated by the pumping liquid itself. So it is important to avoid presence of any abrasive particles in the pumping medium.
Hence pump strainer must be cleaned regularly, by monitoring suction pressure of the pump.
A gradual reduction in the suction pressure of the pump indicates that the suction filter is getting chocked.
Indication of pump parts wear can be identified from abnormal noise, vibration, loss of capacity, reduction in discharge pressure, etc.
Inspect internal parts carefully while overhauling. Internal clearances in the pump, which are vital for its proper function, may have been affected by wear of rotors and bores or liner.
Acceptable wear can be determined only by experience of the actual application. As a rule of thumb the following max clearance values may apply: Between rotor and bores: 0.2 mm, Between rotor flanks: 0.4 mm.
Inspect for any scratches inside.
Check the condition of the mechanical seal especially the mating faces and o-rings. Discard the seal if mating face is damaged or o-rings hardened.
Excessively leaking shaft seals (more than 10 drops per hour) should be changed without delay, as the leakage normally will grow worse and cause additional damage.
Gaskets and o-rings of the pump to be renewed while overhauling.
Check shaft bearing for damages and renew if necessary.
Relief valve, valve seat, springs to checked.
It is advisable to overhaul the motor also along with the pump.
below are common problems that occur with screw pumps for each problem provide a cause and a remedy
1 Wrong direction of rotation
2 The pump cannot be primed
3. No flow
4 Flow too low
5 Pressure too low
6 Pressure too high
7 Drive motor difficult to start or tends to stop by tripping the motor overload relay
8 Noise and vibration
- cause = Electric cables to motor wrongly connected.
remedy = Reverse the terminal connection on electric motor.
- cause = Wrong direction of rotation.
Suction line is not open or pressure drop in the suction line is too high.
Major air leakage into the suction line.
The pump cannot evacuate the air through the discharge line due to excessive counter pressure.
remedy = Check all components in suction line. The inlet condition should be checked with a vacuum gauge at the pump inlet. Check the suction line.
Discharge the air through air purge cock at the discharge of the pump
- cause = The pump is not primed.
The pressure relief valve is set below the designed pressure.
remedy = Readjust the pressure relief valve to correct pressure
- cause = The coupling is slipping
The pressure relief valve is set too low (Discharge pressure also low).Something is restricting the flow in the suction line. (This would usually cause noise).
The pumped liquid contains a significant amount of compressible gas, such as free air. (This would usually cause noise).
remedy = Check the condition of the coupling. Re-tighten, renew coupling pads. Readjust the pressure relief valve to get rated discharge pressure.
Check all components in the suction line (strainers, valves etc.). Go through the system and determine if there are any leaks. Rectify if any.
- cause = The pressure relief valve is set too low. Counter pressure in the discharge line is too low due to a major leakage. The valve piston is stuck in open position. Something is restricting the flow in the suction line. (This would usually cause noise). The pumped liquid contains a significant amount of compressible gas, such as free air. (This would usually cause noise). A too small pump has been chosen.
remedy = Readjust the pressure relief valve. Check the components in the discharge line inclusive the recipients.
Check the valve. Check all components in the suction line (strainers, valves etc.).
Go through the system and determine if there are any leaks. Rectify if any.
Check the capacity of the pump.
- cause = The pressure relief valve is set too high. The oil is too cold (or has higher viscosity than anticipated). Counter pressure in the discharge line is too high
remedy = Readjust the pressure relief valve. Reduce the pressure setting until operational temperature has been reached. Check the discharge line.
- cause =relief valve pressure too high.
Liquid too cold. Motor is undersized for the prevailing conditions. Electrical power supply faulty. Motor overload relay set too low or is faulty.
remedy = Readjust the pressure relief valve to a lower value. Thus the power consumption for the pumping is relieved and overloading due to the high viscosity may be avoided. When the liquid has reached normal temperature and thus flows easily, the relief valve is reset to normal pressure. Check the motor.
Check the motor and motor connection.
Readjust or replace the relay.
Readjust the setting of the starting sequence. The time before the motor overload relay is tripped should not exceed 10-15 seconds.
- cause = The flow to the pump is insufficient.
Insufficient support of pipe work.
Air leakage into the suction line.
Faulty electrical supply.
remedy = Check for pipe vibrations in the pump connections. Check that the pipes are sufficiently clamped.
Check the suction line for air leakage.
Check all three phases of the supply.
with the aid of a sketch explain the operating principle of a reciprocating positive displacement pump
see EOOW ORAL/IAMI sketch pack for drawing
A reciprocating positive displacement pump is shown in the drawing above to demonstrate the operating principle. The pump is double acting, that is liquid is admitted to either side of the piston where it is alternatively drawn in and discharged. As the piston moves upwards, suction takes place below the piston and liquid is drawn in, the valve arrangement ensuring that the discharge valve cannot open during suction stroke. Above the piston, liquid is discharged and the suction valve remains closed. As the piston travels down, the operations of suction and discharge occur now on opposite sides.
When starting the pump, the suction and discharge valves must be opened. It is important that no valves in the discharge line are closed, otherwise either the relief valve will lift or damage may occur to the pump when it is started. Positive displacement pumps are self priming, but where possible to reduce wear or the risk of seizure it should be flooded with liquid before starting. An electrically driven pump only need to be switched on, when it will run erratically for a short period until liquid is drawn into the pump. A steam driven pump will require the usual draining and warming through procedure before the steam is gradually admitted. A relief valve is always fitted between the pump suction and discharge chambers to protect the pump should it be operated with a valve closed in the discharge line.
Most of the moving parts in the pump will require examination during overhaul. The pump piston, rings and cylinder liner must also be thoroughly checked. Ridges will eventually develop at the limits of the piston ring travel and these must be removed. The suction and discharge valves must be refaced or ground in as required.
why do positive displacement pumps have an air vessel fitted?
The function of an air vessel, fitted in the discharge pipe, is to dampen out the pressure variations which occur during discharge. As the discharge pressure rises the air is compressed in the vessel, and as the pressure falls the air expands. The peak pressure energy is stored in the air and returned to the system when pressure falls. Air vessels are not fitted on the reciprocating boiler feed pumps since they may introduce air into the de-aerated water.
explain what is meant by NPSH or net positive suction head for centrifugal pump
NPSH stands for Net Positive Suction Head and is a measure of the pressure experienced by a fluid on the suction side of a centrifugal pump. NPSH is defined as the total head of fluid at the centre line of the impeller. The purpose of NPSH is to identify and avoid the operating conditions which lead to vaporisation of the fluid as it enters the pump , a condition known as flashing. In a centrifugal pump, the fluid’s pressure is at a minimum at the eye of the impeller. If the pressure is below the vapour pressure of the fluid, bubbles are formed which pass on through the impeller vanes towards the discharge port. As the bubbles of vapour are transported into the higher pressure region, they can spontaneously collapse in a damaging process called cavitation. The repeated shock waves produced by this process can be a significant cause of wear and metal fatigue on impellers and pump cases. Cavitation also results in vibration and noise in the pump, placing greater strain on the drive shaft and other components, and also in downstream pipework. This can lead to greater maintenance costs and a higher chance of pump failure.
with the aid of a sketch explain the purpose and operation of a self priming unit
see EOOW ORAL/IAMI sketch pack for drawing
Centrifugal pumps are not self priming. If initially there is no liquid a the eye, there will be no pumping action for a centrifugal pump. In absence of liquid, air (sometimes vapour) will be present at the eye, and owing to its light density air could be thrown out under centrifugal force only if the speed of the impeller is very very high (like in a Turbocharger Blower). In such a case, where normally a the start of the pump the level of the liquid is below the eye of the impeller, we can make use of a self priming unit.
Figure above shows an automatic arrangement for pumping out bilges, using a centrifugal pump, wherein the air (vane) pump will get engaged automatically and draw out any air at the start or during running. Once the air is drawn out it will get disengaged automatically.
Discharge side of the pump is connected with one side of the piston (engage / disengage mechanism). Consider the pump is started with no liquid at the eye of the impeller. Now the impeller will be rotating but the absence of liquid at the discharge (means no discharge pressure) makes the piston to move forward due to spring pressure and thus the bevel connected to the air pump rotor shaft engages with the rotating shaft of the centrifugal pump. This drives the air pump to remove any vapour or air present inside the pump suction and the liquid rises to prime the pump. Once the pump is primed discharge commences, discharge pressure rises which acts on the piston thereby pushing the piston against the spring pressure. Thus the air pump gets disengaged. Hence whenever there is any ingress of air or vapour in the pump suction, discharge pressure reduces and air pump engages to remove the same.
Explain with the aid of diagrams what a centrifugal pump is, how it works and its construction.
see EOOW ORAL/IAMI sketch pack for drawing
Centrifugal pump is a device, which adds to the energy of a liquid or gas causing an increase in its pressure and perhaps a movement of the fluid. A simple pumping system consists of a suction branch, a pump, and a discharge branch. Centrifugal pumps are not self-priming pumps. These pumps must be primed by gravity or by priming equipment external or internal with the pump. These pumps can be radial flow, axial flow or mixed flow type. The pump consists of a rotating impeller within a stationary casing. The impeller construction has two discs joined at in between surface by a set of internal curved vanes. Impeller has an eye (opening) at the centre and is mounted on shaft, which is driven by a suitable prime mover such as an electric motor. Opening in the sides of the impeller near shaft, called eye, communicates with the suction branch Assume there is a certain amount of fluid at the eye of the rotating impeller. The fluid will flow radially outwards (because of centrifugal action) along the curved vanes in the impeller, increasing its linear velocity. The high velocity fluid is collected in specially shaped casing called volute casing, where some of the kinetic energy of the fluid is converted into pressure energy. Fluid under pressure now leaves the impeller producing a drop in pressure behind it at the eye of the impeller. (Throwing off the water from the eye of the impeller leaves the space with vacuum). This causes the fluid from the suction pipe to flow into the pump under atmospheric pressure and subsequently that fluid also gets discharged like earlier one. This way fluid in the pump acts like a piston moving outward causing drop in pressure behind it. However, if initially there is no liquid at the eye, there will be no pumping action as explained, since there is no vacuum formed at the eye of the impeller. Centrifugal pump therefore is not a self-priming pump. In such case, where normally at the start of the pump the level of the liquid is below the eye of the pump, a self priming unit is normally attached to the pump which helps to create vacuum at the eye of the impeller hence priming the pump. As soon as pump starts taking suction self priming unit is automatically disengaged.
what is the purpose of a boiler multi stage feed water pump
Boiler multi-stage feed water pumps are designed to efficiently deliver water to the boiler at high pressure and temperature. A multi-stage pump, utilizes multiple impellers arranged in series. The operation involves several stages, each consisting of an impeller and diffuser, progressively increasing the pressure of the water. This multistage configuration allows the pump to handle the high pressures required in boiler systems.
Water inlet:The process begins with the intake of water, usually from the ship’s seawater system or a freshwater source, depending on the vessel’s design. The water is then directed towards the first stage of the pump.
Multi-stage compression:As the water progresses through each stage, the impellers impart kinetic energy to the fluid, and the diffusers convert this kinetic energy into pressure. This multi-stage compression ensures that the water reaches the necessary pressure for boiler operation.
High pressure outlet:The now pressurized water exits the pump and is directed to the boiler, where it plays a crucial role in the steam generation process.
what maintenance is required for a boiler multistage feed water pump
Maintenance of Boiler Multi-stage Feed Water Pumps
Proper maintenance is essential to ensure the longevity and reliable performance of boiler multistage feed water pumps.
Here are key maintenance practices:
Regular Inspections:Scheduled inspections should be conducted to check for any signs of wear, corrosion, or damage to pump components. This includes examining impellers, diffusers, and seals.
Lubrication:Adequate lubrication of pump bearings is crucial for minimizing friction and preventing premature wear. Regularly check and replenish lubrication as needed.
Alignment Checks:Misalignment can lead to excessive vibrations and wear on pump components. Regularly check and adjust the alignment of the pump and motor to ensure proper operation.
Seal Maintenance:Seals play a critical role in preventing water leakage. Inspect and replace seals as necessary to maintain a tight seal and prevent water from entering the pump housing
what are the responsibilities of a EOOW with regards to a boiler multistage feed water pump
Their responsibilities include:
Monitoring and Control:Marine engineers continuously monitor pump performance and system parameters. They use control systems to adjust pump speed and ensure optimal operation based on the vessel’s load and conditions.
Emergency Response:In the event of a pump failure or any abnormal operation, marine engineers must respond swiftly to address the issue. This may involve troubleshooting, isolating the pump, and implementing contingency measures to maintain boiler feed water supply.
Training and Education:Proper training and education of the onboard engineering team are crucial. Engineers should be well-versed in the operation, maintenance, and troubleshooting of boiler multi-stage feed water pumps to respond effectively to any challenges.
Collaboration with Other Departments:Marine engineers collaborate with other onboard departments to ensure seamless coordination of operations. Effective communication is essential to address any issues that may affect the performance of boiler multistage feed water pumps.
familiarize yourself with the specific pump model installed on your vessel. Each pump has its own unique characteristics and maintenance requirements. Consult the manufacturer’s manual for detailed instructions and troubleshooting tips.
explain how to repair a centrifugal pump?
How to Repair a Centrifugal Pump
Repairing a centrifugal pump casing onboard a vessel involves a series of steps and requires specific equipment and materials.
steps:
Preparation:If welding or brazing is chosen as a repair method, preheat the casing to a suitable temperature to avoid thermal stress or distortion. If epoxy resin or other repair material application is chosen, prepare the casing surface for repair by roughening it with abrasive tools. This helps enhance the bond between the casing and the repair material.
Safety Precautions:Before starting any repair work, ensure the pump is shut down, and the associated systems are depressurized to prevent accidents.Isolate the pump from the system by closing the suction and discharge valves and locking them with chains. Switch off and lock the electrical supply to the pump and attach a warning notice. Drain the pump by opening the drain valves and cracking open the flange joints carefully.
Pump removal:Remove the pump from its location by using a chain block or a crane and place it on a suitable workbench or platform. Remove any external fittings or accessories that may interfere with the repair work.
Pump dismantling:Dismantle the pump by following the manufacturer’s instructions or using a general procedure. Remove the impeller, shaft, bearings, seals, sleeves, rings, etc. from the casing and inspect them for any damage or wear. Clean them thoroughly and store them safely for reassembly.
Inspection:Carefully inspect the casing to assess the damage’s extent and location. Common issues include cracks, corrosion, and erosion. Measure the thickness of the casing wall using a calliper or a thickness gauge, if available, and compare it with the original specifications or acceptable limits. Mark the areas that need repair with a marker or a chalk.
Cleaning:Thoroughly clean the damaged area to remove any contaminants, rust, or debris. Proper cleaning ensures better adhesion of repair materials.
Repair method: choose a suitable repair method for the pump casing depending on the type and extent of damage, availability of materials and equipment, and skill level of crew members.The most common repair methods are welding, brazing, soldering, epoxy resin filling, metal spraying, or chrome plating. Each method has its own advantages and disadvantages in terms of cost, durability, quality, ease of application, etc. Therefore, it is important to weigh these factors carefully before selecting a repair method.
why is pump shaft alignment important?
It refers to the precise positioning of the pump’s motor shaft and pump shaft, ensuring their perfect alignment. Accurate alignment enhances pump efficiency, minimizes wear and tear, reduces energy consumption, and extends the pump’s operational lifespan. Misalignment, on the other hand, leads to excessive vibration, premature component failure, and reduced pump performance.
what is an impeller and what kind of maintenance is required for it?
Impeller: The impeller is a vital component that transfers energy to the fluid, inducing its movement.
Proper maintenance of the impeller is essential for optimal pump performance and longevity.
Regular Cleaning: Impellers can accumulate debris, scale, or corrosion, which can hinder performance. Cleaning the impeller periodically helps maintain efficiency.
Inspection for Damage: Impellers should be inspected for signs of erosion, cavitation damage, wear, or corrosion. Damaged impellers can negatively impact pump performance and require timely repair or replacement.
Balancing: Balanced impellers minimize vibrations and reduce stress on pump components. Periodic balancing ensures smooth operation and prolongs the life of the impeller and other pump parts.
what are bearing and mechanical seals
Bearings:The pump bearings support the hydraulic loads imposed on the impeller, the mass of impeller and shaft, and the loads due to the shaft coupling or belt drive. Proper lubrication and monitoring of bearing conditions are crucial. Overheating, excessive vibration, or abnormal noise from the bearings can indicate problems. Regular greasing and replacement, if necessary, help prevent bearing failures.
Mechanical Seals: Mechanical seals prevent fluid leakage along the shaft. They require regular inspection for wear, proper lubrication, and replacement when damaged. Proper alignment significantly extends the life of mechanical seals. Within the pump, the mechanical seal is the component that acts as a barrier between the rotary components and the stationary elements.
The seal needs to be able to prevent leakage at three different places.
In the space between the faces of the seal (both rotational and fixed).
Between the rotating element and the shaft or sleeve of the pump.
Between the stationary element and the housing for the seal chamber of the pump.
what kind of maintenance is carried on mechanical seals
Lubrication and Cooling: Mechanical seals often require a source of lubrication or cooling, such as a barrier fluid, to reduce friction and dissipate heat generated during operation.
Regular Inspection:Periodically inspect the mechanical seals for signs of wear, damage, or leakage. Pay attention to the condition of the seal faces, secondary sealing elements, and the presence of any fluid leakage.
Seal Flush and Flushing Plans:Depending on the application, a seal flush system may be required to remove solids or prevent clogging of the seal faces. Follow the recommended flushing plan provided by the pump manufacturer.
Seal Replacement:Mechanical seals have a limited lifespan and may require replacement when they exhibit excessive wear, damage, or leakage. Timely replacement helps avoid potential failures and ensures continued pump performance.
what are pump wear rings and what kind of maintenance is required for them?
The primary function of wear rings is to minimize wear between the impeller and the pump casing. Wear rings act as a sacrificial surface that absorbs the wear and prevents direct contact between the rotating impeller and the stationary casing. By reducing the clearance between the impeller and casing, wear rings help minimize internal recirculation and fluid leakage, leading to improved pump efficiency and performance. The pump casing and wear rings should be periodically inspected for erosion, corrosion, or damage. Any issues should be promptly addressed to maintain hydraulic efficiency and prevent potential leaks. The clearance between the wear rings and the impeller/casing is important for optimal pump performance. The clearance should be designed to balance between minimizing wear and avoiding excessive friction. Proper clearance can be determined based on pump design specifications or manufacturer recommendations.
what Common Problems occur due to Improper Overhauling
Misalignment-induced Vibration: Incorrect shaft alignment can result in excessive vibration, leading to accelerated wear on bearings, seals, and other pump components. This vibration can also propagate throughout the system, causing damage to adjacent equipment and negatively impacting overall vessel performance.
Seal and Bearing Failures:When the pump’s shafts are misaligned, it puts additional stress on the mechanical seals and bearings. This increased load can cause seal leakage, premature seal failure, and excessive bearing wear, resulting in costly repairs and downtime.
Reduced Efficiency and Increased Energy Consumption: Misalignment disrupts the hydraulic balance within the pump, leading to reduced efficiency and increased power consumption. Consequently, the pump operates at suboptimal levels, consuming more energy while delivering less output.
