Inspection of pump done in two conditions, one is "On the run inspection" and another one is "Work shop inspection". These two cases are explained below.
1) ON THE RUN CONDITION CHECKS :
WHAT TO CHECK
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HOW TO CHECK
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WHY TO CHECK
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CLEANLINESS
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Check for accumulation of dirt, pulp, grease etc on pump body and base.
( Clean the pump body, base and sealing water basin before proceeding with inspection )
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Dirt etc on the body shall
· Cause corrosion
· Prevent proper inspection since many defects like cracks etc will not be visible
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FOUNDATION
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Check the foundation for
· Cracks
· accumulation of water
· presence of oil
· vibrations
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Damaged foundation will eventually cause vibrations and misalignment.
Oil penetrates the concrete and damage the foundation
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BASE & BASE BOLTS
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Check the base for
· Cracks
· Corrosion
· Vibrations by hand
· Accumulated water
Ensure that the bolts, nuts & washers are not loose or corroded.
(It is preferable to tighten the bolts while the pump is not running)
Ensure that the bolts, nuts washers & base materials are compatible and do not cause corrosion.
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Damaged base, loose bolts etc will cause vibrations and misalignment.
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NOISE
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Listen for any unusual noise. Abnormal sound can be due to metallic parts rubbing together, air entrapment, cavitation or misalignment.
Cavitation and air entrapment sound like small stones passing through the pump.
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Abnormal sound indicates the following abnormality which can damage the pump.
· Bearing damage
· Cavitation
· Air entrapment
· Impeller damage / clogged
· Foreign matter in the pump
· Misalignment, coupling wear
· Looseness
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GLAND PACKING
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For packed gland check that
· The bleed through the packing is not excess or stopped. It should be about 1 to 2 drops per second.
· Stuffing box temperature is normal
· There is flow of sealing water
· There is gap for gland follower
For Mechanical Seal check
· Seal temperature
· Sealing water flow
· Sealing water pressure
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Too tight packing , indicated by high stuffing box temperature and lesser bleed through, will wear the shaft sleeve, reduce packing life and increase the power consumption.
Lack of sealing water will result in wear out and damage of seal. Higher temperature is an indication of high friction between mating parts.
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BEARINGS TEMPERATURE
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Measure the bearing temperature using an Infra Red Temperature Gun.
· Temperature is to be measured close to the bearing location, directly above the bearing.
· . Actual temperature of the bearing will, normally, be 5 to 10 degrees higher than the reading.
· With normal grease the temperature should be less than 70 degrees C.
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High temperature indicates
· Excessive Lubrication
· Insufficient Lubrication
· Bearing damage
· Over load
· Misalignment
· Imbalance
Standard lubricants usually starts to loose its properties at 70 degrees C.
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BREATHER
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Breather is provided for oil lubricated pumps to releave the pressure inside the bearing housing and filtering the air that enters the oil chamber.
Ensure that the breather is not clogged.
It is preferable to install a silica gel breather since it prevents moisture from entering the chamber. It also filter much finer particle of 3 microns.
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A clogged breather will increase the temperature inside the oil compartment and can result in damaged seal.
Moisture as well as particles above 3 microns are harmful to bearings.
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VIBRATIONS
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Vibration is detected by
· Hand feel
· Vibration Pen
· Shock Pulse
· Vibration Analyser
Follow the Vibration analysis schedules.
It is better to check by hand feel also.
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Vibrations can be caused by
· Cavitation
· Entrained air
· Impeller damage/ clogging
· Bearing damage
· Misalignment or coupling wear out
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OIL LEVEL & CONDITION (For Oil Lubricated Bearings)
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Ensure that
· Oil gauge is clean & level visible
· Oil level is at the middle.
Visually inspect oil condition
· Colour of oil matches original oil
· Oil is not milky or foaming.
· No particles present in a small sample taken out.
Spot oil tester can be used on very critical pumps to test the condition of oil.
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· Lack of lubrication will damage the bearings.
· Presence of foreign particles will damage the bearings
· Oil turns milky around 1000 ppm, when only about 20% of life is left.
· Foaming indicates presence of air which can affect the lubrication efficiency.
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PRESSURES
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Check if the pump is operating at Best Efficiency Point.
To determine the BEP, find the pressure difference between discharge pressure & inlet pressure. Find from the pump performance curve the flow and the load ratings for this pressure difference. Compare this with the actual flow and motor load to determine if the pump is operating at its BEP.
( This check is required if there is a problem or to determine the performance and not on a required on a regular basis.)
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Discharge pressure may be low because
· Speed is too low
· There is air entrapped
· Packing / Seal is damaged
· Impeller diameter is small
· Casing & Impeller may be worn out
1% air leak causes a drop of 10% capacity reduction.
15 to 20% of air leak will stop the pump from pumping.
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LEAKAGES
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Check for visible leakages at pump mating surfaces, connection and fittings. Also check for air intake in suction pipe joints by pouring water over the joint and listening for noise.
Check the pipe supports
· Pipes are clamped on supports
· Supports are firmly fixed
· There is no vibrations
Frequent gasket failure is an indication of pipe misalignment / improper support.
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Improper support will cause
· Gasket damage
· Damage to pump because of extra forces coming on the pump casing.
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2) WORKSHOP CHECKS :
WHAT TO CHECK
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HOW TO CHECK
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WHY TO CHECK
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VOLUTE CASING, WEAR PLATE & WEAR RING
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Check inside surface of volute casing & Suction Piece
> Surface should be smooth and there should not be any pitting or wear out
> Specially check the suction piece and the seating of wear ring.
Check wear ring, if provided
> Wear Ring should fix tightly in the step provided for it. The step must be clean and free from dirt, scale etc.
> There should not be any ovality or wear out.
> There should be only running clearance between the wear ring on volute casing/ suction piece and the mating ring on impeller.
Check wear plate , if provided
> Wear Plates on suction side, in case of an open impeller pump, should seat properly on the casing.
> There should not be any wear out.
> When assembled the clearance between the impeller vanes and the wear plate should not exceed 0.5 to 1.0 mm
Check the seating step for fixing the rotor assembly
> There should not be any corrosion, wear out or damage to the seating portion.
> Seating should be thoroughly clean and free from dirt , rust, scaling etc.
> The depth of the step should match the matching step of the rotor assembly.
Check the fixing studs/ tapped holes
> If provided with studs for fixing the rotor assembly ensure that the studs are not bent and threading are not damaged.
> If tapped holes are provided, ensure that all holes are clean and the thread are not damaged.
Ensure that the Vortex Breaker, if provided, inside the suction piece is not damaged
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Smooth surface reduces the friction where as the pitting increases thus the friction and the friction loss
Higher clearance between eye of the impeller and wear ring will affect the efficiency.
Higher clearance between impeller vanes and wear plate will affect the efficiency.
Uneven seating of the rotor will result in vibrations and misalignment.
Rotor should be fixed tightly to the casing to prevent any vibrations while running.
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STUFFING BOX
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Stuffing box
> Bore is clean and matches the Follower OD and Lantern ring OD ( Freely Sliding)
> Sealing water ways are clear and threading for connections are is not damaged & OK.
> Tapped holes for fixing studs are OK.
> Studs are not bend and threading not damaged
Throat bush
> Fit on body of stuffing box
> Bore is not worn out or oval. There is only a running clearance between the bore and the OD of shaft sleeve.
Gland Follower
> Freely fits in to the stuffing box bore
Lantern Ring
> Clean & no scaling.
> The holes are clear.
> It goes sliding into the stuffing box bore
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> Tight fit of follower or the lantern ring inside the bore of the stuffing box shall create problem at the time of assembly.
> Throat bush should be tight fit in the stuffing box to prevent it from rotating. If provided, it should be locked in position by a head less allen screw.
> Higher clearance between throat & Shaft sleeve will result in a) damage of gland packings or b) packing being subjected to higher pressures from insude the casing.
> Jammed holes of Lantern ring shall prevent free flow of sealing water and equal pressure at all points.
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IMPELLER
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> Ensure that the OD is as per the requirement
> There is no wear out/ damage of vanes
> Bore is correct
> Key Way is not damaged & of correct size
> Back vanes, if provided, are not worn out
> Wear ring, if provided , is not worn out and fits tightly on impeller eye.
> Check for, unbalance, Dynamic balancing Pumps running at more than 2000 rpm.
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> Pump will take overload if the OD of the impeller is higher.
> Wear out of vanes will increase the clearances and shall result in lesser efficiency , lesser flow/ head etc.
> Incorrect bore & key way will result in incorrect fixing of impeller causing vibrations/ damage/ problems at the time of assembly.
Higher clearance between Wear ring OD & suction piece will affect the efficiency.
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BEARING HOUSING & END COVERS
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If Oil lubricated , check
> The oil sump to ensure that there is no foreign particles & it is clean.
> The oil passages to bearing and return from bearings to oil sump are clear of any jamming.
> The cut, if provided, on the end cover for oil flow to & from bearing matches the housing.
> The oil gauge/ indicator is fixed properly, the threading for fixing is not damaged and the oil way is clear.
If grease lubricated, check
> The holes in the end cover / on housing for grease to reach bearing.
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> The threading for fixing grease nipples & ensure that the grease nipples are provide are in working condition.
Check that
> The OD of the End Cover steps are ok and matches the housing ID.
> The step depth is correct. Normally the outer race of the bearing on non drive side is locked by end cover & the one on drive side is not locked.
> The grooves prided for oil seal / sealing strip are clean & in good condition and there is no damage.
> The threading of tapped holes to fix the end covers, are not damaged and the depth is ok.
> The base is not damaged ( no cracks etc – to be checked after proper cleaning)
> The base holes are not oval or there damaged.
> The holes for Volute casing are not damaged or become oval.
> The step that locates the volute casing is clean and there is no scaling or accumulated dirt.
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> Proper lubrication is essential to prevent premature failure of bearings.
> Various designs are in use, to ensure that the lubricant (oil / grease) reaches the bearing and the excess lubricant comes back to the sump in case of oil / comes out side incase of grease.
> The system for each pump is to be understood and the openings etc provided for flow of lubricant is to be kept clean. Otherwise the lubrication will not be proper.
> Shorter step of End Cover will not lock the bearing and a longer step will not provide adequate expansion allowance.
> Oil Seal, unless seated properly with adequate support will get damaged resulting in oil leakage / water entering the lubricant sump.
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SHAFT & PROTECTIVE SLEEVE
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Shafts
Check if there is any
> Bend in the shaft : check by a Dial Gauge & rotating it on a lathe
> Wear out / damage at Bearing, Impeller & Coupling seating : Visual check & measurement of Diameter by Vernier Caliper
> Wear out/damage to threading for lock nut fixing.
> Cracks / other damage/ wear out on any other part of the shaft. Especially at the portion where the oil seal comes.
> Damage to key ways for Impeller & Coupling.
> Cracks at the root of all the steps – ensure that there is curvature and the corners are not sharp.
> Deflection / whipping for shafts running at speeds more than 10000 rpm. Check by dial gauge & running it at high speed on a lathe.
Protective sleeve
> Visual check for wear out / damage of sleeve surface.
> Bore & Key Way are not damaged.
> Check the OD of the Sleeve: There should only be a running clearance between Stuffing Box bush ID & OD of the Sleeve
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> Bend on shaft will result in misalignment and vibrations.
> Wear out of seating of bearings, couplings or Impeller will result in looseness of fitting and vibrations.
> Sharp corners at steps results in stress concentration and failure of shaft.
> Shafts operating at high speeds are subjected to whipping effect due to centrifugal force resulting in severe vibrations.
> Uneven / damaged / sharp edges on sleeve surface will result in damage / fast wear out of gland packing.
> High clearance between bush ID & Sleeve OD will result in the pressure inside the volute acting directly on the gland packing and also damaging the packing.
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Summary
To ensure efficient handling of performance according to design expect ions and provide service in the extension period, follow these recommendations with less repairs and closures. Check out the specific pump manufacture's manual for their needs and may not be listed here.
This management recommendation may be difficult to implement, but it is only through a routine line, which increases the security of liquid-maintenance operation equipment, but improves plant safety and environmental protection.