A guide to to most common pump problems

This guide provides a number of checklists that cover most problems.

Before continuing, think about the way the pump is being used:

Have the operating conditions changed?
Is the pump running at the correct speed?
Has the pumped fluid changed recently?
- Does the process fluid still match the original specification.
- Does it contain more abrasive materials?
- Is it more corrosive?
- Are the pump’s wetted parts chemically compatible?

90% of issues occur because of a problem on the suction side of the pump. Check the supply and suction-side pipework including valves, filters and strainers.

What are the common problems with pumps?

What is your pumping problem?	Checklists
The pump won’t start	Is the motor not running? Does the motor stall or the pump fail to turn?
The pump isn’t priming	Is the pump not priming at all? Is the pump priming slowly?
There is no flow/the flow is too low	Is there is no flow at the discharge? Is the flow unexpectedly low?
The pressure is not correct	Is the pressure too low? Is the pressure too high?
The pump isn’t running smoothly	Is the pump noisy/vibrating? Is the pump running hot? Is the pump leaking? Is the power consumption higher than normal?
There is excessive wear	Does the wear problem concern packing/seals? Are the internal parts of the pump worn?
The pump discharge is pulsating/intermittent	Is the pump discharge pulsating? Is the pump discharge intermittent?

Problem not covered here? Please contact us for assistance. However, we are only able to provide assistance for pumps from manufacturers we represent, or have represented in the past.

Glossary

The following articles provide explanations about some of the terms used in this Troubleshooting Guide:

Checklists

Motor won’t start

A pump motor generally fails to start because of electrical problems.

Possible cause	Solution
Power failure	Check all power supplies and switches
Blown fuse	Check fuses on the motor and power supplies
Jammed coupling or motor	Verify coupling, motor and other drive equipment
Motor power supply problem	Check electrical connections and motor wiring

Pump won’t turn / motor stalls

A motor may start but be unable to turn the pump if it has not been used for some time, if the pump has not been primed or if the load is too high, due to a high viscosity fluid or trapped solids.

Possible cause	Solution
Liquid temperature higher than expected	Increases in temperature much beyond what the pump was specified to handle can fail seal elastomers, cause pins and bushings to lose their interference fits, or seize the pump.
Viscosity higher than expected	Rotor and shaft materials, seals, and clearances are viscosity limited and may cause failures if not checked and adjusted. Viscosity increases may stall or damage the drive if not properly sized. Viscosity increases can also cause NPSH problems (watch for cold startups).
Overtightened packing gland	Packing requires some weeping for lubrication.
Pump running too fast for application	Increases in speed increase the pump’s NPSH requirement and line losses on both sides of the pump. This will also increase the power requirement.
Pump jammed	Lubricate as necessary and prime if required.
Diaphragm pumps only
Blocked diaphragm chamber	Remove blockage
Air valve assembly malfunction/seizured	Check all seals, clean & lubricate
Clogged fluid line	Clean line. Increase line diameter
Air connected to exhaust	Check connections

Pump turns, but no flow

If the pump appears to be operating but there is no discharge flow, there is likely to be a problem with the supply, a blockage or closed valve, or the pump has lost its prime.

Possible cause	Solution
Air leak in suction piping (causes a cavitation-like noise.) Suction is below atmospheric pressure causing air leaks in pipework.	Identify and eliminate air leaks.
Vortex forming in supply tank, swirling liquid, reducing level at supply pipe and allowing air to enter pipe.	Raise liquid level in supply tank; install vortex breaker.
Suction pipe at bottom of tank	Lift suction pipe away from bottom of the tank, cut pipe end at angle.
Suction pipe too small or too long	Use larger diameter pipe, minimise length and number of restrictions and elbows.
Pump housing not filled with priming fluid/pump not primed	Reprime pump.
Suction pipework contains high spots causing trapped air pockets	Flush lines until liquid flows free of air. Install vent valve in line at high spot.
System head higher than anticipated	Check pressure gauges and calculations. Increase pump speed. Centrifugal pumps: install larger impeller.
Suction or discharge valve not open	Check that all valves are open
Suction lift too high or insufficient NPSH/NPIP	Pump cavitating due to inadequate suction side pressure. Buildup in suction lines, partially closed inlet valves, dirty strainers, or an increase in liquid viscosity are all potential causes.
Clogged suction line or strainer or impeller vanes
Viscosity or specific gravity too high
Clogged discharge line	Flush line through vent valve.
Suction/discharge pump connections incorrect	Check that the suction and discharge pipes have been connected to the right ports on the pump.
Rotation incorrect	Check the direction of shaft rotation and wiring connections. Centrifugal pumps: check impeller is mounted correctly.
Pump speed too low	Check motor frequency and voltage.
Pump has run dry/supply tank empty/suction pipe not submerged Pump not primed	Check level in supply tank and that suction pipe is submerged. Prime pump. Gear pumps that are frequently run dry will exhibit increased wear and seal problems.
Bypass valve open	Check bypass valve operation.
Relief valve bypassing	Adjust to higher pressure.
Magnetic drives: magnets uncoupled If magnets decouple, stop motor immediately. Operating decoupled weakens magnets and can cause severe damage in the inner drive.	Decoupling can be caused by a broken shaft, a foreign object, solids accumulation, excessive motor power. Verify position of outer magnet. Check temperature and viscosity of fluid. Stronger magnetic coupling may be needed.
Gear pumps only
Head not mounted correctly	Head must align with seal area, refer to manufacturer.
Gear clearances too high for liquid viscosity	Refer to manufacturer. Reduce clearances.
Blockage in internal relief valve.	Close discharge valve to flush line through bypass valve.

Low flow

A reduction in flow is normally accompanied by a drop in pressure so please also refer to the next checklist. Flow loss may occur because a portion of the flow is being diverted by a relief valve or bypass valve. The supply may be constrained or a change in conditions is causing cavitation. Wear of internal components could lead to pump slip whereby fluid leaks back to the suction side.

Possible cause	Solution
Air leak in suction piping (causes a cavitation-like noise.) Suction is below atmospheric pressure causing air leaks in pipework.	Identify and eliminate air leaks.
Vortex forming in supply tank, swirling liquid, reducing level at supply pipe and allowing air to enter pipe.	Raise liquid level in supply tank; install vortex breaker.
Suction or discharge valve not fully open	Open valves fully.
Clogged suction line or strainer or impeller vanes	Flush lines, clean strainer.
Incorrect relief valve setting	Does the system incorporate a recirculation line? Could a relief valve be stuck open resulting in constant recirculation to the feed tank? Valve needs to be set to full-bypass pressure. A valve that is consistently bypassing will cause lower than expected capacity and a heat rise over time.
Pump speed too low	Increase driver speed or use larger pump.
Pump worn or damaged	Disassemble and inspect components. Replace worn parts.
Slipping drive belt	Check wear on any drive belts
Rotation incorrect	Check the direction of shaft rotation and wiring connections. Centrifugal pumps: check impeller is mounted correctly.
Worn or blocked spray nozzles	Check spray nozzles for wear or contamination
Open or leaking bypass valve	Check bypass valve is closed.
Pump cavitating	Are all valves on the suction side fully open during pump operation? Is there a filter prior to the pump? If so, could it have blocked? Operating outside without trace heating may lead to increased product viscosity in the winter months, and hence an increase in suction line frictional losses. Insufficient NPSH_a/NPIP_a. Check pressure gauges and operating conditions.
Gear pumps only
Incorrect head placement (internal gear pumps)	Check head place in relation to the crescent.
Excessive wear	Check pump clearances.
Viscosity too high	Rotor and shaft materials, seals, and clearances are viscosity limited and may cause failures if not checked and adjusted. Viscosity increases may stall or damage the drive if not properly sized.
Diaphragm pumps only
Loss of oil prime in cells	Check oil level
Ruptured diaphragm	Check diaphragms

Pump not developing sufficient pressure

A reduction in pressure generally coincides with a decrease in throughput so please also refer to the previous checklist. The pressure may also be lower if the resistance of the discharge side is reduced.

Possible cause	Solution
Air or gas entrained in liquid	Flush lines until liquid flows free of air. Check for suction side leaks. Is suction line fully submerged in supply tank?
Impeller diameter too small	Check with manufacturer.
System head lower than anticipated	Check calculations.
Motor speed too low or rotation incorrect	Check correct speed and rotation direction with manufacturer.
Bypass valve partially open	Check bypass valve is functioning correctly
Pump cavitating	Improper suction or feed. Are all valves on the suction side fully open during pump operation? Is there a filter prior to the pump? If so, could it have blocked? Operating outside without trace heating may lead to increased product viscosity in the winter months, and hence an increase in suction line frictional losses. Insufficient NPSH_a/NPIP_a. Check pressure gauges and operating conditions.
Gear pumps only
Incorrect head placement (internal gear pumps)	Check head place in relation to the crescent.
Excessive wear leading to pump slip	Check pump clearances.
Diaphragm pumps only
Loss of oil prime in cells	Check oil level
Ruptured diaphragm	Check diaphragms

Pump develops too much pressure

High pressure generally indicates a blockage in the discharge line or that the pump is running too fast.

Possible cause	Solution
Discharge valve not open	Check that discharge valve is fully open.
Incorrect relief valve setting	Valve should be set to full-bypass pressure. A valve that is consistently bypassing will cause lower than expected capacity and a heat rise over time.
Worn or blocked spray nozzles	Check spray nozzles for wear or contamination
Viscosity higher than expected	Viscosity increases can also cause NPSH problems. May also happen during cold startups.
Pump running too fast for application	Increases in speed increase the pump’s NPSH requirement and line losses on both sides of the pump. This will also increase the power requirement.

Pump no longer self-priming

Loss of suction is generally caused by problems with suction side pipework ranging from trivial causes such as blockages to more serious and potentially damaging issues such as cavitation. Most positive displacement pumps can self-prime but sometimes, especially if a pump has not been used for a long time, it is necessary to fill the pump or wet internal components to allow self priming.

Possible cause	Solution
Not primed correctly	Reprime pump: ensure the pump housing is filled fully before starting pump.
Foot valve required	Low viscosity liquids require foot valve to maintain prime.
Closed discharge valve	Open all suction and discharge valves
Leak in suction line	Check pipework for leaks
Suction pipe/foot valve not submerged	Verify suction pipe is submerged
Foot valve jammed	Check operation and seating
Lift exceeds pump ability	Check suction head against pump specification
Suction lift too high/insufficient NPSH/cavitation	Specific gravity or local atmospheric pressure not accounted for in calculations Reassess suction head and NPSH calculations
Mismatch of inner volute and impeller diameter	Refer to manufacturer
O-ring damage	Chemical attack, embrittled, or cut O-ring
Motor rotation incorrect	Correct rotation when viewed from fan end is clockwise FT SP series
Air or gas in liquid	Pump pulling in air through a loose fitting or from the supply tank. Suction line not fully submerged.
Foreign matter in impeller	Has a filter recently been removed from the suction line? Is the process liquid dirty? Obtain max particle size and concentration. Could the pump have run dry or operated while cavitating causing pump components to break off?

Pump primes slowly

Loss of suction is generally caused by problems with suction side pipework. Most positive displacement pumps can self-prime but sometimes, especially if a pump has not been used for a long time, it is necessary to fill the pump or wet internal components to allow self priming.

Possible cause	Solution
Closed or partially closed valve	Open suction and discharge valves
Partially blocked suction line or strainer or impeller vanes	Flush lines, clean strainer.
Suction pipe diameter too large	Use narrower suction line
Air leak in suction piping	Pump pulling in air through a loose fitting or through vortexing in the supply tank. Suction pipe not fully submerged.
Centrifugal pumps
Mismatch of inner volute and impeller diameter	Replace impeller
Inner volute O-ring damaged	Chemical attack, embrittled, cut

Pump is noisy / excessive vibration/pulsation

A noisy pump can be a sign of cavitation, a loss of suction or entrained gas in the pumped fluid. The discharge pressure and flow may also be reduced, fluctuating or pulsating. Mechanical causes include worn components, drive systems, or shaft misalignment.

Possible cause	Solution
Air leak in suction piping	Pump pulling in air through a loose fitting or from the supply tank. Causes a cavitation-like noise.
Pump cavitating	Review suction piping layout. Reduce angles and tees and ensure straight pipe run of at least 5 diameters before suction flange. Are all valves on the suction side fully open during pump operation? Is there a filter prior to the pump? If so, could it have blocked? Operating outside without trace heating may lead to increased product viscosity in the winter months, and hence an increase in suction line frictional losses. Insufficient NPSH_a/NPIP_a. Check pressure gauges and operating conditions. Reduce flow rate to match design specification. Is flow too low, leading to suction recirculation? Install or increase bypass so pump can be operated at specification.
Pump base not rigid	Inspect fixing bolts and grout.
Poor alignment	Check motor, coupling and pump alignment.
Motor or piping not properly secured	Is the suction and discharge pipework fully supported to ensure that there are no excessive loads on the pump casing? Is the adjoining pipe-work flexible or fixed? Was the unit realigned on site once installed? If the unit is long-coupled, has a flexible coupling been used?
Foreign object in impeller	Has a filter recently been removed from the suction line? Is the process liquid dirty? Obtain max particle size and concentration. Could the pump have run dry or operated while cavitation causing pump components to break off?
Air lock	This is a common issue when a suction feed line passes up and over the side of an IBC. Fully vent the system.
Low bearing oil level/bearing failure	Check oil level. Inspect bearing.
Pump running too fast for application	Increases in pump speed raise the pump’s NPSH requirement and line losses on both sides of the pump. This will also increase the power requirement. Check that the motor is running at the correct speed.
Worn bearings	Check pump and motor bearings and replace if necessary.
Magnetic drives only: loose magnet/ drive magnet rubbing	Check bearings on magnetic coupling for clearance between outer and inner magnets
Magnetic drives only: boiling point exceeded in containment shell area: flashing	Use temperature monitor on containment shell, Increase pressure in containment shell. Increase flow to reduce heat buildup.
Diaphragm pumps only
Oil level low or incompatible with operating temperature	Check oil level. Light weight oil needed for lower temperatures to prevent freezing. Check cells are primed correctly after diaphragm change.
Damaged diaphragm	Elastomer incompatible with pumped fluid, puncture by foreign object, excess pressure, pump running too fast. Pump frozen.
Broken or worn valve spring	Cavitation Foreign object in the pump Pump running too fast Spring/retainer material incompatible with fluid being pumped

Pump runs hot

Overheating is generally a sign of a pump running too fast or that the pumped fluid is too hot or viscous. Wear may have reduced the clearances within the pump (valves, gears, bearings) leading to a build-up of frictional heat.

Possible cause	Solution
Incorrect relief valve setting	Valve needs to be set to full-bypass pressure. A valve that is consistently bypassing will cause lower than expected capacity and a heat rise over time.
Pump running too fast for application	Increases in speed increase the pump’s NPSH requirement and line losses on both sides of the pump. This will also increase the power requirement.
Internal circulation malfunctioning	Consult manufacturer
Packing too tight	Loosen packing to allow greater lubrication of shaft. This may increase weeping.
Bypass valve open	Bypass rates in excess of 50% should be avoided. Pump action and recirculation causes temperature rise in pumped fluid supply.
Magnetic drive only: flow lower than minimum required to cool containment shell area	Ensure flow exceeds minimum required for cooling purposes. Install bypass line if process conditions require operation at low speeds.
Magnetic drive only: magnets decoupled	The maximum torque capability of the drive has been exceeded. This can occur during startup or through transient changes in load. Restart pump.

The packing/seal is leaking

Before checking anything else, ensure that nothing has changed in the way the pump is being used. Have the operating conditions changed? Check that the O-rings and gaskets are compatible with the fluid and temperature. If anything has changed, the pump may require a different sealing system. Contact the manufacturer for advice if this is the case.

What causes leakage problems in centrifugal and gear pumps?

Observation	Possible cause
Packing starts leaking after a short period of operation	Is there debris in the process fluid? Are there pressure transients during startup? Is the packing material suitable for operating conditions? Refer to manufacturer. Is the packing material suitable for stationary conditions/downtime? Refer to manufacturer.
Packing extrudes into gland/bush throat	Packing too soft. Are the end rings suitable (such as metal or reinforced PTFE)? Is the clearance too large? Has the packing gland been overtightened? Check torque meets specification. Packing requires some weeping for lubrication.
Leakage occurs around the outside of the gland	Has the packing been fitted correctly? Is the packing the correct size? Is there wear on the gland or stuffing box?
Packing scored on outside, rotates with shaft	Packing is wrong size or the stuffing box is worn
Packing charred	Dry-running, loss of lubrication

What causes leakage problems in reciprocating pumps?

Observation	Possible cause
Seal leaks even when stationary	Incorrect installation Damaged O-rings Seal faces not flat
Seal leaks only when running	Incorrect installation Eccentric shaft Excessive shaft runout Vibrations
Seal leaks after a short period	Debris in process fluid Transients during startup Seat or seal materials not suitable
Seal leaks suddenly after satisfactory operation	Cracked seals Bearing failure Loss of barrier fluid

Excessive wear of the pump internals

Some degree of wear is to be expected after prolonged operation, particularly if a pump is used with corrosive or abrasive feeds. Wear is primarily a function of pump speed and lifetime can be greatly enhanced by a reduction in pump speed.

Possible cause	Solution
Overtightened packing gland	Packing requires some weeping for lubrication.
Pump running too fast for application	Wear due to abrasives increases exponentially with speed.
Unexpected abrasives in fluid	Install strainer in suction line. Reduce pump speed if possible or use larger pump running at lower speed.
Extended dry running	Install power sensor to stop pump from running excessively under dry conditions.
Corrosion	Construction materials incompatible with liquid. Check the specification with the manufacturer.
Discharge pressure too high	Increase discharge pipe diameter, decrease length
Poor pump alignment	Check motor, coupling and pump alignment.

Excessive power consumption

An increase in power consumption could be due to mechanical or hydraulic problems. This could be due to increases in operating speed, pressure, flow or fluid viscosity. Mechanical causes could be wear or alignment issues.

Possible cause	Solution
Excessive flow	Reduce pump speed
Specific gravity or viscosity too high	Heat fluid to reduce viscosity. Reduce pump speed. Increase drive horsepower. Shear sensitive fluids can become more viscous with pumping action and over time.
Pump running too fast for application	Increases in speed increase the pump’s NPSH requirement and line losses on both sides of the pump. This will also increase the power requirement.
Mechanical problems	Bearing wear. Shaft misalignment. Belt drives: poor pulley alignment.
Gear pumps only
Gear clearances insufficient for viscosity and/or temperature	Exchange for gears trimmed for operating conditions.
Rotating parts binding or worn	Disassemble and inspect components. Replace worn parts.

Excessive leakage

Some degree of leakage is to be expected with shaft seals and bearings and is important for lubrication and cooling purposes. Excessive leaks are normally caused by loose or overtightened fittings or wear caused by abrasive solids in the pumped fluid.

Possible cause	Solution
Shaft seal failure	Chemical or thermal incompatibility. Check O-rings and gaskets are compatible with fluid and temperature. Incorrect installation. Check seating of O-rings and gaskets. Torque bolts to specification.
Overtightened packing gland	Packing requires some weeping for lubrication but overtightening may cause overheating and damage to the packing or wear in the stuffing box.
Pump port connections not properly seated	Check O-rings and gaskets are compatible with fluid and temperature. Use Teflon tape or other sealant.
Corrosion of pump housing	Check compatibility of pump construction materials. Decrease temperature of fluid to reduce corrosion rate. Flush pump when not in use. Eliminate any contaminants that may accelerate corrosion wear.
Diaphragm pumps only
Loose connections	Check oil draining piping/filler cap/valve plate and manifold bolts
Is there fluid in the air exhaust? If so, possible causes are:
Over-pressurisation	O-ring forced out of groove. Warped manifold
Ruptured diaphragm	Elastomer incompatible with pumped fluid, puncture by foreign object, excess pressure, pump running too fast.
Outer plate unthreading	Tighten and re-torque

Excessive Pulsations

Some variation in flow is to be expected with reciprocating pumps and this can be reduced by installing pulsation dampeners in the discharge line. With other pump types, such as centrifugal pumps, an irregular, pulsing discharge may be caused by cavitation, air in the system or by poor suction-side pipe layout.

Possible cause	Solution
Air in suction lines	Pump pulling in air through a loose fitting or in a vortexing tank. Causes a cavitation-like noise.
Oil level low	Check oil level. Low level may cause loss of prime in hydraulic cell
Pump cavitating	Are all valves on the suction side fully open during pump operation? Is there a filter prior to the pump? If so, could it have blocked? Operating outside without trace heating may lead to increased product viscosity in the winter months, and hence an increase in suction line frictional losses. Insufficient NPSH_a/NPIP_a. Check pressure gauges and operating conditions. Reduce flow rate to match design specification. Is flow too low, leading to suction recirculation? Install or increase bypass so pump can be operated at specification.
Water hammer	Normally caused by valve closing too quickly. Check valve operation. Consider installing an accumulator tank or pulsation dampener in the discharge line to dampen pulsations.
Poor suction-side pipe layout	Review suction-side piping. Reduce angles and tees and ensure straight pipe run of at least 5 diameters before suction flange.
Diaphragm pumps only
Damaged diaphragm	Elastomer incompatible with pumped fluid, puncture by foreign object, excess pressure, pump running too fast.
Broken or worn valve spring	Can be caused by cavitation, foreign object in the pump, corrosion, pump running too fast.
Reciprocating pumps only
Some degree of pulsation is to be expected with diaphragm pumps and other types of reciprocating pumps. If this becomes excessive, consider installing a pulsation dampener in the discharge line.

Intermittent flow

Intermittent flow may result from a partial blockage in the system or by pump components, such as seals, slipping due to wear, component failure or over-lubrication.

Possible cause	Solution
Over lubrication	Remove air connection into pump, degrease, reconnect and run until clear.
Obstruction	Clear obstruction, check ball valve seating
Shaft seal failure	Replace seals
Diaphragm pumps only
Moisture in air valve	Inspect valve for moisture and dry if necessary. Install air dryer.
Air valve system failure	Check all seals

Getting more help

Before you call…

Make a note of the full duty details and clarify that the pump is operating within its specification. In particular, record anything that has changed since the pump was last performing satisfactorily.

Can you supply photos or a video of the installation?
How long has the pump run before the problems started happening?
Is the pump run on any cleaning cycle? If so list the relevant details: liquid, temperature, speed and pressure.
How long has the pump been installed?
How long since it was last serviced?

Contacting Michael Smith Engineers Ltd

Michael Smith Engineers Ltd provides representation in the UK for specialist pump manufacturers, with particular emphasis on sealless leak-free pump technology.

For general advice please contact us: https://www.michael-smith-engineers.co.uk/contact-us

We have experience of pumping many hard-to-handle liquids including acids, bases, organic liquids, solvents, inorganic liquids, slurries, volatile liquids, corrosives, abrasive liquids, non-lubricating liquids, liquids with entrained gases and flammable liquids.

We are able to provide a wide range of drive options for the various ranges we represent including single phase and three phase motors, inverter control, DC motors, air motors, ATEX approved drives and manual and automatic variable speed units.

As well as supplying a complete range of specialist pumps and drives, we also offer a comprehensive range of accessories including filters, relief and loading valves, flow meters and tubing to complement the different types of pumps.

If you require technical advice, spares or repairs for a particular pump, you can also contact the manufacturer directly.

Contacting the manufacturer directly

Manufacturer	Technical Support
Codip PTFE lined air operated tubular diaphragm pumps.	Web: http://www.codip.it Email: [email protected]
Finish Thompson Drum pumps, barrel pumps, metallic and plastic centrifugal pumps and air-operated double diaphragm pumps	Web: https://www.finishthompson.com/contact-us/ USA: (800) 934-9384 Europe: +49 (0)6181-90878-0
Dickow Metallic single stage and multi-stage centrifugal pumps and side channel pumps	Tel: +49 8638/602-0 Email: [email protected] Web: https://dickow.de/index.php/en/contact
FMI Accurate, valveless , rotary reciprocating piston pumps.	Telephone: 1-516-922-6050 Toll-free: 1-800-223-3388 Fax: 1-516-624-8261 E-mail: pump[email protected]:
HNPM Micro-annular low flow, high accuracy internal gear pumps.	Europe: +49 385 52190-300 Email: [email protected] North America +1 773 766-9669 [email protected]
Hydra-Cell High pressure diaphragm metering and transfer pumps.	Email: [email protected] Tel: + 44 (0) 1252 816847
Liquiflo Magnetically coupled and conventionally sealed external gear pumps.	Telephone: (908) 518-0777 [email protected]
Micropump Magnetically coupled stainless steel gear pumps.	Phone: (360) 253-2008 Phone (Europe): +49 9187 921 9411 Email: [email protected]
Viking Metallic internal gear pumps, external gear pumps, vane pumps and lobe pumps.	https://www.vikingpump.com/contact/technical-support