Pump Troubleshooting

Pump troubleshooting should be systematic. When a pump does not perform normally, the cause may be inside the pump, in the motor or controls, or somewhere in the connected hydraulic system.

Operators should avoid replacing parts based on one symptom. A better approach is to compare flow, suction pressure, discharge pressure, motor current, vibration, noise, valve position, liquid level, and control status before deciding where the problem is located.

Start with the Operating Condition

Before troubleshooting, determine exactly what has changed.

Useful questions include:

• Is the pump running?
• Is there any flow?
• Is flow lower than normal?
• Is suction pressure abnormal?
• Is discharge pressure abnormal?
• Is motor current different?
• Is the pump noisy or vibrating?
• Did the problem begin suddenly or gradually?

A clear description of the symptom helps narrow the possible causes.

Compare with Normal Data

Current readings are most useful when compared with the pump's normal operating condition.

Useful baseline data include:

• normal flow;
• normal suction pressure;
• normal discharge pressure;
• normal motor current;
• normal VFD speed;
• normal vibration;
• normal bearing temperature;
• normal wet-well or tank level.

Determine Whether the Pump Is Actually Running

A control system may show that a pump has received a start command without proving that the pump is actually operating correctly.

Verify, as appropriate:

• motor status;
• motor current;
• shaft or pump operation;
• flow;
• pressure;
• alarm status.

Pump Will Not Start

If a pump does not start, possible causes include:

• no electrical power;
• control switch in Off;
• motor overload trip;
• blown fuse or tripped breaker;
• failed starter or VFD;
• active interlock;
• failed permissive;
• low-level shutdown;
• control-signal failure;
• motor problem;
• mechanically locked pump.

Check Control Mode First

A simple but common problem is incorrect control mode.

Check whether the Hand-Off-Auto selector is:

• in Hand;
• in Off;
• in Auto.

A pump left in Off will not respond to automatic demand.

Check Alarms and Trips

Before resetting equipment, review the active alarm or trip condition.

Possible trips include:

• motor overload;
• high temperature;
• seal leak;
• low suction pressure;
• VFD fault;
• electrical fault.

Repeatedly resetting a trip without identifying the cause can damage equipment.

Motor Runs but There Is No Flow

If the motor runs but no liquid is being pumped, possible causes include:

• pump not primed;
• air in the casing;
• suction valve closed;
• discharge valve closed;
• blocked suction;
• empty source tank;
• lost prime;
• wrong rotation;
• broken coupling;
• damaged impeller;
• plugged impeller.

Check the Source Level

Verify that liquid is actually available to the pump.

Low source level may cause:

• loss of prime;
• air entrainment;
• cavitation;
• low flow.

Check Valve Position

Incorrect valve position can create many apparent pump failures.

Verify:

• suction valve is in the required position;
• discharge valve is in the required position;
• bypass valves are correctly positioned;
• check valve is functioning.

Check for Loss of Prime

A centrifugal pump that requires priming may produce little or no flow if air enters the casing or suction line.

Possible causes include:

• suction air leak;
• leaking foot valve;
• low source level;
• drain-back after shutdown;
• incorrect priming procedure.

Check Pump Rotation

Incorrect motor rotation can occur after electrical or motor work.

Symptoms may include:

• low flow;
• low head;
• poor efficiency.

Rotation should be checked using the approved procedure.

Low Flow

If a pump is producing flow but less than normal, possible causes include:

• low pump speed;
• low source level;
• suction restriction;
• dirty strainer;
• partially closed valve;
• cavitation;
• air entering suction;
• worn impeller;
• increased internal clearances;
• blocked impeller;
• increased system resistance;
• incorrect flow-meter reading.

Use Pressure to Separate Pump and System Problems

Flow should be evaluated together with suction and discharge pressure.

Different pressure patterns can point toward different causes.

Low Flow with High Discharge Pressure

Low flow combined with higher than normal discharge pressure often suggests increased downstream resistance.

Possible causes include:

• partially closed discharge valve;
• blocked pipeline;
• dirty filter;
• higher tank level;
• higher downstream system pressure;
• control valve restriction.

The pump may be functioning normally but operating at a different point on its curve.

Low Flow with Low Discharge Pressure

Low flow combined with low discharge pressure can indicate that the pump is not developing normal head.

Possible causes include:

• wrong rotation;
• worn impeller;
• low pump speed;
• air in the pump;
• cavitation;
• damaged impeller;
• severe internal wear.

Low Flow with Abnormal Suction Pressure

If low flow occurs with lower suction pressure or greater suction vacuum, investigate:

• dirty suction strainer;
• partially closed suction valve;
• low source level;
• blocked suction piping;
• excessive suction friction.

Sudden Loss of Flow

A sudden change is more likely to involve an abrupt event such as:

• valve movement;
• power or control problem;
• blocked impeller;
• broken coupling;
• loss of prime;
• major suction blockage.

Gradual Loss of Flow

A gradual decline may indicate:

• impeller wear;
• increasing internal clearances;
• pipe roughness;
• progressive blockage;
• filter fouling;
• strainer loading.

Low Discharge Pressure

Possible causes include:

• low pump speed;
• worn impeller;
• wrong rotation;
• air in pump;
• low source pressure;
• cavitation;
• high system demand;
• large downstream leak.

High Discharge Pressure

Possible causes include:

• closed or partially closed discharge valve;
• blocked discharge piping;
• high downstream tank level;
• high system pressure;
• control valve restriction;
• operation near shutoff.

Pump Running Near Shutoff

A centrifugal pump operating at very low flow and high head may be near shutoff.

Extended operation can cause:

• liquid heating;
• internal recirculation;
• vibration;
• seal damage.

Pump Operating Near Runout

Very high flow with low head may indicate operation near runout.

Possible consequences include:

• high motor load;
• cavitation;
• poor efficiency;
• mechanical stress.

Cavitation

Cavitation commonly produces:

• gravel-like or crackling noise;
• vibration;
• unstable flow;
• fluctuating pressure;
• reduced capacity;
• impeller pitting.

Check Cavitation Causes

Possible causes include:

• low source level;
• dirty suction strainer;
• partially closed suction valve;
• high suction lift;
• undersized suction piping;
• high liquid temperature;
• excessive flow.

Air Entrainment

Air entering the pump can resemble cavitation.

Possible causes include:

• suction air leak;
• vortexing;
• low wet-well level;
• poor suction-pipe arrangement.

Air entrainment involves actual air entering the liquid, while cavitation involves vapor bubbles formed by low pressure.

Excessive Vibration

Possible causes include:

• misalignment;
• imbalance;
• bearing damage;
• cavitation;
• loose foundation;
• bent shaft;
• damaged impeller;
• debris in the impeller;
• operation far from BEP.

Vibration After Maintenance

If vibration begins immediately after maintenance, investigate changes such as:

• alignment;
• coupling installation;
• impeller assembly;
• mounting bolts;
• pipe strain;
• rotation.

Sudden Vibration

A sudden increase in vibration may indicate:

• foreign material in the impeller;
• broken impeller component;
• bearing failure;
• coupling damage;
• severe cavitation;
• loose equipment.

Gradual Vibration Increase

Gradually rising vibration may indicate:

• bearing deterioration;
• alignment drift;
• wear;
• imbalance caused by deposits.

Unusual Pump Noise

Noise can provide useful clues.

Examples include:

• gravel-like sound from cavitation;
• grinding from mechanical contact;
• rumbling from bearings;
• repeated banging from check-valve slam;
• rattling from loose components.

Sound should be considered together with vibration and operating data.

Bearing Overheating

Possible causes include:

• insufficient lubrication;
• overlubrication;
• wrong lubricant;
• contamination;
• misalignment;
• bearing damage;
• excessive mechanical load.

Motor Overheating

Possible causes include:

• motor overload;
• poor ventilation;
• frequent starts;
• voltage problems;
• mechanical binding;
• operating beyond intended pump range.

High Motor Current

High motor current can result from:

• high hydraulic load;
• operation near excessive flow;
• mechanical binding;
• bearing failure;
• blocked pump;
• electrical problems.

Compare current with pump flow and pressure before assuming an electrical cause.

Low Motor Current

Unusually low current may indicate reduced load.

Possible causes include:

• low flow;
• loss of prime;
• air in pump;
• low pump speed;
• broken coupling;
• pump not moving liquid normally.

Repeated Motor Overload Trips

Do not continue resetting the overload.

Investigate:

• pump blockage;
• mechanical binding;
• bearing condition;
• motor condition;
• electrical supply;
• actual pump operating point.

Seal Leakage

Mechanical-seal leakage can result from:

• worn seal faces;
• dry running;
• misalignment;
• vibration;
• shaft movement;
• poor seal flush;
• incorrect installation.

Repeated Seal Failure

Repeated replacement without identifying the underlying cause can lead to repeated failure.

Investigate:

• alignment;
• shaft condition;
• bearing condition;
• vibration;
• dry-running events;
• seal-flush conditions.

Excessive Packing Leakage

Possible causes include:

• worn packing;
• damaged shaft sleeve;
• loose gland;
• incorrect packing installation.

Packing Overheating

Possible causes include:

• packing too tight;
• insufficient leakage for cooling;
• incorrect packing;
• shaft or sleeve damage.

Do Not Tighten Packing Until It Is Completely Dry

Packed pumps may require controlled leakage.

Eliminating all leakage can increase friction and temperature.

Frequent Pump Cycling

Short cycling can result from:

• incorrect level setpoints;
• small wet-well working volume;
• oversized pump;
• faulty level sensor;
• check-valve leakage;
• poor pressure-control settings.

Check-Valve Leakage

In a lift station, reverse flow through a leaking check valve can cause the wet well to refill quickly after pump shutdown.

Symptoms may include:

• short cycling;
• reverse-flow noise;
• rapid level rebound.

Check-Valve Slam

A check valve that closes violently can create:

• banging;
• pressure surge;
• pipe movement;
• equipment stress.

Pump Runs Continuously

Possible causes include:

• demand greater than pump capacity;
• reduced pump capacity;
• high system resistance;
• incorrect control signal;
• level sensor problem;
• major leak;
• pump too small for current conditions.

Wastewater Wet-Well Level Will Not Fall

Possible causes include:

• pump not producing design flow;
• incoming flow greater than pump output;
• blocked pump;
• force-main restriction;
• partially closed valve;
• multiple pumps unavailable.

Wet-Well Level Falls Too Fast

Possible causes include:

• unexpectedly high pump flow;
• low influent flow;
• incorrect level indication;
• control setpoint problem.

Very low wet-well level can increase vortexing and air entrainment risk.

Booster Station Cannot Maintain Pressure

Possible causes include:

• high system demand;
• main break;
• low suction pressure;
• pump unavailable;
• low pump speed;
• worn pump;
• incorrect valve position;
• pressure sensor problem.

Pressure Is Too High

Possible causes include:

• pressure-control setpoint too high;
• VFD control problem;
• failed pressure sensor;
• closed downstream valve;
• low system demand;
• pressure-reducing equipment problem.

Flow Meter May Be Wrong

Before disassembling a pump because of apparent low flow, consider whether the flow measurement is reliable.

Check:

• meter alarms;
• signal quality;
• comparison with tank level change;
• comparison with pump run time;
• another available flow measurement.

Pressure Gauge May Be Wrong

A blocked gauge connection or failed gauge can produce misleading readings.

When a reading does not match other system evidence, verify the instrument before drawing conclusions.

Use Multiple Measurements

Strong troubleshooting decisions use several related observations.

For example:

• low flow alone gives limited information;
• low flow plus high discharge pressure suggests increased resistance;
• low flow plus low discharge pressure suggests reduced pump head;
• low flow plus more negative suction pressure suggests suction restriction.

Separate Hydraulic, Mechanical, Electrical, and Control Problems

A useful troubleshooting framework is to classify possible causes.

Hydraulic

• closed valve;
• blocked piping;
• low source level;
• cavitation;
• air entrainment;
• high system resistance.

Mechanical

• worn impeller;
• bearing failure;
• misalignment;
• broken coupling;
• seal failure;
• blocked rotating assembly.

Electrical

• loss of power;
• motor overload;
• voltage problem;
• starter failure;
• motor failure.

Control

• wrong HOA position;
• failed level sensor;
• failed pressure sensor;
• VFD fault;
• interlock;
• incorrect setpoint.

Change One Thing at a Time When Practical

If several control settings or valves are changed simultaneously, it becomes difficult to determine which action affected the pump.

A controlled troubleshooting sequence provides better information.

Do Not Bypass Protective Devices Casually

Trips and interlocks may protect:

• motor;
• pump;
• process;
• personnel.

Bypassing protection without understanding the condition can create equipment damage or a safety hazard.

Use Lockout/Tagout for Maintenance

If troubleshooting requires physical work on equipment, required hazardous-energy control procedures must be followed.

Possible hazardous energy includes:

• electrical;
• rotational;
• hydraulic pressure;
• gravity;
• automatic startup.

Automatic Startup Is a Hazard

A pump in automatic control can start because of:

• level change;
• pressure change;
• remote command;
• control-system logic.

Stopping the pump from SCADA or pressing a local stop button is not a substitute for required energy isolation during maintenance.

Use Maintenance History

Previous work orders can reveal recurring problems.

For example:

• repeated seal failure may point to misalignment or vibration;
• repeated bearing failure may indicate lubrication or alignment problems;
• repeated cavitation may indicate a persistent suction-system problem;
• repeated blockages may indicate inappropriate pump selection or upstream screening problems.

Document the Condition Before Repair

When practical, record:

• flow;
• pressure;
• motor current;
• speed;
• vibration;
• temperature;
• alarm status.

This information can help identify the cause and provide a baseline for post-repair testing.

Verify the Repair

After corrective work, confirm that the original symptom has been corrected.

Compare:

• flow;
• suction pressure;
• discharge pressure;
• motor current;
• vibration;
• temperature;
• leakage;
• control operation.

Common Pump Troubleshooting Mistakes

• Assuming every low-flow problem is caused by the pump.
• Ignoring valve position.
• Ignoring source liquid level.
• Replacing parts before checking pressure and flow.
• Resetting repeated overload trips without investigation.
• Confusing cavitation with air entrainment.
• Ignoring suction restrictions.
• Assuming one instrument reading is always correct.
• Ignoring the system curve and downstream resistance.
• Changing several variables at once.
• Ignoring historical trends.
• Bypassing protective controls without identifying the cause.
• Failing to verify performance after repair.

A Practical Pump Troubleshooting Sequence

1. Define the exact symptom.
2. Confirm pump status and control mode.
3. Review alarms and trips.
4. Check source or wet-well level.
5. Verify suction and discharge valve positions.
6. Measure or review flow.
7. Review suction pressure.
8. Review discharge pressure.
9. Check pump speed and motor current.
10. Listen for abnormal noise.
11. Check vibration and bearing temperature.
12. Inspect for leakage.
13. Compare all values with normal historical operation.
14. Classify the likely problem as hydraulic, mechanical, electrical, or control-related.
15. Correct the identified cause using approved procedures.
16. Verify normal performance after corrective action.
17. Document the problem and repair.

What to Remember for the Exam

• Pump troubleshooting should be systematic and based on several related measurements.
• A pump problem may actually be a hydraulic-system, electrical, or control problem.
• Always check control mode, alarms, source level, and valve position early in troubleshooting.
• A running motor does not prove that the pump is producing normal flow.
• Low flow with high discharge pressure often suggests increased downstream resistance.
• Low flow with low discharge pressure can indicate reduced pump head, air, wear, wrong rotation, or cavitation.
• Low flow with unusually low suction pressure or high suction vacuum suggests a suction-side problem.
• A sudden performance change often indicates an abrupt event, while gradual decline may indicate wear or increasing restriction.
• Cavitation can cause noise, vibration, unstable flow, reduced capacity, and impeller damage.
• Air entrainment and cavitation can produce similar symptoms but have different causes.
• High motor current may result from hydraulic load, mechanical binding, or electrical problems.
• Repeated overload trips should be investigated rather than repeatedly reset.
• Repeated seal or bearing failures usually justify investigation of the underlying cause.
• Short cycling may result from control setpoints, sensor problems, oversized pumps, or check-valve leakage.
• Verify suspect instruments before relying on an unusual reading.
• Use maintenance history and operating trends to identify recurring problems.
• Protective trips and interlocks should not be bypassed casually.
• Required lockout/tagout and hydraulic isolation must be used when troubleshooting becomes maintenance work.
• After corrective work, verify flow, pressure, current, vibration, temperature, leakage, and control operation.