Even with correct selection, installation, and operation, pumps can encounter performance or mechanical issues over time. Early recognition and corrective action can prevent costly downtime and damage. Below is a detailed guide to common pump problems, their causes, and practical solutions.
Troubleshooting Approach
Most pump problems trace back to installation issues (alignment, suction design, priming), operational errors (running outside BEP, frequent cycling, dry running), or maintenance neglect (lubrication, worn parts, leaks).
1. Pump Will Not Start / No Flow
Possible Causes
- Pump not primed / air in suction line
- Suction valve closed or blocked
- Foot valve stuck closed
- Pump running in wrong rotation
- Motor/engine not transmitting power (coupling failure, belt slip)
Solutions
- Re-prime pump and ensure suction line is airtight
- Open suction and discharge valves; check strainers for blockages
- Inspect and clean/replace foot valve
- Verify driver rotation matches pump arrow
- Check coupling/belt condition and realign or replace if worn
2. Pump Loses Prime After Starting
Possible Causes
- Suction lift too high
- Air leaks in suction line or fittings
- Foot valve leaking or not sealing
- Inadequate submergence at suction source (vortex formation)
Solutions
- Reduce suction lift or relocate pump closer to water source
- Inspect suction piping and joints for leaks, reseal as needed
- Repair/replace foot valve or check valve
- Increase suction submergence or install anti-vortex baffle
3. Pump Cavitation (Noise, Vibration, Damage)
Warning Signs
Crackling noise like gravel in the pump, excessive vibration, pitting damage on impeller, reduced performance.
Possible Causes
- Net Positive Suction Head Available (NPSHa) < NPSH Required (NPSHr)
- Suction line restrictions (undersized piping, clogged strainers)
- Pump operating too far from Best Efficiency Point (BEP)
- High liquid temperature reducing vapour pressure margin
Solutions
- Reduce suction lift or increase suction head
- Increase suction pipe diameter; remove obstructions
- Operate pump closer to BEP; use variable speed control if needed
- Lower fluid temperature or increase system pressure
4. Pump Vibrates or is Noisy
Possible Causes
- Pump and driver misalignment
- Cavitation inside pump
- Worn bearings or mechanical seals
- Pipe strain on suction/discharge nozzles
- Foundation not rigid, resonance issues
Solutions
- Realign shafts using laser/dial gauge
- Correct cavitation issues (see section above)
- Replace worn bearings/seals
- Install independent pipe supports
- Strengthen foundation or use vibration isolation mounts
5. Pump Delivers Insufficient Flow or Pressure
Possible Causes
- Impeller worn, damaged, or blocked
- Incorrect impeller size or speed
- Air entrainment in suction line
- Excessive system resistance (valves closed, pipe friction too high)
- Pump running at wrong rotation
Solutions
- Inspect and clean impeller; replace if eroded
- Verify impeller diameter and speed match duty requirements
- Eliminate suction air leaks and ensure adequate submergence
- Recheck system design — reduce resistance or upsize pump
- Confirm correct shaft rotation
6. Pump Overheating
Possible Causes
- Running at very low flow (recirculation heating fluid)
- Bearings not lubricated or over-lubricated
- Motor/engine overload
- Cooling system failure (for diesel engines)
Solutions
- Operate near BEP and avoid throttling to low flow
- Check lubrication schedule; avoid grease overpacking
- Verify motor amps/kW within nameplate; reduce load
- Inspect radiator, coolant, or fan system on diesel sets
7. Mechanical Seal or Packing Failure
Possible Causes
- Running pump dry or without cooling flush
- Excessive shaft vibration or misalignment
- Incorrect seal material for fluid handled
- Cavitation or pressure surges damaging faces
Solutions
- Ensure pump is primed before startup
- Re-align shafts and balance rotating parts
- Install seal materials compatible with pumped liquid
- Control system surges; stabilise operation
Prevention Tip
Install a seal flush system on critical pumps. A small flow of clean water to the seal chamber dramatically extends seal life, especially with abrasive or hot fluids.
8. Bearing Failure
Possible Causes
- Misalignment between pump and driver
- Improper lubrication (too much, too little, wrong grease)
- Contamination (dirt, water ingress)
- Excessive vibration or unbalanced impeller
Solutions
- Recheck alignment and install vibration isolators
- Follow manufacturer’s lubrication schedule
- Use sealed bearings or improve bearing housing seals
- Inspect and rebalance/replace impeller
9. Pump Consumes Excessive Power
Possible Causes
- Pump oversized for duty (operating at high flow)
- Incorrect impeller diameter (too large)
- Mechanical binding inside pump (rubbing wear rings, seized seals)
- Fluid viscosity higher than expected
Solutions
- Throttle system or trim impeller diameter
- Recheck duty requirements and resize pump
- Inspect for rubbing parts and repair clearances
- Verify actual fluid properties vs design
10. Pump Shaft Breakage
Critical Failure
Shaft breakage is a severe failure that can cause significant damage and safety hazards. Address root causes immediately if shaft failure occurs.
Possible Causes
- Misalignment or excessive pipe strain
- Hydraulic shock from rapid valve closure (water hammer)
- Running pump at resonance speed
- Metal fatigue from vibration or overload
Solutions
- Correct alignment and support pipework
- Install slow-closing valves and surge suppression devices
- Avoid operating continuously near natural frequency
- Replace with upgraded shaft material if repeatedly failing
Summary
Most pump problems trace back to installation issues (alignment, suction design, priming), operational errors (running outside BEP, frequent cycling, dry running), or maintenance neglect (lubrication, worn parts, leaks).
Preventive Maintenance Program
A disciplined program of routine inspection, vibration monitoring, and flow/pressure trending helps detect issues early, extending pump life and reducing unplanned downtime.
Quick Reference: 10 Common Problems
| # | Problem | Primary Cause Category |
|---|---|---|
| 1 | Will Not Start / No Flow | Installation / Priming |
| 2 | Loses Prime After Starting | Suction Design |
| 3 | Cavitation | NPSH / Suction Issues |
| 4 | Vibration & Noise | Alignment / Mechanical |
| 5 | Insufficient Flow or Pressure | Impeller / System Design |
| 6 | Overheating | Operation / Lubrication |
| 7 | Seal or Packing Failure | Dry Running / Materials |
| 8 | Bearing Failure | Lubrication / Alignment |
| 9 | Excessive Power Consumption | Sizing / Mechanical Binding |
| 10 | Shaft Breakage | Water Hammer / Fatigue |