A centrifugal pump usually does not fail because of one single reason. Most failures are caused by a combination of hydraulic problems, mechanical issues, installation errors, and maintenance practices.
Below is a practical case study that you can use for a customer report, technical presentation, or training document.
Case Study: Repeated Failure of a Centrifugal Pump
Executive summary
Application: Cooling water circulation
Pump type: Horizontal end-suction centrifugal pump
Problem: The pump failed repeatedly within 6–8 months of operation.
Main symptoms:
Excessive vibration
Mechanical seal leakage
Bearing overheating
Reduced discharge flow
High maintenance cost
The investigation found that the primary causes were cavitation, pipe strain, and poor alignment. Correcting the installation and operating conditions increased the pump life to more than three years without major failure.
System overview
Parameter Details
Pump type Horizontal end suction centrifugal pump
Capacity 100 m³/hr
Head 40 m
Motor 22 kW
Liquid Cooling water
Suction line 150 mm
Discharge line 125 mm
Operating hours 20 hrs/day
Failure history
The pump was installed in a cooling water system. Within the first six months, operators noticed:
Noise similar to gravel inside the pump.
Vibration increased steadily.
Mechanical seal started leaking.
Bearings became hot.
Pump discharge dropped by approximately 15%.
The maintenance team replaced the seal and bearings twice, but the same failure reoccurred.
Root cause analysis
1. Cavitation
Inspection of the impeller revealed pitting and erosion on the vane surfaces.
Cause:
Suction pipe had several elbows close to the pump.
Suction strainer was partially clogged.
Available NPSH was lower than the pump's required NPSH.
When pressure at the impeller eye dropped below the liquid's vapor pressure, vapor bubbles formed and collapsed violently, causing cavitation.
Effects:
Impeller erosion
Noise
Vibration
Reduced efficiency
Seal and bearing damage
2. Pipe strain
The suction and discharge pipes were not properly supported.
Their weight was transferred directly to the pump casing.
This caused:
Casing distortion
Shaft misalignment
Increased vibration
Premature bearing failure
3. Misalignment
Laser alignment showed the motor and pump shafts were outside acceptable tolerance.
Although alignment had been performed during installation, thermal expansion and pipe strain caused the alignment to change.
4. Mechanical seal damage
The seal was replaced twice, but it was not the root cause.
The actual reasons for seal failure were:
Shaft vibration
Cavitation
Misalignment
This demonstrated that replacing the seal alone would not solve the problem.
Cause-and-effect diagram
Failure chain
Poor suction piping
Elbows close to pump + clogged strainer
Low NPSH available
Cavitation
Impeller erosion
Vibration
Seal leakage
Bearing failure
Corrective actions
The following modifications were made:
Hydraulic corrections
Cleaned the suction strainer.
Increased the suction pipe diameter.
Relocated elbows away from the pump suction.
Ensured sufficient liquid level in the suction tank.
Verified that NPSH available exceeded NPSH required by at least 1 m safety margin.
Mechanical corrections
Installed independent pipe supports.
Removed all pipe strain from the pump flanges.
Performed laser shaft alignment.
Checked coupling condition.
Replaced damaged bearings and mechanical seal.
Operational corrections
Operated the pump near its Best Efficiency Point (BEP).
Installed pressure gauges on suction and discharge.
Introduced vibration monitoring.
Scheduled periodic strainer cleaning.
Results after rectification
Parameter Before After
Vibration 8.5 mm/s 2.2 mm/s
Bearing temperature 92°C 68°C
Flow rate 85 m³/hr 99 m³/hr
Seal leakage Frequent Nil
Pump efficiency 68% 82%
Major failures Every 6 months None for 3 years
Common centrifugal pump failures and rectification
Failure Probable cause Rectification
Cavitation Low NPSH, blocked suction Improve suction conditions
Seal leakage Misalignment, dry running Align shafts, ensure priming
Bearing failure Misalignment, poor lubrication Correct alignment and lubrication
Low flow Worn impeller, blockage Inspect impeller and piping
High vibration Pipe strain, imbalance Support piping and balance rotor
Motor overload Excessive flow or wrong impeller Throttle discharge or trim impeller
Overheating Dead-heading Maintain minimum flow
Key lessons learned
Do not treat the failed component as the root cause. A leaking mechanical seal may actually be caused by vibration or cavitation.
Check the suction side first. Many centrifugal pump failures originate from inadequate suction conditions.
Proper installation is as important as pump selection. Pipe strain and alignment errors can drastically reduce pump life.
Operate near the Best Efficiency Point (BEP). Continuous operation far from BEP increases hydraulic and mechanical stresses.
Condition monitoring prevents repeated failures. Vibration, temperature, and pressure trends can identify problems before catastrophic damage occurs.
Conclusion
The repeated centrifugal pump failures were not caused by defective pump components but by system-related issues—primarily cavitation, pipe strain, and shaft misalignment. By correcting the suction piping, eliminating pipe strain, performing precision alignment, and introducing preventive maintenance, the pump's reliability improved significantly and the maintenance cost was substantially reduced.
This case study highlights an important principle in pump engineering: the pump and the piping system must be considered as one integrated system when diagnosing failures.