Pump Operation Tips
How to keep a water centrifugal pump inside its working range so it lasts.
Run the Pump Near Its Duty Point
- A centrifugal pump is designed around one flow. Run it well below that flow and the radial load on the shaft rises, the liquid heats up in the casing and the bearings and seal take the punishment.
- Run it well above that flow and the required NPSH rises, which brings on cavitation.
- If the actual duty has moved away from the original selection, it is usually cheaper to change the impeller or trim it than to keep running the pump off its point.
Never Run Dry
- The mechanical seal relies on the pumped liquid for lubrication and cooling. Dry running destroys it quickly.
- Keep the suction supply positive and keep the pit level above the suction on a sump pump.
- Where the supply can fail, fit a low level cut out.
Watch the Suction Side
- Keep the suction valve fully open at all times.
- Keep the suction strainer clean. A blocking strainer lowers the available NPSH and starts cavitation without anything else on the plant changing.
- Rising liquid temperature also lowers the available NPSH, because the vapour pressure rises with temperature.
Limit Starts per Hour
- Every start puts a current surge through the motor and a torque shock through the coupling. Frequent starting heats the motor windings.
- Where the demand varies, a larger sump, a receiver or a variable speed drive is better than short cycling.
Monitor the Right Four Things
- Discharge pressure and flow — a drift away from the baseline usually means wear or a partly blocked line.
- Bearing temperature — a steady rise means lubrication or alignment.
- Vibration — a step change means the coupling, the bearings or the impeller.
- Seal condition — visible leakage from a mechanical seal, or a dry gland on a packed pump.
Temperature and Solids Limits
- Stay inside the limits printed for the series. As an example, the KCP series is listed for an operation temperature up to 80°C and approximately 10 per cent solid content, and the VNP series for approximately 20 per cent solid content.
- Thermoplastic wetted parts such as PP, PE and UHMW-PE lose strength as temperature rises. Do not exceed the stated operation temperature.
Operation Tips FAQ
Why should a pump not run at very low flow
Below its design flow the radial load on the shaft rises, the liquid recirculates and heats inside the casing, and the bearings and the seal take the load. Sustained low flow shortens pump life.
What causes cavitation
The available NPSH falling below what the pump requires — a blocked strainer, a throttled or partly shut suction valve, a rising liquid temperature or a falling suction level.
How many starts per hour are acceptable
Follow the motor manufacturer's figure. Frequent starting heats the motor windings and shocks the coupling.
What temperature can the thermoplastic pumps handle
The KCP series is listed for an operation temperature up to 80°C and the VNP series up to 80°C. Do not exceed the figure for your series.
Is throttling the discharge valve acceptable
Yes for control, within limits. Throttling the suction valve is not.
Question About Operation Tips
Send the pump series, the size and what you are seeing on site and we will come back to you.