A centrifugal pump is not too complicated. It has a rotating impeller in a chamber and a motor to turn the impeller. Centrifugal pumps come in two forms: horizontal pumps, with horizontal impeller shafts and vertical impellers, and vertical pumps, with an opposite orientation, like a sump pump. You can often notice problems with a centrifugal pump by the sound the pump makes or a change in the pump's rate of discharge or suction. There are five problems that are directly observable when the pump is in operation and three problems that can be ascertained from the pump's maintenance files.
Listen to the pump. A high-pitched whine, a cyclic thumping or a grinding sound may be accompanied by vibration and may indicate a bent shaft, a misaligned pump head, a distorted casing, defective bearings or motor problems. Check the alignment between pump and motor, check the deflection of the impeller shaft and inspect the pump's bearings.
Look at the pump. If the pump is leaking, check the seals and replace if necessary. If the pump is vibrating but making none of the noises one would expect from a pump that is not working properly, check the pump's gauges for high or low output levels and check the motor using its troubleshooting guide. If the output levels and motor are in order, check the alignment between pump and motor, check the deflection of the impeller shaft and inspect the pump's bearings.
Read the gauges. If the output is "0," see if the supply tank is empty, the suction valve is closed, the pump speed is too low or the pump is turning in the wrong direction. If the pump speed is too low and the pump is properly sized, the problem lies with the motor or power supply. If the suction valve is open and the supply tank has sufficient liquid, so that the pump does not lose prime, check to see if the impeller is clogged. The direction of rotation is marked on the pump's casing and, if the impeller is turning in the opposite direction, reverse the polarity of the motor. If the output is too high, the problem is not associated with the pump.
Check the pump's power consumption. If the pump is consuming excessive power, check the motor's speed and voltage: a motor designed to operate with 110 VAC running on 240 VAC will have a skewed power consumption and a short, exceedingly high-speed life. Replace the motor or change the power source.
Read the pump's maintenance history. Short seal or bearing life can indicate cavitation; if the pump is above the supply tank, increase the level of the liquid in the supply. If the supply tank is higher than the pump, increase the height of the tank. Misalignment between the motor and the pump can cause bearings and seals to wear more quickly as can bent impeller shafts, improperly sized pumps and damaged impellers.
Tips & Warnings
- Double check the pump's specifications before you start. Using an improperly sized pump can send you looking for internal problems that don't exist.
- A centrifugal pump is rotating machinery---appropriate safety precautions should be observed.