Cavitation is an undesirable vacuous space in the inlet port of the pump normally occupied by fluid. The lowest pressure point in a pump occurs at the pump inlet - due to local pressure reduction part of the fluid may evaporate generating small vapor bubbles. These bubbles are carried along by the fluid and implode instantly when they get into areas of higher pressure. If cavitation occurs this will result in loss of pump efficiency and noisy operation. The life of a pump can be shortened through mechanical damage, increased corrosion and erosion when cavitation is present.
When sizing pumps on highly viscous fluids care must be taken not to select too high a pump speed so as to allow sufficient fluid to enter the pump and ensure satisfactory operation. For all pump application problems, cavitation is the most commonly encountered. It occurs with all types of pumps, centrifugal, rotary or reciprocating. When found, excessive pump speed and/or adverse suction conditions will probably be the cause and reducing pump speed and/or rectifying the suction condition will usually eliminate this problem.
This phenomenon is known as cavitation and has undesirable effects:
- The collapsing cavitation bubbles can erode the vane surface, especially when pumping water- based liquids.
- Noise and vibration are increased, with possible shortened seal and bearing life.
- The cavity areas will initially partially choke the impeller passages and reduce the pump performance. In extreme cases, total loss of pump-developed head occurs.