Cavitation Case on Pump

CAVITATION OUTCOME.

Cavitation is one of the pump failure that very common in Centrifugal pump. At design stage, The system must be verified to have NPSHa ( Net position suction head available ) is higher than NPSHr ( Net Position suction head requreid by pump ). This configuration will allow fluid at suction line has pressure above the vapor pressure of liquid at operation condition, in order to avoid the vaporization of liquid and formation of gas bubbles. 

As addition to that, the other conditions which may lead decrease the fluid pressure :

Minimize any sharp change on the suction line due to it will increase the friction loss.

Operate the pump at best efficiency operating area, so less or more flow will not a case because it will change the friction loss on the system.

Therefore, ensure your selected pump has less NPSHr compare to your NPSHa of the designed system, so cavitation will not your interest.

This failure was iniated the any bubble inside the pump, so the power from driver will use to expanding the bubble instead of bringing more liquid into the pump. so the bubble move from low pressure section to the high pressure zone of the pump, then the bubble can collapse and this will make the liquid strikes the metal parts at the speed of sound. That is way, you will hear abnormal noise on your pump during this phenomena.

The following some options to solve cavitation problem :

• Replace the impeller material with more cavitation resistant material.
• Upgrade the pump which meet to NPSHa and system head.
• Reduce the pump capacity by trim the impeller.
• Throttle the pumps to operate at lower capacity wherein the NPSHa exceeds the NPSHr.
• Use VFD to reduce speed and pump capacity.