Here is a "quick and dirty" way to 6

[jhelm]

Here is a "quick and dirty" way to verify whether or not you have cavitation in many pump applications. Cavitation typically produces noise (often sounding like gravel or marbles in the pump or piping) and vibration. If it is not a safety hazard or detrimental to your process, you can use a petcock or small valve on the pump suction to add a slight amount of air into the liquid and determine whether the noise and vibration are indeed cavitation.

Typically, the pump suction is operating at a relative vacuum when cavitation could be an issue. There is usually a gauge connection on the pump suction flange or the adjacent piping. Fitting a valve or petcock to this connection and opening it, will often allow air to be drawn into the suction due to the vacuum.

If cavitation is occuring, this additional air will actually decrease or eliminate the noise and vibration. The reason is that the addition of the air is relieving the vacuum which is the source of the cavitation in the pump. You have changed the suction condition (inadequate NPSH or Net Positive Suction Head), that is causing cavitation.

This technique is particularly applicable to a suction lift situation. Be careful to observe the pump suction pressure first, to verify the vacuum or low pressure and always follow appropriate safety procedures.

 

[seventhstream]

hey - thats a good tip - thanks.

 

[Gerryod2]

Karrasik says that you have to keep the air to about 1% volume percent, that it is very difficult to keep it to 1%, anymore and you'll start having trouble. Have you not found this to be so? Karrasik says that any more and it starts hurting the pump's hydraulic performance.

 

[luciom]

does the pump have to be working "at a relative vacuum" for cavitiation to be an issue ? Can we not have cavitation outside of this ?