During the working of a positive displacement pump, vacuum is created at the inlet of the pump. This allows atmospheric pressure to push the fluid in. In some situations, the vacuum may become excessive, and a phenomenon known as cavitation occurs. When the pressure of the liquid reaches a low enough level, it vaporizes or boils. Cavitation is the formation of oil vapor bubbles due to a very low pressure (high vacuum) on the inside of the pump. The low pressure also causes air, which is dissolved in the oil to come out of the solution and form bubbles. These air and oil vapor bubbles collapse when they reach the outlet side of the pump, which is under a high pressure. The collapsing of these vapor bubbles causes extremely high localized pressure and fluid velocity. These pressures are so high that they cause pitting of metal and consequently decrease the life and efficiency of the pump.

Factors Causing Cavitation
Cavitation is caused by the following factors:

1. Undersized plumbing.
2. Clogged lines or suction filters.
3. High fluid viscosity.
4. Too much elevation head between the reservoir and the pump inlet.

Rules to Eliminate (or Control) Cavitation
Following are the rules to control cavitation:

1. Keep suction line velocities below 1.2 m/s.
2. Keep the pump inlet lines as short as possible.
3. Minimize the number of fittings in the inlet line.
4. Mount the pump as close as possible to the reservoir.
5. Use low-pressure drop inlet filters.
6. Use proper oil as recommended by the pump manufacturer.