Cavitation

From GAWDAwiki

Cavitation is a process that occurs when bubbles form and implode in pump systems. Liquid in pumps is pressurized, and if the pressure drops or the temperature is increased, the liquid begins to vaporize. However, since the resulting bubbles cannot escape such a small, sensitive system, they implode and damage the pump. The two types of cavitation are suction, or classical, cavitation and discharge, or recirculation, cavitation.^[1]

The most common form of cavitation is when the liquid level in a bulk tank gets so low that it can no longer supply liquid to feed a pump that is connected to that tank via a liquid supply line. At that point, the bulk tank starts sending gas to the pump instead of liquid. The cryogenic pump will make a significantly different sound when this happens and if the pump is not stopped quickly, the pump can be severely damaged by the heat of friction which is normally dissipated by the cryogenic liquid.^[2]

References

1. http://www.wisegeek.com/what-is-cavitation.htm
2. John Gabris, ceekay.com