Rotary Pumps:

Rotary pumps operate on the principle in which a rotating screw, vane, or gear traps the liquid within the suction side of the pump casing and forces it to the discharge side of the casing. These pumps are fundamentally self-priming because of their capability of erasing air from suction lines and generating a high suction lift. Within pumps designed for systems needed high suction lift and selfpriming characteristics, it is necessary in which all clearances among rotating parts, and among rotating and stationary categories, be kept to a minimum in sequence to decrease slippage. Slippage is leakage of fluid from the discharge of the pump back to its suction.

Because of the close clearances in rotary pumps, it is essential to operate these pumps at associatively low speed in sequence to secure reliable operation and manage pump capacity over an extended period of time. Or else, the erosive action because of the high velocities of the liquid passing by the narrow clearance spaces would soon cause excessive wear and raised clearances, resulting in slippage.

There are several categories of positive displacement rotary pumps, and they are generally grouped into three basic types in which involve screw pumps gear pumps, and moving vane pumps.