Rotary vane pump

They can endure short periods of dry operation, and are considered good for low-viscosity fluids[citation needed].

The vanes are allowed a certain limited range of movement within these slots such that they can maintain contact with the wall of the cavity as the rotor rotates.

A small amount of oil may be present within the mechanism to help create a better seal between the tips of the vanes and the cavity's wall.

On the discharge side of the pump, the vane chambers decrease in volume, compressing the fluid and thus forcing it out of the outlet.

Pumps for mid-range pressures include applications such as carbonators for fountain soft-drink dispensers and espresso coffee machines[citation needed].

These are found in such applications as providing braking assistance in large trucks and diesel-powered passenger cars (whose engines do not generate intake vacuum) through a braking booster, in most light aircraft to drive gyroscopic flight instruments, in evacuating refrigerant lines during installation of air conditioners, in laboratory freeze dryers, and vacuum experiments in physics[citation needed].

In 1858, a US patent was granted to one W. Pierce for "a new and useful Improvement in Rotary Pumps", which acknowledged as prior art sliding blades "used in connection with an eccentric inner surface".