Vane pumps operate according to the Positive displacement principle.
The moving vanes, which are guided radially in a rotor and are supported in an eccentric stroke ring (stator), create an increasing geometric displacement (suction side) and reducing geometric displacement (pressure side) during a revolution.
Due to the very narrow sealing on the vanes on the stroke ring, vane machines are generally only used for medium pressures (170 to 200 bar).
If the stroke ring has a suitable curved path instead of a circular path, then each vane can make two or more strokes during one revolution (multi-stroke hydrostatic pumps/motors). With this design, the shaft load is compensated for, but it cannot be made adjustable.