Hydraulic pumps of type PVQ are vane pumps with constant displacement. The rotor running in a stator ring is located on the tooth profile of the drive shaft. The slots of the rotor accommodate the vanes which are pressed against the internal surfaces of the stator ring by the centrifugal force upon rotation of the rotor. The displacer chambers are laterally sealed by the control plates. Due to the double-eccentric design of the stator ring, there are in each case two pressure chambers opposite of two suction chambers, which provides for hydraulic unloading of the shaft. So it only has to transmit the torque. The vanes are partially unloaded upon passage through the suction range. This unloading has a wear-reducing effect and ensures high efficiency. By simply removing the cover, the pump insert (consisting of rotor, vane, stator ring and control plates) can be removed without the need of removing the housing from the pump carrier.