The invention relates to a hydraulic pump wherein a barrel is in sliding connection with a shaft and is driven in rotation by the shaft. A housing is formed in the barrel, the shaft sliding in the housing while projecting from the front face of the barrel. The housing and the shaft defining between them a balancing chamber, the balancing chamber being connected to a delivery aperture in such a way that fluid in the balancing chamber exerts a compressive force on the barrel which tends to press the barrel against a port plate.