A reservoir for a hydraulic system has a housing with an interior space and a fluid outlet, a hydraulic driving device coupled to a shaft extending in the housing to introduce a torque, and a separating device in the housing, for dividing the interior space into two separate sections. The fluid outlet is fluidically connected to a first section. The separating device extends along the shaft in the housing and sets the size ratio of the two separate sections by pivoting at least one first surface, coupled to the shaft, of the separating device about an axis defined by the shaft. The separating device is coupled to the hydraulic driving device such that the at least one first surface exerts a pressure on a fluid in the first section which is dependent on a surface area of the first surface and the torque.