Abstract: A fluid-actuated, such as a pneumatically actuated, hydraulic pump of either the single acting or the double acting type is controlled in its operation by a main valve member which has two connecting compartments the fluid in one of which is always at the atmospheric, and in the other always at a superatmospheric, pressure. The main valve member has two end faces, one larger than the other, the smaller being always acted upon by the superatmospheric pressure of the fluid and the larger one intermittently. An auxiliary valve member controls the admission of the pressurized fluid to the larger end face and is open only during the reversal of the hydraulic pump from suction to pumping stroke, while the pressure acting on the larger end face is relieved during reversal from the pumping to the suction stroke. A duct communicates one or the other of the connecting compartments of the main valve member which an actuating compartment of an actuating unit, depending on the position of the main valve member.