Abstract: The device comprises a cylinder-piston unit B, the chambers B1 and B2 whereof are connected with the delivery of control pump A and with the control member K2 of utilizer K1. The movable part 14 of the said cylinder-piston unit B is subjected to the influence of spring means 16 and presents a calibrated opening D, said opening being co-axial with the said cylinder-piston unit, while means 20 and 22 sensitive to the pressure building up in chamber B2 of the cylinder-piston unit B control the communication between the said chamber B2 and discharge A1. Said means 20 and 22 are combined with adjustable members 24, 28, 36 which counteract the action of the pressure building up in chamber B2 of the cylinder-piston unit B. It is thus possible to fill the actuating group K2 within a pre-determined period of time.