Control circuit for lift driven by variable displacement pump

Abstract

Described is a control circuit for a hydraulic power lift driven by a displacement pump which has a check valve releasable at least for lowering movements of the power lift, a actuation means switching the check valve off and on to control the flow from a pump line into an operating line leading to the power lift and vice-versa, and a load-sensing line carrying the load pressure and connected to the operating line, by which the variable-displacement pump is capable of being activated. The actuating means has an actuating unit switching the check valve off and on and a servo valve, activated simultaneously and controlling the flow to and from the power lift, with at least three switch positions. In the starting position of the actuating means, the latter connects the load-sensing line and the operating line, by way of the servo valve, with the tank and, after passage through a central position, the operating line with the pump line. To provide that on connection and disconnection of the pilot pressure outside of the neutral position of the servo valve, pressure reactions occur in the operating line downstream of the shut-off block, the actuating unit has two actuation sides opposing one another, of which the actuation side acting on the check valve in closing direction is relieved in the end positions of the control spool of the servo valve. There is in addition provided a pressure-equalizing means which, in the central position of the servo valve, provides that the pressures on the two actuation sides may be equalized with a time delay.