HYDRAULIC CONNECTING DEVICE FOR SINGLE-ACTING HYDRAULIC CYLINDER

A hydraulic pre-switching device for feeding a single-acting hydraulic cylinder with working pressure hydraulic fluid directly or via a pressure transformer and for actively withdrawing used hydraulic fluid from the hydraulic cylinder when retracting the piston rod. The pre-switching device includes a hydraulic motor and a discharge pump coupled thereto as well as a reversing valve. The reversing valve and the hydraulic motor are connected in such a way that the reversing valve in a switching position has a connection for the hydraulic cylinder, bypassing the hydraulic motor, and the unloading pump is supplied with hydraulic fluid under working pressure and, in a different switching position, feeds the hydraulic motor with hydraulic fluid under feed pressure, which thereby drives the discharge pump, which applies negative pressure to a connection for the hydraulic cylinder.