Abstract: A hydraulic control system has a three-position valve which in its central position disconnects the high-pressure and low-pressure sides of a pressure source from outlet lines but connects these sides of the source together through a low-pressure valve. Moved to either of its end positions the valve is disconnected from between the sides of the pressure source and the output lines are connected to the high-pressure and low-pressure source sides. A pressure-limiting valve is connected between the sides of the source. In addition, the high-pressure side is connected via pressure-reducing valve and a restriction to a pair of pilot valves which are in turn connected to the low-pressure side. These pilot valves are also connected to opposite chambers of a pilot cylinder that controls the valve body. The pressure-reducing valve between the pilot valves and the high-pressure side maintains a medium-pressure level in the system when the valves move from its central position.

Abstract: An electrohydraulic control unit which regulates the flow of hydraulic fluid to and from one or more consumers by way of a directional control valve has a cylinder for a piston which is mechanically connected with or constitutes the spool of the directional control valve and divides the interior of the cylinder into two plenum chambers connected to the outlet of the pump, either directly or by way of a pressure reducing valve. The chambers are further connected with the tank and each of the fluid supplying and evacuating conduits for each of the two chambers contains a flow restrictor. Th flow restrictors in conduits for admission of fluid to the chambers are mounted upstream of check valves and the flow restrictors in conduits for evacuation of fluid from the chambers are mounted upstream of or constitute integral parts of two solenoid-operated auxiliary valves. The four flow restrictors together constitute a hydraulic bridge circuit.