Abstract: An electrohydraulic, two-stage, proportional displacement valve comprising an advance (servo) control stage and a main control stage, the main control stage being in the form of a follower piston in which the advance control stage in the form of a second piston is guided. The second advance control piston is rotatable in the main control piston and has control edges, or control surfaces, which are inclined in the form of a helical thread. The main control piston is axially displaceable but is not freely rotatable, whereas the advance control piston is axially fixed and may be rotated around its axis by a stepping motor. Both the advance control piston and the main control piston are centered in their respective movement domains by springs. In order to adjust the position of the control edges (or surfaces) with respect to the two spring-centering mechanisms, a lever is attached to the follower piston which lever has a radial slot, indentation, or fork which engages a pin eccentrically mounted in the housing.

Abstract: A hydro-pneumatic tensioning unit, particularly for use on a tracked vehicle for pressing a guide wheel against the tensed track comprising a cylinder and a tensioning piston, which piston defines a working space in the cylinder. A volume of gas is separated from said working space by a partition and a membrane which will withstand compression and acts against the partition. The edge of the membrane is attached either to the cylinder itself or to the interior of a hollow piston, by a holding member employing prestressing or compressive force. At least one penetration opening is provided in the partition which is attached to the cylinder or the piston. The partition limits the excursion of the membrane in the direction of the working space and its surface which faces the membrane is contoured to match the shape of the membrane.

Abstract: A hydraulic priority switch for preferential feeding of a low consumption primary loop in fluid communication with a hydraulic reservoir which is chargeable from a pressure medium source via a flow control means, against a non-preferential secondary loop which can be switched in with the aid of a priority value when said primary loop is sufficiently pressurized, said hydraulic priority switch having protecting means for protecting both loops from excess pressure comprising a pressure-limiting valve which functions to make an outlet flow path available when pressure is excessive.