Abstract: A pilot controlled servo-valve has four main flow connections, an axially sliding main control piston with four control edges and a front restoring spring that defines a spring-centered middle position of the main control piston. A control sleeve has ring shaped openings for the first, second and third main flow connections and a front opening for the fourth main flow connection. A first front face of the main control piston is axially opposed to the front opening. A pressure compensation surface is formed by the second front face of the main control piston in a spring chamber. The main control piston applies the pressure in the fourth main flow connection on said pressure compensating surface through a pressure relief channel. A traverse bore connects said pressure relief channel to an auxiliary connection chamber connected to the third main flow connection by the forth control edge.

Abstract: A two-port cartridge type seat valve has a valve sleeve with a stepped guide bore for a poppet. The poppet includes a piston flange that divides the second step of the guide bore axially into an end-face first pilot chamber and an annular second pilot chamber. A first connection channel through the valve sleeve connects the annular second pilot chamber with an annular chamber into which a lateral main flow port opens. The free cross-section of a valve seat and of an axial main flow bore correspond approximately to the cross-section of the first step of the guide bore.

Abstract: A pilot stage for pressure control valves includes an axially displaceable valve piston which bounds a valve chamber axially on one side and includes a valve seat for a closure cone therein. Valve piston has an actuating surface in a pressure chamber that is substantially larger than the free cross section of the valve seat. By pressurization of this pressure chamber, a large hydrostatic force is exerted on the valve piston which opposes the closing force of the pressure-setting spring. A housing stop fixes a first axial end position of the valve piston in the direction of this hydrostatic force. The pilot control stage has improved properties for both manually adjustable pressure control valves and proportional pressure control valves.

Abstract: A pilot-operated servo valve design for efficient mounting in a control block has at least three main-stream ports. An opening into a control sleeve for a first main-stream port is disposed opposite an end surface of a main control piston. The main control piston has a pressure-equalizing surface disposed in a pressure-equalizing chamber, which is fluidically coupled by a pressure-equalizing duct in the main control piston to the first main-stream port. A return spring urges the main control piston toward a first axial end stop to clearly define a safety position. The valve exhibits good dynamic properties.