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.

Abstract: A position controlled proportional directional control valve has a main control piston for controlling flow between passages to a pump, a tank, and to passages which may be connected to an operative device, such as a hydraulic motor. The main control piston may be moved in one direction by an operating piston slidably disposed in a centring flange which serves as a mechanical stop for movement of the main control piston in the opposite direction. Acting on the end of the main control piston opposite the operating piston is a centring piston having one end in a pilot control chamber, and which may urge the main control piston against the centring flange either by pressure fluid in the chamber, or upon failure of pressure, by the spring in the chamber. A pilot control valve, under the control of an electrical magnet, moves proportionally to the current in the electrical magnet, to admit fluid under pressure from a pump passage into the pilot control chamber.

Abstract: A proportional valve comprises two electrically actuated proportional throttle valves, each having an outlet connected to a non-return valve, to each of which a seat valve is connected, each seat valve being pilot-controlled by one of the proportional throttle valves; the electric actuation of the proportional throttle valves proportionally controls and regulates the functions of a hydraulic cylinder. The two throttle valves and the two seat valves are mounted on a housing block which has a planar face at which are connections to a pressure line, a tank line and working lines.

Abstract: The throttle-part of the valve comprises a two-way seat valve with a follow-up throttle valve (8), which is driven by a differential guide piston (12) and an edge control system (20). The guide piston is pressurized via a pressure-spring (16) in a pressure-spring compartment in the direction of the closed position of the edge control system. The drive is effected via a pilot line A which pressurizes or depressurizes the pressure-spring compartment (18) via a proportional directional control valve (6), while the position of the guide piston (12) is determined by an inductive displacement transducer.

Abstract: The main control piston (8) is controlled hydraulically by pilot control slide valves, operated in each case via two control magnets (4, 6) with force build-up proportional to the control current. In the case of failure of the electrical activation, the valve is always positioned in the center position by pressure centering and in the case of failure of the pilot control pressure it is positioned in the center position by spring centering.

Abstract: The control block consists of four seat valves arranged in pairs above one another and opposite one another in two planes parallel to the base surface of the control block, the valves located diagonally opposite one another being controllable in pairs via a pilot valve. The logical combination of the invididual elements makes it possible to construct a compact, space-saving and handy control unit with a sealing surface arranged according to the customary standard pattern.

Abstract: An adjustable throttle valve is controlled by a low pressure control pressure acting on a spring urged adjusting cylinder for positioning the end of a follow-up piston adjacent the end of a discharge channel extending the length of a throttle piston; power fluid flows from a source through a discharge opening between a housing and the throttle piston with the spring force, the control pressure, infeed pressure and discharge pressure acting in concert to maintain the end of the follow-up piston adjacent but slightly spaced from the end of the discharge channel for maintaining throttle piston equilibrium.