Abstract: A valve assembly (1) operable to allow or prevent the flow of fluid to or from a working chamber of a fluid-operated machine, comprising radially spaced apart inner and outer annular valve seats (8, 15) defining an annular passage therebetween, a valve member comprising a sealing ring (21), and means (3, 7, 26, 25) for moving the valve member axially between a first position in which the sealing ring (21) is in seating engagement with the annular valve seats to close the annular passage to fluid flow therethrough and a second position in which the sealing ring (21) is spaced from the annular valve seats (8, 15) so that the annular passage is open to fluid flow therethrough. The valve assembly further comprises axially spaced apart first and second valve guide means (6) for guiding the valve member during axial movement between its first and second positions.

Abstract: A multi-chamber fluid working machine has at least one electromagnetically controlled poppet valve linking each working chamber with respective high and low pressure fluid manifolds whereby displacement control is achieved by real time control of the electrically selectable poppet valves. Each valve seals via annular parts on the valve and its seat and is moved by reaction between a solenoid coil and a ferromagnetic part on the valve stem.

Abstract: Displacement control of a multi-piston fluid pump is achieved by real time control of electrically selectable inlet poppet valves in one or more of the cylinders. Microprocessor control permits desired variable output characteristics to be matched. An electrically actuable poppet valve using an annular permanent magnet to latch to a solenoid is described.

Abstract: A hydraulic valve has a tapered plug rotatable in a complementary tapered bore in a stationary housing so that the axial position of the plug controls the magnitude of a leakage path between the two parts. The magnitude of the leakage path is sensed and used to control the axial position of the plug in a negative feedback arrangement so that the valve plug floats on a film of escaping hydraulic fluid and can be readily rotated by a low power actuator. Ports in the stationary member and passages in the plug are arranged so that both static and preferably also dynamic and hydraulic forces acting on the plugs are balanced. The valve is contained in a closed housing, preferably together with the actuator.