Abstract: A pressure cylinder, such as a master cylinder or wheel cylinder for an hydraulic vehicle braking system has a plastic molded body within which a threaded insert is engaged and restrained rotationally and axially. A seal is positioned within the body between surfaces of the insert and body. The insert provides a seat against which is clamped, in use, a corresponding seat on a flared end of a pipe, the letter being retained within the body by a pipe nut threadedly engaged with the insert. Long-term thread torque and clamping force are sustained by the insert rather than by the plastic body which can be subject to "creep".

Abstract: A pressure cylinder, such as a master cylinder, primarily for use in a vehicle brake or clutch hydraulic system includes a cylinder component molded from plastics material, and an initially separate flange component which is preferably but not essentially, also molded from plastics material. The two components are provided with an interconnecting arrangement capable of transmitting axial thrust between the two components, and also resisting relative rotation therebetween.

Abstract: A master cylinder has a pressure cylinder and an outwardly projecting mounting flange mounted thereon by arms extending longitudinally of the cylinder in spaced relationship therewith and being connected to the cylinder at locations remote from the flange outside the area swept by seals carried by a piston. The cylinder, flange and arms are formed as an integral plastics molding.

Abstract: A master cylinder includes a pressure cylinder and a pressure-generating piston movable therein. The cylinder is closely surrounded over part of its length by a separate reinforcing member in the form of a sleeve which acts to prevent significant expansion of the cylinder under the effect of internally applied pressure. In the example shown, the pressure cylinder forms part of an integral moulding which includes a fluid reservoir.

Abstract: A tandem master cylinder includes a pair of separately molded plastic cylinder half portions joined together. Each contains a pressure chamber and a piston of the tandem circuit. Coaxial cylindrical bodies surround the cylinder portions, each joining to its respective cylinder portion at a location axially beyond the limits of inward axial travel along the cylinder of seals carried by the pistons so as to account for any differential shrinkage in molding. The cylindrical bodies interconnect at their ends to form a sealed joint locating the cylinder halves in correct radial and axial alignment. Reinforcement members around the cylinder halves resist expansion from internal pressure.

Abstract: A brake pressure control valve (1) for use on a vehicle having a modulated self-levelling air suspension system comprises a valve body (2) sealingly secured to the wall (4) of a pressure chamber of the suspension system to close an aperture (7) in the wall. A brake pressure apportioning valve set (11) is located within the valve body and has a control member (15) the upward force (A) on which determines the cut-in pressure. Fluid pressure within the pressure chamber (5) is communicated to a control chamber (18) via a small orifice (21) in a steel cup (20) which closes the bottom of the valve body. Pressure within control chamber (18) is applied to a diaphragm (20) which permits pressure transfer to a pressure plate (16) abutting the control member (15) but prevents loss of fluid from the control chamber (18).

Abstract: A control valve for controlling the distribution of pumped hydrodynamic fluid to the trailer brakes of a tractor and trailer combination in response to hydrostatic pressure applied from the tractor braking system has an inlet for pumped fluid, a spool valve operable in response to a control piston to control the flow of pumped fluid to a first working trailer braking circuit through an outlet and to a tank, or reservoir, through an outlet, a flow control valve which provides a passageway communicating with a first flow path for pumped fluid to the spool valve and which is operable in response to pumped fluid pressure to control the flow of pumped fluid to a second working implement circuit through an outlet, and a second flow path for pumped fluid extending between the inlet and spool valve independent from and parallel with the first flow path, so that the spool valve controls the flow of pumped fluid through the second flow path to the fluid outlet leading to the trailer braking circuit.

Abstract: A fluid-tight connection between a pair of pipes containing hydraulic fluid is formed by a pair of connectors of the invention. Each connector has a body part engaged respectively with the pipes, the body parts being coupled together by a coupling sleeve which engages a shoulder 20 of one of the body parts and is locked to the body parts by a circlip 23 engaged within grooves 22 and 25 respectively in the other body part and the sleeve. Each body part has a respective seal member each incorporating a diaphragm sealing over an end of its associated body part and a bead engaging the internal wall of the sleeve. Air trapped between the diaphragms is expelled past the seal members during insertion of the connector parts into the sleeve. Application of system pressure subsequently ruptures the diaphragms to establish communication between the pipes and urges the seals outwardly to seal against leakage of system fluid.

Abstract: In a vehicle hydraulic system of the open center kind, hydraulic fluid for operating vehicle services is circulated continuously, normally by an engine-driven pump. A closed center booster which requires a substantially constant pressure differential to operate it, is included in the open center system, the pressure differential being provided by a fixed restriction. The fixed restriction may be operative when the pump is operative, or only when the booster is operative. The booster is arranged so that in operation, high pressure fluid entering a boost chamber displaces an equal volume of fluid from a forward chamber into the system. The booster may also include a one-way valve allowing flow of fluid from the forward chamber to the boost chamber.

Abstract: An hydraulic booster has a housing provided with a bore, an inlet connected to a source of pressure fluid, and an outlet connected to a reservoir for fluid, a boost piston being advanced in the bore in response to pressurization of a boost chamber, the boost chamber being pressurized under the control of a valve mechanism operative in response to a load applied to an input member. Two connections are provided between the source and the boost chamber, both connections being closed when the booster is inoperative, and when the booster is operated the first connection is opened following initial movement of the input member, and the second connection is opened following initial movement of the boost piston in response to pressurization of the boost chamber. Thus the booster is in a closed center mode when inoperative, but operates in an open center mode. The connections are preferably controlled by valves. The input load may be applied in tension or compression.

Abstract: A pair of tandem master cylinders have primary pressure spaces connected to the brakes on one pair of wheels on opposite sides of the vehicle, and an actuator for the brakes on a trailer is supplied with fluid under pressure from pipe-lines connected to each of the four pressure spaces and under the control of first and second disabler valves. Each disabler valve has a pair of inlet ports, each connected either to respective primary pressure spaces or respective secondary pressure spaces, and an outlet port connected to the actuator. When one master cylinder is operated on its own both disabler valves are closed to prevent the actuator from being operated. Failure of one pressure space, when both master cylinders are operated simultaneously, causes the corresponding disabler valve to close but the actuator can still be operated from the operative pressure spaces, through the other disabler valve.

Abstract: A fluid flow control valve assembly has a housing with first and second ports, and a valve mechanism for controlling fluid flow by closing either port or permitting fluid flow between them. The valve mechanism comprises two relatively movable members, a first member for controlling flow through the first port in response to a first spring, a solenoid, and the pressure differential across the first member; and a second member for controlling flow through the second port in response to the first member, the pressure differential across the second member and a second spring.

Abstract: In a high pressure hydraulic system a slave unit is supplied with fluid from a source through a control valve assembly. The assembly has a valve mechanism to control flow between ports communicating with the source and slave unit. The valve mechanism has two members, a first member controlling flow through the first port in response to a spring, a solenoid, and the pressure differential, the solenoid being unable to move the member against a significant pressure differential, and a second member controlling flow through the second port in dependence on the first member, the pressure differential and a spring. The first port has an elastomeric seal preventing leakage when the port is closed. The system has particular advantages when it is used as a vehicle suspension levelling system, in which an electronic control system controls the supply of fluid from an accumulator through a manifold and control valve assemblies to hydraulic suspension struts in accordance with ride height signals.

Abstract: In a vehicle braking system of the kind in which brakes mounted on opposite sides of the vehicle are associated with respective pedals (1) and can be operated together for normal vehicle retardation or independently to assist vehicle steering, the brakes are connected to respective chambers (14, 15) of a tandem master cylinder (5) through respective control devices (7) which are actuated by the pedals (1) and control communication between the respective chambers (14, 15) and a reservoir.

Abstract: In dual control assemblies for hydraulic braking systems of vehicles, the valve assemblies comprise a pair of control valves clamped together in side-by-side relationship in each of which a back-up piston works in a greater diameter portion and a hollow spool works in a smaller diameter portion of a stepped bore, the piston and the spool being operated by a push- or pull-rod in turn operated by a pedal. The spool controls communication between pressure spaces of the valves and their respective recuperation, inlet and transfer ports. The recuperation ports are connected to a common reservoir for fluid, the inlet ports are connected to a common hydraulic power source and the transfer ports are interconnected. Each pressure space is connected to a brake via an outlet port.