Abstract: An hydraulic control valve and particularly such a valve for use as an automotive brake pressure modulation valve to maintain optimum adhesion and traction between the tire of the vehicle and the road surface during braking when the wheel shows a tendency to lock. The valve comprises one or more solenoid operated valves in which the solenoid core defines a chamber for a fluid under pressure. Preferably the valve member is in the form of a spool connected to or constituting the armature and is slidable within the core. The core has a narrow waisted portion provided to establish a preferred flux part through the armature. This arrangement enables the core of the valve to withstand the necessary operating pressure without the need for complex and carefully controlled welding. Smaller solenoids can be used by pressure balancing the valves.

Abstract: A hydraulic braking system for agricultural tractor-trailer combinations, taking hydraulic power from a pump on the tractor. The system includes a pressure control valve movable by the main hydraulic service supply to connect the main supply with a chamber in communication with a restricted bore and an outlet for the by-passed braking fluid. A pilot valve responsive to braking pressure, or manually operable, admits fluid to the trailer brakes and operates a check-valve closing a connection between the chamber and a return line for fluid not required for braking. The check valve enables a clean switching action and eliminates any tendency to meter at some intermediate pressure. Both constant flow and constant pressure systems are described. The return line may be connected to a low pressure sink or to the flow at the services outlet port preferably via another check valve.

Abstract: Spool type brake valve for use in motor vehicle braking systems. The valve has an exhaust valve assembly and an inlet valve assembly. The former having a spool displaceable by a brake pedal or the like to disconnect the brake-port from an exhaust port and the latter having a spool movable within a sleeve upon subsequent displacement of the exhaust valve to supply pressure fluid to the brake port.

Abstract: A vehicle braking system incorporating two circuits serving driven and non-driven axles respectively and in which both air-actuated service brake units and spring brake units for parking are provided on both axles. The system includes relay valving which is operable upon failure of the service braking in either circuit and responsive to the service pressure in the other circuit to provide a graduated actuation of the spring brake units in the circuit where service braking has failed. The spring brake on the driven axle and/or the relay valving is so constructed as to attenuate the force applied by the spring brake units on the driven axle.

Abstract: A tractor-trailer hydraulic braking system in which the tractor braking circuit and trailer braking circuit are inter-connected by releasable hydraulic couplings including both service and emergency line connections each with its associated return line. The trailer circuit also includes a pressure storage unit or accumulator and a emergency valve operable to apply the trailer brakes in the event of loss of emergency line pressure. To avoid leak down of the accumulator over a period following de-coupling of the trailer an expansion tank or chamber is connected into the trailer circuit so as to receive fluid leaking into the return lines from the accumulator and to retain such fluid until the pump can return it to the accumulator.

Abstract: A fluid-pressure operated dual circuit braking system in which each circuit serves a rear axle brake and at least one front axle brake, one circuit only including a load sensing valve. The braking pressure in the other circuit is controlled by a relay valve in response to the modulated pressure from the load sensing valve. The relay valve includes a piston which is normally balanced but moves in the event of a failure in the circuit embodying the load sensing valve, to connect the unmodulated pressure in the relay valve circuit directly to the rear axle brakes.

Abstract: A hydraulic ram system for tilting a vehicle cab which is resiliently mounted on the vehicle frame includes a ram cylinder of which that end in which the ram piston is located when the cab is in the lowered position is of increased bore diameter to render the piston passive in this position, a restriction being provided in the lower ram line across which a pressure drop is created when fluid is pumped through the line, while in the upper ram line a valve is provided responsive to the pressure differential across the restriction and thereby operable to interconnect the upper and lower ram lines.

Abstract: A pressure control valve for controlling the operation of spring-actuated fluid pressure released brake units in vehicle braking systems. The valve described requires less operating effort than for conventional control valves of this kind even those including a follow-up means. It has a plunger-type valve element slidable within the carrier and controlling the flow of fluid between inlet and delivery ports. The carrier is biassed towards an open position of the valve in opposition to a spring force by the delivery pressure and the valve element is responsive to delivery pressure to open the valve in opposition to another spring force. The carrier spring has a substantially greater rate than the valve element spring which can be adjusted so that the effort required to operate the valve can be kept to moderate limits while retaining the advantage of a follow-up valve action.

Abstract: A load-sensing valve for an air pressure braking system comprises a diaphragm responsive to a signal pressure, as from a brake valve, and actuating through a rockable beam a two stage valve for controlling flow of pressure air to the brakes, the beam fulcrum being displaceable in accordance with vehicle load, and a further diaphragm having operable connection with the two-stage valve and responsive to delivery pressure, the two-stage valve consisting of a pilot valve operable alone where air usage is small to provide high sensitivity and a main inlet valve which is brought into operation with increased inlet pressure and larger air flow.

Abstract: A hydraulic ram system for tilting a vehicle cab which is resiliently mounted on the vehicle frame includes a ram cylinder of which that end in which the ram piston is located when the cab is in the lowered position is of increased bore diameter to render the piston passive in this position, an auxiliary valve being provided in the upper ram line held by a spring-loaded detent in a closed condition and adapted to open when during a lifting operation the piston moves out of the increased bore zone.

Abstract: An air brake system for truck and trailer combinations comprises a vehicle load sensing valve in the rear wheel brake line of the truck, a truck-mounted relay valve incorporating a piston or piston assembly responsive to truck braking pressures and adapted to actuate valve means to control delivery of pressure to the seervice brake line, and an additional piston, piston assembly or piston/diaphragm assembly in the relay valve which also actuates the valve means and which is responsive on opposite sides to the input and output pressures respectively of the vehicle load sensing valve.

Abstract: A slack adjuster to be used in association with the actuating cam of an internal expanding shoe type brake comprises a body member embodying a brake-actuating arm movable around the axis of the cam shaft, a worm rotatably mounted in the body member and meshing with a worm wheel keyed to the cam shaft, a member oscillatably mounted on the body member and co-operating with a non-rotatable member to impart motion to the worm through a sprag clutch when a pre-determined angular movement of the brake-actuating arm is exceeded, and a friction clutch also in the drive from the oscillatable member to the worm and operable to dis-engage the drive if attempt is made to rotate the worm while it is still under braking load.

Abstract: A dual brake valve for use in a twin-circuit fluid pressure-operated vehicle braking system comprises a housing, two sets of ports therein each including an inlet port and a delivery port, and two co-axial valve assemblies associated respectively with the two sets of ports, the valve assemblies each comprising a poppet-type valve element the head of which is subjected to delivery pressure, which pressure also acts on an oppositely-directed face of the valve element such that fluid pressure across the valve element is balanced. Preferably an axial exhaust passage is provided in part by a tubular member located co-axially between the valve assemblies by a diaphragm assembly which is also subjected to delivery pressure on both sides thereof.

Abstract: A hydraulic ram system for tilting the cab of a large commercial vehicle to provide access to the engine and other mechanism, where the end of the ram cylinder in which the ram piston is located when the cab is in the lowered position is of increased bore diameter and provides enough clearance around the piston to render the ram passive in this position, and the length of the increased diameter portion of the cylinder bore is sufficient to accommodate the maximum movement of the cab on its suspension.

Abstract: A full-power hydraulic braking system comprises two independently-powered service circuits serving separate sets of brakes, a common pedal-actuated dual brake valve controlling operation of said circuits, a spring brake actuator fed from both service circuits through separate lines and, in each of said lines, a pressure responsive protection valve operable in the event of a failure in either service circuit to cut off the spring brake actuator from that service and ensure continued operation of said actuator from the other service circuit.

Abstract: A full-power hydraulic braking system comprises two independently powered service circuits serving separate sets of brakes, a common pedal-actuated dual brake valve controlling operation of said circuits, a spring brake actuator incorporating two hold-off pistons and having a common output to the brakes or brake linkage, and a dual hand control valve for effecting controlled operation of the two sections of the actuator respectively from the two service circuits.

Abstract: A spring brake unit for use in a vehicle braking system comprises a housing, a piston movable therein and connected to a brake or brake linkage, a spring interposed between the piston and a detachable end wall on the housing and urging the piston in a direction to apply the brakes fluid under pressure being introduced to the housing in a controlled manner to hold the piston in brake-off position, and the housing and/or detachable end wall being formed to define one or more drainage channels opening into a gaiter which bridges the joint between them and which includes a drain outlet.