Abstract: In an hydraulic anti-skid braking system of the pump and de-boost type operation of the pump is initiated by an operating piston co-operating with the plunger of the pump. There is a danger that fluid trapped in a chamber between adjacent ends of the piston and the plunger by a one-way valve of the pump may cause the pump to operate accidentally. This is prevented by adapting the one-way valve to act as a pressure relief valve and establish a return path from the chamber to a reservoir when the plunger has moved relatively away from the piston through a predetermined distance insufficient for the plunger to co-operate with a drive mechanism.

Abstract: In an hydraulic anti-skid braking system of the pump and de-boost type the position of the de-boost piston in the bore is determined by a volume of fluid trapped in a space by a dump valve. The dump valve operates in conjunction with a restrictor which, at least at pressures above a pre-set level, restricts the rate of release of fluid from the space when the dump valve is open. Decreasing the flow rate of the dump valve decreases the time period for each anti-skid cycle. The pump no longer has to pressurize to maximum (brake) from zero which reduces the amount of energy which otherwise would have been consumed in the re-application mode. In addition the rate of release of fluid at pressures below the pre-set level can be increased which is of particular advantage when the vehicle is travelling over surfaces having low co-efficients of friction.

Abstract: In a master cylinder of the quick-fill type, communication between the quick-fill chamber (8) and the reservoir (13) is controlled by a valve assembly comprising a pressure responsive valve which opens when the pressure in the quick-fill chamber (8) reaches a predetermined level, and a one-way valve (20, 22) which allows free flow of fluid from the reservoir to the quick-fill chamber. The valve member (20) and seat (15) of the pressure responsive valve have confronting surfaces which define between them, when the valve is closed, a restrictive passage for pressure equalization purposes, and any dirt becoming trapped between the surfaces is washed away by the fluid flow on opening of the valve.

Abstract: In an hydraulic anti-skid braking system of the pump and de-boost type, the de-boost piston is held in an advanced inoperative position by a volume of fluid trapped in a space and supplied by a pump. A bleed device communicating with the space is held in an open position during initial bleeding of the system by a friction device which acts as a stop and which is releasable when the bleed device is subjected to a predetermined pressure. This enables initial bleeding to be carried out automatically and without an operator operation to open and close a bleed device. After initial bleeding, the device can be opened manually to enable subsequent bleeding to be carried out, with the spring assembly acting on the de-boost piston also acting to close the bleed device following release of the manual force.

Abstract: An hydraulic brake actuator comprises opposed pistons which work in bore portions in a housing and fluid pressure in a pressure chamber urges the pistons in opposite directions to separate adjacent ends of a pair of brake shoes. A pressure proportioning valve controls communication between pressure spaces constituted by the pressure chamber. The valve is normally open to equalize the pressure in the pressure spaces but closes at a predetermined pressure so that any further increase in pressure is operative in only one pressure space, the pressure in which space acting to keep the valve closed. In use in a brake of the one-leading one-trailing shoe-drum type the increased pressure acts on the piston which applies the trailing shoe to the drum, in order to equalize the torque.

Abstract: A servo booster is provided with a tube coaxial with the booster output rod for relieving the booster housing of braking reaction forces. The housing of a tandem master cylinder has an externally threaded rear end which is threadedly engaged with internal threads formed on a reduced diameter front part of the tube. The retracted position of the primary piston of the master cylinder is determined by abutment with the booster output rod, and this can be adjusted by turning the master cylinder housing relative to the tube.

Abstract: In a power-operated hydraulic booster for a vehicle braking system pressurization of a power chamber in a housing on one side of a boost piston is controlled by an assembly of at least two separate spool parts which work in bores in the boost piston and the housing, and a boost chamber is defined in the housing between the power chamber and an output piston having an effective area less than that of the boost piston.