Abstract: An hydraulic braking system of the brake-by-wire type has an hydraulic pressure source comprising an hydraulic accumulator adapted to be charged by a pump. An accumulator isolating valve is so positioned and biased to correspond to the direction of flow from the accumulator to a solenoid-operated proportional valve. The valve is biased into a closed position in opposition to the flow from the pump to the accumulator.

Abstract: A solenoid-controlled valve assembly comprises a solenoid (1) for controlling operation of a spool valve (2), and the solenoid is contained within a solenoid body (3). The spool valve comprises a spool (40) working in a bore (41, 42) in a spool housing (12), and the housing is, in turn, sealingly received in a spool body (10). The housing (12) may be of differential area and may be sealingly received in a complementary stepped bore (11) in the spool body, with the housing arranged in such a manner that when subjected to equal pressures over different area a resultant force tends to urge the housing in a given direction. In a modification the housing (12) may be resiliently biased away from the spool body (10) and relatively towards the solenoid (1) by a resilient member such as an annular ring (70) of elastomeric material, or a spring washer (71).