HYDRAULIC MASTER CYLINDER, A VEHICLE BRAKING SYSTEM AND A VEHICLE

A hydraulic brake master cylinder () for a vehicle braking system defines a first smaller fluid path () and a second larger fluid path () for connecting a working chamber () with a fluid reservoir at ambient pressure when the cylinder piston () is retracted and the brakes are not applied. A pressure relief valve () normally closes the second fluid path but is arranged to open when subject to a pressure differential at or above a threshold value. The first fluid path allows a restricted return flow of fluid to the reservoir should a standard knock-back event occur. If a larger knock-back event occurs causing a fluid pressure spike at or above the threshold value, the pressure relief valve () opens to allow a higher volume return flow through the second fluid path to dissipate the pressure quickly.