Brakes (Pcrv): Description and operation

PCRV

The PCRV is a twin valve unit that reduces the hydraulic pressure supplied to the rear brakes to maintain vehicle stability under braking. A mounting bracket attaches the PCRV to the RH inner wing.

The PCRV comprises two cast housings, one connected to the primary brake circuit and one connected to the secondary brake circuit. The two housings are bolted together and connected by an internal passageway. The passageway in each housing contains a piston sleeve, poppet valve and associated seals and springs. One housing incorporates a vent from the internal passageway, which is sealed by a rubber vent plug.

On ABS variants, only the rear brake pipes are connected to the PCRV. On non ABS variants, both the front and the rear brake pipes are connected to the PCRV, but the flow to the front brake pipes is unregulated.

When the brakes are applied, pressurized brake fluid from the inlet ports passes through the piston sleeves and the open poppet valves to the rear brake outlet ports. On non ABS variants, pressurized brake fluid also passes directly from the inlet ports to the front brake outlet ports. Hydraulic pressure, on the outer ends of the piston sleeves, moves the piston sleeves against spring pressure towards the centre of the PCRV. When the piston sleeves contact the poppet valves, the rear brake outlet ports are isolated from the inlet ports.

As the pressure from the master cylinder increases, the poppet valves remain closed until, at₂ approximately 25 bar (367.5 lbf.in ), hydraulic pressure overcomes poppet valve spring pressure to allow a restricted flow through to the rear brake outlet ports. The restriction causes a pressure drop across the poppet valves, to give a front : rear brake pressure differential of 10 : 3.