Sectioned view of PCRV - non ABS (Brakes) (page 2 of 2)

On non ABS variants, in order to balance the hydraulic pressure to the rear brake outlets, the two piston sleeves act in opposition to each other at either end of a common spring. Any difference in pressure at the two inlet ports causes the position of the piston sleeves to be biased towards the lower pressure circuit. This causes an increase in the pressure drop across the poppet valve of the circuit with the higher pressure. The subsequent pressure at the outlet port is then approximately the same as the pressure at the outlet port of the low pressure circuit.

When the brakes are released, the piston sleeves are moved outwards by spring pressure. This opens the poppet valves, releasing hydraulic pressure from the rear brakes and allowing brake fluid to flow back towards the master cylinder.

In the event of failure of an internal seal, fluid will enter the centre chamber of the PCRV and, when the brake pedal is applied, will cause the vent plug to rupture and allow brake fluid to escape.