Solenoid Valve

Solenoid or isolation valves are used to equip the anti-lock braking system (ABS, from German Antiblockiersystem) to prevent fluid from entering the wheel brake area when ABS is used.

The normally closed valve is then energized (opened) releasing pressure from the wheel causing a pressure drop across the isolation valve.

The above causes the isolation valve to move closing a ball seat valve which isolates the master cylinder (pedal) from the wheel (pump, solenoid, etc).

The pressure generated by the pump causes the actual movement of the isolation valve: hence, filters placed in the system avoid contamination that could cause a valve to fail to open or to close.