The prebooster pump of the unit is activated with positive and negative supply directly by the control unit during an ASC/DSC control phase.
When activated, the pump delivers brake fluid from the reservoir of the tandem master brake cylinder into a chamber between two pistons of the piston unit.
A second line leads from this chamber back to the reservoir. The throttle nozzle installed in the return line facilitates the necessary pressure build-up (backpressure principle).
A pressure relief valve in the pump prevents the pump pressure increasing to more than 15 bar. If the pressure set at the pressure relief valve is exceeded, the valve opens hydraulically and a short-circuit occurs in the pump. This effectively prevents further increase of the inlet pressure.