The hydraulic booster applies force to the master cylinder when the brake pedal is applied. Brake pedal movement controls the power steering fluid flowing through the booster head.

The power steering fluid enters the booster at the inlet port. Power steering pump fluid flows through the control valve and the seat and exits through the outlet port and the flow switch before returning to the power steering pump.

The hydraulic booster cylinder rod attaches to a piston that contains the control valve seat. The assembly moves when pressure is applied to the brake pedal. As the control valve moves closer to the control valve seat in the piston, fluid flow is restricted and the pressure builds on one side of the piston. The pressure overcomes the return spring and moves the piston to a balanced position. The piston is balanced when the pressure on each side of the return spring equals the pressure of the hydraulic fluid flowing through the control valve and the seat. The piston pushes the cylinder rod and applies pressure to the master cylinder as the piston moves.

A relief valve inside the booster head limits the pressure to 4 826 kPa (700 psi). The limiting of the pressure in the booster head limits the brake line pressure at the master cylinder to 1 3455 kPa (1 950 psi). The pressure level provides firm braking without damaging the brake pipes or the hoses. The relief valve allows fluid to bypass the piston when actuated. Fluid constantly flows through the booster head when the engine is running.

There is a flow switch in the hydraulic booster pressure hose which closes if the pressure becomes too low for the booster operation. This activates an electric pump to provide the needed pressure.