POWER BOOSTER

A hydraulic booster in which the booster piston return spring is formed as a tubular conduit to conduct hydraulic supply pressure to a closed center valve. Upon actuation, the valve opens to permit supply pressure to flow into the power chamber and by valving action controls the exhaust of pressure from the power chamber so as to establish the desired actuating pressure therein. The tubular conduit forming the power piston return spring and transporting the supply pressure to the closed center valve permits a shorter overall axial length of the hydraulic booster by accommodating the movement of the supply pressure chamber at the closed center valve. It also permits less charged supply pressure leakage by accommodating a better pressure seal arrangement.