Abstract: A hydraulic brake booster (10) includes a housing (12) which defines a pressure chamber (16) and a piston (18) within the housing (12) is movable in response to pressurized fluid within the pressure chamber (16) to effectuate a brake application. The piston (18) encloses a storage chamber (60) and forms a pair of passages (80, 90) communicating the storage chamber (60) with the pressure chamber (16). A valve member (100) is disposed within the first passage (80) in order to control communication between the storage chamber (60) and pressure chamber (16). The valve member (100) permits pressurized fluid within the pressure chamber (16) to be communicated to the storage chamber (60) in order to charge the storage chamber (60). The valve member (100) also permits high pressure fluid above a predetermined pressure level within the storage chamber (60) to be communicated to the pressure chamber (16).