Hydraulic booster

Claim 1

In a hydraulic power system including a high pressure source and a low pressure fluid reservoir, a hydrauic servomotor comprising: a housing defining an actuating chamber and a pressure chamber and having a bore communicating the actuating chamber and the pressure chamber; piston means slidable in said bore and separating the actuating chamber from the pressure chamber; said piston means including an outer piston and an inner piston disposed within the outer piston; a distributing valve communicating with the high pressure source and the low pressure fluid reservoir to control the pressure in the actuating chamber; operator actuating means cooperating with said distributing valve to communicate the actuating chamber with the high pressure source; said piston means being responsive to the pressure in the actuating chamber to move in the bore and effect pressurization of said pressure chamber; releasable coupling means between the inner piston and the outer piston to permit the inner and the outer pistons to move in unison when the pressure in the actuating chamber is above a predetermind value and to disengage the inner piston from the outer piston when the pressure in the actuating chamber is below the predetermined value and said operator actuating means is engageable with the inner piston to move the inner piston relative to the outer piston; abutment means attached to said housing; said inner and outer pistons having openings to receive said abutment means to limit the movement of the inner and outer pistons in the bore when said abutment means engages the inner and the outer pistons.