Triple power booster for brake systems

A power booster for a brake system including a housing having an interior and a pair of diaphragms separating the interior of the housing into three chambers. A power piston assembly is coupled for movement with the diaphragms and includes an output member. A reaction member is coupled to the power piston assembly, and an input member is adapted to be coupled to a movable brake pedal. An air valve assembly moves between open and closed positions to selectively admit atmospheric air into selected ones of the chambers. This induces an output force on the diaphragm that is transferred to the output member of the power piston assembly. The triple booster adds an additional working chamber with an added approximately 45% increase in power boost. The triple power booster retains many of the same components as prior dual or tandem boosters to provide an economical solution to increase booster output without the need for new tuning procedures or added booster diameter.