Pneumatic assisted brake apply system

A brake apply system includes a power booster in which, when released and at-rest, a leg of a stop engages a clip and an extension of a valve body engages the clip so that an annular rib of the valve body is axially spaced away from the stop by a distance G. At the same time, a first valve seat is engaged with a first annular valve element closing a pressure supply conduit off from a variable pressure chamber and a second valve seat is spaced away from a second annular valve element by a distance T, opening the variable pressure chamber to an atmospheric pressure chamber. When the power booster is applied, the second valve seat moves the distance T and engages the second annular valve element closing the variable pressure chamber off from the atmospheric pressure chamber and the first valve seat separates from the first annular valve element opening the pressure supply conduit to the variable pressure chamber. The stop moves against the annular rib of the valve body so that when the pushrod is initially released the second annular valve element moves away from the second valve seat a distance equal to G+T. A pressurized air supply communicates with the power booster and includes a compressor and a dryer. When the compressor is turned off a solenoid valve opens and a quantity of dry air contained in a regeneration reservoir passes through the dryer, regenerating the dryer.