Service-brake chambers (Fig. 11) convert compressed air pressure energy into mechanical force and movement, which apply the vehicle’s brakes.

When you press down on the foot valve, air pressure enters the pressure side of the brake chamber through the inlet port and forces against the diaphragm, which moves the push rod assembly forward. When air pressure is released from the service-brake chamber, the return spring returns the diaphragm and push rod to their released positions.