Valve member 1 is held on its seat by spring 2. Space a under the valve member is connected to the compressed air tank. When the brake pedal (not shown) is depressed, compressed air is delivered from the brake valve through port 4 an it bends diaphragm 3 downward, thereby open valve member 1. Compressed air from space a passes into space d and is delivered to the brake chambers of the rear wheels. At the same time, the compressed air tends to force diaphragm 3 upward. When a definite pressure is reached in the brake chambers, equilibrium is set up between the forces acting above and below the diaphragm. At this, valve member 1 is closed, shutting off further air delivery to the brake chambers. To increase the braking force, it is necessary to apply more force to the brake valve pedal. Then the pressure in the brake valve and, consequently, above the diaphragm is increased, opening valve member 1 again and admitting a new amount of air into the brake chambers. After this, equilibrium is reached again. Diaphragm 3 rests on rings e and f, and is subject to the action of spring 5. To release the brakes rapidly, the brake pedal is released, the pressure in port 4 drops and the diaphragm, bent upward by the pressure of the air in the brake chambers, connects space d to port 6 which leads to the atmosphere. In this case, the diaphragm rests on ring e. Thus, the acceleration valve is also the valve for rapidly releasing the brakes.
$4047$EHP,Va$