The relay valve air inlet is connected to the air reservoir and the air outlet to the brake air chamber. When on the brake pedal the brake valve 9730110500 output pressure as a relay valve control pressure input under the control pressure the intake valve open so the compressed air by the reservoir directly through the inlet into the brake chamber without flowing through the brake valve which greatly shortened the brake chamber air pipeline accelerate the process of the air chamber. Therefore the relay valve is also called the acceleration valve.