The J1 relay valve is a high capacity diaphragm-operated, self-lapping relay valve consisting of an O-ring packed piston stem and a double- seated rubber check valve. Its purpose is to supply and exhaust brake cylinder air pressure during brake applications and releases. This relay valve is designed to develop in the brake cylinders a pressure approximately equivalent to that developed in the control pipe leading to it.
The operation portion is mounted on a pipe bracket to which all of the pipe connections are made. These are identified as follows: Supply, control, delivery