Electric pneumatic relay valve with multi-stage output function

The electric pneumatic relay valve with the multi-stage output function is composed of an upper end cover, a spring pressing plate, a valve element assembly, a valve body assembly, a valve rod assembly, a piston assembly, an elastic diaphragm plate, an electromagnetic valve and a bottom cover assembly, a gas circulation channel and a movable cavity are formed in a valve body, and the gas circulation channel comprises a gas inlet channel and an exhaust channel; the movable cavity is connected with the air inlet channel, the electromagnetic valve and the exhaust channel, the movable cavity is divided into a total air pressure cavity, a brake pressure cavity, a feedback pressure cavity, a first pre-control pressure cavity, a second pre-control pressure cavity, a third pre-control pressure cavity and a fourth pre-control pressure cavity, and the brake pressure cavity and the feedback pressure cavity are connected through a throttling bolt. According to the first pre-control pressure and the second pre-control out