The invention relates to a
relay valve, in particular to a
relay valve used in automobiles, which comprises a valve body
assembly, valve bonnet, pistons and the like. The valve body
assembly is provided with an input air pressure inlet, an output air pressure opening, an air exhaust opening, a valve and a spring. The valve bonnet is provided with a control air pressure inlet. The valve body
assembly and the valve bonnet are internally provided with pistons. An
air cavity 3 is formed between the valve body assembly and the pistons. An
air cavity 1 is formed between the valve bonnet and the pistons. An
air cavity 2 is formed among the valve body assembly, the valve bonnet and the pistons. An
electromagnetic valve arranged on the valve bonnet is provided with an air vent. The air cavity 2 iscommunicated with a control air pressure cavity arranged on the valve bonnet or the air vent arranged on the
electromagnetic valve which is disposed on the valve bonnet, and is controlled by the
electromagnetic valve. When vehicles are in idle load, the electromagnetic valve is in work and the
relay valve of the invention works as the ordinary
relay valve. When the vehicles overload, the electromagnetic valve does not work. And the
settling time of the pressure of a
brake cylinder can be largely shortened through the effect of the air cavity 2, and the
relay valve acts in amplification. The case is very beneficial to the vehicles which overload, in particular to braking for overloading and overspeed.