Contaminant-ejecting relay valve for a pneumatic brake system

Abstract

A contaminant-ejecting relay valve for a pneumatic brake system is disclosed. Two embodiments of the valve are disclosed: in one embodiment, the valve is actuated by pilot air pressure, which is either supply air pressure or control air pressure; in another embodiment, the valve is solenoid-actuated. In both embodiments, the valve comprises a housing enclosing a chamber; a control port in the housing in fluid communication with the chamber; an exhaust port in the housing permitting removal of contaminants from the chamber; a main piston mounted within the chamber and movable between a first position and a second position; an exhaust passage through the main piston connecting the chamber and the exhaust port in fluid communication; and a blocking member movable between an open and closed position for opening and closing the exhaust passage, such that when the blocking member is in the open position it permits pressurized air from the control port to eject contaminants from the chamber. Preferably, the main piston includes a hollow stem, and the blocking member comprises an exhaust piston slidably mounted within the hollow stem and movable between an exhaust passage open and an exhaust passage closed position. The main piston may include an inverted conical face adjacent the chamber to direct contaminants toward the exhaust passage and away from valve seals and lubricants.