Contaminant-ejecting relay valve for a pneumatic brake system

A contaminant ejecting valve for a pneumatic brake, comprising:

• a housing enclosing a chamber;
• a pilot port in the housing;
• 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 said main piston connecting the chamber and said exhaust port in fluid communication;
• and
• a blocking member movable between an open and closed position for opening and closing said exhaust passage, such that when said blocking member is in the open position it permits pressurized air from said control port to eject contaminants from the chamber, and wherein said blocking member closes said exhaust passage in response to pressurized air from said pilot port.

A contaminant-ejecting relay valve for a pneumatic brake, comprising:

• a housing enclosing a chamber;
• a control port in the housing in fluid communication with the chamber;
• a pilot port in said housing;
• 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 said main piston connecting the chamber and said exhaust port in fluid communication;
• and
• a blocking member movable between an open and closed position for opening and closing said exhaust passage, such that when said blocking member is in the open position it permits pressurized air from said control port to eject contaminants from the chamber,
• wherein said blocking member closes said exhaust passage in response to pressurized air from said pilot port,
• wherein said blocking member opens said exhaust passage under influence of control pressure upon release of pressurized air from said pilot port.