A relay valve for use in a vehicle air brake system includes a movable piston and a movable shuttle controlling the flow of air pressure between a supply port, a delivery port and an exhaust port. The piston has a seal in alignment with a seal on the shuttle, which seals are effective, when the piston has closed upon the shuttle, to create generally equal and opposite air pressure responsive areas on the piston to balance it within the valve. In like manner, the shuttle has spaced seal members, generally aligned and generally of the same diameter, to create equal and opposite air pressure responsive areas on the shuttle to balance the shuttle within the valve. both the shuttle seal members and the seal members providing generally equal air pressure responsive areas on the piston are generally in alignment and generally of the same diameter.
A gas-actuated relay valve having an outlet port alternately connectable through opposed inlet and exhaust valve seats to inlet and exhaust ports, a lower downwardly opening valve head spring-urged for normally closing the seat to the inlet port, an upper upwardly opening normally unseated valve head for closing the seat to the exhaust port, and coaxial inner and floating outer pistons respectively connected to the lower valve head and mounting the upper valve head, the outer piston presenting a larger area than the inner piston to actuating gas received in a common actuating gas chamber for preventing loss through the exhaust port of operating gas introduced through the inlet port by closing the upper exhaust valve seat before opening of the inlet valve seat.
A relay valve apparatus having two relay valves are located in a single housing with their longitudinal axes parallel to one another. The two relay valves each include a double seat valve and a relay piston. The two relay valves are located one behind the other in the direction along their longitudinal axes so that the two double seat valves are located between the relay pistons. An outlet chamber of the first double seat valve and an outlet chamber of a second double seat valve empty into a common fluid pressure outlet leading to the atmosphere.
