Patent ID: 7077481

Claim:
A spring brake modulating relay valve, comprising: (a) a housing, said housing further comprising: a plurality of ports formed in said housing; an internal chamber in selective communication with said plurality of ports, and wherein said plurality of ports further comprises: (i) a supply port for receiving pressurized air, a delivery port, and an exhaust port formed in a lower portion of said housing; (ii) a port for a primary brake circuit and a port for a secondary brake circuit, said ports being formed in an intermediate portion of said housing; and (iii) a control signal port formed in an upper portion of said housing; (b) a relay piston mounted in said chamber, wherein said relay piston further comprises a first internal shoulder; (c) a modulating piston mounted in said chamber, wherein said modulating piston further comprising a second internal shoulder; (d) an auxiliary piston mounted in said chamber and forming an extension of a bottom portion of said modulating piston; (e) a first spring for engaging one side of said first internal shoulder and one side of said second internal shoulder, and wherein said first spring permits said relay and said modulating pistons to move as a unit under predetermined pressure conditions; (f) a retention ring for providing an abutment surface for an opposite side of said first shoulder and for defining the engagement between said relay and modulating pistons in an absence of air pressure; (g) a second spring mounted between said housing and said modulating piston for urging said relay, modulating, and auxiliary pistons toward a first or upper position; (h) an exhaust valve for engaging and forming a seal with said auxiliary piston; (i) a third spring for urging said exhaust valve toward a seated position within said housing such that said supply port cannot communicate with said delivery port; (j) a first check valve in communication with said control signal port normally biased for permitting communication between said control signal port and said relay piston and preventing communication between said control signal port and said primary brake circuit port; and (k) a second check valve normally biased to preclude communication between said control port and said supply port.