Dual circuit brake valve

A brake application valve including a housing having a first inlet and a first outlet, a second inlet and a second outlet and an exhaust outlet, a first shuttle in said housing normally closing communication between said first inlet and outlet, a second shuttle in said housing normally closing communication between said second inlet and outlet, said shuttles normally maintaining communication between said outlets and said exhaust outlet,

• a first piston in said housing yieldingly urged away from said first shuttle, a second piston in said housing yieldingly urged away from said second shuttle, said second piston having inner and outer concentric portions, mechanical means carried by said first piston and positioned to cause said second piston inner portion to follow inward movement of said first piston, inward movement of both pistons moving said first and second shuttles to open communication between said inlets and outlets and close communication to said exhaust outlet,
• said second piston outer portion having a circumferential surface exposed to fluid pressure at said first outlet to cause movement of said second piston in response to fluid pressure supplied to said first outlet, said second piston inner and outer portions having surfaces exposed to fluid pressure at said second outlet whereby the ratio between the exposed surfaces of said second piston inner and outer portions determine the relationship between pressures applied at said outlets,
• said valve including a housing inner wall defining an annular chamber, the outer surface of which is formed by said housing, the inner surface being formed by said wall, said second piston outer portion being movable in said chamber and including inner and outer seals bearing against said housing and said housing wall and further including a concentric skirt extending outwardly, said second piston inner portion being confined by said skirt and carrying a seal which is in sealing engagement with said skirt.

A brake application valve including a housing having a first inlet and a first outlet, a second inlet and a second outlet and an exhaust outlet, a first shuttle in said housing normally closing communication between said first inlet and outlet, a second shuttle in said housing normally closing communication between said second inlet and outlet, said shuttles normally maintaining communication between said outlets and said exhaust outlet,

• a first piston in said housing yieldingly urged away from said first shuttle, a second piston in said housing yieldingly urged away from said second shuttle, said second piston having inner and outer concentric portions, mechanical means carried by said first piston and positioned to cause said second piston inner portion to follow inward movement of said first piston, inward movement of both pistons moving said first and second shuttles to open communication between said inlets and outlets and close communication to said exhaust outlet,
• said second piston outer portion having a circumferential surface exposed to fluid pressure at said first outlet to cause movement of said second piston in response to fluid pressure supplied to said first outlet, said second piston inner and outer portions having surfaces exposed to fluid pressure at said second outlet whereby the ratio between the exposed surfaces of said second piston inner and outer portions determine the relationship between pressures applied at said outlets,
• said valve further including a coil spring biasing said second piston inner portion away from said exhaust outlet and a second coil spring biasing said second piston outer portion away from said exhaust outlet.