Vehicle load-controlled brake pressure regulating valve device

A vehicle fluid brake pressure control valve device including a self-lapping piston valve assembly common to a relay valve portion, a load-responsive regulating valve portion and an emergency valve portion of said control valve device, said piston valve assembly being operative to control the vehicle brake cylinder pressure in accordance with the differential force between a brake valve supplied control pressure and the effective brake cylinder pressure acting opposingly on a first member of said piston valve assembly that is movable relative to a second member thereof, said first member including a third member movable relative to said first member, said third member having a valve element engageable with a supply valve seat on said first member to control the delivery of supply fluid pressure and an exhaust valve seat on said second member to control the venting of brake cylinder fluid pressure, said second member being positioned relative to said first member according to the vehicle load condition, thereby varying the effective pressure area of said first member subject to said brake cylinder pressure, said emergency valve portion including actuating piston means engageable with said first member responsive to the loss of said control fluid pressure for controlling brake cylinder pressure via said common piston valve assembly.