Vehicle load-controlled brake pressure regulating valve device

A vehicle load-controlled brake pressure regulating valve device for fluid pressure operable brake systems, said regulating valve device including a relay valve portion having a first control chamber for controlling delivery of fluid pressure from a fluid pressure source to brake cylinders and a vehicle load-responsive portion for controlling operation of the relay valve portion, said relay valve portion having a relay piston subjectable to actuating brake pressure in said first control chamber supplied thereto via a brake valve, and a valve member carried by the relay piston and actuated thereby to an open position for effecting said delivery of fluid pressure to said brake cylinders in response to said actuating brake pressure when sufficient for overcoming opposing compressive force of a biasing spring also acting on the relay piston, the compression of said spring being varied by the position of a hollow rod member of said load-responsive portion interconnected between said relay piston and a load lever positionally adjustable in accordance with vehicle load, said rod member being engageable with said valve member for effecting operation thereof to an exhaust position in which fluid pressure is released from the brake cylinders upon reduction of fluid pressure in said control chamber, said relay valve portion and said vehicle-load responsive portion comprising a unitary brake pressure regulating valve device disposed in a common housing.