Trailer control valve device for the trailer brakes of a tractor-trailer vehicle

A fluid pressure control valve device comprising:

• (a) first and second inlets, an outlet, and a vent port, said first inlet being connected to a control fluid under pressure and said second inlet being connected to a first source of fluid under pressure;
• (b) a differential piston abutment having a first pressure area subject to said control fluid pressure to urge movement of said piston abutment in one direction;
• (c) valve means operative in response to movement of said piston abutment for controlling fluid pressure communication between said second inlet and said outlet and between said outlet and said vent, said outlet fluid under pressure acting on a second pressure area of said piston abutment to urge movement of said piston abutment in a direction opposite said one direction;
• (d) an auxiliary piston subject to one side to said control fluid under pressure and subject on the opposite side to a spring;
• (e) auxiliary valve means carried by said auxiliary piston and operable for connecting said control fluid under pressure to a third pressure area of said piston abutment to urge movement thereof in said opposite direction;
• (f) an adjustable member spaced apart relative to said auxiliary valve means an adjustable distance so as to effect said operation of said auxiliary valve means when the force of said control fluid pressure acting on said auxiliary piston is sufficient to compress said spring a predetermined amount corresponding to the distance said adjustable member is spaced apart from said auxiliary valve means;
• and
• (g) a stop fixed relative to said adjustable member to limit the maximum adjustable distance said adjustable member can be spaced apart from said auxiliary valve means.