A valve for use in applying brake releasing pressure to brake chambers in a vehicle air brake system having reservoirs each containing air for either service or emergency use and having air pressure supply lines. The valve includes a housing. A chamber is formed in the housing. A port permits air communication between the valve and a supply line. A passage interconnects the port and the chamber. Reservoir ports interconnect through the passage. A first plurality of one-way check valves in the passage permit air to pass therethrough from the port to the reservoir ports. A second plurality of one-way check valves in the passage permit air to pass therethrough from the reservoir ports to the chamber.

A configurable control valve for use with air brake systems is provided. This control valve includes: a first or top body portion, a second or bottom body portion, and a connector for attaching the first body portion to the second body portion. The first body portion may include an actuator or handle having either a linear translation a rotational translation, and the second body portion may include either horizontal or vertical port configurations. The connector cooperates with the first body portion and the second body portion to provide complete 360.degree. lateral rotation of the body portions relative to one another.

A fluid control system for use with vehicles, in particular, trailers, includes a branch conduit (19, 25, 42, 80, 96) which is to be connected to a pressure supply line (20) and a control line (22) to enable priming of the control line (20) so that signals generated upon application of the vehicle brake pedal are more quickly transmitted to the trailer brakes. This overcomes problems associated with delay in application of the trailer brakes. An electrically operated solenoid valve (11) controls fluid flow through the branch conduit so that upon application of the vehicle brake pedal the solenoid valve is operated to open the branch conduit to allow pressurized fluid to flow from the supply line (20) to the control line (22) for a predetermined time period to prime the control line (22). Pressurized fluid from the branch supply conduit is directed longitudinally down the control line (22) by a longitudinally arranged outlet (35, 57) so that substantially all of the fluid is directed to backfill the control line. The system may be embodied in a block arrangement in which bores are drilled in a block housing and in which the branch conduit (19, 25) is formed by passages drilled in the block or may be formed from discrete hose sections and couplings.

A two knob control for tractor and trailer parking brakes providing single knob application of both tractor and trailer parking brakes. It also provides for maintaining the tractor parking brakes in the applied condition while charging the trailer brake air system and for applying the trailer brakes independently of the tractor brakes. Automatic application of trailer parking brakes is provided upon trailer breakaway or a significant reduction in tractor reservoir air pressure.

A fluid pressure braking system for a tractor trailer vehicle includes a supply line connecting the tractor and trailer braking systems. A low pressure responsive switch responds to the pressure level in the supply line for actuating a warning device when the pressure level in the supply line drops below a predetermined pressure level to thereby warn the driver before a brake actuation is effected that a low pressure level exists in the trailer braking system. A normally open stoplight switch is connected in series with the low-pressure responsive switch so that the signal generated by the low-pressure responsive switch is prevented from actuating the warning device when the tractor is operated in the "bobtail" mode without a trailer.