The present invention is a pulse valve which imparts a force to a piston means for a limited duration of time or over a given distance. This pulse valve can be incorporated into a manual control valve. The manual control valve is particularly useful in an air parking brake control system for an air parking brake system.

A full function skid control valve assembly for use in an air brake system which provides for brake control utilizing a compact single assembly. The system provides for the maintenance of certain minimum operating pressures so that, when the air pressure within the vehicle brake system falls below predetermined levels, the valve assembly automatically partially or entirely exhausts the air pressure sometimes causing the spring parking brakes to engage. Once the air pressure within the brake system returns to predetermined levels, the valve assembly will allow a reservoir to be charged and the spring brakes to be deactuated. During operation, the assembly provides control of the service brakes while preventing undesired skid conditions.

A limited service application of the service brakes of the trailer portion of a tractor trailer combination vehicle is applied and held while the vehicle operator gets out of the cab to make a pre-trip inspection. The service actuation is initiated by releasing the trailer parking brakes while the tractor parking brakes remain applied and then making a momentary service brake actuation by use of the vehicle dual control valve. A control valve assembly responds to the service actuation to hold a service actuation of the trailer brakes until either the tractor parking brakes are released or the trailer parking brakes are applied.

A tractor/trailer vehicle fluid pressure braking control system enabling two line control of trailer service and secondary braking includes for tractor braking a service brake control valve for controlling the fluid pressure applied both to service brake actuators and to a trailer service brake control line, a secondary control valve which controls the magnitude of a counteracting pressure applied to tractor spring brakes and also to a relay valve which controls a pressure in a trailer secondary spring brake control line.

A traction control system is disclosed for use with a vehicle braking system including a plurality of driven wheels connected by differential means, wheel brake means associated with each driven wheel, and spring brake-operating means for operating each of the wheel brakes, respectively, each of said spring brake means including a brake diaphragm operable between brake-engaged and brake-released positions, a locking spring operable to place the brake diaphragm in the brake-engaged position, and a spring diaphragm operable between a normal spring-disabling position and a spring-enabling position in which the locking spring is inoperative and operative, respectively; characterized by the provision of means for generating for each driven wheel a velocity sensing signal, comparison circuit means for comparing said sensing signals to produce a control voltage when the rotational velocity of one driven wheel exceeds another by a predetermined amount, and means operable by said control signal for placing in the spring-enabling position the spring diaphragm associated with the faster driven wheel, thereby to effect braking of the faster driven wheel and to produce transfer of driving torque to the slower driven wheel. Furthermore, the invention has utility in conjunction with tandem wheel vehicles including pairs of said driven wheels which are connected through interaxle differential means, means being operable when the velocity of one pair of driven wheels exceeds another by a predetermind amount for placing in the spring-enabling positions the spring diaphragms associated with the wheels of the faster driven wheel pair.