A trailer air braking system has combined spring brake and service brake actuators, and the service brake chambers of the actuators are controlled by a combined emergency relay and modulator valve assembly of known construction. In order to ensure that the spring brake function does not become operative due to a moderate loss in the pressure of the trailer reservoir, such as would occur in the event of an anti-skid test in which the reservoir is isolated from the emergency line and the modulator...

A release mechanism for a normally applied, spring-loaded brake includes a valve manually operable by a control cable to direct pressurized fluid from a residual source to the brake to release it. The valve includes pump device whereby further operation of the control cable will pressurize residual fluid in the valve to release the brake if system fluid pressure is lost. The valve is below sump oil level so that it is always flooded with oil. This supplies fluid to the valve pump device during l...

The spring-operated parking brakes of a tractor-trailer are controlled by a novel electro-pneumatic system. Pneumatic valving through which compressed air is conducted is mounted on the tractor chassis and coupled via an electronic circuit to two hand-operated control devices on the dash of the tractor cab, one for the trailer parking brakes only and the other for the tractor parking brakes. The latter device inherently operates the trailer parking brakes via the circuit if they are not already ...

An improved friction brake system for a transit vehicle is disclosed. The conventional friction brake system for a transit vehicle utilizes an integral service brake and emergency-parking brake actuator. The service brake portion is air powered while the emergency-parking brake portion is spring powered. It has been conventional to apply full service air brake and emergency spring brake during emergency stops. An accelerometer switch is typically connected in circuit with the service brake porti...

A fluid pressure control system engages the power take-off of a tractor-trailer combination vehicle equipped with air brakes while simultaneously applying the parking brakes of both the tractor and the trailer. However, when the vehicle is to be moved and the power take-off disengaged, the vehicle operator must, in addition to moving the power take-off control to the position disengaging the power take-off, must also operate the parking control valves which release the parking brakes on both the...

The invention is directed to a fail-safe brake arrangement for hydraulically powered road rollers. The operating means of the brake system are completely separate from the normal road brake of the roller thereby enabling the fail-safe brake to be manually operated by the driver in an emergency situation. The brake also operates automatically as soon as the hydraulic system of the roller ceases to function. The fail-safe brake according to the invention utilizes the oil pressure to compress one o...

Spring-applied, pressure-released brakes are useful, for example, in construction vehicles or other vehicles that require an automatic braking in the event of an engine failure. In order to tow the vehicle for service, the brakes must be released. Most brake release systems require an alternate pump and associated valves on each vehicle with the fluid from the alternate pump being controlled by the brake valve on the vehicle. The alternate pump on each vehicle add cost to the vehicle and the spo...

A fluid pressure braking system for a tractor-trailer vehicle in which the braking system of the tractor is connected to the braking system of the trailer through trailer control and trailer supply lines includes a relay valve which controls communication between service reservoirs on the tractor and the trailer control line in response to operation of the vehicle brake valve. Use of the relay valve to control the communication to the trailer control line permits greater volumes of air to be sup...

A brake control for a vehicle, especially a heavy work vehicle, having both service and emergency braking systems, each system having its own hydraulic actuator, having a fluid reservoir, a hydraulic pump and a manually actuable control valve wherein the control valve includes a variable pressure regulating portion having an inlet from the pump, an outlet to the service brakes and a spool controlling the outlet pressure to the service brakes. The control valve also has a three-way valve portion ...

A hydraulic emergency braking system for a vehicle also having service brakes wherein a hydraulic directional control valve provides input pressure to a dump valve having a pressure outlet to spring apply, pressure-release brake actuators and a dumping outlet to the hydraulic reservoir. Internal conduits in the dump valve housing assure continuous transmission of inlet pressure to the pressure outlet thereby releasing the pressure-release brakes, while preventing reverse flow with a check valve ...