How the Truck Relay Valve Works

Whether you are driving a truck, trailer or any other heavy vehicle, the truck relay valve plays an important role in the braking system. It is a device that connects the front brake pedal to the rear brakes. The brake pedal signals the valve to send air pressure to the rear brakes. Using this device reduces the time it takes to brake the rear wheels. It is also used in the truck air brake system.

The air from the service brake chambers of the tractor is merged with the air from the secondary reservoir through a two-way check valve. This reduces the amount of air required by the delivery port of the relay valve. This allows the driver to have more control over the brakes. If the tractor braking system fails, the service brakes can be controlled through the relay valve.

The truck relay valve is located near the service brake chambers of the tractor and connected to the air tank. A large diameter pipe connects the service reservoir to the relay valve. The valve also has two or more outlets. It is located on the rear of the truck, next to the brakes.

Air is pushed through the valve from the service brake chambers to the rear wheels through a large diameter pipe. It is also cooled by incoming air. The valve also contains a quick-release valve. This valve allows the valve to be removed from the truck without having to remove the air tank.

The control line of the relay valve connects to the COM contact of the NC contact. This connection allows the valve to be energized and de-energized. When the relay valve is de-energized, the armature is pulled up by the spring. The armature has magnetic energy in the iron core. This energy is transmitted by a current flowing through the coil. It creates a magnetic field that pulls the armature down.

The air from the foot-valve delivery port is merged with the air from the secondary and primary reservoirs through a two-way check valve. The control pressure from the foot-valve then enters the inlet valve of the relay valve. The inlet valve is larger than the exhaust valve. The air from the foot-valve then dead-ends at the relay valve's control port. The control pressure is the same as the pressure used in the working principle of the relay valve's control input.

Generally, the relay valve is located underneath the vehicle frame. The delivery ports are generally oriented horizontally. The valve stem is sometimes pushed through a rocker arm, tappet or lifter. The valve is often mounted on a separate mounting bracket. The valve may also include a metal washer under the screw head. The valve may be re-configured by rotating the cover.

In some applications, the relay valve is used in tandem with a spring brake cylinder. In this system, the spring brake cylinder is overlapped to prevent overloading the mechanical transmission element. This prevents the driving and parking systems from operating at the same time.