What does the trailer air supply knob do?
The trailer air supply control on newer vehicles is a red eight-sided knob, which you use to control the tractor protection valve. You push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes.
What happens to trailer parking brakes when the red valve is pushed in?
Pressing the red knob supplies air through the red line to fill the reserve tank on the trailer, inflate the air suspension, and release the brakes. Pressing that knob also opens the valve for the blue line, which supplies air to the service side of the brake chambers when the brake pedal is pressed.
How do you test air is flowing through all trailers?
How can you test that air flows to all trailers? Use parking brake and/or chock wheels. Wait for normal air pressure, then push “trailer air supply” knob. You just studied 5 terms!
Where is the air supply valve on a trailer?
The trailer supply valve is usually a push/pull type valve near the driver that supplies air to the trailer’s brake system through the supply line (See Diagram 5-3). This valve normally has a red, eight-sided knob that the driver pushes in to open and supply air to the trailer and pulls out to close or when no trailer is attached.
What happens if you fail to close the trailer supply valve?
Failing to close the trailer supply valve when there is no trailer attached allows a large amount of air to escape from the towing vehicle’s air brake system. To prevent all of the air from being lost, the trailer supply valve is designed to close automatically.
When does a trailer air brake valve close?
To prevent all of the air from being lost, the trailer supply valve is designed to close automatically. If the valve is open and air escapes or, if the trailer breaks loose from the towing vehicle, the valve closes automatically when air pressure in the trailer supply line drops to between 138 and 311 kPa (20 and 45 psi ).
What is the air brake subsystem of a trailer?
The air brake subsystem of a trailer includes air tanks and automatic spring brake application. Trailer couplers or “gladhands” are used to connect the air brake system of the towing vehicle to the air brake system of the trailer. In most cases, trailer couplers can be identified by their colour and are designed to prevent cross-connection.