Pull out the trailer air supply control, or set it in the “emergency” position, when testing:
Answers
The trailer emergency brakes.
The parking brake.
The trailer service brakes.
The landing gear.
The Correct Answer and Explanation is :
The correct answer is The trailer emergency brakes.
When testing the trailer emergency brakes, the trailer air supply control (also known as the trailer air supply valve or the red push-pull valve) should be pulled out or set to the “emergency” position. This action isolates the trailer’s air system from the tractor’s air supply and ensures that the emergency brakes on the trailer are functioning properly. Here’s why:
- Function of the Trailer Air Supply Control:
The trailer air supply control controls the air connection between the tractor and trailer. When you pull out the air supply control, it cuts off the supply of air to the trailer’s air system. This isolates the emergency brakes of the trailer, which are designed to apply automatically in case of a failure of the service brakes or loss of air pressure. - Testing the Trailer Emergency Brakes:
In an emergency, if there’s a loss of air pressure in the system, the trailer emergency brakes will apply automatically. To verify that the trailer emergency brakes are working correctly, the air supply must be disconnected. Pulling the valve into the emergency position allows you to test whether the emergency braking system engages as it should when air pressure drops. - Why Not for Other Brakes or Functions?
- The Parking Brake: The parking brake of the tractor is not directly tested by pulling the trailer air supply control, which only affects the trailer. The parking brake would be tested separately by applying the brake in the usual manner.
- The Trailer Service Brakes: These brakes are used during normal driving and braking. To test these brakes, the air supply control is typically pushed in, not pulled out, so the service air system is intact.
- The Landing Gear: The landing gear does not involve the air brake system. It is manually operated and does not require the air supply control to be in the emergency position.
By setting the trailer air supply control to the emergency position, you can test the functionality of the trailer emergency brakes effectively.