Air Brake Practice Test

What is the purpose of the tractor protection valve in an air brake system?

1. To protect the compressor from overheating

2. To ensure air supply to the brakes

3. To prevent air loss during a disconnect

4. To regulate brake pressure

The correct answer is: To prevent air loss during a disconnect

The tractor protection valve plays a crucial role in maintaining the integrity of the air brake system, particularly during a disconnect situation. When a trailer is uncoupled from the tractor, the tractor protection valve automatically closes. This action prevents the loss of air pressure from the tractor's air brake system, ensuring that the brakes on the tractor remain operational and preventing accidental rollaway. The valve effectively isolates the air supply systems of the tractor and trailer, making it possible for the truck to remain safely stationary even when the trailer is detached. This is especially important for safety, as it ensures that if the trailer's brakes were to fail, the tractor is still able to stop effectively. While the other options relate to various aspects of air brake functionality – such as protecting equipment, ensuring air supply, and regulating brake pressure – they do not specifically address the primary function of the tractor protection valve, which is focused on preventing air loss when the tractor and trailer are disconnected.