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Ontario Air Brake Practice · Question

What is the purpose of a relay valve in an air brake system, particularly in long combination vehicles or trailers?

Relay valves are positioned closer to the brake chambers on longer vehicles or trailers. They receive a small pilot air signal from the foot valve, then use mai

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Question: What is the purpose of a relay valve in an air brake system, particularly in long combination vehicles or trailers?

Answer options:

  • To allow the driver to manually release the parking brakes. ✅ To speed up the application and release of air to distant brake chambers.
  • To regulate the overall maximum air pressure in the system.
  • To combine air from multiple reservoirs into a single line.

Correct answer: To speed up the application and release of air to distant brake chambers.

Explanation: Relay valves are positioned closer to the brake chambers on longer vehicles or trailers. They receive a small pilot air signal from the foot valve, then use main reservoir air to quickly apply or release the brakes, reducing response time for distant brakes.

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