Where is a relay valve usually installed?
- On the steering wheel.
- Near the rear brake chambers. ✓
- In the air reservoir.
- On the brake pedal.
Answer: B. Near the rear brake chambers.
A relay valve is usually installed near the rear brake chambers.
Why this is the answer
The handbook describes a relay valve as a remote-controlled air valve that responds to a control signal from the foot valve. It says these valves are usually mounted on a frame rail close to the air chambers they operate, and that they are primarily found on rear axle brakes. That location lets the valve deliver air rapidly to the chambers and reduce lag when the brakes are applied or released.
Why the other answers are wrong
- A. On the steering wheel. — The relay valve is not a driver control on the steering wheel; it is remote-controlled by a signal from the foot valve and mounted near the air chambers it operates.
- C. In the air reservoir. — The relay valve is supplied with air from the primary or secondary reservoirs through a large supply line, so it is not installed inside the air reservoir.
- D. On the brake pedal. — The relay valve responds to a control signal from the foot valve, but it is not mounted on the brake pedal; it sits close to the air chambers it operates.
Remember it
Remember that a relay valve sits close to the chambers it works with, mainly at the rear axle, not up at the pedal.