Rear Relay Double Check Valve Operational Check Operational Check

1. Block the wheels.
2. Start the engine.
3. Charge the air supply to the air compressor governor cut-out point.
4. Stop the engine.
5. While you check each wheel, ask an assistant to apply the brakes hard and then release the brakes several times.
6. Insure that the brakes apply and release promptly at each wheel.

If the brakes do not apply and release promptly, overhaul or replace the relay valve (double check type).

7. Remove the wheel blocks.

Rear Relay Double Check Valve Operational Check Leakage Test

1. Start the engine.
2. Charge the air system to the air compressor governor cut-out point.
3. Stop the engine.
4. Release the brake pedal.
5. Pull out the park control knob.



6. Inspect the exhaust port and inspect the area around the exhaust port retaining ring for air leakage. Air leakage less than a 25.4 mm (1 in) bubble in 3 seconds is acceptable.

If air leakage is excessive, overhaul or replace the relay valve.

7. Push in the park control knob.
8. Inspect the exhaust port for air leakage. Air leakage less than a 25.4 mm (1 in) bubble in 3 seconds is acceptable.

If air leakage is excessive, overhaul or replace the relay valve (double check type).

9. Inspect the outside of the valve where the cover joins the valve body for air leakage. Air leakage is not permitted.

If any bubbles appear, overhaul or replace the relay valve (double check type).

10. Disconnect the balance port air line.
11. Start the engine.
12. Charge the system to the air compressor governor cut-out point.
13. Stop the engine.
14. Inspect the balance port for air leakage. Air leakage less than a 25.4 mm (1 in) bubble in 3 seconds is acceptable.

If air leakage is excessive, overhaul or replace the relay valve (double check type).

15. Connect the balance port air line.
16. Remove the wheel blocks.