Air Brake Double Check Valve Operational Check Operational Check

1. If the vehicle has trailer provisions, connect the vehicle to a known operating trailer.
2. Block the wheels.
3. Start the engine.
4. Charge the air system to the governor cut-out point.



5. Push in the park control knob and push in the trailer air supply knob, if equipped.
6. Stop the engine.
7. Drain the rear service air reservoir.
8. Verify the following items:

•	The park control knob and the trailer air supply knob should remain in the applied position and not pop out.

•	The spring brake chamber assemblies must remain in the released position. If the assemblies are not in the same position, overhaul or replace the double check valve.

•	For models with trailer provisions, the brake pedal should apply the trailer service brakes. If the brake pedal does not apply the trailer service brakes, check the trailer air brake control valve. If the control valve is operational, overhaul or replace the double check valve.

9. Start the engine.
10. Charge the air system to the air compressor governor cut-out point.
11. Push in the park control knob and push in the trailer air supply knob.
12. Stop the engine.
13. Drain the front service air reservoir.
14. Verify the following items:

•	The park control knob and the trailer air supply knob should remain in the applied position and not pop out.

•	The spring brake chamber assemblies must remain in the released position. If the assemblies are not in the same position, overhaul or replace the double check valve.

•	For models with trailer provisions, the brake pedal should apply the trailer service brakes. If the brake pedal does not apply the trailer service brakes, check the trailer air brake control valve. If the control valve is operational, overhaul or replace the double check valve.

15. If any of the items does not function properly, overhaul or replace the double check valve.
16. Start the engine.
17. Charge the air system to the air compressor governor cut-out point.
18. Check for proper brake operation.
19. Stop the engine.
20. Set the parking brake.
21. Remove the wheel blocks.

Air Brake Double Check Valve Operational Check Leakage Test

1. Block the wheels.
2. Drain all of the air reservoirs. Refer to Draining Reservoirs .



3. Remove the double check valve. Refer to Air Brake Double Check Valve Replacement .
4. Plug the delivery port.
5. Connect an air supply to one of the supply ports. Apply approximately 861 kPa (125 psi) of air pressure.
6. Apply a soap solution to the opposite supply port.
7. Check that the leakage is less than a 25.4 mm (1 inch) bubble in 5 seconds. If the leakage exceeds these specifications, repair or replace the double check valve.
8. Disconnect the air supply and repeat steps 4-6 on the other supply port.
9. Shut off and disconnect the air supply.
10. Unplug the delivery port.
11. Install the double check valve.
12. Start the engine.
13. Charge the air supply system to the air compressor governor cut-out point.
14. Stop the engine.
15. Check for proper brake operation.
16. Remove the wheel blocks.