Air leakage is defined as measuring the size of a bubble formed over a specified period of time. A 25.4 mm (1 in) bubble formed over 5 seconds is equivalent to 100 standard cubic centimeters per minute (sccm). A 25.4 mm (1 in) bubble formed over 3 seconds is equivalent to 175 sccm.

Use a soap solution in order to perform all air leakage tests. This allows a bubble to form at the site of the air leak, giving a visual aid for diagnosing the air loss rate.

1. Inspect all tubing for kinks or dents.
2. Inspect all hoses for signs of wear, drying out, or overheating.
3. Inspect the suspension of all of the tubing. Support he tubing in order to eliminate vibration.
4. Inspect the suspension of all of the hoses. Position the hoses in a manner that will avoid the following conditions:

•

Abrasion

•	Overheating

5. Apply the parking brake.
6. Start the engine.
7. Charge the air system to the governor cut-out point.
8. Stop the engine.
9. Apply and release the service brakes.
10. Check the air leakage.

•	Check that the dual air pressure gauge on vehicles without trailer controls does not drop more than 28 kPa (4 psi) in 2 minutes.

•	Check that the dual air pressure gauge on vehicles with trailer controls does not drop more than 41 kPa (6 psi) in 2 minutes.

•	If the dual air pressure gauge reading drops more than specified, check for leaks at the following locations:

-	The air line connections

-	The application valve

-	The trailer control valve

-	The relay valve

-	The park brake control valve

-	The governor

-	Any other components on the supply side of the application valve

11. Start the engine.
12. Charge the system to the governor cut-out point.
13. Stop the engine.
14. Firmly apply the brakes and hold the brakes.
15. Check the air leakage.

•	If the air pressure drops 10% or more, check the brake adjustment at each wheel for excessive lining and brake drum wear. Refer to Air Drum Brake Adjustment .

•	Check that the dual air pressure gauge on vehicles without trailer controls does not drop more than 41 kPa (6 psi) in 2 minutes.

•	Check that the dual air pressure gauge on vehicles with trailer controls does not drop more than 55 kPa (8 psi) in 2 minutes.

•	If the dual air gauge reading drops more than specified, test for leaks at the following locations. Double check the valves, the quick release valve, the relay valve and the other parts on the delivery side of the application valve.

-	The air line connections

-	The valves

-	The quick release valve

-	The relay valve

-	Any other components on the delivery side of the application valve

16. Start the engine.
17. Charge the air system to the governor cut-out point.
18. Stop the engine.



19. On vehicles with trailer provisions, move the trailer air brake control valve handle up to the full ON position.
20. If air leakage is less than 41 kPa (6 psi), check for leakage at the following locations:air line fittings, trailer air brake control valve, towing vehicle protection valve, and any valves on the trailer.

•	The air line fitting

•	The trailer air brake control valve

•	The towing vehicle protection valve

•	Any valves on the trailer.

Test the reservoir drain valve periodically for leakage. Leakage is not permissible. Replace the reservoir drain valve if necessary.

1. Set the parking brake.
2. Start the engine.
3. Charge the air system to the governor cut-out point.
4. Apply a soap solution in order to cover the reservoir drain valve.
5. If bubbles appear indicating air leaks, replace the reservoir drain valve.