1. Set the parking brake.
2. Start the engine. Charge the air system to the governor cut-out point.
3. Stop the engine.
4. Apply and release the service brakes.
5. Observe the rate that the air pressure drops as registered by the dash air pressure gauges.

•	The rate of the drop should not exceed 14 kPa (2 psi) per minute.

•	If the air pressure gauge reading drops more than specified, check for leaks at the air line connections, the application valve, the park brake control valve, the governor and other parts on the supply side of the application valve.

6. Start the engine. Charge the system to the governor cut-out point.
7. Stop the engine.
8. Firmly apply and hold the brakes.
9. Observe the rate that the air pressure drops as registered by the dash air pressure gauges.

•	The rate of drop should not exceed 21 kPa (3 psi) per minute.

•	If the air gauge reading drops more than specified, test for leaks at the air line connections.

•	Double check the valve and other parts on the delivery side of the application valve.

Manual Drain Cock

The drain cock should be checked periodically for leakage. No leakage is allowed. Replace the drain cock if necessary.

1. Set the parking brake.
2. Start the engine. Charge the air system to the governor cut-out point.
3. Apply a soap solution to cover the drain cock.
4. Replace the drain cock if bubbles appear. The bubbles indicate an air leak.