Front Air Brake Limit Valve Operational Check Operational Check

1. Install the test pressure gauges in the supply and the delivery lines of the limiting valve (4).
2. Start the engine.
3. Charge the system air pressure to the governor cut-out point.
4. Turn off the engine.
5. Apply the parking brake.
6. Apply the brake pedal slowly.
7. Check the pressure registered in the delivery line.

The pressure should be approximately half of the supply line pressure. The 50 percent reduction should occur while the supply line pressure is below 275 kPa (40 psi).

8. Replace the valve (4). Refer to Front Air Brake Limit Valve Replacement .
9. Check that the delivery pressure catches up to the supply pressure when the supply line pressure exceeds 275 kPa (40 psi) but isless than 413 kPa (60 psi).
10. Check that the delivery line pressure is equal to the supply line pressure when the supply pressure exceeds 413 kPa (60 psi).if the pressure is not equal.
11. Replace the valve (4). Refer to Front Air Brake Limit Valve Replacement .
12. Release the brakes.
13. Turn off the engine.
14. Remove the test air gauges.
15. Reconnect the lines.

Front Air Brake Limit Valve Operational Check Leakage Test

1. Block the wheels.
2. Apply the parking brake.
3. Start the engine.
4. Charge the system air pressure to the governor cut-out point.
5. Have an assistant apply the brake pedal.
6. Apply a soap solution to the exhaust port and around the seam between the cover and the body.



7. Check that no bubbles appear around the seam.
8. Replace the valve (4) if bubbles appear. Refer to Front Air Brake Limit Valve Replacement .
9. Check that the exhaust port leakage is less than a 25 mm (1 in) bubble in 5 seconds.
10. Replace the valve (4) if the leakage exceeds this amount. Refer to Front Air Brake Limit Valve Replacement .
11. Remove the wheel blocks.