Reservoir Check Valve Operational Check Operational Check

1. Apply the parking brake.
2. Block the wheels.
3. Start the engine.
4. Charge the system to the air compressor governor cut-out point.
5. Stop the engine.
6. Drain the air pressure from the supply air reservoir. Refer to Draining Reservoirs .

Important: Applying and releasing the brakes repeatedly drains the supply air reservoir pressure. This can eventually cause the brakes to appear sluggish.

7. Ask an assistant to apply and release the brake pedal two times.
8. Verify that the front and rear slack adjusters move smoothly and promptly.

•	If the front brakes are sluggish or fail to move, overhaul or replace the single check valve at the front service air reservoir.

•	If the rear brakes are sluggish or fail to move, overhaul or replace the single check valve at the rear service air reservoir.

9. Start the engine.
10. Charge the system air pressure to the governor cut-out point.
11. Stop the engine.
12. Remove the wheel blocks.

Reservoir Check Valve Operational Check Leakage Test

1. Apply the parking brake.
2. Block the wheels.
3. Start the engine.
4. Charge the system to the air compressor governor check-out point.
5. Stop the engine.
6. Drain the air pressure from the supply air reservoir. Refer to Draining Reservoirs .



7. Disconnect the air line on the supply side of the single check valve.
8. Inspect the single check valve for air leakage. Air leakage must not exceed a 25.4 mm (1 in) bubble in 5 seconds.

If leakage is excessive, overhaul or replace the single check valve.

9. Connect the supply port air line.
10. Start the engine.
11. Charge the air system to the governor cut-out point.
12. Stop the engine.
13. Test the brake for proper operation.
14. Remove the wheel blocks.