Inspecting the Brake System Valves

Clean the valves exterior and inspect them for corrosion and damage.

Inspect the air lines connected to the valves for signs of wear or damage. Replace the lines as needed.

Check the valves for leakage.

Apply the service brakes and hold them on a full line pressure of at least 80 psi (552 kPa).
Check the air line fittings for leaks; tighten or replace the fittings as needed.
Coat the exhaust port and body of the valves with soapy water, and check for leakage. Leakage is excessive if it produces a 1-inch (25-mm) bubble within 5 seconds.
If a brake valve does not function as described above, or if leakage is excessive, replace it with a new or remanufactured unit. Repeat the leakage checks before placing the vehicle in service.