- Block the wheels.
 
- Have an assistant apply the brake pedal.
 
- Coat the exhaust port and the body of
the application valve (4) with a soap solution.
 
- A 25 mm (1 in) bubble leakage in 3 seconds
is permitted.
 
-  Replace or overhaul the valve (4) if the leakage exceeds
this amount. Refer to 
Air Brake Application Valve Replacement 
 or 
Air Brake System Description and Operation 
.
 
- Check that the brakes are operating.
 
- Remove the wheel blocks.