Air system leaks and pressure loss

Test the way the inspector does

1. Build to governor cutout, shut down, and time the static leak-down with the brakes released, then again with them applied.
2. Listen at glad hands, brake chambers, the dryer purge valve and every fitting on the tanks.
3. Soap-test anything you suspect — sound travels and will fool you.
4. Time the build-up rate from 85 to 100 psi. Slow build points at the compressor, its discharge line, or a leak big enough to keep up with it.
5. Drain the tanks and look at what comes out. Oil in the tanks means the compressor is passing oil and the dryer cartridge is saturated.

Common failures

• Air dryer purge valve leaking constantly, especially in cold weather.
• Cracked nylon air line rubbing on a bracket.
• Leaking brake chamber diaphragm — you will hear it change when you apply.
• Governor set wrong or failing so the compressor never unloads.