Leaking Purge Valve

[gmfryer]

After reading about changing the desiccant cartridge in the AD-9 Air Dryer I thought I would give it a try. It went smoothly enough but now I have a leaking purge valve.

Air pressure builds up then the audible air blast to signal max air pressure achieved then I can watch an attached air gauge steadily bleed pressure down until the process starts over again.

I couldn't find where the leak was coming from until I shut the engine down and then it was evident it was coming from the purge valve.

Any ideas on what the solution is?

[gmfryer]

UPDATE - I took the purge valve out and cleaned it and re-greases the o-rings. Now I am getting a 5 1/4 minute purge to pressure to purge time at engine idle. I think this may be OK.

Comments?

[OldForester]

That 5 1/4 minute is longer than mine. I am not in position to power up the engine at this time and test it, but I've replaced most of the stuff that relates to the air system leading to the purge valve, short of the compressor. If it's pressured up, memory tells me more like a minute between pressure up, purge valve off, and pressure up again.

It sounds to me like you have an air leak, or a control issue separate from the purge valve. I would make sure you don't have any leaks to the air dryer, like in the hoses attached to it.

I replaced the purge valve, and it's a relatively cheap part. But you may have something else leaking. I would first go to the pressure regulator on top the air compressor and tap it gently with a hammer or wrench to make sure it's not partially stuck. It may be causing the unloader valves in the compressor to unload prematurely, or may be partially stuck. Another potential culprit is the quick release valve, which is mounted above the driveshaft, and may also be sticking, and providing a slow leak instead of closing an opening.

These air leaks or controllers are tricky. You think you have it fixed, and it happens again. My experience says start simple, and first check for leaks everywhere you can -- to the air dryer, in the hoses to the air tank, to the quick release valve, to the air bags, to the roto-chamber (parking brake actuator), and around it, and to the dump solenoids on the air bags. These are not easy to check with the engine running, but you can air it up, shut the engine off and see if the air gauge shows a steady leak. If you don't have that, then I would go to the control systems above and check them out with the engine running, but make sure I had jackstands under the coach, or blocks, drive the coach up on blocks, or put the jacks down, to make sure you don't have a big air leak while you're inspecting, to make sure the coach doesn't crush you.

You can also put air on the coach through the air chuck with an external air compressor to check for leaks while you jiggle the lines that attach to everything on the air system without the engine running.

These are just a few ideas. If you have continued problems, PM me and I'll give you a phone number you can talk to me and I'll help you as much as I can.

[JLMunsil]

I read in the installation instructions for the air dryer that the recommended minimum off time for the compressor was 10 min in order for the dryer to work properly. My compressor was cycling about once per minute. I found the air line to the turbo loose. After tightening, the compressor would be off for 50 min before coming on again while idling. This is on a coach with an ISL 400 engine.

[OldForester]

I mis-read the original message. I was thinking the opposite way, while it was pumping up, and not after the parking brake had been applied. On a steady-state situation, parking brake on, engine running, I am in the more than one minute range but not in the 50 minute range; more like 3 to 5 minutes, and I know there's no leaks. So I think the original post after cleaning the purge valve and regreasing the o-rings is probably in the ballpark.

[gmfryer]

Thanks for the suggestions, I had no idea the air compressor powered so many items. Looks like I have to put my coveralls back on and get out the Go-Jo.
I especially like the idea about powering up from the outside air chuck instead of running the engine.

Thanks, OldForrester & Jim