How often do AD-9 purge valves fail?

belfert · September 26, 2011, 03:17:48 PM

I heard an air leak after shutting down my bus today. I crawled under and traced it to the air dryer purge valve. I replaced the purge valve back in December. At least it is an easy 15 minute fix. It will take longer to run and get the new part than to install it.

Is it common for these to fail after just 9,000 miles? I haven't pulled it off yet to see if there is any oil or anything that indicates a compressor problem. It looks like the part will be replaced under a 1 year 100,000 mile warranty.

Len Silva · September 26, 2011, 03:24:05 PM

This may be of interest to you.
http://www.bendixvrc.com/itemDisplay.asp?documentID=5016

belfert · September 26, 2011, 04:34:00 PM

The one that is in there now is a soft seat base valve based on the part number. I'm 99.9% sure I never had the one with two o-rings. It wasn't leaking until today so I kinda doubt the choice of valve is wrong, but it could be that I hard seat model at first.

belfert · September 26, 2011, 08:17:36 PM

No oil or any buildup on the valve so I have no idea why it failed prematurely. I got the new one this evening and then I have to fill out the warranty paperwork.

buswarrior · September 26, 2011, 08:27:41 PM

sometimes, poop happens?

happy coaching!
buswarrior

Busted Knuckle · September 27, 2011, 12:44:48 AM

Brian you are using the little tube of lube on the rubber parts before installing aren't you?

Only time I ever saw one fail so soon was lack of lube when installing allowed the o-ring to "pinch" going in.

BK

bevans6 · September 27, 2011, 04:15:55 AM

Was the compressor working when you heard the leak? What I understand is that while the air compressor is unloaded, there is no air pressure in the air dryer. It only gets pressure when the governor hits cut-in, loads the compressor and air pressure is delivered to the system. when the system hits cut-out pressure, all the air in the air dryer is purged out and no air should be left in it to leak. If you ran the bus up to pressure and the air dryer purged, it should be empty. In that case, an air leak could come past the check valve to the wet tank.

Brian

belfert · September 27, 2011, 04:25:43 AM

Yes, I lubricated it. When the sun comes up today I will install the new one and be good to go.

The compressor was not running because the engine was off. I did check the air pressure after it quit leaking and the pressures seemed normal. This was the first time I had heard a leak like this.

bevans6 · September 27, 2011, 05:22:37 AM

Brian, it doesn't matter if the engine is running or not, I was unclear. What matters is if the air governor is in the loaded or unloaded state. If you did what I almost always do, you ran the engine until the compressor unloaded, the air dryer purged, and then shut the engine off. At that point the purge valve is supposed to be open, at least on my air dryer. It only closes when the pressure drops below cut-in pressure (engine on or off). So if you heard air leaking when the purge valve was open, maybe it was the check valve to the wet tank that was leaking.

Which brings up a point - in cold weather such as we are entering, it's good practice to fan the brakes to force the compressor into a charging cycle before turning the engine off. That ensures that the purge valve is closed, so if it freezes it freezes closed.

Brian

buswarrior · September 27, 2011, 05:31:55 AM

What bevans6 says!

Air system in the cold is like being in hostile territory:

Leave it loaded, configured to fire.

Less disappointment in the morning.

happy coaching!
buswarrior

Oonrahnjay · September 27, 2011, 07:54:07 AM

Quote from: bevans6 on September 27, 2011, 05:22:37 AM(snip) Which brings up a point - in cold weather such as we are entering, it's good practice to fan the brakes to force the compressor into a charging cycle before turning the engine off. That ensures that the purge valve is closed, so if it freezes it freezes closed.

Thanks for this info, Brian. (OK, coastal NC isn't like the GWN, but we get chilly sometime.)

niles500 · September 28, 2011, 12:38:14 AM

I'm with Brian - it sounds more like the governor - FWIW