Air Dryer Purging when Engine if Off

[flyboy013]

I have a 2018 Newmar Mountain Aire on a Spartan K3 chassis. For some time (probably ever since I owned the coach) I would notice that the "Front"/Secondary air tank would have about 60-70 psi of air after a few days. I figured I had a slow leak and I've had one or two of those leaks repair at the Hadley air manifold. But I've started to notice that the air dryer would randomly purge air while parked and not running. I recently noticed it about 15 minutes after shutting down the engine but I've noticed it other times, but at the time didn't think much of it.

It would seem to me that since the air dryer purges air after the tanks are full, there shouldn't be any air pressure in the air dryer to purge at these random times. Am I understanding things correctly? So now I'm wonder if I have any issue such as air seeping back through a check valve to the air dryer? Also, it would seem that the purging of air from the dryer would require an electrical signal to initiate a purge. If that's the case it would seem that the Spartan Control Module (SCM) is directing the air dryer to purge, but again why is there air to purge if there's a check valve after the air dryer.

The purging of air hasn't been a problem, as the tanks will fill once the engine is running. I'm trying to understand what's happening and if its normal or not.

 

[TJ&LadyDi]

I haven't noticed the purging once we get our 2018 MADP parked and settled, but the slow decrease in air pressure over time has occurred in both of our Newmar coaches. It appears to be quite normal.

TJ

 

[Chargerman]

The air dryer purges at a pressure level and there is not an electrical connection. It certainly should not purge with the engine off since the compressor is not running to make additional pressure. It would appear that your pressure switch/blow off valve are malfunctioning

 

[flyboy013]

The air dryer purges at a pressure level and there is not an electrical connection. It certainly should not purge with the engine off since the compressor is not running to make additional pressure. It would appear that your pressure switch/blow off valve are malfunctioning

Ok. I did a bit more research. While the air dryer does have an electrical connection (making me think that the purge may be controlled electronically), I've learned that this electrical connection is for the heater built into the air dryer.

I'm thinking that the only time there should be air in the dryer when the engine is turned off, is if the compressor was filling the tanks when the engine was turned off. That may explain why I've only heard the purging noise every so often. So if that is the case, is the dryer designed to purge that air or would it just stay in the air dryer until the engine is started again (or the air leaks out of the air dryer)?

 

[Chargerman]

It should only purge when the Max pressure of the blow off valve is reached. Should not ever purge with the engine off

 

[Ken C]

It should only purge when the Max pressure of the blow off valve is reached. Should not ever purge with the engine off

In 20+ years and 3 diesel motorhomes, 2 on Spartan, have never had a dryer purge with engine off. I think a call to Spartan would be in order.

 

[J&JD]

Could one of the drain valves on one of the air tanks possibly be bad and that is what you are hearing release? Unlikely but worth a shot pulling the release cables for each tank.

 

[flyboy013]

Could one of the drain valves on one of the air tanks possibly be bad and that is what you are hearing release? Unlikely but worth a shot pulling the release cables for each tank.

I was standing next to the compartment where the air dryer is located when I heard the air the last time, I quickly opened the compartment and I’m 99% sure that the air dryer was purging air. I may set up my camera on a tripod after my next outing and record in order to verify.

The tank valves are all up front (except for the ping tank), so it’s definitely not from the tank valves.
At this time I don’t have a problem over se. Everything seems to be working fine, I just find it odd.

 

[RKins]

Did you add something like Active Air?

 

[flyboy013]

Did you add something like Active Air?

No, but the coach has always had the Hadley equivalent.

 

[flyboy013]

I was doing some maintenance today and decided to look at the air dryer issue a bit more. What I found was that after the air dryer purges the valve is slow to fully close. A small (compared to the purge) but constant air flow is expelled for an additional 15 seconds. After another 2 minutes (give or take 30 seconds), the air dryer would expel more air for about 15 seconds. It's not a high psi purge, but a constantly flow just like what occurs after the purge. Two minutes later this would occur again, but this time is would only last for about 10 seconds due to the air compressor kicking in. As @Chargerman suggested, it's probably the purge valve.

I've contacted Spartan to see about getting this taken care of under warranty (it expires tomorrow). I already have a service appointment scheduled to get the tone ring on my driver's side tag axle replace due to an ABS fault.

 

[Chargerman]

Considering that you are about to be out of warranty I would make a recording of it happening and make record of the date on it and also mention that you called Spartan about it on this day just in case there is an issue with them covering it although I suspect they will not give you a hard time

Good luck and let us know how you make out.

 

[flyboy013]

Funny thing is that Spartan already replaced the air dryer once ... while we were at the Spartan Academy in September 2018. They did their inspection and determined that it needed to be replaced. To the best of my knowledge, it was working just fine at that time, but I suspect there was some systemic issue.

 

[flyboy013]

I took the coach in for service on Friday. Spartan had agreed to replace the air dryer under warranty and had shipped the replacement part to them. The air dryer has been replaced and all is good.

The other issue that I was there to have taken care of was my ABS fault. I'm still in discussions (to put it nicely) with Spartan as to whether they are paying for a replacement tone ring as I'm told that the one on the vehicle is bent.

 

[NWIP]

Thanks for the follow up always good to hear of problems resolved. I hope you get a good resolution on the ABS fault.

 

[Chuggs]

I read your thread and you were on the right track. I don't know the model you have...but they generally work the same way. To purge, there needs to be air. With the compressor not running or running but unloaded...[ie at cut-out pressure and not bled down to cut-in pressure]. Once the purge has happened at cut-out...it should exhaust all of the air held in the cartridge body and purge tank either external or internal. No more air should be available. If the purge valve leaks air after about 30 seconds...the air could be backing up thru the discharge check valve, most likely, as you eluded to. (inside the port that the line to your wet tank connection is screwed into,,, Port 2.1 on a lot of dryers). The check valve and likely the system hasn't bled down to cut-in pressure yet...thus holding the purge valve open. But...there are other locations that might need attention. Your governors interntal o-rings or the inlet/exhaust seal could be fouled. The air could seep from the turbo cutout valve if it's stuck, exhaust port on governor. So, at some point, you kinda have fo verify where on the system the air is actually escaping. It's helpful to know...does the Purge valve start leaking when your tanks are empty, and the compressor first starts running and you has not reached cut-out pressure? Or does it happen only after cut-out but before cut-in? Etc...

It's a simple but complex little device.

I had one leaking at the purge valve on startup. Purge valve for sure... yeah, no...I took the purge valve out, examined it, and reinstalled it with new lube. Twice to no avail. Still lets air out. I put a new air dryer on the coach, because we didnt have time to kill. Now, at home, I cleaned and lubed the outlet check valve, governor, turbo cutout, purge valve...and tested it on the bench...adjusted governor cutout pressure...all works good on that unit again. You won't believe how gummed up these valves can get over time. Having a heavy duty set of split ring pliers, cleaning materials, lubricant...will generally fix the problem unless you find a bad component...o-ring, piston body or valve seat, spring, etc... but they sell little kits for all of these components. Wabco has blueprints of the different dryers they make. If you can read a pnuematic circuit diagram...it really helps understand the operation and pathways.