Pure Air Plus Air Dryer

Topic: Pure Air Plus Air Dryer (Read 3204 times) previous topic - next topic

Re: Pure Air Plus Air Dryer

Reply #50 – September 02, 2018, 08:48:48 am

The funny (sad) thing is, even after participating in that discussion 2 years ago, I have no idea at what psi the pressure relief valve on my AD-9 air dryer would open. I have changed our dryer twice since we got our coach, and never bothered to look at the valve. Now that this discussion has made me curious, I cannot (so far) find this info anywhere online! My dryer relief valve might be rated to open at 1000 psi for all I know.

I'm still looking...

Re: Pure Air Plus Air Dryer

Reply #51 – September 02, 2018, 09:24:58 am

Steve,

Nobody ever answered your question about the 2 black sticky pads. Probably because nobody knows what they're for.

My guess is they are some kind of anti noise or vibration material, meant to fit into the air dryer mounting bracket somewhere...? If there were no instructions with the dryer, and you didn't see anything like that when you removed your old dryer, then I (personally) would not worry about them. I stick mysterious little parts like that away in a drawer, and eventually (sometimes decades later) come up with a use for them.

Whenever taking my advice, remember: I am not really a mechanic, but I do portray one on this Forum.

Re: Pure Air Plus Air Dryer

Reply #52 – September 02, 2018, 09:46:11 am

Thanks Chuck, I never found any reference to them in the short instructions that came with the dryer and it is all in now except I have to go get a eye fitting for the ground wire.

I did figure out another handy item besides a dead blow hammer is a ratchet strap

Re: Pure Air Plus Air Dryer

Reply #53 – September 02, 2018, 12:30:27 pm

Done, and no appearance of any leaks

Thanks everyone for your help

now to go home and take shower so I will quit dripping on everything in the coach

Re: Pure Air Plus Air Dryer

Reply #54 – September 02, 2018, 02:16:10 pm

Quote from: Chuck & Jeannie – September 01, 2018, 11:52:16 pm

...................... Why Foretravel makes this change in relief valves is beyond me. I cannot imagine any situation where a 200 psi safety valve would be preferable to a 175 psi safety valve, especially since the air system should never (even in the event of D2 failure) exceed 150 psi (rating of the pressure relief valve in the wet tank).....................

.......................In the second paragraph quoted above, the tech is using the term "unloader valve" but did not adequately explain what he was talking about. He is not talking about the D2 governor. The unloader valve is a internal part of the air compressor. It is located in the top of the compressor cylinder head. It is the mechanism that reacts to the pressure signal from the D2, and directs the compressor to start and stop compressing air. It can get dirty, become noisy, and if not serviced, eventually (after many thousands of miles) might cause the compressor to malfunction.............................

Chuck,
I'm not sure why FT changes the Pure Air Plus relief valve from the standard 175 psig to the 200 psig, but I'd bet that there is a good reason. I also don't know whether that applies to all models of engines, or just those engines with Holset compressors and turbo saver valve assemblies installed.

However, I do know that the Pure Air Plus mounted relief valve has nothing to do with the coach air system(s) downstream of the air dryer. That's what the wet and brake tank reliefs are for. Instead, the Pure Air Plus Dryer relief valve is there to protect the Holset compressor and the the air dryer itself:

If oil is blown by the compressor and saturates the desiccant and coalescing filters, then the compressor output will keep climbing until something relieves (better the relief valve set at 200 psig than the Holset).

The same for ice in the Pure Air Plus Dryer and purge valve. An ice block could cause a lot of internal compressor and/or dryer damage - hence the need for the protective relief valve in the dryer base.

The same for certain D2/Air Dryer failure modes that could close the air dryer isolation valve but not shift the purge valve.

With regard to your second paragraph above, the Holset compressor operates in a "gas spring" mode when it is "unloaded", to reduce horsepower burden.

Air Dryer Rapid cycling?

The "unload" pressure signal from the D2 causes the compressor intake and discharge valves to shut and each cycle of the piston, the trapped air is first compressed and then expanded (to first require work from the engine and then return energy to the engine). In Mike J's case, if the compressor is not properly operating in "gas spring mode", it might be the source of a changed or unusual "noise/rattle/clatter". But only experienced ears on the sound can detect that and Mike said that he was going to have an experienced service center give a listen.

HTH,
Neal

Re: Pure Air Plus Air Dryer

Reply #55 – September 02, 2018, 02:58:31 pm

Quote from: Neal Pillsbury – September 02, 2018, 02:16:10 pm

I'm not sure why FT changes the Pure Air Plus relief valve from the standard 175 psig to the 200 psig, but I'd bet that there is a good reason.

There may be a "good" reason, but it certainly is not a "well publicized" reason. If this is a Foretravel policy, then it should be made very clear to owners of the affected coaches. A BIG BOLD warning in the Owner's Manual would be nice. We'll have to ask Mike J (or other owners with the same dryer) to comb through their books and see if any such notification exists.

Still, it is hard for me to think of any logical reason for this change. Under all the scenarios that you postulate, what could possibly be the benefit of employing a safety relief valve with a higher opening pressure? Someone at FOT must know the reason, but who?

Re: Pure Air Plus Air Dryer

Reply #56 – September 02, 2018, 03:11:02 pm

May be because that's what they could get at the time,or because the relief valve can be 10% either way,who knows,would put a call into James T.
Here's a better idea,if any of the men halves of the ladies driving school are out there,you will have a bunch of classes,ask away about this and anything else you can think of.

Re: Pure Air Plus Air Dryer

Reply #57 – September 03, 2018, 12:20:22 am

Quote from: Chuck & Jeannie – September 02, 2018, 02:58:31 pm

.................Still, it is hard for me to think of any logical reason for this change. Under all the scenarios that you postulate, what could possibly be the benefit of employing a safety relief valve with a higher opening pressure?....................

Chuck,

I don't know the exact answer to your question, but based upon Mike J's experience where his OEM Pure Air Plus Dryer with a 200 psig relief valve worked fine without inappropriate actuation, but (2) remanufactured units with 175 psig relief valves (contrary to FT specification) would inappropriately actuate whenever engine RPM was increased, my best guess would be that there are "stacked" air flow resistances (pressure drops) and engineering tolerances that drive the need for the higher (200 psig) relief valve part.

Logically, there are a lot of pressure drops between the Holset compressor outlet and the wet tank (150 psig protected) where the D2 governor control valve senses its pressure. But, apparently, at the particular point that the Holset Compressor relief protection valve is located on the PAP Dryer, within that series string of pressure drops, 175 psig isn't quite high enough (a 175 psig relief valve will lift inappropriately), at least on some coaches. But a 200 psig valve "beats" the stacked pressure drops and tolerances and does NOT inappropriately lift, while still affording protection to the compressor and dryer under blocked conditions that the D2 governor cannot see or remedy.

While it would be interesting to know, I wouldn't expect FT to explain that level of engineering detail, or provide bold cautions in an owner's manual on the use of a 175 psig vs. 200 psig relief valve on a subcomponent. If they were expected to do that, then I can think of hundreds of other engineering decisions and design basis minutiae that would be equally interesting to know.

It is more curious to me that others have not experienced this before. I know that when I have done my Air Dryer change outs, whether complete remanufactured units or kits, I either blindly followed directions or just replaced parts with like parts and it never occurred to me to question the engineering. So, either through luck or lack of curiosity, I never happened to find myself in Mike J's sequence.

HTH,
Neal

Re: Pure Air Plus Air Dryer

Reply #58 – September 03, 2018, 10:28:36 am

Quote from: Neal Pillsbury – September 03, 2018, 12:20:22 am

It is more curious to me that others have not experienced this before.

Thanks, Neal, for your concise, logical analysis of this unusual occurrence. I have to agree with everything you said. Your conclusions certainly fit the facts reported by Mike J.

What troubles me is exactly what you say in the line quoted above. Why hasn't this ever been reported before? It would be interesting to know how many Pure Air Plus dryers are replaced/rebuilt at the factory, versus the number done by owners and/or other service shops. The factory, we are told, installs a 200 psi safety valve. Clueless owners and other shops more than likely will utilize the 175 psi valve included with the DQ6026 rebuild kit and (I assume) with complete rebuilt dryers. One would presume that this problem would be fairly common. And yet, my search of the Forum archives found no other mention of a similar dryer malfunction. I did find one interesting thread on the Pure Air Plus dryer. It illustrates the lack of knowledge (among Forum members) about dryer service requirements , but nowhere is there any mention of the safety relief valve issue:

Pure Air Plus Air Dryer - An Ounce of Prevention...

I looked at the data sheet for the Pure Air Plus dryer. It indicates in a couple places that the 175 PSI valve (KN31527) is "correct" for this dryer. Does this imply that the the conditions requiring substitution of the 200 psi valve are unique to (some) Foretravel coaches?

Pure Air Plus Air Dryer Troubleshooting Guide

All in all, quite a nice little mystery that bears additional investigation. Hopefully all Forum members with the Pure Air Plus dryer are now aware of the fact that the safety valve should be checked for proper pressure rating when rebuilding or replacing their dryer.

What if we were to discover that most of the Pure Air Plus dryers currently fitted to our member's coaches have 175 psi safety valves installed? Then it might follow that Mike J's problem had nothing to do with the dryer safety valve...

Re: Pure Air Plus Air Dryer

Reply #59 – September 03, 2018, 10:48:06 am

Is it possible that some use higher level D2 units (130 psi rather than 120), and this increases the likelihood of safety relief activation?

Re: Pure Air Plus Air Dryer

Reply #60 – September 03, 2018, 10:52:50 am

Quote from: Chuck Pearson – September 03, 2018, 10:48:06 am

Is it possible that some use higher level D2 units (130 psi rather than 120), and this increases the likelihood of safety relief activation?

I would think not, because any excess pressure situation induced by the D2 setting is downstream of the dryer anti back flow check valve, and would be relieved by the 150 psi safety valve in the wet tank.

Re: Pure Air Plus Air Dryer

Reply #61 – September 03, 2018, 10:56:00 am

I wonder if it has anything to do with the difference in the engines from my 97 C8.3 and Mike J's 02 400 ISL ? and maybe different compressors?

Re: Pure Air Plus Air Dryer

Reply #62 – September 03, 2018, 11:02:03 am

There was a reference somewhere about the isolation valve disappearing at a certain year or build number. That is probably when the compressor brand was changed. Just a guess though.

Re: Pure Air Plus Air Dryer

Reply #63 – September 03, 2018, 12:38:25 pm

Think were getting away from the answer,the relief valve is there to protect the air drier body,the other vessels in the system do
have their own relief valves.

Re: Pure Air Plus Air Dryer

Reply #64 – September 03, 2018, 12:50:10 pm

My reply was for the fact that the compressors changed when the isolation valve was eliminated and that is when the issues on the pressure relief valve seem to be showing up. Holset to Wabco.

Re: Pure Air Plus Air Dryer

Reply #65 – September 03, 2018, 01:06:07 pm

Quote from: craneman – September 03, 2018, 11:02:03 am

There was a reference somewhere about the isolation valve disappearing at a certain year or build number. That is probably when the compressor brand was changed. Just a guess though.

Craneman,
You may be referring to BJ Holden's (Corndog)'s summary of the long pursuit and eventual discovery of a solution to the internal/external isolation valves mystery. In that time frame, if an owner did not use the proper air dryer/isolation valve combination for one's engine, it would cause an oily mess. It was not easy to discover/understand what was causing the problem and what combination was needed:

Haldex air dryer isolation valve

As I understand it, Cummin's change from Holset to Wabco engine driven compressors plus the standardization of Bendix as well as Midland Air Dryer isolation valve designs (now universal and internal) has pretty much eliminated that issue.

Quote from: Chuck & Jeannie – September 03, 2018, 10:28:36 am

.....................What if we were to discover that most of the Pure Air Plus dryers currently fitted to our member's coaches have 175 psi safety valves installed? Then it might follow that Mike J's problem had nothing to do with the dryer safety valve...................

I agree with you, Chuck.

I didn't want to cause Mike J any alarm and his current solution may well be a final solution, as long as he always uses a 200 psig safety on his PAP Tower. I don't see an URGENT need, but IMHO, Mike needs to have a well qualified "ear" give a listen to his compressor's "noise/rattle/clatter". Is it new owner acclimation or is there something else there that may relate to the 175 psig relief lifting? I know that the compressors on both of our coaches have struck me as overly noisy on certain occasions, but eventually I acclimated to the sound of the compressors. And just changing the D2 governor, always changes the routine sounds up a bit, as well as, the sounds change appreciably from cold iron to operating temperatures.

But, I'm still concerned that Mike may still have a unique situation that was/is driving his 175 psig relief valve lifting, because I can't believe that some undefined large population of air dryers has been "accidently" maintained with the FT specified 200 psig relief valve over this long a period of time. There have been too many opportunities for this to happen before. But stranger things have occurred , I suppose.

HTH,
Neal

Re: Pure Air Plus Air Dryer

Reply #66 – September 03, 2018, 01:11:05 pm

Haven't done it on mine and mine runs good but I have a book on my engine that instructs about pulling and cleaning a metal
line from the air compressor that may "carbon up" in some cases,will find the book and try and find more info.

Re: Pure Air Plus Air Dryer

Reply #67 – September 09, 2018, 09:22:24 pm

Neal,

Your description/details fit my situation perfectly. The rebuilt air dryer Haldex units had 175 psi "safety" limits. The original appears to be 200psi. (as described to me by shop tech).

The clatter noise. Good news here too, I think. There was an air leak as Chuck and others suspected. 6 months ago an air line was added from the rear brake supply to rear of coach to serve the M&G air modification done to our tow vehicle. A shop in our hometown of Medford Oregon did the work and they routed the line straight back to the receiver hitch. Bad decision. The line made enough occasional contact with the drive line to wear a hole. The air compressor was making all the air it could and was purging off at the air dryer every 2-3 minutes. Every time compressor (unloader?) would reach 130 as measured at rear tank, (not wet tank) the noise would get louder, like marbles in a tin can. Once air purge occurred the compressor would be quiet again. Escaping air was initially hard to find because once the parking brake is set a lot of air is already out of line where leak was. By time we got to Moscow Idaho it was big enough to hear standing next to coach even after brake was set.

Fixed the air line and rerouted it up and over the rear axle and zip tied to existing brake air lines. Now everything moves in sync with the suspension. The clattering noise diminished immediately and the time between air purges at dryer stretched way out. (I haven't timed it yet). We have driven over 400 miles since repair and clattering noise is completely gone now. Went to Cummins shop in Spokane recommended by OMC and they agreed about the "unloader valve, carbon build up etc. on the compressor". Head tech listened very closely to engine. Tested it three times by dumping air thru the brakes with engine off then running engine until air dryer purged. Sounds normal to him and I agree. Sweet diesel rumble and compressor noise no different than when we got coach last year.

Of course none of this answers why FT would have 200psi on our air dryer instead of 175 that everyone else is happy with. Is the change over between compressor manufacturers for the Cummins ISL a clue?? The Cummins shop in Eugene Oregon that OMC consulted knew about the problem.

So glad forum members have dug into this. I'm happy we seem okay again but not totally satisfied with my understanding of the "why it now works". I hope this thread continues for a few more postings. It also sounds like Steve has had no problems with his replacement. That's good news!

Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 06, 2025 ...

Re: Pure Air Plus Air Dryer

Reply #50 – September 02, 2018, 08:48:48 am

Re: Pure Air Plus Air Dryer

Reply #51 – September 02, 2018, 09:24:58 am

Re: Pure Air Plus Air Dryer

Reply #52 – September 02, 2018, 09:46:11 am

Re: Pure Air Plus Air Dryer

Reply #53 – September 02, 2018, 12:30:27 pm

Re: Pure Air Plus Air Dryer

Reply #54 – September 02, 2018, 02:16:10 pm

Re: Pure Air Plus Air Dryer

Reply #55 – September 02, 2018, 02:58:31 pm

Re: Pure Air Plus Air Dryer

Reply #56 – September 02, 2018, 03:11:02 pm

Re: Pure Air Plus Air Dryer

Reply #57 – September 03, 2018, 12:20:22 am

Re: Pure Air Plus Air Dryer

Reply #58 – September 03, 2018, 10:28:36 am

Re: Pure Air Plus Air Dryer

Reply #59 – September 03, 2018, 10:48:06 am

Re: Pure Air Plus Air Dryer

Reply #60 – September 03, 2018, 10:52:50 am

Re: Pure Air Plus Air Dryer

Reply #61 – September 03, 2018, 10:56:00 am

Re: Pure Air Plus Air Dryer

Reply #62 – September 03, 2018, 11:02:03 am

Re: Pure Air Plus Air Dryer

Reply #63 – September 03, 2018, 12:38:25 pm

Re: Pure Air Plus Air Dryer

Reply #64 – September 03, 2018, 12:50:10 pm

Re: Pure Air Plus Air Dryer

Reply #65 – September 03, 2018, 01:06:07 pm

Re: Pure Air Plus Air Dryer

Reply #66 – September 03, 2018, 01:11:05 pm

Re: Pure Air Plus Air Dryer

Reply #67 – September 09, 2018, 09:22:24 pm

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