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Air system howling/squeeling

I have noticed this since we bought our MH back in the spring. The air system works just fine, No issues, no major leaks. Starts filling the tanks when it gets down between 95 and 100 and shuts off at 125.

However, everytime it fills or if we have a heavy usage of air we get this howling squeeling noise as the air moves through the system. Probably just something age related, but would like to quiet it down if possible. Thoughts/Facts?

Thanks, Mike

Mike in AL
2001 U295
8.3 ISC 350
Build 5918

Re: Air system howling/squeeling

Reply #1 –
Mike,

Can you identify the source of the noise?

Is it constant when high air demand or is it coincident with air pressure building to CUT-OUT PSI?

The air dryer would  be high on the suspect list, particularly if it hasn't been replaced/serviced recently.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Air system howling/squeeling

Reply #2 –
If the noise is coming from the front end of your coach, I would suspect the inlet check valves on the two brake tanks.  Those valves are comprised of a spring loaded flat metal disc that seals on a flat round hole inside the valve.  We sometimes get a weird moaning noise from our inlet check valves.  I surmise it is a harmonic vibration caused by a specific combination of flow rate and pressure differential across the valve seat.  Since I already replaced the original valves with new (identical) ones several years ago, I have decided I can just live with the occasional noise.

If your noise is coming from the same source, there may be a different check valve design that would not make this noise, like for instance a valve that uses a spring loaded round steel ball that seals on a concave seat.  Might be worth trying to find one in the correct size and pressure rating.

Link below to a description of the inlet check valve used on my coach.  This is the part originally fitted to my coach at the factory, and also the part number I used when I replaced my OEM valves several years ago.

Part Number Collection

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air system howling/squeeling

Reply #3 –
Quote from: Chuck & Jeannie –
We sometimes get a weird moaning noise from our inlet check valves.  I surmise it is a harmonic vibration caused by a specific combination of flow rate and pressure differential across the valve seat. 
I know exactly what you're referring to because I get this very same sound, only when I start to fill the tanks from empty.
1987 Grand Villa ORED
2001 U320 4010

Not all that wander are lost... but I often am.

Re: Air system howling/squeeling

Reply #4 –
No not belt related. All are new and all tensioners are new. Also air pump is not belt driven.
2001 U295

PO stated the dryer was serviced earlier this year. But he did not say replaced. I was planning to add that to my winter early spring to do list as there is no solid evidence of when it was done. I do know some of the telltale white dust is present, when I was trying to work on my entry step slide a few weeks back.

It is coming from both the front and the rear of the coach. As the Air enters the tanks during filling, or as the air enters the tanks during maintain. Also as air leaves the tanks. Very noticeable when system is full and refilling. the minute the pressure hits 125 cutoff the noise stops.

ELLIOT, good to hear someone knows exactly what I am referring to. Not a terrible thing, but  annoying at times. ? is, what might be causing it.

CHUCK,  will check out your recommended search, sounds like might be a possible culprit. If it were only on occasion wouldnt bother with it, but it is all the time.
Mike in AL
2001 U295
8.3 ISC 350
Build 5918

Re: Air system howling/squeeling

Reply #5 –
No question, if you have dryer desiccant (white powder) in the air system, there could be a number of valves that are not working properly.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Air system howling/squeeling

Reply #6 –
Well I would tend to agree, but other than the noise the system works fine. But it could be that darn dust on a valve causing it to act as a whistle of sorts.

I plan to deal with the air system more closely over winter or spring.
Mike in AL
2001 U295
8.3 ISC 350
Build 5918

Re: Air system howling/squeeling

Reply #7 –
Sounds like could be the check valves on the 3 air tanks sqealing.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Air system howling/squeeling

Reply #8 –
If the check valves are squealing could you remove them and spray some oil or silicone lube in each end, just a bit, and reinstall them?

I have no idea if this would help or hurt something else.

My check valves (replaced 3 yrs ago) whine too.

Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Air system howling/squeeling

Reply #9 –
Mike, did you buy your coach at MOT or from some PO who had work done at MOT? Does it squeal (or briefly howl) in the front of the coach when pressuring up for travel mode? I had MOT install two pressure regulators which worked well for about 6 months and then started squealing when airing up. MOT said alot of owners were complaining about this very issue (and is a known issue with a certain batch of regulators). MOT said the regulators were good but for some reason would start squealing after 6 months or so. MOT has since moved to another regulator. I cannot recall the manufacturer/model but (if interested) could take a look at mine when I am back in town (to see if we have the same parts). Mine squeal. MOT said nothing is wrong with them and were not interested in replacing my pressure regulators (under warranty) since they test good but were just momentarily noisy during initial airing up. Kind of embarrassing when at some of the parks we visit but I refuse to replace something I recently paid to have installed...
Walt, Dawn, Matt & the Poodles
99 36' U320 #5515 MC #17977 "Axle"
Not All Who Wander Are Lost (not original but I like it)

Re: Air system howling/squeeling

Reply #10 –
Quote from: Roger & Susan in Home2 –
If the check valves are squealing could you remove them and spray some oil or silicone lube in each end, just a bit, and reinstall them?

I have no idea if this would help or hurt something else.

My check valves (replaced 3 yrs ago) whine too.

Does anyone know the answer to this?  Can you lube the check valves just a bit to quiet them?
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Air system howling/squeeling

Reply #11 –
I always coat he rubber seat with Dow Corning 111 compound on hose check valves when I have then apart during checking. The thought of reason is that it helps the rubber stay pliable and may make a sticky place for junk to collect rather than further down the system.

The other thing that howls or did (till I installed a better muffler) was on the exhaust of the ride height valve as they squeal and oink.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Air system howling/squeeling

Reply #12 –
Quote from: Roger & Susan in Home2 –
Does anyone know the answer to this?  Can you lube the check valves just a bit to quiet them?
I don't KNOW the answer, but I'll hazard a guess, FWIW.

IF my supposition is correct - that the noise is caused by a harmonic vibration between the sealing device (steel disk or ball) and the valve seat - then I would guess that lube applied to the valve innards would only subdue the vibration as long as it stayed in place.

Following that line of reasoning, a more viscous lube would work better for this purpose.  IE, grease would be better than oil.

Were I to try this "fix" I would probably grab the tube of Super Lube that I carry in my coach tool box.  It is stable over a wide temperature range, does not harm rubber seals, and does not absorb moisture.

Amazon.com: Super Lube-21030 Synthetic Multi-Purpose Grease, 3 Oz. : Automotive

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air system howling/squeeling

Reply #13 –
I have that lube, maybe apply with a long swab. 

The noise I hear is louder inside than outside probably because the engine is running. And it varies in pitch. It ponly happens when the compressor is adding air to the tanks.  With the engine not running, if I add external air to the air system through the connection I added at the air dryer the same noise occurs. I also hear the noise (although. not as much) when the HWH compressor runs which adds air to the HWH tank and to the air leveling manifolds without going through either of the check valves mounted to the service tanks.

A curious problem.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Air system howling/squeeling

Reply #14 –
Wells sounds like most feedback is thinking along the same lines I am, such that the sounds is probably coming from the tank check valves areas.

Oh yes use the silicone grease all over the place around my place. I live in the deep humid south. I'll plan to start by pulling the check valves and seeing if there is anyway to clean them and maybe do any sort of lubing on any sealing surfaces. As there is poor history on most of any service other than a phone call to the PO reflected. Ive already replaced lots of 20 year old aged items, I plan to go ahead and replace the Dryer vs any sort of rebuild as the replace seems to be the preferred path both here at FF as well as many other RV forums.

I did buy it from MOT, and though the PO had service work done there in the past, there was none done recently or prior to them listing it for the sale. Its been doing it since I test drove it. Ive ridden in others that also makes these noises, but just curious if there is a cure as at times it is quite annoying.
Mike in AL
2001 U295
8.3 ISC 350
Build 5918