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Topic: Air Pressure (Read 1076 times) previous topic - next topic

Air Pressure

My pressure drops from 100+ to about 60 in a few hours, and then holds at 60 for a day and slowly goes down over a few days. Any ideas what is happening?
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Air Pressure

Reply #1 –
Those numbers are fine.  You can spend a lifetime tracking down small air leaks that have no effect on coach performance.
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R

Re: Air Pressure

Reply #2 –
Quote from: amos.harrison –
Those numbers are fine.  You can spend a lifetime tracking down small air leaks that have no effect on coach performance.

When these were new I was so happy when the coaches on the lot held 100% pressure overnight.  Every morning I would check. 

Bob
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: Air Pressure

Reply #3 –
Quote from: prfleming –
My pressure drops from 100+ to about 60 in a few hours, and then holds at 60 for a day and slowly goes down over a few days. Any ideas what is happening?

Exactly the same as ours.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Air Pressure

Reply #4 –
Peter

Same for me too.  My leak is the step cover air cylinder in the retracted position.  Does not leak when extended.  Credit Keith Risch for knowing just where and how to look.

With system pressure up, extend cover, remove pin holding cylinder shaft to step, retract shaft leaving cover extended, spray soapy water on shaft seal and watch the bubbles.
Rudy Legett
2003 U320 4010 ISM 450 hp
2001 U320 4220 ISM 450 hp
1995 U320 M11 400 hp
1990 Granvilla 300 hp 3208T
Aqua Hot Service Houston and Southeast Texas

Re: Air Pressure

Reply #5 –
Peter,
your lucky that's all it drops. my front air bags are cracking and have a leak. I am going to have to replace all four front bags.
1988 40ft grandvilla u300 6v92ta 4speed allison

Re: Air Pressure

Reply #6 –
The most common leaks are the floor slide at the entry door and the two cylinders for the fold down step (on my 2001).  After replacing the step, and correcting some other small leaks I suppose, it takes about two weeks for leak down to zero when parked in travel mode
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Air Pressure

Reply #7 –
In my case replaced the door slide cylinder, few regulators, few bad connections, DC air pump, check valves and added a SPST toggle switch to compressor, the seal around the slide stays tight after a month with compressor off, HWH level off and lowered, seems good enough, but with the DC compressor turned on auto, it runs every 6-8 hours, what is leaking, have no idea, why the SPST switch.
Might have added a check valve where it should not be, with compressor off, the slide seal will not retract by engine driven compressor, so turn on the lil comressor, all is well.
Dave M

Re: Air Pressure

Reply #8 –
Air brake tanks supply air to brakes and all the air accessories, like steps, leveling, etc. Each tank has a "Protection Valve" that only allows accessories to have air pressure until tank get down to about 60 psi, at which time the accessories no longer can continue to drain tanks. Protection valve preserves enough pressure to stop coach.

Tanks leaking down to 60 psi indicate bigger leaks are in accessory systems and not brake system.

While the engine air compressor may now be able to keep up with leaks, beware that leaks only get worse and serious leaks can jeopardize having enough air for brakes, and should be fixed.

Re: Air Pressure

Reply #9 –
I am trying to think of a good way to respond to this that makes some sense and leads to study of any particular coach to be sure what you hear is correct. I found with some air pressure management issues while parked that there is/was some significant variation in coaches around the 1999- 2003 timeframe.  I would find out information, try to apply it and then two technicians would discuss, disagree at times and we had to prove or look.  It had to do with the manner in which the auxiliary compressor functioned and to which tanks and especially related to the check valve system at least in the 2001.

I had leaks in the check valves that allowed air to migrate where it was not intended and it also had the consequence of causing the auxiliary compressor trying to maintain the brake tanks and that little compressor running much much beyond the HWH limit.

Just to say, I gather these systems were not all the same.  May be wrong, but some good technical folks thought it one way at times where upon close inspection it was not and it changed the diagnosis and solution. 
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Air Pressure

Reply #10 –
Peter,
I have the same year and model coach as you.  Mine leaks about 1 psi/hour.  In cold temps this increases by 3x.  I still need to do a search for it I can remember when it took 3 days before the air compressor kicked in. 
Here's a the a list of the places where I have found leaks over the years:
(in no particular order)
- check valve on 120VAC compressor under steps:  Right on the output before the hose.  It looks just like nipple with a wrench hex on it.  Internal spring was not stainless and moisture got to it.  Air slowly back flowed through compressor.  This is a common part available for many garage air compressors.  Also check the stem of the hand valve that feeds the utility hose.
- Thermostatic valve for cooling fan:  this valve controls the air clutch on the radiator fan.  Its mounted on the PS head, at the very end (facing radiator).  Two small air hoses attached to it.  When engine is cool it passes air to clutch to release it; when it's hot, it cuts off air.  I had a intermittent failure - sometimes to would seal good, sometimes not.  I was able to hear the hissing and cover the vent hole with my finger to confirm.  Purchased a new one from DD but most diesel part houses will carry them or can order - IRC, it's a Bendix part.
- Air springs:  When old and cracked.  Leaked through crack in rubber.  Easiest to check when raised to maximum height.
- Ride height valve:  original valves had a plastic housing with brass inserts for air line connection.  Plastic cracks around inserts and can start to leak there.  New version of valves are all metal.  Good idea to replace if still original - these do wear out anyway and "dead band" at neutral point gets larger and larger.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Air Pressure

Reply #11 –
Just finished chasing a bunch of air leaks. 2 Pressure Protection valves(PPV) 3 pressure regulators (from Home Depot) for front suspension, step, and step slide cover, misc loose fittings. The hunt goes on all 3 ride height valves leaking slightly. Yours sounds like it's fine as others have said you can spend forever hunting small leaks, and you will never find all of them.
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 Pressure

Reply #12 –
The suggestion to replace the 120 V compressor check valve was spot on. After being parked for 10 days, the pressure is at 60 psi, amazing.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Air Pressure

Reply #13 –
Peter, it sounds like you have found the little bugs. Mark
Mark Freeman 1995 grand villa, Brimson Mn
8.3 Cummins  G95 4709 40 WTBS U280 WE21
 

Re: Air Pressure

Reply #14 –
Yes, it drives the DW crazy (but we are still married after 24 yrs).
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B