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Topic: How long to build air pressure? (Read 10624 times) previous topic - next topic

How long to build air pressure?

After we've been sitting for several days, the air pressure is at or close to zero. It normally takes 10-15 minutes for the air pressure to get up to 120 psi. Is this normal? I've always thought it was. Today I was talking with our neighbor, who tows an Elite Suites fifth wheel with a pretty fancy semi. He says it ought to take no more than a few minutes.

His first thought was that my air compressor needs an overhaul. When I told him that I had a rebuilt one put in a couple of years ago he thought that maybe there is a leak in the line going from the engine area to the tanks up front. Once pressure is up I have no problems maintaining pressure. Given that these are most likely the original lines, ought I think about replacing those lines?

Re: How long to build air pressure?

Reply #1 –
I think 10 minutes or around that is ok. You have 8 air bags that inflate also plus your air tanks.
91 GV U300 Unihome 40' Build 3811
6V92TA Detroit

Re: How long to build air pressure?

Reply #2 –
Stump, your too fast... A Semi pulling a 5th wheel only has to fill air tanks. A coach with 8 air bags has several times the volume to fill up to full pressure. You're fine with 10 - 15 minutes.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: How long to build air pressure?

Reply #3 –
Speed up the process by bumping the idle speed to 1000- 1100 after oil pressure builds. Also warms the engine faster.
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: How long to build air pressure?

Reply #4 –
Air bags?
How long do you hold  80 PSI post shutdown?  If more than 6 min i think you pass , but still have some slight leak/s.
  Maybe you have a slow pump, slipping belt , weak governor.  Check the belt first if you hold PSI for 6 min. IMHO.   
  Funny. I have 4 air bags and pressure in about 6 min. Sounds about right.

Re: How long to build air pressure?

Reply #5 –
Or install a high capacity 12V compressor like some of us have (did), air up quietly without needing to run the big engine for 15 minutes before pulling out of camp. Scroll up to also see Acousticart's 12V compressor.

Do air bags level coach for extended periods without running the engine?
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: How long to build air pressure?

Reply #6 –
Quote from: Ralph –
A semi has to fill it's tanks, 4 air bags on tractor, trailer tank, 4 air bags on trailer, 2 air cab air bags, and an air bag on the drivers seat...11 air bags and more/bigger tanks, a good bit more volume than our FT's.

Ralph
96 U270
Ralph, good point, this was a Semi tractor pulling a 5th wheel, I amended my post above.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: How long to build air pressure?

Reply #7 –
I thought my pressure guage was broke always shows 110 psi, for a week so far the longest. Dumped the air tanks and found out it wasn't the guage. KS DMV gives you 3 minutes to rebuild pressure after pumping brakes till the alarm sounds to get back to minimum operating pressure. So smaller tanks or higher rpm may be encouraged. DUH! Now to fix my governor and unloader which appears not working correctly.
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake

Re: How long to build air pressure?

Reply #8 –
Lots of good input above.  I'd consider a 2 step diagnostic approach.  First I'd look at the leak down rate expressed in PSI per unit of time.  For example 3 PSI per minute or 20 PSI per hour.  Then compare that leak down rate with similar model coaches.  If your leak down rate is significantly higher than others, you could consider chasing down the leak(s).

On the other hand if your leak down rate is comparable to the other similar coaches, then I'd start looking at the compressor.  Again, I'd compare with similar model coaches and look at how long it takes the others to build pressure from a known starting point (0 PSI?) to full pressure.

Our main engine compressors are so robust that it's pretty easy for them to overcome smaller leaks and maintain pressure once the pressure is in the operating zone.

Regarding Peter's great suggestion on larger aux compressors, another alternative is a cheap 120V compressor.  I have a $110 pancake compressor from Home Depot in one of my bays and have it plumbed into the aux air system via an air drying system.  While I'm still on shore power I can use it to pre-charge the entire coach with nice dry air (including the wet, front and rear tanks) without starting the engine.  Once I start the engine I'm ready to roll from a braking and leveling perspective.  It's a disposable item at $110 and a way of preserving my $850 12V compressor.
Mark Duckworth
2003 U320 4220
Build 6199, Motorcade 17971

Re: How long to build air pressure?

Reply #9 –
Quote from: RvTrvlr –
I made it off the road and into a U Haul facility, where they helped me with a few spare air fittings to make a male-male adapter and backfeed air from my porter cable compressor into the RV hose built into my stair bay.
That little "male-male" quick connect air hose adapter should be a part of every coach owner's permanent tool kit.  There are any number of possible situations where it would be handy to be able to add air to the wet tank (without starting the big engine).  Of course, it would be better if this air is first passed through a dryer, but in a emergency (at least to me) that would be a secondary consideration.

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: How long to build air pressure?

Reply #10 –
All good comments. One minor point. The 6v92 air compressor is gear driven not belt. So no slipping belts. You Cummins/Cats guys may want to check your belts. :)

see ya
ken
The selected media item is not currently available.ken & dori hathaway & Big Agnes
🍺1992 U300 GrandVilla WTBI #4150 FOT FBP 2011
✨6V-92TA DDEC Parlor Coach 350HP Series 92
🏁2011 Nissan XTerra Pro-4X

Re: How long to build air pressure?

Reply #11 –
Quote from: kenhat –
All good comments. One minor point. The 6v92 air compressor is gear driven not belt. So no slipping belts. You Cummins/Cats guys may want to check your belts. :)

see ya
ken

Same for most Caterpillar and Cummins.  Gear driven, not belt driven.  I don't now about the old Cat 3208 or DD 8.2 however.
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: How long to build air pressure?

Reply #12 –
I think you are all wrong...  (this is at the end of a long, trying day that I will address in another post)

SO :o
I takes me about the same time David is talking about to get air pressure up...
The air bags have nothing to do with it. They were full and have stayed full.

Chuck and a few others have posted about how long their systems hold air after fixing the leaks.
My main culprit is the adjustable valve in the front feeding the front 6-pack ( to slow down the front air raise).

I have not known any better for several years now so I suspect other than the above mentioned valve I will be content (well, maybe)

Elliott & Mary Bray
ex. 1996 36' U295 - Build 4879
ex. 2018 Coachmen Leprechaun 319MB
 

Re: How long to build air pressure?

Reply #13 –
Quote from: Old phart phred –
I thought my pressure guage was broke always shows 110 psi, for a week so far the longest. Dumped the air tanks and found out it wasn't the guage. KS DMV gives you 3 minutes to rebuild pressure after pumping brakes till the alarm sounds to get back to minimum operating pressure. So smaller tanks or higher rpm may be encouraged. DUH! Now to fix my governor and unloader which appears not working correctly.
My alarm comes on my crane at 60 psi and will rebuild to 120 quickly, I haven't timed it but I will. I don't know what KS DMV considers minimum operating pressure. Here is an interesting page from Cal. DMV on air brakes.

Section 5: Air Brakes
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: How long to build air pressure?

Reply #14 –
At high idle from 0 psi, my air system will turn off the warning bell in 1:00 minute and reach 120 psi and dryer purge in 2:05 minutes.
Steve DeLange
2005 U320T 40'
Pearland, Texas

Re: How long to build air pressure?

Reply #15 –
I just added a link about brake testing.
2000 U320 mid entry  #5688
2006 Jeep Liberty


USMCR retired
SDFD retired
FEMA US&R TF8

Re: How long to build air pressure?

Reply #16 –
If your compressor governor has not been replaced in the last couple of years, replace it.  Truckers have assured me that it is the main cause of slow pump-ups..  I changed mine and was amazed the difference in time it made.  Paid about $thirty dollars for it and installation took about thirty minutes. 
Laurel Hill, FL
 To do is to be---- Nietzsche
  To be is to do-----Kant
  Do be do be do----Sinatra
 

Re: How long to build air pressure?

Reply #17 –
Looked at my manual today. Foretravel allowable leak down rate is 6 psi per hour of 60 psi in 10 hours (overnight).  DOT leak down allowable is 2 psi a minute.  I know mine will last several days before it's down to 60 psi.  The Foretravel standard is quite doable. 

Air system should be able to charge from 85 to 100 psi in 45 seconds at normal operating rpm.  If you can get that after fixin leaks you are going to need to suspect compressor and governor.  Since it is prudent to carry a spare governor, that should be an easy swap to test.
Steve DeLange
2005 U320T 40'
Pearland, Texas