On-Board Compressed Air

[patmsp]

I am a NEWBIE. We have had this coach for 2 months and we are still stocking it up for our first trip and also learning about it. There is a hookup for an airhose so I picked up the appropriate hookups and tried to top off the tires. Many have mentioned that I should have two tire gauges to insure proper readings. So I bought those too. The last time they were filled they were filled to front (120) rear duals (110). As expected, they were low. I tried to fill it with the on-board hose but it did not seem to want to fill the tires. I filled our bike tires, so I know it's working. So, is it possible that it only puts our around 100psi so it can't top off the tires? Or is it possible that it just takes an awfully long time to top off one of these monster tires.

thanks folks

[ShapeShifter]

Quote:

Originally Posted by patmsp So, is it possible that it only puts our around 100psi so it can't top off the tires? Or is it possible that it just takes an awfully long time to top off one of these monster tires.

Yes, and Yes. I have had similar disappointing results trying to top off my MH tires with the on-board air.

I believe that there is a safety valve in that air line that prevents you from using up all of the air and bringing the tank pressure to less than 60 psi. That's so a leak in that branch cannot drain all of the air pressure and disable the brakes. I believe the air horn and suspension air bag lines have similar valves. I've not measured the resulting pressure in the air hose, but it seems like that safety valve may be decreasing the available pressure. (I'm going to be doing some spring chores on the rig tomorrow, I think I may try measuring the available pressure on that line.)

But even if there is enough pressure, it still does take a long time to top off those tires. I just bought and installed an 80 gallon two stage 175 PSI compressor in my garage. Lots of air! And it still takes a while to fill up those tires.

[Batman_777]

I have the Providence and only get about 100-108 psi from the MH onboard air. I carry a separate Porter-Cable compressor just for that reason. It is a 6 gallon 150 psi pancake style compressor. Works great and a 6 gallon working tank can air up a house. Lightweight: LOWES
Attached Images

[Sixpack98]

Quote:

Originally Posted by Batman_777 I have the Providence and only get about 100-108 psi from the MH onboard air. I carry a separate Porter-Cable compressor just for that reason. It is a 6 gallon 150 psi pancake style compressor. Works great and a 6 gallon working tank can air up a house. Lightweight: LOWES Attached Images

After 2 years of messing with the onboard compressor to top off the tires I bought the same compressor.

The trick is to force the onboard compressor to fill and keep the tanks at 120 psi, otherwise you will never fill the tires and likely to fill the onboard tank with air from the tire if the tire exceeds the tank pressure. It is a pain to keep the onboard tanks above tire pressure. You need to keep the engine running, fill a little, make sure the onboard tank psi is above the tires. If not, use the brakes to get the tank psi below 90 which will then turn on the onboard compressor. More trouble than it is worth and the Porter Cable makes airing up much easier.

[patmsp]

I cannot tell you how much I appreciate your feedback. As you probably have felt in the past "did I buy something with problems?" Knowing that this is typical really sets my mind at ease. Thank you for your feedback.

Pat

[Flagelpater]

FWIW I question the tire pressure you are trying to put into your front and rear tires. Have you weighed your coach? Have you checked the tire chart for your brand of tire? I put 100 PSI in front and 85 psi in my rear. Never had a problem filling with the Coach Air although you do need to have the engine, Compressor, running some of the time. I have a gage that reads the tank pressure when I am Not filling the tire and Tire Pressure as I fill it. The gage should read the same as the gage in the cab.

[ShapeShifter]

Quote:

Originally Posted by Flagelpater FWIW I question the tire pressure you are trying to put into your front and rear tires. Have you weighed your coach? Have you checked the tire chart for your brand of tire?

Yes, while I can't speak for others, I have weighed mine and checked the tables, and it comes out to 95 for the rears and 105 psi for my front tires. It is very difficult to fill tires to 95 or 105 psi when the cut-in pressure for the compressor is around 90 psi.

I had the same problem with my old 15 gallon shop compressor that would go up to 120 psi, but had a cut-in pressure of 90 psi (much like the on-board air.) When it filled the tank, I could put the chuck on the tire, and get about 20 to 30 seconds of air flow into the tire before the tank pressure would drop to the point where it was just a trickle. Then I would have to bleed air from the tank until it got below 90 psi, at which point the compressor would kick in and start pumping up the tank again. Then I would have to quickly put the chuck on the tire and get another 30 to 45 seconds or so of good air flow until the compressor kicked off and I would use up the useful air. Then I would have to bleed it down again, and repeat, repeat, repeat. As frustrating as that was with the old shop compressor, it was twice as frustrating with the on-board air, as it has a lot more air to bleed down.

I'm so glad that old compressor started to get a leak at the tank fitting, as it was the perfect excuse to get rid of it: "But dear, that old compromised tank is an explosion hazard!" The new 175 psi compressor has a 140 psi cut-in pressure, so it always has useful pressure in it, and I never again will have to bleed the tank down to get the pressure back up into the low 100's range.

I'm glad the on-board air works for you, but for me it was an exercise in frustration.

[dmason]

After following similar threads on this subject last year I went out and bought the Porter-Cable from Lowes. Never tried filling the tires using the onboard air. Besides, once your own one there's all sorts of things that need a quirt of compressed air every now and them.

[Flagelpater]

I was questioning patmsp about his tire pressure. 120 psi sounds quite high. When I indicate I have never had a problem servicing my tires with the coach air, I am talking about adding less than 5 psi to a tire. Most of the time I only need 1 or 2 psi except for severe seasonal changes. Before I start, I make sure the pressure is at its 120 psi setting and rarely need to reset it while servicing all 10 tires, including the Toad. I always do the Toad last. As far as using it for shop projects it would be of little help.

[Steve Ownby]

I feel your pain trying to use the on board compressor to get to a pressure over 110 psi. You need to weigh your coach and see how much weight your steer axle is carrying. It is rated to carry up to 13,000 lbs and that is where the 120 psi figure comes from. If you only weigh 10-11,000 on the front then you can back down the pressure some. If you weigh 11,000 lbs then you can back off to 105-110 psi which is much more achievable with the chassis compressor. Your rear axle is rated at 20,000 lbs so 95 lbs will carry that weight. If your steer axle weights up close to the rated 13,000 lbs then when I replaced tires I would go with 295/80R22.5 on the steer axle.

If you need to get the last pound of pressure out of that chassis compressor then use an air chuck with an air release on it. Hit the air release for 30 seconds until you are sure the compressor is running and then put the chuck on the valve stem until about one minute after the air dryer pops off. That will give you the max out of your on board compressor. You can turn up the air governor but I would not want to exceed 130 lbs.

You may be a newbie but kkep learning and asking questions. That 2000 dynasty is a great coach & is built to do the miles.

Good luck,
Steve O

[HRScepter]

You may want to look at the PowerTank CO2 system POWERTANK - CO2 Air Systems We searched for a way to inflate our eight tires (tag axle) up to 120 psi in a reasonable amount of time. We came across the PowerTank website and purchased the REG-7000 regulator kit and TIG-8340 Accessory Kit. It is a system that uses a high pressure regulator on a CO2 tank. The CO2 tank produces 700 - 800 psi and the regulator steps it down to 200 psi or less. It makes it possible to inflate the tires to the proper pressure within minutes. The CO2 molecule is larger than an air molecule so tire pressure loss over time is reduced considerably. We are very pleased with this system and how fast it inflates our tires.

[patmsp]

The previous owner had the rig serviced and maintained in MI. I had found a receipt from the service shop that said that they had filled the tires to 110 front and 120 rear. That is where I got that figure from. From what has been mentioned it seems that I should find a place around Knoxville that has a scale that I can use to get the actual weights. Once I do that, does someone know the formulae that I would use to calculate tire pressure?

Thanks again for all your help.

Newbie

[ShapeShifter]

Quote:

Originally Posted by Flagelpater When I indicate I have never had a problem servicing my tires with the coach air, I am talking about adding less than 5 psi to a tire. Most of the time I only need 1 or 2 psi except for severe seasonal changes.

Sorry, when I originally went back and looked at his post, all I saw was 110, which is not far from my pressures. I missed the 120, and I agree that's high unless he's heavily loaded.

For a simple top-off, on-board air can work in a pinch, and I would go ahead and try it if in a campground. But at home, with a better compressor available, it's just not worth the effort messing around with the on-board air, at least for me.

And as dmason put it, once you have a compressor available, you find so many things that can use a shot of air. I find it invaluable to have one around the house (although most won't need or want one as big as mine.) It would be much less convenient to fire up the DP engine every time I want air.

And I found one more use for the compressor: while parked over the winter, the air bags slowly lost pressure, and started to sag after a couple months. I didn't want to start the engine, because I hear it's not a good thing to do if you can't take it out for a drive to fully warm it up (being snowed in, I wasn't about to dig it out just to get it all salty.) I connected my compressor to the air inlet fitting by the generator (the one that a tow truck uses to build air pressure and release the parking brakes) and it filled the tanks right up, and brought the suspension back to normal ride height.

Quote:

Originally Posted by patmsp The previous owner had the rig serviced and maintained in MI. I had found a receipt from the service shop that said that they had filled the tires to 110 front and 120 rear. That is where I got that figure from. From what has been mentioned it seems that I should find a place around Knoxville that has a scale that I can use to get the actual weights. Once I do that, does someone know the formulae that I would use to calculate tire pressure? Thanks again for all your help. Newbie

You can usually find scales at truck stops, for a nominal charge. Also, often times places that deal in bulk commodities (gravel pits, grain silos, etc) have scales they may let you use.

Once you have the weights, a chart for Michelin tires is HERE and Goodyear is HERE

This book by Michelin gives very good information on how to get the four corner weights, and how to calculate the required pressure: RV Tire Guide. Even if you have Goodyear tires, the procures and information in there are still applicable, just substitute the Goodyear tables when looking up the pressures.

[a k]

Small bottle of dry nitrogen for topping off with a 600 LB regulator.