To inflate or not inflate

[Geom]

OK, so for a while now, we'd been keeping the air system pressurized using an add-on air compressor connected to the air system. It's worked quite fine at keeping the bags full and a decent job of maintaining a minimal amount of level (assuming the spot is fairly level).
That pressurization is also what gave that air-hose the opportunity to leak while we're standing still here rather than on the road (definitely a good thing).

My question is this, should I continue to do that?
Is it better for the bags to stay full and the suspension be operating as it's designed when we're stopped? Or is it better to let the system depressurize and let the bags deflate and just sit on the stops?

We're going to be living in this full-time and constantly getting in and out and moving around in there. I'd like to do what is best for the health of the bags, and keeping them full seems to be a good idea; as that is how they'd be in the real world running nonstop all day everyday. I'm also not sure if it's good for them to deflate and just sit there empty.
In addition, I feel that if the air system actually has air in it, then condensation/water can't get in and stay there; assuming I drain the tanks of course.

So what are your thought? Is it better to keep them full or empty? I really don't mind running the additional compressor and it does a fine job keeping the system pressurized, only running a couple of times a day to keep things at about 100 psi; and is the reason I bought it in the first place.

Thanks
George

[bevans6]

My air bags stay up for months, now that they are all new.  I'm far happier keeping them inflated and the bus off the bump stops.  Letting the bus down onto the bump stops can put a lot of torque into the chassis, I've heard tales of windshields cracking etc.

Brian

[skihor]

The P.O. of our bus defeated/unhooked the stock leveling valves. The airbag system was then replumbed to the dash with 1 valve for each corner. I have only had to add air twice in 10 years now. Even thn it was only 2 or 3 LBS. Hard to believe but that's the truth. I've read that many times that the deflating air bag "syndrome" can be traced to the stock leveling valves. One bonus of what the P.O. did is the ability to use the bags as a poor man's leveling system. Our system was done with 1/8" line and I got tired of how long it takes to air back up. I just use "lego" style blocks. Fast and easy. Another advantage is the ability to "fine tune" your ride. With the 6V92/auto change the rear ride height is very critical due to a shorter driveline. Through trial and error I keep 80# in the rear and 60# in the front.
Don & Sheila

[PP]

Our Prevost came with the levlow system. When we park, I use the control valves to level up the bus and then place wood blocks under the rear engine cradle and frame (4 points) because the rear will leak down in a few days while the front stays up and level for eternity. This keeps us level and solid when parked for longer than a few days (usually by the month or longer) and the bags aren't crushed from being deflated. We also have a portable compressor built into the area behind the front bumper that I can turn on to pre-air everything before firing up the diesel so we can get moving faster. I originally installed it to keep the bus leveled while parked, but I couldn't adjust to the sound of it coming on in the middle of the night. It usually only comes on once a day when parked like that though.
Will

[Dave5Cs]

George we leave ours aired up all the time 70 lbs in front and 80 in back while driving unless a long tipped road then I adjust to the tilt and so on. When parked we adjust to level at a campspot each corner. I have it plumbed to each corner through paddle valves. When we are parked at the ranch I leave it on one side full and the other side at 20 front and 30 in the back because where I park the bus has a tilt to it to drain water away from it. Never had a problem leaving air in it. Some drop it down because they don't care for the floating feeling while walking around in their coach when parked. Our's is pretty stable either way.
We also have a compressor that when we get ready to leave and need to adjust air before we get on the road from campground then I just turn a 1/4" ball valve and start the extra compressor we have in the bay and let it fill the brake system and then adjust the bags if needed to travel without running the engine.
You should be fine as long as you drain your tanks because shop compressors develop a lot of water and slug that will push through the system if you don't.

Dave5Cs

[OneLapper]

Same as Tom.  I replaced the leveling valves, airbags and installed new lines.  They never deflate now, but the longest the bus has sat is maybe three months or so.

[Geom]

Well, as the temps have continued to drop over the last few weeks, I find myself asking this question again, under a different context.

Should I be keeping my bags full when it's freezing and below outside?

The compressor I use does develop some moisture in its tank, that it eventually pushes to the main wet-tank side and occasionally to the dry-tank side.
I try to drain the tanks about once a week. When I do, I get a small burst of water mist from the (external) compressor tank, a second or two burst of fine white mist from the wet-tank side purge, and sometimes a burst of white mist on the dry-side tank.
I hardly get anything out of the aux tank (under driver's seat) or back tank unless I neglect to empty the other tanks for a while. 

My question is two fold:
1) Am I harming by bags by using them (with us moving around inside) when it's below freezing outside? My initial inclination is no, since these things would've been installed on a commercial vehicle operating at well below freezing, but I want to make sure.
2) Am I doing harm to my air system (valves, lines, etc) doing so?

I also assume that I can't possibly be getting all the water out of the system entirely; and even if I do, the first time the compressor kicks on, it just puts more in. So now freezing water is a possible issue.
I've seen posts (here and elsewhere) about using air-brake line antifreeze. My concern with using this stuff is that a lot of people warn about it being bad on valves and especially on air-bags. Is there a recommended brand that doesn't cause these problems?

Another thing that I've noticed is that when the temps are relatively warm out (+50) I can hold air in those bags for hours at a time and the compressor only kicks in about 2 or 3 times a day. When the temps drop as low as they have been (<30), that seems to drop off precipitously and I notice the compressor running more and more frequently, sometimes as often as every hour! I suspect a valve is sticking, or maybe air is somehow escaping around the bags as they get cold and we move around, but I'm not sure. Any thoughts on that?
My suspicion of a valve sticking is due to hearing one of the (what I believe to be) leveling valves stuck open with a slight hiss. Tapping the metal bar next to it (what I believe is the leveling mechanism) both increased and then eventually stopped the sound. I have not, however, heard any hissing when listening to it now, even though it's requiring a top-off once an hour.

As always, thanks for all the help and advice.
George

[Iceni John]

I use a small inline air filter for my on-board electric air compressor:  http://www.harborfreight.com/mini-air-line-filter-68225.html   It works well, and self-drains when the pressure drops.   I also ran a drain line and valve from the electric compressor so I can easily drain it along with the bus's four reservoirs.   If you do this, you won't introduce any extra moisture into the bus's accessories air system.   (Just don't use rubber air hose  -  it eventually leaks!   Now it's all DOT 1/4" nylon air line and DOT fittings:  no more leaks.)

John

[Jon]

First a disclaimer: I know about Prevost systems and that is it. So take the following comments with a grain of salt if they do not apply to your coach or how you use your coach.

In general the continuous use of an auxiliary compressor has proven on a lot of coaches to be a very poor way to compensate for a needed repair. It is like taking an aspirin for a brain tumor. The real need is to fix the leaks that cause the suspensions to lose air. That may sound to be an expensive answer to deal with a problem can can be managed for free using campground electric to run the aux compressor. But it is not free. First, the leak is going to get worse to the point the compressor will burn up or not keep up. Actually if the compressor would quit running you might be better off because rarely does an aux compressor installation include a means of drying the air. Rarer still is the owner that routinely drains the water trap even if one is installed, or the aux air tank.

Once water starts migrating through the system, and especially complex systems like the Prevost has the Norgren valves, leveling valves, protection valves and check valves really start getting internal corrosion and damage.

If you are sitting on a level site, just dump the air in the suspension and turn off the compressor. Internal to the air bags are bump stops and it does no harm to allow the coach to sit all the way down. For 25 years I have done that. Cut an air bag open and you will see doing that is OK.

If you own a Prevost with the level low suspension depending on the vintage the loss of aux air pressure may on early coaches cause the valve that retains an open path between the tag axle air bags and the drive axle air bags to close, and the air in the tag axle air bags to vent to atmosphere. Later model coaches (around late 95 or 96) used a different system logic and when the key was off the three five port Norgren valves went to the normal position and locked air in all the air bags. So if you coach is leaning or settling down it could be a loss of aux air pressure, or it could be a leak in the suspension system from the 5 port Norgren valves all the way to the air bags and their associated fittings. It is not a big deal to have a leak free suspension, but it is a serious big deal if you allow water into the system, especially if temps go below freezing.

[Dave5Cs]

George
"Heet" is a good one but you only need that if you are frozen up and need to move the coach or drive somewhere. If your bags don't fill because of ice and you need to fill them. Sounds to me if your compressor is always coming on there is a leak somewhere or a check valve that is not closing or needs replacing. Truckers have been using that stuff for many years without any problems from it. Other than with "Heet", don't ever spill any on your hands or pants.( Don't ask me how I know that). Old timer told me they would just use rubbing alcohol, but  I would think that would mess with any rubber seals or parts and dry them out. Not good. If you put the Filter in that Iceni John was talking about that should keep the water out as long as you drain it or get the one with the automatic one.
Agree with Jon if you think you are getting any water or oil through that system you really need to drain the tanks more or even pick a day when your away and leave the drains open so it can run out. If you are getting spray out of them , you are not really draining them. The air is pushing some out but really going over whats in there and just letting wet air escape.

Dave

[jbnewman]

Heet is methanol. Aka methyl alcohol or wood alcohol. It is, according to its MSDS, incompatible with rubber.

[Dave5Cs]

What else would you suggest then because when you talking to trucker that's what they talk about using and say no problems.
He was asking what to use and most including myself said ideally to drain his tanks regularly and either have an airdryer or a filter before air entered the system to begin with. Deicers Heet and CRC has been used for years and yes it is not the best for rubber but take a long time and should not be used more than a few times before fixing what ever is causing the problem.

[eagle19952]

Isopropyl alcohol is a major ingredient in "gas dryer" fuel additives. In significant quantities, water is a problem in fuel tanks, as it separates from the gasoline, and can freeze in the supply lines at cold temperatures. Alcohol does not remove water from gasoline; rather, the alcohol solubilizes water in gasoline. Once soluble, water does not pose the same risk as insoluble water, as it will no longer accumulate in the supply lines and freeze. Isopropyl alcohol is often sold in aerosol cans as a windshield de-icer. Isopropyl alcohol is also used to remove brake fluid traces from hydraulic braking systems, so that the brake fluid (usually DOT 3, DOT 4, or mineral oil) does not contaminate the brake pads, which would result in poor braking.
PS. Air lines are not rubber....they are synthetic material.
PSS. I would also fix the leaks...as a priority.

[Scott Crosby]

Once I replaced the leveling valves and bags and air lines the bags stay up for at least 4 months.  I've never not ran it longer than that but I'd bet money they would stay up for years now. 

They used to deflate 30-60 min after shut down.  Apparently for many years like that.  The old bags showed a lot of wear from being deflated over and over and over.  Creases were worn through the cords from where they folded down each time.  I don't think they are made to ever deflate.  If you left your tires go flat every time you parked your bus for an hour or more you would expect them not to last as long.  Just my opinion but I'd fix the leaks.  They should stay up without an air compressor.  From my personal observation the repeated deflation did cause harmful extra wear on the airbags. 

[Jon]

I do not disagree with Scott's observation relative to his coach, but all coaches are not alike. An older Prevost with an air tight suspension system will still sag in the rear if the aux air pressure drops below about 30 / 35 PSI because the 3 port Norgren valve between the tag and drive air bags will dump tag axle air. A simple solution instead of using wood blocks is to put a pipe plug in the exhaust port on the Norgren valves that are on the frame between the tag and drive axles. That will prevent the loss of air pressure so if the rest of the suspension in the rear is leak free the coach will not settle.

However, that change will not allow the lifting of the tag axle.

As to harm to air bags, some may get damaged by allowing the coach to be lowered all the way down. The ones used on all my 3 coaches never suffered any ill effects from having the coach fully lowered. Due to the configuration of my driveway in fact I actually have to drive for 50 feet or so on fully deflated air bags when entering my garage. Obviously I drive very slow but there has not been any consequences from doing that. As a preventive maintenance I change all my air bags every ten years. Regardless of condition. I throw away perfectly good air bags because over the last 25 years of Prevost ownership I have determined from that age on I could begin to have issues and I am not willing to risk any while on a trip.