Post 2 of 2 - Air Gauges

[Roscott]

OK, some of you may remember a post I had some time back (thanks for the responses) where it was thought I might have a bad HCV in the rear due to the fact that the rear of the unit would lower fairly rapidly after turning off the ignition and that the rear air gauge on the dash, when driving, would read about 102 to 105 psi then lose some pressure (down to about 90 or 95) and then return to 100 or above (ie. compressor working as normal). However, the front air pressure holds steady between 105 and 110, while driving, so I don't quite understand why the rear is doing that. Additionally, when I bought the DS, I was told the front air gauge is for the front suspension and the rear gauge is for the rear suspension...is that true? The reason I ask is that I ordered a new rear HCV and took it to the shop for replacement. As luck would have it, the warehouse sent the wrong valve so it could not be replaced. However, the mechanic did remove the existing valve, cleaned it up, looked it over, checked the hoses and the rest of the system and found no problem. He put the original valve back on and I returned the wrong valve and received the correct one (have not had it put on yet). Here's the funny thing, I've run the DS twice now and instead of releasing the air in the suspension, I left it and it seems to be holding (with respect to the height of the unit). It's been sitting for a week now and the rear has not lowered a bit. Now I'm confused. Are those gauges on the dash for the suspension or something else? I cannot find anything in the manuals. I have pics of the gauges below and a pic of the rear after 6 days of sitting. Sorry if I'm rambling, but would be interested to hear from others on this.

Note: the picture of the gauges was taken as soon as I turned on the ignition. So, those are the readings after 6 days of sitting.

[jtovo]

The gauges are the pressure in the tanks not the suspension, the air bags shouldn't leak down they should hold there pressure for months. When I park I drop the air in the bags just to keep them from wearing out sooner (not real sure if it helps).
Your air compressor does sound like it cuts of a little to soon, you could adjust the govener to shut off at 120-130 Lbs. also you do have a slight air leak, you could build the pressure & crawl around with a cup of soap suds & brush it on fittings & lines at the valves & find the leaks.

[harleyman134]

Roscot, I tend to ramble to, so here goes. A basic air system has a series of air tanks (usually 3 even though you only have gauges for two of the tanks). The two tanks with gauges are supply or "reservoir" tanks, one of the reservoir tanks is dedicated for the brakes and the other "reservoir" tank is for the air bags and other air accessories (air horn etc.). One of the gauges on your dash monitor the air pressure in the brake supply tank and the other gauge monitors the air pressure in your air bag supply tank. Based on your post it sounds like your "rear" gauge monitors the tank for your air bags (this is just a wild a$$ guess on my part, heck it could be for the brakes). The governor controls the operation of the compressor and usually has a 15 or 20 lb swing, based on your description the governor kicks the compressor on at 90lbs and kicks it off at about 105 lbs. In theory once you shut your engine off and are stationary the air pressure in the tanks should remain the same until you use the motorhome again, so it looks like you have some kind of leak. I'm no expert but it looks like to me you system is working ok, you just have a small air leak somewhere in the system.


To more directly answer your question, in your system one air tank supplies the air to you brakes and the other tank supplies the air to your air bags, and one of your gauges monitors the air for your brakes and the other one monitors the air for your bags.

[harleyman134]

Oops. It looks like Jtovo replied while I was typing my reply, sorry if I repeated the same thing he did.

[driedl]

I have the same coach as you and have replaced both senders over the past 3 years. (They're easy to replace - pm me if you want more info). Unlike the other commentors, my experience is that the front sender is for the suspension of the front wheels and the rear sender tells you the status of the rear suspension. They may actually be telling you the status of a tank as the others suggested but there's a direct correlation between the pressure gauge readout and the status of the front and rear air bags.

[Roscott]

Thanks all, for the information.

Dan, I've sent a PM.

[Roscott]

As an FYI, I ordered my height control valve from Dayton Air Control Products (Air Suspension Component Distributor - Dayton Air Control Products distributes Air Suspension components for HD Truck, Trailer, Bus, RV and Work Trucks). They may have sent the wrong valve the first time, but mistakes do happen and it was corrected quickly. The customer support while I was searching for the right valve and then after the sale was excellent. Rob Haviland is the guy to talk to...knows his stuff.

[jporietis]

Ive looked at the information in this thread for a while. Im confused.

Ive driven large trucks and have owned 2 MH with air brakes. Whenever I have seen front and back gauges these are for the brakes. Air brakes are divided into 2 separate units. A front and back. Loosing one system still leaves you with the other. I believe your gauges show the pressure in the two tanks for the front and rear brakes.

My guess would be that you have a gauge problem. Both gauges should read similar air pressures, usually between 110 to 130 depending on how your system is set up. The compressor will kick back in after about a 10% drop in pressure in either tank.

Your air horn and air bags are a separate system usually protected so as not to compromise the braking system

These are just my opinions but look into your issues with the manufacturer for the most reliable fix

[twinboat]

You are getting bad information here. That could be dangerous, when dealing with air brakes.

jporietis, has it right, about the dual system.

Tank #1 is a wet tank, no gauge. Called wet because it gets it's air from the compressor.

Tank #2 and #3 are front and rear brakes. They get air thru check valves from tank #1.

Things like air ride and horn are hooked to tanks 1 or 2. If air is being used or leaking, that tank ( and gauge ) will go down. The other will stay full.

As the tank, that is using air goes down, so does the wet tank ( no gauge, there ).

Once the wet tank gets to about 90 lbs, it signals the compressors to come on and refills the wet tank and the tank that is using air.

Since the tank that is still full, don't need air it just sits there.

When you step on the brake ( a dual control valve ) both gauges (tanks) will go down.

Your air ride , will use air, while driving, so expect some gauge movement and air loss, from whatever tank it is running off.

If it seems excessive, you need to check it out.

If your air pressure drops below 65 or so pounds in tank #1 or tank #2, there are valves that stop the flow, saving the remaining air, for your brakes. Below 60 lbs the parking brake will come on stopping you, where ever you are.

One other important thing to check is if your parking brake chambers are leaking. Block the wheels, push in the button and watch the gauge. At first, one will drop, but should recover. If it keeps dropping and recovering, you can go near each rear wheel, to listen for a leak. If you hear a leak, go to a air brake shop and get it fixed.

Without experience, changing rear brake chambers can hurt.

Hope I made some sense.

[harleyman134]

jporietis, I agree with you that big truck have two tanks one for the front and one for the rear. I have a Spartan chassis on my RV. I have 3 separate tanks on my RV, the first one is the wet tank that feeds into the two reservoir tanks. (this is verified by three lanyards that are used to purge the tanks of water) My two gauges monitor these two reservoir tanks. If I'm aired up and with the engine not running I can pump the brakes and watch the gauge in one of the tanks (front) eventually drop to zero if I continue to pump the brakes, the other tank will remain full. I also have a small air leak in the system that operates the air bags. If I haven't run my mh for a few weeks, when I look at it the air has leaked out of the bags and the mh is sitting a couple of inches lower on chassis, when I look at the gauges one of the tanks (rear) shows zero, and the other tank shows I'm at 120 psi and I can still release the emergency brake without cranking the engine and recharging the tanks. There might be separate chambers in the reservoir tanks but in my case my gauges monitor one tank that is for brakes and another tank that is for air bags, at least that's the way I understand it and verified based on my observations stated above.

[jporietis]

harleyman134 As far as know ebrake gets blended air. In other words the blend valve takes air from the tank with the highest pressure, so if one still has enough air it will release the brakes. To verify where your air bags get their air, with all tanks full dump the air from the air bags with your leveling system and see where your gauges are.

[harleyman134]

jporietis, Thanks, I'll check that out. Before I bought this mh I knew absolutely nothing about air systems. I had a problem with the air and carried it to a shop and they replaced all kinds of parts and didn't fix the problem so I took charge and tried to learn how the system worked, after spending thousands of dollars with a shop and not getting it fixed I fixed it myself with a new $18 governor. I thought I had a good understanding but I guess not. When I'm aired up and with the engine off, I can pump the brakes to bleed the air from one tank and the other tank stays full, as the one tank bleeds down the emergency brake will pop on at about 60 lbs with the other tank full, so I'm still confused but will check out your suggestion.

[jporietis]

contact the chassis manufacturer. They will know exactly haw that chassis is set up. To me it sounds like someone may have changed the gauge setup, or you have a gauge error. The only time I saw an airbag gauge was in a kenworth flat deck and it was a third gage that we used to monitor when we got to a full load. If I recall 55 pounds was a full load.

[jporietis]

I see you also ride a Harley. I ride a Liberty edition myself