[Archived]

One of the hard things to understand is when you are parked your suspensions (there are three, a front, LH rear, and RH rear) are isolated from the auxiliary air system. Air is locked in each system when the key is off.

That means you can bleed all the air from all of the three air systems on the coach (primary, secondary, and accessory or auxiliary air) and the coach should not lean, drop or move when the key is off.

Conversely, you can have a leak in any of the three suspensions causing the coach to drop or lean, and not lose a single PSI from the bus air systems if the key is off.

What you describe is a leak somewhere in the aux system. The leak can be on the Prevost installed part of the aux system (excluding the suspensions), or on the converter installed part of the system. More than likely based on the age of the coach you are going to have multiple air leaks of various sizes and they could be anywhere with the possible exception of the suspensions because you said the coach stays level when parked or the brakes because those gauges hold..

In your case I would not start looking for leaks at the air bags or anything associated with the suspension downstream from the Norgrens which control air flow to the air bags or the Norgrens between the tag and drive axles. Instead I would start with the easy stuff. Frequently reported leak points have been the regulator and valve at the rear belt tensioner, the driver’s seat, and push in fittings. Open the steer compartment and spray some soapy water on all the fittings you can see. Do the same at the rear valve and regulator. Plug the line to the seat to see if that stops some leakage. Usually the leak at the seat is related to the lumbar adjustment switches.

Don’t bother checking the brake systems or the various valves if those gauges are holding. Check the petcock under the aux air tank(s).

You will need a lot of patience.

[Archived]

Thanks Jon, that gives me something to start with. I do notice that my belts become slack and don’t stay taught when the coach is parked, even for a day.

[Jerry]

Not normal for quickleak down. Having spent nearly a month chasing air leaks I’ll list the following major sources of air leaks.

1) check valve on AUX compressor- replacement suggested every 2 years

2) AUX filter usually mounted in drivers bay. This filter is the moister trap but over time small pieces of dirt keep the discharge open. You will probably never hear this one. Using soapy water on the discharge tube and watch very close.

3) Air toilet flush handle

4) If your mfg used any SMC rotating manifold valves…with your bus age they leak.

5) recently I had developed a very slow leak on AUX air again. With the help of an electronic leak detector found the AUX air valve for blast of air on the back-up camera to clean the lense. leaking. i rarely use this and have been thinking of capping off this line to prevent any future leaks

6) drain valve on AUX green tank in drivers bay. If you see a round disc gate valve get rid of it. Over time the surfave inside the valve will not seal tightly. I have found that valve leaking on most tanks. It’s just not made for the long haul.

All is back to normal with appox 5 day leak done until compressor cut-in.

[Greg]

Start there because that is often a reported problem area. But if the leak is elsewhere, and the belt tensioner does not have a check valve or a good check valve I would expect the belts to go slack.

I want to add a comment. When I said not to concern yourself with the suspension because the bus is not leaning. That’s partly true. The Norgren valves that lock air in the suspension can leak on the inlet side so aux air is leaking from them. But start elsewhere because you want to get the easy stuff first. If you cannot identify leak sources easily then the next step is to advance to more difficult methods. Listening for leaks and spraying soapy water are the easy ways to isolate leaks. But when that fails you have to start pressurizing the various systems, looking for pressure drops, and then moving downstream until you get to the leaky component.

I would rather eat bees than have to chase leaks. I lack patience and to make a coach leak free or nearly so involves a lot of methodical, detailed, and time consuming effort.

[jack]

Call Prevost parts in Ft Worth for the engine mini bag check valve. Exactly the one needed for elimination of mini bag leak down.

If it does continue 2 new mini bags could be in your future

Take a look at this section page 10, air leak repair. 63 postings with pictures on repairing this system.

[AL]

Al,

What check valve did you use for the aux compressor? I suspect mine is leaking.

What part did you use to change the drain cock on the aux air tank?

[Dick]

Check valve available at W W Grangers in store or on line. Page 3643 part # 6D-914

The tank valve pictured is the replacement on my green tank. It might be a little hunting to find a narrow in length valve that clears the bay floor.

Jon, talked me into a custom valve made for high heat. I believe the Granger valve is rated around 200 temp deg. service. The red line on the brass is the check valve. I first believed that piece of brass was a coupler. Fooled me.

If you replace it every couple of years I think it would be fine. When they leak it discharges air through the compressor air intake. If you want to check it, remove the air filter, screw in a short piece of pipe, put a kids balloon and it will inflate.

You need to leave the balloon on for a couple of hours for a good test. After the balloon sat about a hour it inflated to walnut size.

AL

[AL]

major leakers are park brake valve tag valve back of gauges and where they hook in to system in steering bay rear air bags for belts regulator drain cocks on tanks and seat if both primary and secondary go down equal check park brake valve if aux goes down also check tag valve easy to replace the r14 valve can also leak those things down, I don’t think the aux air should go below the pressure protection valve rating I think but not sure on your year of coach like Jon said the seat is also bad for that I put valve there to shut off air when key was off

[Rick]

For anyone contemplating a check valve for the aux compressor, keep in mind that the compressor adds a lot of heat to the air as it is compressed so if possible locate the check valve as far away from the compressor as possible. If you cannot do that try to minimize the heat the check valve is exposed to by adding a copper loop or two between the compressor and the check valve. The compressor check valve is a common failure point, however most compressors have an internal check valve. This is a case of using a belt with your suspenders.

When chasing leaks the first thing that should be done is to have Kinkos or any print shop print the PDF file for your pneumatic system as big as possible, and then use the pnuematic diagram to follow the individual air lines. Prevost has done a great job of having the diagram quite accurate with respect to depicting the various fittings and valves and their orientation. That is a huge help in identifying components within a system known to leak.

Just keep in mind that none of the converters air system will be shown on the Prevost pneumatic diagram. You will have to get help from your converter or isolate each of the converter installed systems so you are not chasing your tail.

[Tom]

If you can’t find a shut off valve short enough to clear the floor below the aux compressor’s tank consider a 90 degree fitting.

You don’t need to be concerned with compressor heat if you install the check valve at the output of the aux compressor tank, if your aux compressor has a tank. The check valve should be at the output of the aux compressor tank anyway to prevent any leaks in the tank/compressor affecting the aux air fed systems. It your aux compressor has a traditonal air regulator this will purge excess pressure coming from the Prevost or aux compressors without the check valve on the output of the aux compressor tank.

[Archived]

Just be aware that Gil’s comments regarding locating the check valve at the tank are valid only if the tank has a dedicated inlet and separate outlet, or if you use a “T” at the single inlet / outlet with the supply from the compressor entering the tank between the tank and the check valve. In addition there has to be provision for draining any tank in the system, and especially a tank immediately downstream from the compressor.

In case it is not clear the check valve has to be oriented so it allows flow from the compressor or the tank.

[Jim]

The second check valve located on top of reserve tank. With the Marathon air operated sewer hose / electric cord drop door beneath the water bay on drivers side.

Marathon has another reserve air tank behind the hot water heaters. A direct line runs from green tank too this hidden tank.

I don’t recall but this hose has it’s own color to ID this feed. Marathon owners can watch the pressure gauge drop quickly when operating the drop door or the sewer hose. With the addition of this 2 ad tank and a knife valve both work smooth. The second tank makes this happen.

Marathon cut in pressure is suggested at 80-85 psi to start AUX compressor.

You can see an additional check valve coming off silver valve. This was added by me for leak down line test to second air tank set up. It did leak finding a SMC manifold valve leaking on top of second tank.

[Archived]

As you all know, Royale’s are pretty simple and has very few “air” operated devices in the coach. Since my step well cover is not working right now and is going to be repaired at Panterra when we do some remodeling at the end of the month that is my first place to look. There are basically 3 “builder” items that have air. The dump valves, drivers seat and the step cover.

I’m going to check the valves for the belt tensioners because they are loosing air in less than 5 hours after parked. Thanks for all the other advice, I will try and hunt this down before I take it to Angola. I plan on getting service done at prevost this summer so I should have enough time to at least rule a few things out.

[Archived]

Here’s one of those times wheer Jon and I will differ slightly. Although there is obvious benefits to locating a check valve between the compressor and the tank, as Jon suggests, I recommend you locate the check valve, like Al did at the last connection on the compressor/air tank before the air line goes to aux systems.

There are too many possibilities for leaks in many of the standalone compressor/tank systems. The compressor, the pressure cut-off switch, the drain, the regulator, and the associated connectors are all subject to leaking. That’s why the check valve should be at the final output of the compressor/tank. If your aux air system is combined with the Prevost air system there is no sense in feeding these leaks with the Prevost compressor when you are driving.

I’m not suggesting there not be a check valve at the output of the compressor and there typically is as all compressors leak down when not operating. I am suggesting that you not overlook putting one on the final supply output to the aux systems.

[Archived]

Gil, That’s what I said. Glad you are finally realizing I am right.