Can't find an air leak ....

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Can't find an air leak ....

August 01, 2015, 04:33:13 pm

We are just fine going down the road ... but when we stop for the day, both front and rear pressures leak down to 30 within about 3 hours. Jeff has sprayed enough soapy stuff under the coach in years past, that we should be blowing bubbles when we head down the highway ... but this is a new one. Where would you look first? This must be a significant leak!

Re: Can't find an air leak ....

Reply #1 – August 01, 2015, 04:49:17 pm

Carol there are one way valves between the major air tanks to prevent leaks below 60psi. I have found that there are two areas where this amount of air can be lost. At thy wet tanks and at the stair manifold.

Re: Can't find an air leak ....

Reply #2 – August 01, 2015, 04:52:55 pm

Since both tanks are rapidly losing air, I would look at items that are connected to both front and rear tank manifolds. On my air system diagram, that would include things such as the treadle valve (brake pedal), the spring brake control valve, the throttle valve (and cruise control), etc. Your air system will be different, of course, but you get the idea. If the inlet check valves are holding, leakage from the wet tank (or anything connected to it) should not drain your front and rear tanks.

Re: Can't find an air leak ....

Reply #3 – August 01, 2015, 06:12:48 pm

Check the front step. But you have to put it out in order to test it and then push the rod back in after you disconnect it.

Also there are a couple regulators right on the tank that leak as well. They have weep holes and not at the air connection.

Re: Can't find an air leak ....

Reply #4 – August 02, 2015, 12:28:13 am

Quote from: esaulten – August 01, 2015, 04:49:17 pm

Carol there are one way valves between the major air tanks to prevent leaks below 60psi. I have found that there are two areas where this amount of air can be lost. At thy wet tanks and at the stair manifold.

The one way valves can leak, i.e., they are no longer one way valves. My understanding is that the air escaping via the one way valves can escape through the compressing systems in ways that are almost undetectable. Our coach has a much slower leak down rate since FOT replaced one or more check valves.

Re: Can't find an air leak ....

Reply #5 – August 02, 2015, 01:59:00 am

Agree about the check valves for the front, rear, and wet tanks. They would be the most likely if Jeff has not found visible leaks.
The wet tank check valve would leak back through the air dryer, and would be hard to detect.

I would also check the air regulator for the front air bags, the regulator for the step (slide) cover, and the two-way valve for the step cover. (just replaced our two-way valve, which was leaking.) Bubble juice should show leaks there, but the seals on the step cover cylinder can also leak, and it's pretty hard to see or spray it. John Haygarth put an air cutoff valve (electrical) in front of the step cover two-way valve to solve that problem, since the two way valve keeps the cylinder under air pressure at all times (at least until the pressure drops...) Step cover
(And it's on my list to do.)

Re: Can't find an air leak ....

Reply #6 – August 02, 2015, 09:04:00 am

I looked and looked for an air leak and finally took it to FOT. They quickly found that the plastic jar at the aux compressor had a small crack not seen from the front in it and that is where the leak was located; but, I think the 2002 year coaches are very well made. Just ensure the caps were repaired at FOT. Never where you look. You will find it just keep looking.

Re: Can't find an air leak ....

Reply #7 – August 02, 2015, 10:02:14 am

I just had a big leak in a regulator just behind the front service tank. I could hear it. I took it out, took it apart and cleaned it. Sprayed all the internal parts with corrosion x and reassembled and reinstalled it. No leak. I do have a check valve (or all of them) that leaks. It sounds like somebody softly snoring under the front end after we stop. After a while it stops. No visable leak. I am justbgoing to replace them all. Roger

Re: Can't find an air leak ....

Reply #8 – August 02, 2015, 12:10:35 pm

My take is that possible reverse check valves on tanks and step slide as Dave K said too. They were my main leaks and now air pressure does not go down to 30 for maybe 5 or more days. The step leak can be checked by manually pulling the slide half out and sticking your head under it to see if you can spray some soapy water thru the hole the shaft comes thru. There is a "boot" on hole but mine was ripped so I could see the mass of air bubbles coming out of cylinder end seal. That cylinder is a job to get too ( I got mine out as I can stand under coach) and it was shot. I put it back then did as Dave said put in cut off air valve. Works great and not a problem to activate when you want stairs or driving.
Other issues could also be problem.
JohnH

Re: Can't find an air leak ....

Reply #9 – August 02, 2015, 04:47:50 pm

If you need to change the check valves on the wet tank and the brake tanks, the Haldex part # is KN23000.

Re: Can't find an air leak ....

Reply #10 – August 02, 2015, 06:53:59 pm

Bill is correct and they cost about $8 each. Tough to get off tank unless you can get under them.
JohnH

Re: Can't find an air leak ....

Reply #11 – August 03, 2015, 06:09:29 pm

Wondering if you still have the problem after two days. Sounds like maybe check valves to me, but air leaks are funny. Each tank has a check valve at the inlet. The wet tank as long as it has pressure will feed the two brake tanks until pressure equalizes. Pump up the pressure, shut off engine. Check for air leaking out the filter/dryer exhaust after a few minutes (it's supposed to leak some air for a minute or so, not just the initial blast when the compressor shuts off). If that is the case then probably the check valves are leaking and maybe the filter dryer needs service too. If air is not leaking out the filter/dryer exhaust or a connection; then drain the wet tank. When air stops coming out of the drain, close it and wait awhile. Open the wet tank drain to see if pressure has rebuilt in the wet tank. Even bad check valves leak slowly in most cases, and 3 leaking check valves at once? I did have 2 leaking and replaced all 3. Hope this helps.

Re: Can't find an air leak ....

Reply #12 – August 04, 2015, 12:09:13 am

Pop the parking brake valve.. and verify it isn't the problem.. pc

Re: Can't find an air leak ....

Reply #13 – August 04, 2015, 02:11:37 am

Best price I see for the Haldex KN23000 check valve is about $18! Are there three of these total (one for each tank)? I figured there might be a few more check valves of different sizes as well as the ones for the air tanks.
Don

Quote from: John Haygarth – August 02, 2015, 06:53:59 pm

Bill is correct and they cost about $8 each. Tough to get off tank unless you can get under them.
JohnH

Re: Can't find an air leak ....

Reply #14 – August 04, 2015, 07:08:33 am

Quote from: Don & Tys (AKA acousticart) – August 04, 2015, 02:11:37 am

Are there three of these total (one for each tank)?
Don

That is correct.

Pamela & Mike

Re: Can't find an air leak ....

Reply #15 – August 04, 2015, 11:22:34 am

Quote from: Pamela & Mike – August 04, 2015, 07:08:33 am

That is correct.

Is this same part number (KN23000) applicable across all model years, or does it only work on Unicoach?

Re: Can't find an air leak ....

Reply #16 – August 04, 2015, 01:27:51 pm

Wow Don I only paid $11 for all the ones I changed out here in Penticton. So I just did a currency exchange to get the $8.
JohnH

Re: Can't find an air leak ....

Reply #17 – August 04, 2015, 01:35:59 pm

What the heck! I went ahead and ordered three of them at $17 and change apiece. I know we made new diaphragms for the old check valves, but that mystery wet tank leak down still bugs me so I m just going to replace them all. I will be missing the pit!
Don

Quote from: John Haygarth – August 04, 2015, 01:27:51 pm

Wow Don I only paid $11 for all the ones I changed out here in Penticton. So I just did a currency exchange to get the $8.
JohnH

Re: Can't find an air leak ....

Reply #18 – August 04, 2015, 02:58:50 pm

Quote from: Chuck & Jeannie – August 04, 2015, 11:22:34 am

Is this same part number (KN23000) applicable across all model years, or does it only work on Unicoach?

Chuck,

This was the same check valves that was on our '92 U-240 and I have seen them on a U-300 also. As far as ALL coaches I'm not sure. If in doubt I would just take a quick look.

Pamela & Mike

Re: Can't find an air leak ....

Reply #19 – August 15, 2015, 09:04:02 am

After some great service at ZipDee, Jimmy located two leaking bits on our awning stuff in the bay that Jeff never found. Replacing those parts has pretty much taken care of the issue. We also need to replace the air relief valve on our aux air compressor. The solenoid will stick and it just constantly exhausts air and the compressor runs and runs and runs until we need to pull the fuse ... usually me, at 4AM because Jeff doesn't hear it. We have been leaving the fuse out pretty much all the time and just start the coach and build up air to readjust or reveled or bring in the slide before moving.

Re: Can't find an air leak ....

Reply #20 – August 15, 2015, 09:50:17 pm

Carol,
You can wire a simple On/Off toggle switch in series with that fuse. Won't help solve the problem, but sure makes it easier than pulling the fuse to shut off the compressor. As you probably know, with the fuse out and the HWH pad in Emergency Stop, the compressor will not run.

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