Air Leak

Topic: Air Leak (Read 3355 times) previous topic - next topic

Air Leak

May 23, 2016, 10:03:46 am

I have been reading old post about air leaks and it is a little confusing, I have changed all 8 air bags so it stays put and does not drop, I rebuilt dryer a few years ago and it has not gone to many miles I replaced 2 air solenoids on front 6 pack (lower- up/down RF) so I can't hear anything leaking, But in a period of 8 hours, PSI gauge drops most of the way down both white & red evenly, Any suggestions?

Re: Air Leak

Reply #1 – May 23, 2016, 10:10:15 am

Quote from: prevostart – May 23, 2016, 10:03:46 am

But in a period of 8 hours, PSI gauge drops most of the way down both white & red evenly...

Welcome to the wonderful world of air leaks!

First question, about the red (front tank) and white (rear tank) needle movement. Do they stop, or at least pause for a day or two, around 55-60 psi, or do they drop straight down to zero? The answer will indicate the condition of your protection valves.

Re: Air Leak

Reply #2 – May 23, 2016, 10:13:25 am

In an 8 hours period it falls pretty much all the way down

Re: Air Leak

Reply #3 – May 23, 2016, 10:51:29 am

OK, this indicates your protection valves are not functioning properly. I would suggest your first step should be to replace these valves. There are two reasons for this priority.

First, the protection valves serve a very important safety function. If you are driving down the road, and have a massive failure (hose blows, fitting breaks off, etc) in one of your air components (air suspension, air step, air horns, etc), properly functioning protection valves will prevent the pressure in your front and rear air tanks from falling below 60 psi. This will insure that you have enough air pressure to operate your service brakes and bring the coach to a safe stop.

Second, if the protection valves are working, it greatly reduces the possible places you might be leaking air. Replacing the valves will make the job of tracking your air leak a LOT easier.

Here is my thread on replacing the air tank valves. It is not a difficult job, and your air system will thank you for the time spent.

Air Tank Valves R&R

Re: Air Leak

Reply #4 – May 23, 2016, 11:39:45 am

Art,

Here is another suggestion. If you do decide to tackle replacing your air tank valves, you should also check the condition of your tank inlet check valves. This is easy to do. Pressure up your air system to about 120 psi. With engine off, open the water drain valve on your wet tank, and let the pressure bleed down to zero. Close the drain valve. Go inside and check your air gauge. Both needles should still be showing around 120 psi. If one or both of the tanks has dropped to around zero, this would indicate the check valve on that tank is totally inoperative. If the pressure in one of the tanks has gone down some, but not to zero, then the check valve is leaking.

Either way, you will want to repair the offending check valve. Remove the valve, and take it apart. If it is just plugged up with gunk, but otherwise OK, it can be cleaned out and reinstalled. If it is corroded, seat destroyed, spring broken, etc...replace it.

The check valves are important - they keep a leak in the wet tank from totally draining the pressure in the front and rear tanks. Once again, this is a safety issue, for exactly the same reason as stated above for the protection valves.

Re: Air Leak

Reply #5 – May 23, 2016, 07:32:24 pm

So if I air up and drain wet tank should the pressure protection hold pressure in front & rear tanks?
Also Chuck are those part # for protection valve& shuttle valve good for my coach?

Re: Air Leak

Reply #6 – May 23, 2016, 07:52:36 pm

Quote from: prevostart – May 23, 2016, 07:32:24 pm

So if I air up and drain wet tank should the pressure protection hold pressure in front & rear tanks?

yes

Re: Air Leak

Reply #7 – May 23, 2016, 08:45:45 pm

Quote from: prevostart – May 23, 2016, 07:32:24 pm

So if I air up and drain wet tank should the pressure protection hold pressure in front & rear tanks?
Also Chuck are those part # for protection valve& shuttle valve good for my coach?

When you air up the coach, and drain the wet tank, what you are testing is the inlet check valve on the front and rear tanks. This valve keeps air pressure from escaping backwards through the supply line from the wet tank. The protection valve is on the outlet port of the tanks. Both valves are intended to preserve braking pressure in the tanks in the event of system malfunction. The two terms are often confused.

As to the part numbers...since you have a newer model coach, I cannot know if it uses the same part numbers. You need to take a close look at the valves on your coach, and see if they look like the photos I posted. If so, the part numbers I used should work. If yours look different, you might be able to find part numbers on the old valves, and see if they are still available or if crossover parts are available.

Re: Air Leak

Reply #8 – May 23, 2016, 09:25:36 pm

Art,

If you have the white FT book you might find an air system schematic near the back. If not, see if you can get one for your specific coach from FT. It is important to get one for your coach because while there are many common elements the details change from year to year. Just as my 2001 is significantly different from a 2003 and is certainly different from your 1996, your 1996 maybe different from a 1993.

Roger

Re: Air Leak

Reply #9 – May 23, 2016, 09:39:51 pm

This is what I got with coach

Re: Air Leak

Reply #10 – May 23, 2016, 09:49:47 pm

Quote from: prevostart – May 23, 2016, 09:39:51 pm

This is what I got with coach

That is the air system schematic, and it is very handy for tracing the layout of the air lines. Almost every air line installed by Foretravel is marked with a unique number, which can be referenced on the schematic. Unfortunately, it does not list part numbers for all the various valves. There is no such listing, as far as I know. The only way to find part numbers is like I said: look at the old part and hope to find a number on it. If you are lucky, the OEM part number will still be available. If not, you will have to find a suitable substitute.

Re: Air Leak

Reply #11 – May 23, 2016, 10:12:45 pm

That is the one, different from mine. The number in the CN box (4722) is the coach number for which this drawing first became effective. Your coach number is 4871. Glad you found it.

Re: Air Leak

Reply #12 – May 23, 2016, 10:50:01 pm

Took a couple of pictures

Re: Air Leak

Reply #13 – May 23, 2016, 11:18:44 pm

Sometimes the part number is stamped on the part but it is hard to see. Wipe it off and rub it with some sidewalk chalk or plain white chalk and then wipe it off again. Usually the part number will be pretty easy to see.

Re: Air Leak

Reply #14 – May 23, 2016, 11:31:38 pm

There may also still be the tag with id# on. I know most of my valves have it still on. You may have to clean the valve to see it but it is a small white sticker.
JohnH

Re: Air Leak

Reply #15 – May 23, 2016, 11:55:12 pm

Some of those fittings can be very difficult to access and in some cases require partially dropping the air tank to get clearance to remove one. The air plumbing "trees" which pile fitting on fitting can leave the innermost one almost inaccessible. When removing the check valves from the front and rear air tanks, it was almost impossible to get at the check valve for the front tank. removing some of the mounting hardware from the tank and loosening the rest let one end of the tank down just enough to back out the fittings at the top of the "tree". When I replace the check valves again, I am going to put in stainless steel pipe unions on the root of the "tree" so I can remove those parts without the bad words.
Don
Edit: I should mention that this was done at John H's pit. Without that, it would have been impossible get the necessary leverage to remove those fittings, bad words or not!

Re: Air Leak

Reply #16 – May 24, 2016, 08:28:28 am

Quote from: Don & Tys (AKA acousticart) – May 23, 2016, 11:55:12 pm

I should mention that this was done at John H's pit. Without that, it would have been impossible get the necessary leverage to remove those fittings, bad words or not

I have never been under a Unicoach...from what you say the tanks must be much harder to access. I sympathize, and I feel your pain. One of the many benefits of the Unihome - everything up front is fairly easy to reach and work on.

I agree with you about the check valves...those suckers were in there TIGHT. I had to use a serious "cheater" on my wrench to break them loose. I was hoping my valves were non-typical in that respect, but apparently not.

The good thing is, once you have removed them and then reinstalled with fresh pipe dope, the NEXT time they should come off a lot easier.

Re: Air Leak

Reply #17 – May 24, 2016, 08:32:28 am

Quote from: prevostart – May 23, 2016, 10:50:01 pm

Took a couple of pictures

I'm sorry, Art, but I can't see enough in your photos to tell what you've got.

Re: Air Leak

Reply #18 – May 24, 2016, 08:39:35 am

Chuck,

I have sent a PM to you. Did you receive it?

Re: Air Leak

Reply #19 – May 24, 2016, 08:43:52 am

Rudy,

No, I have not received your PM.

Re: Air Leak

Reply #20 – May 24, 2016, 08:49:46 am

Can you take a minute and call me please, 7 one 3 8 one 8 3234, Thanks

Re: Air Leak

Reply #21 – May 24, 2016, 09:32:13 am

Quote from: Rudy – May 24, 2016, 08:49:46 am

Can you take a minute and call me please

Done

Re: Air Leak

Reply #22 – May 24, 2016, 09:41:13 am

So looking at schematics it looks like there is a check valve on all 3 tanks, For maintenance do you remove and clean or replace?

Re: Air Leak

Reply #23 – May 24, 2016, 09:44:37 am

Quote from: prevostart – May 24, 2016, 09:41:13 am

For maintenance do you remove and clean or replace?

Already answered. See reply #4 above.

Re: Air Leak

Reply #24 – May 24, 2016, 10:02:15 am

Nice! I see , Is there anything in book that explains letters on schematics like( I ) must be check valves (H) is protection valve (K) Is another shuttle valve? only on front tank (U) is the shuttle valve ? I took a few pictures and down loaded to computer so I can check it out Is

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