Air Leak Down

Topic: Air Leak Down (Read 1418 times) previous topic - next topic

Air Leak Down

January 21, 2018, 09:07:55 am

My air seems to be pumping up to 110 psi OK but after I shut the engine down the leak down rate is about 2 psi in 3 minutes.

Thing is that both gauges are decreasing at the same rate so I am guessing that my leak is someplace between the compressors and the tanks.

So just where might I start looking?

Thanks

Can you tell I just got this home???

Re: Air Leak Down

Reply #1 – January 21, 2018, 09:21:44 am

That size leak should be pretty easy to find-- both noise and soap bubbles will sure show it.

There are check valves on tank inlets that should prevent flow "backwards". But, they do fail. If the check valves are bad, and compressed air is allowed back to the dryer, a very good likelihood that the dryer needs service. It is a commonly neglected item.

My suggestion on the dryer is to replace it with a factory (only the factory that made it) Reman. All new valves and heater as well as filters.

Re: Air Leak Down

Reply #2 – January 21, 2018, 09:27:44 am

With both tanks leaking down together look for leaks in the hose fittings that connect the 2 dry air tanks together. If it is check valves that are on the inlet side of the dry air tanks it would be both of them leaking internally. Which is possible also.

Pamela & Mike

Re: Air Leak Down

Reply #3 – January 21, 2018, 09:49:30 am

Quote from: Super8mm – January 21, 2018, 09:07:55 am

So just where might I start looking?

Air leaks are a continual source of entertainment with these coaches. How much time you devote to chasing them depends on the condition of your coach and your personal standard of "good enough".

One of the essential tools for diagnosing air system "health" is the factory air schematic. You must have this document to really understand how the compressed air is routed on your coach. If you don't have it, try to find one and get a copy.

With your air system schematic in front of you, use the Forum search tool to find discussions about "air system leaks". There will be many to choose from. After reading through a batch of these threads, you will have a good idea of the common "trouble spots" where leaks are most likely to occur. The air dryer mentioned by Brett (above) is one of them.

The check valves (also mentioned by Brett) serve important functions in your air system. They keep the air moving in the correct direction, and prevent back flow. They divide the air system up into distinct "sections", and if they are working make it easier to isolate a leak. They also serve a safety function, providing sufficient reserve air pressure to safely stop the coach in the event of a catastrophic air system failure. You will need to identify the location of the check valves on your coach, and test them to ensure that they are operating correctly.

Once you have accomplished the steps listed above, you will be in a much better position to go leak hunting.

Re: Air Leak Down

Reply #4 – January 21, 2018, 10:05:30 am

Chuck, i found at times the check valves leaked but internally so as not external then soapy water not work. I had one bad enough you could listen very carefully to air back-flowing. Hope that helps Super if there is a question by him on those valves. Actually the behavior of the air pressures pretty well led me, with the schematic and forum, to those being the culprit.

Re: Air Leak Down

Reply #5 – January 21, 2018, 10:24:40 am

Quote from: Michael & Jackie – January 21, 2018, 10:05:30 am

Chuck, i found at times the check valves leaked but internally so as not external then soapy water not work.

Yes...when I say "test the check valves" I should be more specific. What I should say is "verify proper function". As you note, the check valves don't leak externally, so soap solution is no help. A "function test" is required to identify malfunction.

This would be a simple example of one such test:

1. Run engine until compressor cut-out pressure is achieved. Shut off engine. The entire air system is now at the same pressure.

2. Check (record) the reading on both dash air pressure gauges.

3. Open the water drain valve on the wet tank, and allow pressure to blow off to zero.

4. Check (record) the reading on both dash air pressure gauges.

5. If both dash gauges read the same pressure in step #2 and step #4, then the inlet check valves on the respective tanks are good.
Clarification: With "good" check valves, the "front" and "rear" air tanks should not lose any pressure when you drain the wet tank.

6. If either, or both, of the dash gauges lost pressure between step #2 and step #4, the inlet check valve on the respective tank is bad.

Each coach owner, by studying the air schematic for their coach, can come up with similar tests for many of the air system components. You can say "If I pressure up the system, then release air pressure at this point, then if this "thing" is operating properly, I should not lose any air pressure upstream (or downstream) of "it" (whatever "it" is). This will work for most of the check valves in the system, as well as the brake tank protection valves and several of the multi-function shuttle valves.

Re: Air Leak Down

Reply #6 – January 21, 2018, 10:33:59 am

Agree with Mike on the soapy water. For the valves that leak internally, a 3 ft piece of 3/8" soft plastic tubing can help pinpoint the leak. Put one end in your ear and the other on the suspect fitting/valve. They do make electronic versions if you have lots of money. Ultrasonic Leak Detectors - Nonelectrical Properties Testing - Grainger...

Re: Air Leak Down

Reply #7 – January 21, 2018, 10:34:12 am

Thanks Brett, replacing the air dryer is on my list of things to replace

Re: Air Leak Down

Reply #8 – January 21, 2018, 10:41:31 am

Thanks Chuck, I tried to listen for any leaks going from the front to back and in all the compartments but could not hear anything. With both dropping at the same rate leads me to believe that a common source is where the leak is.

I do have a remote microphone for my hearing aides, guess I will charge it up and use it to see if I can hear something.

I do have the original books and they are very well used by the PO, I will see if there is a schematic for the air system in the red one.

Wish I could get a digital set "LOL"

Re: Air Leak Down

Reply #9 – January 21, 2018, 10:45:02 am

Thanks Mike, that is what I was thinking. I hope I can hear something with my remote mic

Re: Air Leak Down

Reply #10 – January 21, 2018, 10:48:12 am

Quote from: Chuck & Jeannie – January 21, 2018, 10:24:40 am

3. Open the water drain valve on the wet tank, and allow pressure to blow off to zero.

Thanks Chuck, when you say wet tank are you talking about the water tank for the fresh water system?

Re: Air Leak Down

Reply #11 – January 21, 2018, 10:51:42 am

Quote from: jcus – January 21, 2018, 10:33:59 am

a 3 ft piece of 3/8" soft plastic tubing can help pinpoint the leak. Put one end in your ear and the other on the suspect fitting/valve.

Thanks jcus, I have just the thing for this, it is what I use to vacuum the bottom of my aquarium with. Wonder if my fish will mind

Re: Air Leak Down

Reply #12 – January 21, 2018, 10:58:59 am

Quote from: Super8mm – January 21, 2018, 10:48:12 am

Thanks Chuck, when you say wet tank are you talking about the water tank for the fresh water system?

Another Chuck,
No he is referring to the first tank in the system that has the drain valve in front of the drivers sider rear tire.

Re: Air Leak Down

Reply #13 – January 21, 2018, 11:00:02 am

Quote from: Super8mm – January 21, 2018, 10:48:12 am

Thanks Chuck, when you say wet tank are you talking about the water tank for the fresh water system?

No, the rear air tank. Drain petcock is just in front of the driver's side rear tire.

Re: Air Leak Down

Reply #14 – January 21, 2018, 11:00:39 am

Quote from: Super8mm – January 21, 2018, 10:48:12 am

Thanks Chuck, when you say wet tank are you talking about the water tank for the fresh water system?

No. The first air tank after (downstream of) your engine air compressor is called the "wet tank". You will see it identified as such on the air system schematic. It is so called because any moisture that gets by the air dryer is hopefully trapped in the "wet tank" where it can be expelled when you open the water drain valve.

Re: Air Leak Down

Reply #15 – January 21, 2018, 11:03:28 am

Wow, three correct answers in under 2 minutes.

Re: Air Leak Down

Reply #16 – January 21, 2018, 11:08:20 am

Thanks guys, you are amazing

Re: Air Leak Down

Reply #17 – January 21, 2018, 06:56:53 pm

Well I did get it slowed down to 15 psi in 52 minutes, with the mic for my hearing aids I could hear a faint hiss from the air chuck on the air hose so I removed it.

I never did find a air tank at the rear of the coach but I did find 2 in the front.

I will call FOT tomorrow and see if the have a schematic of the air system tomorrow.

Re: Air Leak Down

Reply #18 – January 21, 2018, 07:32:28 pm

Have your build number ready, I got mine via James T

Re: Air Leak Down

Reply #19 – January 21, 2018, 08:16:49 pm

Quote from: Tim Fiedler – January 21, 2018, 07:32:28 pm

Have your build number ready, I got mine via James T

Thanks Tim

Re: Air Leak Down

Reply #20 – January 21, 2018, 09:15:20 pm

I'm chasing a pretty good air leak, too. My coach is older, so specifics are likely different, but the general ideas ought to be pretty much the same.

I asked Beau and Mel to see if they could find some of my air leaks. I suspected that at least some of the problem would be taken care of by replacing the eight 25-year-old air bags. That helped, but not all that much. (The ride, though, is decidedly better.) They found and fixed a couple of problems, but there is still a problem. NONE of us, though, thought to check the air like for the air hose. I'm guessing that I'll find something there.

Beau DID replace a check valve on one of the two front tanks, and also replaced the drain valves with new ones with lanyards. Prior to that work, the pressure on both tanks would drop to zero within a couple of days. Now, the red needle is just over 60, while the white needle is down to zero. That one dropped to zero within a few hours. I'm guessing that when I next crawl under and look at the tanks I'll be able to easily see that one tank has a shiny new device on it and that if I get another one just like it and put in the corresponding place on the other tank I'll probably see both tanks staying at around 60.

Re: Air Leak Down

Reply #21 – January 21, 2018, 09:46:46 pm

David,

You probably already know this, but I'll repeat for the benefit of Super8. The two tanks in the front of the coach have valves at both the inlet and (one of) the outlets. At the inlet there is a 1-way check valve. Purpose is to prevent backwards flow of air from tank. At one of the outlets there is a "protection valve". Purpose is to retain enough pressure in the tank(s) to operate the respective brake set (either front or rear) in the event of catastrophic air system failure. The protection valve is usually set to retain about 60 psi in the tank, even if you have a leak downstream of the valve.

SO, if one (or both) of the tanks at the front of the coach bleeds down to 60 psi, and then holds (for a while) at that pressure, you can assume that the leak is downstream of that protection valve, and that the protection valve is functioning correctly.

However, if one (or both) of the tanks at the front of the coach bleeds down to zero without ever stopping and holding (for a while) at 60 psi, then the leak may be downstream of the protection valve (which is malfunctioning), or it may be in the other air line (if any) coming off that tank.

In other words, there are more possible locations for the leak in the second case.

Re: Air Leak Down

Reply #22 – January 21, 2018, 10:23:54 pm

Quote from: Super8mm – January 21, 2018, 06:56:53 pm

Well I did get it slowed down to 15 psi in 52 minutes, with the mic for my hearing aids I could hear a faint hiss from the air chuck on the air hose so I removed it.

I never did find a air tank at the rear of the coach but I did find 2 in the front.

I will call FOT tomorrow and see if the have a schematic of the air system tomorrow.

The air chuck is a common leak point. Suggest installing a ball valve just before the chuck.

Whether you find the tank or not (probably not without crawling under the coach), the tank drain is easy to access as mentioned above (forward side of driver's rear wheels)

Re: Air Leak Down

Reply #23 – January 21, 2018, 10:46:39 pm

Quote from: wolfe10 – January 21, 2018, 10:23:54 pm

The air chuck is a common leak point. Suggest installing a ball valve just before the chuck.

Whether you find the tank or not (probably not without crawling under the coach), the tank drain is easy to access as mentioned above (forward side of driver's rear wheels)

Thanks Brett, so is the drain not screwed into the tank, or is there plumbing coming over to the side with a petcock?

All I could see there is the wall of the rear compartment, a tube for the drain hose. I even opened the bed and looked down from above.

Is it the same size as the two small tanks up front?

Re: Air Leak Down

Reply #24 – January 21, 2018, 11:04:43 pm

Quote from: Super8mm – January 21, 2018, 10:46:39 pm

Thanks Brett, so is the drain not screwed into the tank, or is there plumbing coming over to the side with a petcock?

All I could see there is the wall of the rear compartment, a tube for the drain hose. I even opened the bed and looked down from above.

Is it the same size as the two small tanks up front?

You are looking in the right area, it is a tube and it is near the drain hose holder.

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