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??? ;D
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.
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
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.
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.
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.
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... (https://www.grainger.com/category/ultrasonic-leak-detectors/nonelectrical-properties-testing/test-instruments/ecatalog/N-bct)
Thanks Brett, replacing the air dryer is on my list of things to replace ^.^d
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"
Thanks Mike, that is what I was thinking. I hope I can hear something with my remote mic
Thanks Chuck, when you say wet tank are you talking about the water tank for the fresh water system?
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 :o
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.
No, the rear air tank. Drain petcock is just in front of the driver's side rear tire.
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.
Wow, three correct answers in under 2 minutes.
Thanks guys, you are amazing ^.^d
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.
Have your build number ready, I got mine via James T
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.
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.
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?
You are looking in the right area, it is a tube and it is near the drain hose holder.
Oh ok, I was looking for the whole tank "LOL" I crawled under as far as I could in front and behind both rear wheels looking for a tank and did not find one. Then went inside and raised the bed and could not see one there either.
I did get to inspect where they fixed the rear bulkhead real good though ^.^d
The wet tank is probably mounted up fairly high in the frame, somewhere around the rear axle. I can't actually see ours unless I'm under the coach (with safety blocks installed). The tank may or may not be similar in size and shape to the tanks at the front of your coach, but it will be easy to identify once you see it.
The drain line is usually a small 1/4" nylon tube attached to the bottom of the tank. The tube runs over to the side of the frame, and has a small valve on the end of the tube. The valve is mounted with a bracket in front of the driver side rear tire, near the bottom of the wheel well opening. With coach air pressure up, when you open the valve it should blow dry air, if you are lucky. If unlucky, you will get water or a muddy mixture of water and other junk when you open the valve. Let it keep blowing out the junk until it's only air coming out.
Then we'll talk about air dryers.
Thanks Chuck, I was looking for something big so I may have missed a small tube but I do remember seeing a sticker on the inside of the rear compartment that said something like "air system". :-[
If I make it back out there today I will give it another look.
The drain is a line from the bottom of the tank that goes to the front of the left rear tire where a petcock is located. No need to crawl under to check the wet tank for signs of dryer failure (water or powder) .
I'm sure there must be something in past topics, but wouldn't it be a rather easy task to install " remote " drains for the three tanks in the front of my coach ?? Why FT didn't do this is puzzling. They must enjoy watching old fat boys like me crawl under the coach to purge the tanks. Pretty entertaining !!
Yes. Easy. Worthwhile. Do it.
If this helps I had a air leak and what I did was use an external air source with a double male connector to my air hose and found my dash parking brake P/E switch leaking and my brake chamber along with door step.
Are you talking about where you would attach an air hose to air up your tires?
Thanks,
Trent
Yes it was where the hose plugs into the coach air line. I just unplugged it but I still have some leaks someplace.
When I let the air out of the wet tank I held my hand under it and only felt 2 things hit my hand but there were so small I could not see them. After the tank was empty I checked the gauges and both read the same but about 4 psi less than when i got out to bleed down the tank and get back.
What you felt might be desiccant balls, not good. The air experts will post more as I don't have time right now.
While "something hitting your hand" could indicate a failed dryer, remember that the wet tank drain is in the left rear wheel well (read that as in a "dirty" area).
So, if this was just for the very first second you opened the petcock, it could just be dirt in the petcock. Let that clear out and THEN see what you have.
Yes I did that, did something similar to what FT did with the rear wet tank. I removed the petcocks and replaced with brass ells and black plastic lines over to a new location for the petcocks forward of the right front wheel. I put the petcocks there to stay away from the heat from the generator. I had to make a steel bracket to hold the petcocks and fasten it to a frame member. I rarely get any water out of those petcocks, but I do have a few more chances for a leak or road debris damage.
Thanks guys, I am going out tomorrow and go over some stuff and take pictures of my dryer so I can order the correct one. I will air it up again and then let it dump out and see if there is anything else coming out. If I dont feel anything I will take it for a short run to check my power issue after replacing the switches.
I did get a copy of my air schematic yesterday from FOT so I will looking over a lot of stuff ^.^d
Remember, if you make any modifications to the air system that involve the wet tank or the front and rear brake tanks, you are messing with the components that make your brakes work. I think (but don't know for a fact) that any fittings and plastic lines used should be meet DOT approved standards. Plastic line, especially, should be high quality, because the heat under the coach and around the rear axel and engine compartment can get pretty high. I learned this lesson when I first installed my air pressure gauge in our engine compartment. I ran cheap plastic tubing from the D2 regulator up to the gauge. On our first trip after the installation, the plastic line got so hot (from engine proximity) that it softened and pulled out of the compression fitting on the back of the gauge. This, in turn, caused the D2 to not register the pressure in the wet tank, so the engine air compressor did not know when to cut out. My first clue was when both our dash air pressure gauges pegged out at 150 psi. When I walked to the back of the coach, I could hear the 150 psi safety relief valve (LOUDLY) blowing off excess pressure in the wet tank. Luckily, I had used a small brass needle valve on the D2 port where I connected the plastic line. Closing the needle valve restored everything to proper operation. Once we got home, the cheap plastic line was replaced with a DOT rubber hose with braided stainless outer cover.
My long-winded way of saying "Always use high quality fittings and air lines on any air brake tank mods".
Thanks Chuck, as a retired Mfg Eng I always lean that way and sometimes to the extreme ^.^d
I just changed my dryer out last week, not to hard of a job... NAPA can get the Haldex remanufactured dryer assembly for ~250 plus a $99 core charge for you old one back. I pulled mine to have to compare when the one I ordered came in. you will need the 3 fittings off your old one cause the new one doesn't have them.... about a 2 hour job off and on