Air Leak

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

Re: Air Leak

Reply #25 – May 24, 2016, 10:17:08 am

The only "legend" I know of is the one in the lower right corner of the schematic. Somewhere, buried deep in a long-lost file drawer at FOT, there is a "Key" to all the letters on every model year air schematic. Only Indiana Jones would be able to find it, and he retired.

Correct. "U" is the 4-way shuttle valve. "H" is the protection valve. "I" is a 1-way check valve. "K" (front tank) is a 2-way check valve, which is very similar (internally) to a shuttle valve.

Your air schematic actually has a lot better notation than the one for our '93 model coach. I have to "guess" about the function of just about everything on our diagram.

Re: Air Leak

Reply #26 – May 24, 2016, 02:10:15 pm

To any members who might be watching this thread:

While we're talking about air leaks, I would like to make another suggestion. If you have any interest in really knowing what is going on in your air system, you need a way to monitor the pressure in your wet tank. Foretravel, to my knowledge, did not ever install a wet tank pressure gauge.

There are two ways to rectify this situation. I decided to mount my gauge in the engine compartment. There is a unused tapped "reservoir" port on the D2 governor. I installed a small needle valve in this port, then ran a line to my gauge. I hung it where it is visible looking through the slats in the engine compartment cover. See photos.

An even easier way is available, and it works just as well. I believe all the Foretravel coaches have the factory installed air hose for filling the tires. This hose comes directly off the wet tank. You simply rig up a pressure gauge with a male quick connect air hose fitting. Then when you want to read wet tank pressure, plug the gauge into your air hose and open the valve. Voila!

Knowing your wet tank pressure can help you isolate and identify pesky hard-to-find air leaks. It is also handy for checking/adjusting the setting of the D2 governor, without having to run all the way up to the driver compartment. A highly recommended mod!

Re: Air Leak

Reply #27 – May 24, 2016, 02:49:29 pm

Chuck:

What is the 0-30 psi gauge reading?

Re: Air Leak

Reply #28 – May 24, 2016, 03:07:23 pm

Quote from: prfleming – May 24, 2016, 02:49:29 pm

What is the 0-30 psi gauge reading?

Fuel pressure - comes off the inlet line to the injection pump, using a Tork Tek snubber.

Re: Air Leak

Reply #29 – May 24, 2016, 03:13:39 pm

Definitely a worthwhile and easy to accomplish mod... I did both methods you described back when I had the air dryer failure. Speaking of which, today I let it idle while watching the wet tank gauge and can confirm that the wet tank pressure drops while the front and rear tanks hold steady at 120psi. I had a feeling of dejavu while doing this and now remember that I had already done this a year or so ago. The pressure drops until the governor kicks in and engages the compressor. Funny thing though, at fast idle, it didn't seem to drop much if at all... I didn't watch it very long so I may just be obfuscating the issue, because I can't think of any mechanism that would make a difference between fast idle and regular idle as regards the wet tank losing pressure from 120psi. Of course, it builds pressure much faster with fast idle... scratching head and moving on. For now...
Don

Quote from: Chuck & Jeannie – May 24, 2016, 02:10:15 pm

To any members who might be watching this thread:

While we're talking about air leaks, I would like to make another suggestion. If you have any interest in really knowing what is going on in your air system, you need a way to monitor the pressure in your wet tank. Foretravel, to my knowledge, did not ever install a wet tank pressure gauge.

Re: Air Leak

Reply #30 – May 24, 2016, 03:58:05 pm

Quote from: Chuck & Jeannie – May 24, 2016, 02:10:15 pm

To any members who might be watching this thread:

... you need a way to monitor the pressure in your wet tank ...

An even easier way is available, and it works just as well. I believe all the Foretravel coaches have the factory installed air hose for filling the tires. This hose comes directly off the wet tank. You simply rig up a pressure gauge with a male quick connect air hose fitting. Then when you want to read wet tank pressure, plug the gauge into your air hose and open the valve.

Hey Chuck. In our 2001 coach the aux air comes off the rear brake tank after the protection valve. Adding air to this aux air connection does allow you to adjust height using the air bags but does not add air to either front or rear tanks or the wet tank.
I have an air pressure gauge that I can plug into the aux air connection. If all of those tanks are empty and I air up the air bags using the aux air and disconnect the air supply I will read about 110 lbs (what is in the retarder accumulator and the aux air line) assuming the check valves are working. Concept is similar, details change.

Re: Air Leak

Reply #31 – May 24, 2016, 04:00:57 pm

Quote from: Chuck & Jeannie – May 23, 2016, 11:39:45 am

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.

Chuck,

I ran the test this morning and the dash white needle went to zero and the red down about 5 lbs. indicating the rear tank inlet check valve is not working and perhaps the front one is leaking. Time to remove and see what's going on. This is an excellent and easy way to test these valves. A healthy air system is also a safe one!

Jerry

Re: Air Leak

Reply #32 – May 24, 2016, 04:06:37 pm

Quote from: Don & Tys (AKA acousticart) – May 24, 2016, 03:13:39 pm

...today I let it idle while watching the wet tank gauge and can confirm that the wet tank pressure drops while the front and rear tanks hold steady at 120psi.

So, we both have basically the same problem: something that comes directly off the wet tank is leaking air. You lose 20 psi in 5-6 minutes; I lose 120 psi overnight. In both cases, our check valves on the front and rear tanks are holding - that is good!

On our '93 GV, if I rule out the inlet line from the dryer (protected by a known good check valve), that only leaves 4 other outlets from the wet tank.

1. 3/8" nylon line that terminates at the air hose (tire filler hose).

2. 1/4" nylon line to air tank remote drain valve.

3. Main 1/2" braided cloth line going to front and rear air tanks.

4. Multi-outlet manifold with 3 ports. One port is the safety pressure relief valve (I have already removed, cleaned & reinstalled). One port is the 1/4" braided cloth supply line going to RES port on the D2 governor. The last port is a 3/8" nylon line that goes to the isolation valve (I think that is what it is called) on the air dryer.

Rusty Socket has recommended spraying the braided cloth supply line to the D2 with soap solution. I plan to try this at the next opportunity.

Jerry (coastprt) suggests trying to tighten the packing on the brass valve on the (tire filler) air hose. I did that this morning, but have not yet tested to see if it helped.

If neither of these pan out, I plan to put a ball valve on every line coming off the wet tank, and close them all. Then open them, one at a time, until I find the leaky hose. I'll let you know if I have any success!

Re: Air Leak

Reply #33 – May 24, 2016, 04:22:47 pm

Quote from: coastprt – May 24, 2016, 04:00:57 pm

Time to remove and see what's going on.

Glad the test worked, and successfully indicated items needing attention. Eat Your Wheaties before you tackle removing the check valves!

Re: Air Leak

Reply #34 – May 25, 2016, 09:14:21 pm

Some definitions needed please
What is the "D2 governor"?
How is the "Protection Valve" different from a check (one-way) valve?
What is the "PIE Interface Mod". On my air schematic each of the front tanks go to this. (2004 295)

Re: Air Leak

Reply #35 – May 25, 2016, 09:52:45 pm

Hi Larry,

The D2 governor, operating in conjunction with the unloading mechanism, automatically controls the air pressure in the air brake or air supply system between a maximum (cut- out) pressure and a minimum (cut-in) pressure. The compressor runs continually while the engine runs, but the actual compression of air is controlled by the governor actuating the compressor unloading mechanism which stops or starts the compression of air when the maximum or minimum reservoir pressures are reached. D-2TM governors are provided with mounting holes which allow direct mounting to the compressor or remote mounting. Porting consists of three reservoir ports (1/8 inch P.T.), three unloader ports (1/8 inch P.T.) and one exhaust port (1/8 inch P.T.).

Haldex D2 Governor Service Data

The protection valve is like a check valve but it stops any leakdown at a preset minimum pressure. This keeps a minimum pressure available for the braking system. Probably a better description somewhere but that is what I understand.

No PIE interface on my air schematic. There is however a PIE interface just below my nose. Apple anyone?

Re: Air Leak

Reply #36 – May 25, 2016, 09:54:11 pm

Quote from: Larry Rubin – May 25, 2016, 09:14:21 pm

What is the "D2 governor"?

LOTS of discussion on the forum about the governor - just do a quick search and you'll get more info that you thought you wanted

It controls upper and lower limits for the engine-driven compressor.

PIE Interface module is likely the blue module in the dash that takes air pressure and displays it on your dash gauges. A couple of folks have had it fail (Dan Spoor I recall being one). Search on "blue module" for his posts on the subject.

Re: Air Leak

Reply #37 – May 25, 2016, 10:02:57 pm

Oh, the dreaded Blue Module, mine is gray. They seem to fail incrementally. My air gauges and volt meter have died. Replaced air gauges with direct connected mechanical gauges. As these fail they casue your "annunciator" to beep all the time. A switch fixes that. VMSpc shows voltage as reported by the engine ECM.

Re: Air Leak

Reply #38 – May 29, 2016, 11:27:34 pm

Quote from: prevostart – 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?

You've received some good suggestions on the safety side of the air system, but they may not solve all the air leak problems. Some other places to look based on my experience.

In my case (1997 U295) I had a similar situation which was initially traced to leaking air cylinders for the step and step cover. When these were replaced the leaking slowed considerably but did not stop completely (pressure would gradually fall off over about 36 hours). One remaining leak is in the body of the antilock brake control valve for the front brakes.

It seems that this last one could fool a protection valve as it might be seen as a steady application of service brake, but I don't know that with any certainty as it's not clear to me just how the protection valve functions to allow air to the service brakes.

Unfortunately, there is no easy solution to the valve body leak. Haldex lists the valve as obsolete with no replacement. FOT service said they had researched it once and Haldex suggested a non antilock replacement but didn't know what that replacement was.

Kieth Risch at MOT recommended just continuing to drive the coach and said many others are driving coaches with more severe leaks than this one.

Re: Air Leak

Reply #39 – May 29, 2016, 11:58:58 pm

Quote from: BillO – May 29, 2016, 11:27:34 pm

...it's not clear to me just how the protection valve functions to allow air to the service brakes.

The purpose of the protection valve is to "protect" brake function in the event of failure in one of the auxiliary air systems. The air lines to the brake system come off the front and rear tanks upstream of the protection valve. The protection valve can do nothing to prevent air loss due to a leak in one of the brake components. A leak in either front or rear brake components will drain the corresponding "brake" tank and the wet tank. When driving, if the engine air compressor was unable to keep up with the air loss, then brake failure would be the inevitable result. Leaks in the brake system should not be ignored. If the original component is no longer available, a suitable replacement might be available, but may require some modification of the system. Any modification of the brake system should only be performed by a qualified (certified) air brake technician.

Re: Air Leak

Reply #40 – May 30, 2016, 09:35:45 am

Quote from: BillO – May 29, 2016, 11:27:34 pm

...it's not clear to me just how the protection valve functions to allow air to the service brakes.

In addition to what Chuck said maybe this will help. The brake system protection valve is a check valve with a pre-set cutoff pressure. It stays open until the cutoff pressure is reached and then it closes. So, let's say you park and your coach pressure starts at 120 psi. If there is a slow leak, say in one of your air bags for example, the pressure will slowly go down in a few hours, until the brake system protection valves shut off at 65 psi. Then if your brake system is solid, the pressure (both needles) will stay at 65 psi (hopefully) for many more hours.

Note: This type of slow leak, say overnight or a few days, in the coach auxiliary system is not necessarily a problem, many coaches have small leaks, but a lot of us enjoy tracking them down

. A fast leak (pressure loss in say in an hour or 2) should be addressed. (The DOT pressure loss requirement is 120 psi in an hour).

As Chuck said, if the source of the leak is in the brake system - or in the coach auxiliary system and the protection valve(s) are faulty, your air pressure will go all the way to zero, without a noticeable time period holding at 65 psi. In this case the problem should be found and fixed as soon as possible.

Re: Air Leak

Reply #41 – May 30, 2016, 06:39:54 pm

Quote from: prfleming – May 30, 2016, 09:35:45 am

Note: This type of slow leak, say overnight or a few days, in the coach auxiliary system is not necessarily a problem, many coaches have small leaks, but a lot of us enjoy tracking them down . A fast leak (pressure loss in say in an hour or 2) should be addressed. (The DOT pressure loss requirement is 120 psi in an hour).

As Chuck said, if the source of the leak is in the brake system - or in the coach auxiliary system and the protection valve(s) are faulty, your air pressure will go all the way to zero, without a noticeable time period holding at 65 psi. In this case the problem should be found and fixed as soon as possible.

I fully intend to get a replacement for the bad anti-lock control valve once I find someone that I trust to work on the air system. In the meantime, the leak is well below any DOT specs. (it takes 36 hours to drop from 120 to 0) so I'll drive it until I find that person/company.

Mostly I put this out for Art to consider other sources of leaks based upon my experience.

Re: Air Leak

Reply #42 – July 03, 2016, 01:50:40 pm

Quote from: Chuck & Jeannie – May 24, 2016, 04:22:47 pm

Glad the test worked, and successfully indicated items needing attention. Eat Your Wheaties before you tackle removing the check valves!

Chuck,

I successfully replaced the the protection valves, the one way check valves, and the tank inlet check valves on the front tanks. I also replaced the inlet check valve on the wet tank along with the safety blow out valve. Tough going at first but thanks to your instructions along with pics made it not so complicated. It took a lot of elbow grease but got it done.

I'm now in the process of replacing the ad-4 dryer with an ad-9. I built an emergency air dryer bypass to check things as they progressed. Removing the rusted/seized hoses from the old dryer fittings was a royal PITA and a real test of my manhood! I didn't have an air wrench so I finally had to break them loose with a couple of pipe wrenches. It's hard to get a good bite on those fittings in that cramped compartment. I finally had to take the dryer off the bracket and move it around to get enough torque.

The by-pass works and the compressor builds air but doesn't stop at the governor cut-off. I replaced the governor with a new one and the problem still persists. The compressor is a Bendix 501 and the governor has two lines coming out. One for the dryer control from the unloader port and the other one for the wet tank. I'm beginning to think the unloader mechanism (valve) is stuck and won't stop building air. Does yours work the same way or do I have to have the dryer hooked up for the governor to work properly? It worked fine before with the old dryer and d2 governor. I changed back to the old d2 with the same results. I noticed on your pics it looked like there was an extra line other than the one from the d2 that you used for the wet tank air pressure gauge. I sure hope that I don't have to service the unloader mechanism on the compressor. I don't know if the compressor has to be taken off the engine to do this. It would would probably be easier to remove the compressor and replace with an upgraded model with more cfms.

Thanks.

Jerry

Re: Air Leak

Reply #43 – July 03, 2016, 02:53:48 pm

Jerry,

Sounds like you are deep into your "Air System" investigation. I feel your pain from removing the old frozen dryer connections! It took every tool I had, and the longest "cheater" pipe I could get into position, to break those big suckers loose! I am sure you have already seen my old thread on this subject, but if not:

Air Dryer Bypass Demo

We (myself and all the other contributors to that thread) got into a very detailed discussion about what needs to be plugged, and how, when using the bypass. We finally decided on this basic procedure:

"You disconnect the big air line that attaches to the isolation valve. You disconnect the big air line that attaches to the bottom of the dryer. You connect those two hoses together with the EDB. That takes the air dryer (with isolation valve still attached) completely out of service. The next step is to plug the line that runs from the D2 governor to the dryer. The last step is to plug the black nylon air line (from wet tank) that is attached to the Isolation Valve. That completes the bypass procedure."

You have a different engine, and it sound like your air compressor/D2 governor setup is different from mine. Is your D2 mounted directly on the air compressor? My coach had the AD-9 Dryer as original equipment. My D2 governor is mounted on the frame and had (originally) three small air lines connected to it. One (reservoir pressure port) comes from the wet tank to the D2. One (unloader port) goes from the D2 directly to the air compressor (which is mounted on the engine block about 15" inches away). The 3rd line (unloader port) goes from the D2 to the air dryer. I also added a 4th line (reservoir pressure port) to the D2 for a pressure gauge.

On my coach, if I follow the steps listed above, the D2 will still function correctly to control the compressor. The fact that the dryer has been removed has no bearing on the D2/compressor operation. The D2 only needs one input to operate: reservoir pressure. As long as it can see this input, it should supply the "load" and "unload" signals to the compressor at the preset pressures.

When using the dryer bypass, be sure you have plugged the small line that goes from your D2 (unloader port) to the dryer. If this line is left open to atmosphere, the D2 cannot send a "unload" (pressure) signal to the compressor.

Re: Air Leak

Reply #44 – July 03, 2016, 03:56:12 pm

Chuck.

My D2 is mounted directly on the compressor. I connected the big inlet and outlet lines from the dryer together and put a plug on the small line for the dryer control. I think I forgot to include the isolation valve from the delivery port on the by-pass. I'll go check.

Thanks,

Jerry

Re: Air Leak

Reply #45 – September 18, 2016, 10:10:46 pm

Chuck,

I finally figured out my problem. After getting the intake hose and fitting off the compressor, I was able to get a look at the unloader valves and my suspicions were correct. The unloader valves were rusted shut and not working at all! They probably had been that way for a long time due to never being checked for operation by the prior owners. I didn't realize the compressor was never unloading and the air pressure was only being controlled by the governor cut-off and the blast purge of the air dryer. With the dryer by-pass connected the governor should still control the pressure cut-off if the unloaders are working properly.

Unfortunately with a Bendix Tu-Flo 501 compressor you have to remove the head to service the unloaders properly if they are stuck. Also on the 6V92 the compressor is mounted on a slant with the intake connector facing down. You have to have a mirror to see inside! The hardest part is breaking the intake, discharge and coolant lines loose. You also want to be careful to not break any of the six head bolts when taking the head off. If you have a Bendix Tu-Flo 550 or above you can easily change the unloaders without removing the head.

Since I had to remove the head I bought a field service maintenance kit and plan to service the intake and discharge valves at the same time. I didn't detect any air leaks with my shop compressor but the inside showed a lot of rust and crud buildup. Internal air leaks can go undetected and regular maintenance on the unloaders, air lines, etc will help the compressor run more efficiently and last longer. My compressor was never unloading and never getting a break to cool off. Might even help with the hp and mpg too!

Jerry

Re: Air Leak

Reply #46 – September 18, 2016, 10:56:12 pm

Very interesting post! I have never seen the inside of any of the air compressors mounted to Foretravel coaches, so the photos are a big help. Glad you discovered your problem. One more "symptom" we will need to be aware of and watch out for: failure of compressor to unload. Thanks for the report!

Re: Air Leak

Reply #47 – September 18, 2016, 11:26:33 pm

Air leaks are very hard to detect for sure. The corrosion by very highly oxygenated water in an compressed air system is a problem along with bits of rust fouling up control components. Dryers help when maintained (BTW some desiccant dryer filter crystals can be revived by baking in an electric oven to drive the moisture out). To reduce the amount of moisture going through the system it may be a step forward to relocate the intake to inside the coach to take advantage of somewhat dehumidified air while running our air conditioning. Additional desiccant air dryers/micron filters may be beneficial at the inlets of $$$$ leveling system components. Just don't add them to the brakes or other safety systems. JMO

Re: Air Leak

Reply #48 – September 19, 2016, 12:21:56 am

Chuck,
Thanks to your posts on the air dryer by-pass I was able to figure what was wrong. If there are no major leaks and the governor and dryer are working properly, you shouldn't be building air after cut-out and before cut-in. The Bendix tech support also told me that in my situation the unloaders were the likely suspect. Here's a pdf on the Bendix Tu-Flo 501 air compressor and a short video on how the unloaders work. You can see how the valves are pushed up with air pressure from the unloader port via the governor at cut-off to unseat the intake valves and make the compressor unload.

Jerry

BENDIX TU-FLO 501 AIR COMPRESSOR MANUAL Pdf Download.

http://www.youtube.com/watch?v=y6u_hFztHZo

Re: Air Leak

Reply #49 – September 19, 2016, 09:22:30 am

Quote from: coastprt – September 18, 2016, 10:10:46 pm

Internal air leaks can go undetected and regular maintenance on the unloaders, air lines, etc will help the compressor run more efficiently and last longer.

I just skimmed through the manual you linked. I'm trying to understand what the coach owner can do to avoid the situation you encountered. Being a typical owner, I never give any thought to "maintaining" my air compressor...it either works, or it doesn't. On our coaches, is the air going into the compressor being filtered by the big engine intake air filter? I ask because I have never actually investigated the flow of air into the compressor. Besides providing clean filtered air to the compressor inlet, and watching for leaks or unusual behavior, what else can the owner do?

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