Finding "air leaks" with fluorescent dye - has anyone done this?

[Mike Shumack]

I have some small air leaks on my coach. Well not really that small as I will drop to under 30 psi in just two days. I have not been able to find the leak(s). Even spraying soapy water on the various fittings and valves did not turn up anything. Some of the valves are just real hard to get to.

I'm thinking of adding fluorescent dye to the air discharge coming line off the air compressor. I have plenty fluorescent dye left over from my days doing AC work.

I could add a couple of ounces of dye along with some "air brake alcohol" to act as the transport fluid, then fill the air tanks by running the engine. Once the system is full I shut off the engine and just let it leak down. I think the dye will then show up with my blacklight detector at any location where there is an air leak.

I would be sure Not to step on the brake or release the parking brake as the dye would then show up on that valve's exhaust port. And I will ignore any dye that shows up on the air dryer exhaust from the governor/dryer purge.

What do you think?
If no one has a reason not to do this (i.e. something I'm overlooking) I'm going to try this out.
__________________

[Eric Palmer]

Hey Mike. I don’t have a answer for you, I just wanted to add that I have a leak in my air system as well. A day and a half and my system is at 0 and I can visually see the gauge very slowly decreasing after the governor cuts out. I was wondering where and how I should start finding the leak. Any suggestions would be great!

[Mike Shumack]

The usual method is to fill a spray bottle with water and a little dish soap then spray all the air valves and fittings. A large enough air leak will show up as growing bubbles.

A second method is to use a mechanics stethoscope (like  the electronic "Steelman" https://www.amazon.com/Steelman-65001-STEELMAN-EngineEAR-Stethoscope/dp/B00FAC38QG/ref=pd_lpo_sbs_263_t_2?_encoding=UTF8&psc=1&refRID=NA5Q9GKST72Q3T07XSVW ) and listen for the leak. Bu you need to get the probe tip right on the fitting to hear it leak.

I have a set of HWH "six-pack" valves mounted over the transmission that I can't reach with dropping the driveshaft. I would be nice to be just be able to see the dye/leak.

I'm thinking that this dye may be a third method. If it works (for those have a blacklight leak detector) it would be easy since you don't have to be right on top of the fitting/valve to see if it is leaking.

[Pat Long]

Mike     I would be looking at the Smoke Machine method.   I have heard you can even make your own smoke by mixing bleach and brake fluid if I remember correct.   I use an ultrasonic leak detector listening system made by sound trap.

https://www.amazon.com/Smoke-Total-Tech-Leak-Detector/dp/B000U05VYA

[Gerald Farris]

Mike,
My impression of your plan to use alcohol and dye to find an air leak is that, I do not think that it will work because the alcohol will condense into a liquid and pool in the bottom of the first air tank, therefore not distributing the dye through the system the way that refrigerant does as it travels in a complete loop through the system. However, I could be wrong, especially if you can atomize the alcohol enough to get it through the entire system before it condenses back to a liquid.

Gerald       

[Lee Welbanks]

I totally agree with Gerald, unless you have a very large leak the dye may never get there. I chased a few air leaks in my 06 PT in the HWH system and they were always in the leveling side of it. Twice has been air pressure switches in one of the manifolds, which usually leak out of the set screw hole, had on solenoid Oring leaking and a couple of the push to connect air fittings. Everytime I find one of them leaking it gets replaced with a Parker brass air brake compression fitting.

[Dave Atherton]

Lee, well said in most cases air systems air leaks will occur in air valves, chafed air lines over
sharp edges, push on quick connectors, loose air fittings. There is really not a easy way to
chase an air leak other than pressure gauge and a good ear and soap bubbles to fitting on
Outside. Going deeper than the above, there is a check valve located between the first air
tank called the wet tank that goes in between the dry air tank . Air loss at air dryer pop off
valve on bottom and air compressor valves sticking and leaking back. Dave Atherton Retired Cat Mechanic

[Frank Bergamo]

  Mike, have you checked the air governor? Does it take a while to air up system? If so, could be governor. Spray it with soapy water and look for bubbles. Hope this helps.

[Eric Palmer]

Well, spent all day crawling around in the dirt under my MH spraying everything I could see connected to the air system. Found 2 small leaks, one easily fixed, the other is connected to the brake actuator and is in a really tight space but I should be able to get a wrench in there to hopefully tighten the connection tomorrow. These leaks are not the problem unfortunately. I think one of my airbags has a leak. The reason being, when siting still, the leak rate is approx 1 psi/minute. When driving it drops 25psi/minute. So i'm thinking a hole on the airbag would be partially sealed when sitting, but while driving  the airbag is flexing and moving opening up the leak. I did spray the airbags today, but not very thoroughly as sections of them are difficult to reach. I will have to remove the wheel well liners to get to the airbags located in front of the wheels both front and back. Back under the MH tomorrow!

[Mike Shumack]

  Mike, have you checked the air governor? Does it take a while to air up system? If so, could be governor. Spray it with soapy water and look for bubbles. Hope this helps.

No leakes at governor or any of the easy to reach places. Coach airs up normally. Just leaks down over a two day period.

[Mike Shumack]

The Dye idea did not work. I appears it could not get further than the wet tank.

I went back the the bubble test method. I did find a couple of leaking fittings. They were not leaking as fiercely as I thought they should (based on how fast my air pressure is dropping). But it is a starting point. I will replace these fittings and keep looking.

[Lee Welbanks]

Mike, Those leaks don't look to bad, I have had air leaks in the past that actually blew the water/soap out of the way and did not bubble, but didn't leak enough to actually hear the leak. Take and mix up a solution of almost 100% soap and use a paint brush to brush it on the joints. On my coach the worst leaks I found on the HWH manifolds, the air switches are prime suspects, solenoid O-Rings 2nd on the list and 3rd is some of the plugs in the aluminum block.

[Mike Shumack]

Hi Lee,

I already bought the O-rings for the HWH valves.

But I have not found any leaks at the rear set - maybe because I really can't get very close to them without removing the driveshaft. I can spray the bottom side (the solenoid side) from a distance but I don't see any bubbles. I can't see the other (top) side of the valves. The rear valve banks are located over the back of the transmission (I can't get to it from the front or back without taking something apart). If I drop the driveshaft, I will just replace all those o-rings, regardless. It's too much work just to get at the valves to not "do something with them.

Next I plan to get under the front and do a spray test on that HWH valve bank. Just need to move my wood ramps from the back to the front. If I find any big leaks at the front or elsewhere that slow the air loss a lot, I will leave the rear HWH valves as is. I really don't want to drop the driveshaft.

[Lee Welbanks]

Mike, I would strongly recommend you not remove all the solenoid valves just to change a non-leaking O-Ring. I only found one minor leak at the base of one of the solenoid valves, the air switches is where I found two leaks that caused the coach to sag down. Once on the left side and once on the right. After I bought a new one I figured out that you can repair the air switch valve yourself. I doesn't take much of a leak to cause the suspension to sag, I was surprised of how small a leak would cause the coach to sag.

[Mike Shumack]

My suspension is not dropping any (so maybe the HWH valves are not leaking) but the coach air will drop from 120 psi to 30 or less overnight. That seems like a big leak to me - but nothing obvious  has been found yet (other than what I posted). I still have the front end of coach to check.