Minor air system repair

September 27, 2015, 09:00:35 pm

I recently repaired a minor air leak on my 2002 U295. I thought this might be of interest to others, so I have attached my notes below.

I parked the coach in the driveway, leveled it, and shut it off. When I got out of the coach I could hear a leak (hissing sound) from somewhere between the front wheels.

I put the coach on its blocks and climbed underneath. The leak was large and easy to find. It was leaking from the push-to-connect side of a 90° elbow fitting on the rearmost of the three air tanks under the front of the coach. The elbow is on the front of the tank on the passenger side. It is on the left side of photo 1.

Before removing the elbow I opened the drain valves on all four tanks (3 in front and 1 in the rear) and disconnected the 12 V compressor.

Photo 2 shows what the fitting looks like in close-up after unscrewing it from the tank (tubing still inserted).

It was easy to remove the elbow from the tank with a crescent wrench because the threaded end of the elbow rotates with respect to the elbow. So it was not necessary to remove the plastic air line from the elbow before removing the elbow from the tank.

I tried many things, but was not able to get the plastic hose to disconnect from the elbow. I ended up buying an inexpensive plier-type tubing cutter and cutting it off as close to the fitting as possible. There was just enough length in the tubing, which runs from the tank toward the rear of the coach, for that to work. The cut made by the tubing cutter was clean but not exactly square. It does not seem to have caused a problem.

The flexible tubing is 5/8-inch O.D. I think it is black nylon.

The threaded end is a 1/2-inch NPT (tapered iron pipe) fitting. For NPT pipe the size is the inside diameter. The nominal outside diameter is 0.84 inches.

I was unable to find a matching fitting here in town. I tried two truck parts places and a steel fabricator that sells pneumatic fittings. The 5/8-inch tubing, in particular, seems to be an unusual size. Also, I don't think any of the fittings that they had in stock rotated on the threaded end. I ended up ordering the fitting from Foretravel. It was only $10 plus shipping.

The original and replacement parts are both made by SMC. Although I did not need it, since I got the part from FOT, I found an online catalog of their Heavy Vehicle Parts http://content2.smcetech.com/pdf/kv2.pdf I believe this part is a KV2L15-37S.

Reinstalling the part was relatively easy. I cut the tubing to remove the old fitting and inserted the fresh-cut end of the tubing. The threaded end came pre-coated with teflon sealant. I carefully threaded the fitting into the tank and tightened it snug. To reduce the risk of cross threading, it would have been better to screw the elbow into the tank before inserting the tubing, but I wanted to be sure that the tubing seated properly. That would have been more difficult with the elbow already attached to the tank. In the end, it worked out fine.

I closed all the drain valves on the air tanks, started the coach, and let the air pressure come to normal. The audible leak is gone, so I think the problem is solved.

Re: Minor air system repair

Reply #1 – September 27, 2015, 09:21:16 pm

I am some what surprised the fitting was an issue to get, a brass type with an olive would work. I have pretty regular success with the push connect fittings with the following method.

Drain air pressure from the hose
Blow off the fitting with air in particular between the fitting and the collar
Spray some lubricant between the collar and the body
Push the air line further into the fitting to release the grip
Push the collar into the fitting while holding inward pressure on the hose
Hold pressure on the collar and pull out on the hose

I have a fairly inexpensive set of tools for pushing in on the collar I will get a picture of them and the packaging tomorrow they are quite simple but the leverage and the wear it saves on my fingertips is well worth it.

Re: Minor air system repair

Reply #2 – September 28, 2015, 03:59:34 pm

+1 on the tools to release the line

Re: Minor air system repair

Reply #3 – September 28, 2015, 09:10:21 pm

Those are named Dot quick connect fittings they are approved for air brake systems.You can do a google search. It's a good idea to carry a few with you and some extra tubing just in case.

Re: Minor air system repair

Reply #4 – September 28, 2015, 09:22:16 pm

I tried posting this three times from my phone sorry for the delay.

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