stop these compression fitting leaking

[hd002e]

I have these compression fittings in my diesel fuel lines and they leak, it is not kuch but it is enough to make everything greasy and stinky. How do i compat the mess? Any tricks? Thank you!

[Uncle Bob]

Originally Posted by hd002e

I have these compression fittings in my diesel fuel lines and they leak, it is not kuch but it is enough to make everything greasy and stinky. How do i compat the mess? Any tricks? Thank you!

They are not a compression fitting but a flare fitting, the section that screws into whatever needs to be sealed, usually with teflon tape and then the flare nut is screwed down tightly onto it. I have them on my fuel system and they are great.

[Emmalina]

nothing wrong with them but you shouldn't use copper pipe for diesel !

[Kastaway]

Looks like it is a single flare (difficult to tell from the picture), if you have enough length, cut off the old flare and re-flare the end using a double flaring tool.

[hd002e]

These are used in the fuel lines for the diesel heater. There are a bunch of them (some are solid cast and only two of them are flared from a thin walled pipe like in the photo). I have fitted them with teflon tape or thread sealent, lets see how they hold up. Thanks for your help guys!

[Bycrick]

Most of my diesel fuel plumbing is copper tubing with flare fittings. My first boat had hydraulic steering with flare fittings. If they’re done correctly, they don’t need any sealant or tape to keep them from leaking.

[Chotu]

They are one of the most reliable ways to seal things. I use them for propane. Not a bit of a leak in five years or six years now.

If you have properly formed the flare using the right tool, That’s what keeps the liquid or gas in the copper line. The thread has nothing to do with it. The thread is just squishing the flare fitting together.

No treatment of the threads required at all.

If it is still leaking, you’re going to have to cut off the flare that exists in the copper like mentioned above, and just make a new flare.

Take some little scrap of copper tubing and play around with it. Make a bunch of flares. You’ll become an expert in about half an hour.

[Shrew]

I believe that you can use both, though I was under the impression that yellow PTFE tape (gas and oil) is the recommended for that type of application.

I ended up using yellow to connect the fittings for my Reverso oil changer.

Any thoughts??

[Bowdrie]

Nothing wrong with properly done flare fittings.
If you have access to a refrigeration supply, you will find that the best quality flare nuts are forged, with thick walls, not the thin walls that the typical machined brass ones have.
The forged ones don't distort under heavy torque.
Copper tubing has been used for, oh, perhaps going on 100 years in diesel applications with sucess, just needs sections of hose at connections subject to vibration.
Double flares are for steel brake lines and some aircraft use, not for copper tubing in fuel/refrigeration use.
With a proper flare there is no need for tapes/sealants, etc.
Most failures/leakage of flare joints can be traced to poor quality flares made by cheap tools and/or distortion of the nut.

[Cheechako]

I like flared fittings and have found them to be trouble free for copper fuel lines. The devil is in the details;
1) the flare cannot be too big at it's major diameter or it interferes with the nut threads.
2) the flared surface must be clean, not dimpled and pit/debris free.

[Bycrick]

There are good nuts and lousy ones. Plus long and short nuts. The tubing has to be square with the fitting, before you tighten anything. Any dirt or nicks on the fitting or the tubing and it can leak. If you overtighten, you can crack the flare which will almost certainly leak.

[jeanathon]

You don't use teflon tape or anything else on flared fittings. First of all teflon tape is not a sealant it is a lubricant to properly tighten other fittings. Second tape will get in between the flared surfaces causing a leak.

[MicHughV]

I've used copper pipe with flared ends on engines for years..never had a problem...copper is soft, so when pressed onto it's other connection, it tends to be soft enuff to mate to any minor surface imperfections.
Flaring tools can be purchased at any hardware store. There is a bit of an art to it. As stated above, not to much flare or you can crack the end, etc. The end to be flared must be cut perfectly perpendicular to the pipe, and any rough saw edges removed. The flaring tool usually comes with a blade tip you can insert into the pipe to clean the edges. No teflon tape required.

[Sand crab]

What's that divit right behind the flare?

[deblen]

You need a flaring tool set.
Cut off your leaking flare & re-do it per this video.
Pay particular attention to inspecting the fit of the flared tubing against the flare sealing surface per video.Look carefully for cracks in the flare,especially in old copper tubing,which tends to get brittle with age.

Practice on a scrap piece of tubing until you get it right.
No sealant or teflon tape should ever be used on a flare fitting. If it leaks,just tighten it another 1/8th turn or re-do the flare.
Never use compression (olive in UK) fittings on anything that may vibrate or move during use & never on propane,nat.gas or gasoline-(flammables).
Cheers/Len


EDIT:Make sure you use a tubing cutter & de-burr the tubing per second video

https://www.youtube.com/watch?v=3e103_ULgpI

https://www.youtube.com/watch?v=VueCOJS2TKc