1\4 copper tubing leak

[techforay]

Last night I installed an under the sink hot water despenser. The 1\4 inch copper tubing that feeds the devise is leaking at the tee. How tight should you have to tighten the ferrule connection. I was told finger tight plus a quarter turn more but I have gone beyond that and I still have a leak.

[Gary Swart]

Tighten it more. The hand tight plus 1/4 turn refers to P traps. It take a bit of pressure to compress the copper tubing and ferrule.

[techforay]

Thank you for your expertise Gary

[SteveW]

If that doesn't work, back the nut off and put a drop or two of regular oil, like 3-in-1, on the threads and try again.

Terry taught me that trick on this site - compression fitting manufacturers sometimes recommend oil on the threads, which allows you to tighten the fitting a bit more than without.

Don't use Teflon tape or pipe dope - those work against you on compression fittings if you put them on the threads.

(Some folks have good luck putting a little pipe dope on the ferrule itself - again, not the threads...)

[Lakee911]

Why does the pipe dope work against you on the threads? I would think that the kind with teflon would help lubricate them like the oil does.

Jason

[SteveW]

I think it has to do with how thick the pipe dope is - most I've seen (not that many, admittedly) are very viscous, so the notion is that they may actually make it more difficult for the nut to engage as many threads as when you use oil alone. In the normal use of pipe dope, where you have tapered pipe threads, this isn't a problem.

When I've tried it myself, it did seem that oil alone does tend to let you screw the nut on further, with about the same amount of force, compared to pipe dope on the threads.

[jadnashua]

In a compression fitting, the nut is not making any water-tite seal...it is there to give you the mechanical force necessary to hold the ferrule tight to the body of the seat and the pipe, so pipe dope just can gum things up. But, metal on metal can gall and prevent things from smoothly tightening those last few degrees so you can get a good 'feel' for when tight-enough has been reached (especially with some of the poor quality controlled stuff out there now). Lubricating the threads makes it much easier to snug it up 'just right'.