Compression fittings need to stop leaking

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IPDQKWID

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I have been installing all the shut-off valves on an addition project. I'm using quarter turn angles or straights, 5/8OD inlet and 3/8OD outlet like the one pictured here. The install went fine on the cold water side, but now I am installing the hot side and I'm 3-for-3 on leaks. It's been a week since I did the cold side, maybe I forgot how to tighten a compression fitting?
Valve.jpg

The leak is a slow drip from the inlet side, best I can tell from the far side of the nut where the copper slides through. I have a couple questions that other websites don't seem to have the answer to.

If I overtighten the compression nut, can I ever use the ferrule (and nut?) again? If I did overtighten it, the copper stub wasn't visibly damaged, I wire brush cleaned it a bit and tried again, still leaked. Used a new valve, still leaked. Moved on to the next location, new valve, that one leaked too. I've been trying to stick to the recommended method - hand tighten until resistance is felt, then 1/2 turn with the wrenches.

Can I use a small amount of pipe joint compound (maybe put it on after the ferrule goes on?), or is that just crazy talk? Thank you if you's can lend any insight.
 

James Henry

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IPDQKWID

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their not reusable.



garbage advice, tighten until tight and doesn't leak.



always do that.

Thank you for the advice James. If I can rather easily slide the ferrule off the copper stub, does that mean I didn't tighten enough?
And if using pipe dope, do I try to get some between the ferrule and pipe, or is that impossible, and dope goes just on the outside of the ferrule?
 

James Henry

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If you can slide the ferrule it's not even close to being tight. put a small amount of dope on the threads of the water stop and a small amount on the ferrule and tighten the nut until you think you can feel the ferrule compress. turn the water on, if it drips tighten it some more until the drip stops.
 

IPDQKWID

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If you can slide the ferrule it's not even close to being tight. put a small amount of dope on the threads of the water stop and a small amount on the ferrule and tighten the nut until you think you can feel the ferrule compress. turn the water on, if it drips tighten it some more until the drip stops.

Thank you for the details, very much. I think I've been way too concerned with overtighteningo_O
 

SteveW

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Some of the compression stops have instructions to use a drop or two of oil on the threads, which makes it easier to tighten them adequately. I think a lot of us DIY homeowners err on the side of not tightening enough. It's a knack that a real plumber probably picks up pretty quickly. Like James Henry said above, you can feel the ferrule compress into the pipe -- especially if the threads have been lubricated.
 

jadnashua

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The threads on some of them are not all that nice, clean, and smooth. That's why a little lube can help make the tightening a little easier, otherwise, they can stick, so you can't get that small, incremental rotation you want. Bigger wrenches can help, but a slight amount of lube is usually all it takes.

If you overtighten it, it won't usually leak, but it will deform the pipe, making replacement more of a pain down the road.

If the pipe had a deep scratch, I suppose that could allow it to leak. Make sure the valve is bottomed out against the end of the pipe as you tighten things up.

As said, if you can move the valve easily, it's not tight enough. It should be essentially rigid once it's installed.
 
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