Compression fittings

I love DIY and am trying to learn new skills slowly and sensibly. My latest project has involved changing some shut-off valves. One such valve used a compression fitting.

My question is as follows. When is a weeping compression fit a problem? I tightened the compression fitting and it weeps VERY SLOWLY. In a day it may drip perhaps once, perhaps not at all. Often the drip evaporates before it has time to form. I do not want to overtighten the compression, so am living with it in the hope it will just ‘fur up’. Is this sensible?

I did not reuse the compression fitting (it was a new one) and I did clean the pipe. My only oversight was to forget to use teflon tape.

So when is a leak, a leak?

No tape on compression fittings. How did you determine how tight to makeup the joint? You could tighten it a little more.:slight_smile:

A leak is a leak when you can see water on the outside.

Thanks Brian. I still am unsure whether teflon should be used in a situation like this. On a compression thread it may act as a lubricant rather than a sealant and cause the joint to leak. I usually hand tighten plus a quarter turn.

Hand-tightened plus a 1/4 turn is not likely enough. No teflon tape on compression fittings period.:smiley:

What Charles said.:smiley:

Tighten it until you feel a little “bite”.
Tef. tape is not needed.

You Will Need To Re Tighten A Compression Fitting Twice
It Takes A Lot Of Torque To Seal

Very Common

I coat the compression ferrule with a dap of teflon paste before I tighten everything up. No teflon tape. The paste will fill all of the various nooks between the fitting parts.

One should always check the shutoff cocks for leaks. I wrap a piece of toliet paper around the valve. It will soak up any leaks.

2 kinds of shutoff valves under sinks

1 that leaks and 1 that will leak soon enough…

I have found in a new installation that most people over tighten these fittings. I recommend that you do not use teflon tape. Hand tighten and then using a wrench tighten about 1/2 to 5/8 turn to snug up. Then water test. This will allow you if it drips, to tighten until leak quits. This works well on Brass valves and Chrome supply lines. Vynyl supplies use plastic ferrouls, be more careful not to over tighten.

they basicly always leak the first time you turn water back on
re-tighten, check, re-tighten
what you are doing is compressing that ferrel (spelling?)
do not use tape or dope
do use 2 wrenches and be sure to not let copper or tubing bend


I’ve been using pipe dope on these for ten years with no problems. If you read the package on supply valves it will say to use plumbers grease on the ferral.

thanks JAE


the small compression fittings for, say, an icemaker, are usually no sweat.

you get up to the 1/2 inchers plus and you typically have to turn it quit a bit more than the recommended “quarter turn”

No pun intended?