On Wednesday, 22 February 2017 16:59:33 UTC, newshound wrote:
On 2/21/2017 11:27 PM, tabbypurr wrote:
On Tuesday, 21 February 2017 20:35:56 UTC, newshound wrote:
On 2/21/2017 8:15 PM, tabbypurr wrote:
On Tuesday, 21 February 2017 20:05:29 UTC, newshound wrote:
On 2/21/2017 7:56 PM, tabbypurr wrote:
On Tuesday, 21 February 2017 19:32:23 UTC, newshound wrote:
On 2/21/2017 7:03 PM, tabbypurr wrote:

3 plumbing joints done with ptfe tape all leak. I mostly don't use ptfe to seal joints. 2 of the joints are 15mm compression tee (with one male end, one female end) onto an extension piece, the other is extension piece onto brass threaded ballcock. 1.5 turns of yellow/gas ptfe tape each, all neatly in place. I admit to not being clear how the nut would seal to the tee it's on. The one joint done with fibre washer & gloop works fine of course, but I don't think that approach can be used with the other joints.

I'm clearly making a basic mistake here. Did I mention I don't like plumbing?


NT

When you say compression tee, do you mean the pipe has an olive on it?

Like an ordinary compression fitting (that takes pipe with olive) except that one end is reversed, ie male not female. It thus has a nut on that screws onto another fitting. I've added 2 threaded extension pieces, one on each port, to make the combined fitting long enough to reach both pipe and ballcock.

So where is the seal?

I thought the ptfe between the screw threads was going to do it, but clearly not.

Assuming these are parallel threads, you will need
a soft washer on the axial face (unless you fill up the thread clearance
with some sort of fluid sealant)0

yes, hoping I have a suitable washer now.

IIRC fittings to a ballcock are also normally done with an olive.

Neither the current or previous one were/are. The male bit of the compression elbow is screwed onto the ballcock.

OK then you need another soft washer (fibre or rubber) on the axial face.

right

You should not be trying to use PTFE tape to seal any significant water
pressure. But IMHO it is worth using tape on compression fittings *to
reduce the friction*, which means you get more axial pressure for a
given torque. Lots of people tell you that you must not put tape *over*
the olive or the cones but a single turn won't matter.

There are basically three ways to seal with threaded connectors.

One is using tapered threads, these are sealed with fibre, traditionally
hemp but now usually Loctite synthetic thread. A smear of "Boss White"
is also needed.

The second is the washing machine or garden tap connector. You need a
soft washer, either rubber or fibre, trapped in the female (hose)
fitting against the end face of the tap. Tap fittings use a variant of
this, with a thinner fibre washer trapped against the tap by a flange on
the male fitting.

The third is the compression fitting, where you are trapping an olive
between cones on the male and female parts. This relies on squeezing the
olive tightly enough on the pipe so that fluid cannot flow between the
olive and the pipe (sometimes a problem with chromed pipes).

There are liquid sealants which can be applied to threaded joints, I
usually think they are a bit of a "bodge" but sometimes you are
constrained by, for example, a damaged cone on a fixed part, or a scored
pipe. I always carry some in my plumbing toolbox.

I'll see if I can get washers in there, but from a quick look I doubt I can. In which case I could use some sort of fairly quick setting stuff, but that still won't seal the nut to the male end of the compression fitting.

elbow is like this:
https://www.raygrahams.com/images/th...052314_700.jpg

That needs a tapered male thread although you might get away with a washer

I'm more than puzzled by the idea of using a tapered thread with it

Tapered threads are sized so that they become completely tight before
the male thread has bottomed in the female component. On its own, a
tapered thread can't normally make a gas-tight seal, but the leakage
path will be small, so it can be sealed by something like boss white. A
down-side of tapered joints is that you don't have much control of the
orientation of the parts at the point where they become tight. However
by having something like hemp threads wrapped around the male threads,
you can influence the point at which it becomes tight, and hence control
the angular orientation. Tapered threads are not so commonly used in
copper systems, but they were the standard system in "old" iron pipe,
e.g. in "gravity" hot water systems, and are sometimes used for
hand-rails and guard rails. It's a bit of an art building a complicated
"3D" system in iron.


extensions look like this but without the nut on:
https://www.raygrahams.com/images/th...038720_188.jpg

I would expect there to be an olive between the nut and the fitting

which nut and which fitting? I can't imagine how one would get an olive between the extension piece and the elbow.

This picture shows two components. A sort of sleeve with a female thread
at one end, and a male thread on the other.

that's what the extension pieces are

There is a nut on the male
thread. I would expect there to be an olive "inside" the nut. This would
let you seal a piece of copper pipe to the right hand end of the
fitting, by tightening the nut (with the olive in place).

But that lot doesn't come into it. No nut, no olive, no pipe.


NT

The bottom line is, this explains why you are getting leaks with PTFE
tape only.

You either need a rubber or fibre washer to give an axial seal, or taper
threads with sealant, or perhaps some sort of bodge with a setting sealant.