On Tue, 10 Jul 2007 08:57:46 +0100, Andy Hall wrote:

On 2007-07-10 08:10:58 +0100, "DJB" said:

I've fitted a new immersion cylinder but am having a problem with the
drain-off valve. When I bought the valve I thought it should have a fibre
washer, but a friendly plumber told me that it doesn't and I should instead
use 13 turns of PTFE tape. The problem is that even though I've tried this
a few times I can't get the damn thing to point downwards - and it leaks!
(the irony - having to use the drain-off valve for the first time because IT
leaks... grrrrr.) To me it doesn't seem right: the face of the valve seems
smaller than the face of the outlet on the cylinder as if something else
should be there. Searching the archives has left me thinking that this is a
1/2" BSP parallel thread and that what the plumber told me is probably
correct, but it still seems odd (to my naïve plumbing skills) that the
immersion element came with a nice washer but the valve didn't. I'm going
to try again this morning with even more tape, but thanks if anyone can put
me out of my misery and tell me if I'm doing anything wrong. I've put a
picture up he
http://myweb.tiscali.co.uk/dbecker/drain-off-valve.jpg
David

He's right, these should just screw in and have PTFE tape - no fibre washer.

One thing that can happen on some fittings - some cylinders and
radiators are bad for this - is that the thread tolerance is a bit poor
to the extent that the fitting is rather loose.

This suggests use of a lot of turns of PTFE tape (like his suggested
13), but sometimes the tape is then cut by the thread or bunches at one
end and the fitting leaks.

I've found two solutions that generally work well.

- Get some PTFE tape for gas. This comes on a yellow reel and is
thicker than the mimsy stuff for water. Try about 4-5 turns or so on
the fitting and screw in by hand. It should be possible to turn the
fitting in your fingers with a certain amount of effort but it should
not require a wrench until final tightening and should not be so loose
that it turns easily. If either then remove and apply more or less
tape as appropriate.

- Get some Boss Green and some hemp. Apply a small amount of the
sealing compound then wrap some hemp onto the threads (right way round
as for tape) and finally another smear of compound.

Both should work well and you should not have a leak.

Or loctite 55 pipe sealing cord - looks like dental floss. Works really
well. Lets you slacken a fitting aftrer tightening and still get a seal.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
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Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards