I've never done threaded joints before. The standard instructions always
seem to say to wrap hemp around the threads opposite to the way it gets
screwed in. I'm not really sure what this means.
1. How thick a clump of hemp should be used?
2. Do you wrap the hemp inside the channel of the thread, or across the
3. If you run inside the threads, do you start from the end away from the
joint or towards the joint?
P.S. this is for radiators, no potable water involved.
On Fri, 28 Nov 2003 12:27:24 -0000, "Christian McArdle"
This is so that when you screw in the fitting, the hemp as wound on to
the male threaded component does not unwind.
Let's say you are holding the radiator valve tail in your hand. Point
the tail towards you and apply a small amount of Boss White or
equivalent sealant to the threads - just enough to hold the hemp in
The hemp should be wrapped onto the thread in a clockwise direction so
that the ends that are left when fully wrapped point in a clockwise
direction. Apply a little more sealant if needed (you don't need to
plaster it on or you will waste it). Then screw the fitting into the
radiator and tighten. Since you are tightening in a clockwise
direction, it will tend to wrap the hemp more tightly around the male
threaded tail. Had you wound it the other way, the hemp would tend
to unwind and come off of the threads and you might not get a seal.
If you have enough hemp and sealant, you should find the fitting
somewhat stiff to turn after the first few turns but you should still
be able to get it a fair way in with your fingers. Tighten the rest
of the way with a spanner or wrench. If you have put in too much
hemp then the fitting will be difficult to tighten - too little and it
will be rotatable by hand even when fully in.
About the equivalent to two to three pieces of ordinary string, but
adjust as described above.
Spread the hemp out a bit and wrap along the line of the threads but
getting it also over the high points. The objectinve is not to get a
single length neatly in the thread groove. Equally, you don't need a
You don't really. I have never found that it matters as long as you
get the direction right.
I do quite like to use hemp and Boss White sometimes simply because it
has a smell of "real plumbing" about it.
I think it's also useful where you have realtively loose threaded
fittings like radiators and valve tails, but especially for things
like outside taps on a wall bracket. This method allows for a lot
of adjustment and seems to hold the pieces in place well.
Having said that, PTFE tape is also very effective. Wrap in the same
way as for the hemp using about 6 turns or so for a radiator tail.
This may need to be adjusted up or down a bit depending on the
particular items used. Again you can get an idea by feel as to
whether you have a good result.
Another option that I have used effectively is thread sealant fluid.
BES have a range of these manufactured by Loctite and others.
Look for product code 10623 (Loctite 575)
I Used Loctite 575 on the last lot of radiator work I did about a year
ago and it works really well. No other material is required.
I tend also to put a smear of it on the unions of the radiator valves.
Theoretically, you shouldn't need it because they should be a perfect
ball and cup joint, but I have had occasions when tightening really
hard only just about stops a tiny seep. This eliminates that. The
mating surfaces should in any case be very clean. One advantage of
having the sealer in a tube is that it is less likely to get grit in
Generally it's because the threads are already fairly closely matched
and in effect almost any PTFE is too much.
I suspect that the Boss White used with hemp helps to lubricate and
spread the hemp filing material more effectively.
This is another case where the Loctite sealer is a good bet
To email, substitute .nospam with .gl
Indeed, it usually means that the threads in the rad are particularly rough
and need cleaning up with a 1/2" BSP tap (as in thread cutting device - not
to be confused with any other sort of tap!) before fitting the valves.
Incidentally, I once bought some valves whose threaded bits had been factory
coated with something akin to PTFE - and didn't require any additional tape
or hemp etc.
Use PTFE tape, much easier. I use about 10 turns, wound such that
it is not unwound by the action of assembling the join. Join should
become tight when assembled -- if not disassemble, remove mangled
tape and replace with more turns. If you can check for leaks using
compressed air to at least 2 atmosphere's pressure with gas leak
detector spray, that's much easier than doing it by refilling with
water and looking for drips, draining down, remaking joint, etc.
On 28 Nov 2003 14:12:09 GMT, email@example.com (Andrew
In this connection, it makes sense to run the system for a day or so
after completion and initial flushing to check for leaks and pressure
drop. Then put in some system cleanser and run for a few days,
checking again. Finally flush and add inhibitor.
This avoids wasting inhibitor if draining is needed to fix a leak.
On another practical note here, using Pegler Terrier lockshield valves
which can be bought with a drain cock on the radiator side means that
if work is required, you can turn off this valve and the TRV using the
isolating cap that comes with them. You can then drain easily and
fix a problem in this area without a total drain down. These are a
nice quality valve IME.
(Christian, for your benefit, if you don't have valves, Travis Perkins
heating centre in Reading near to PC World in Basicngstoke Rd. have
the Pegler ones)
To email, substitute .nospam with .gl
I do already have the valves. However, by some stroke of coincidence, I have
indeed bought the stated valves several weeks ago from that very branch of
Travis Perkins, along with some Invensys TRVs.
As for the connections, in practice, I have just would a large "sheet" of
hemp round the threads in no particular direction with a large mound of Boss
White spread over the top (at 85p a tub, I'm not worried by wastage!) I
wiped off excess Boss White with bog roll. We'll see if it leaks soon
On Fri, 28 Nov 2003 16:04:29 -0000, "Christian McArdle"
Well there's a coincidence :-)
I think that that ought to do it. Of course, smelling of Boss
White and hemp and going into the merchants ought to be worth a few
more points of discount.
However, you do need to practice your Whitley accent, call everyone
"mate" (because that is their name), make sure your backside is
hanging out of your jeans and remember to leave the gold card at home.
That hemp reminds me so much of those kiddie play farms. I almost expect to
turn round and see a goat eating the curtains.
I went to Meadway School, so had my original RP beaten out of me and can
manage "mate" and "cheers" with the best of them. Turning up in my minibus
(i.e. van with windows) and parking as obviously close to the door as
possible whilst asking for very specific items ensures no problems getting
the required discounts, even whilst paying cash/credit card. They gave me
40% off the TRVs and threw the drainable lockshields in for free...
I'd agree about PTFE for rad tails but for the record I butter the thread
with boss white, take about as much hemp as you'd get wool in a strand of
thin knitting wool and wind it around inside the channel of the thread
generally starting at the joint end and working backwards, then paste down
over the hemp with boss white. I use these mainly for outside taps into
wallplate elbows where you need a joint that gets very stiff and tight but
lets you carry on until the tap's vertical.
Women always generalise
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