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.
Christian.
P.S. this is for radiators, no potable water involved.
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 place.
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 huge amount.
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 it.
.andy
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Occasionally.
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
.andy
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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.
Have you never had those tricky buggers, where the thread strips all the Teflon off as you insert it ? ONLY hemp has sealed those for me !
Steve
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 c*ck 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)
.andy
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I'd say if the thread strips off the PTFE, it's such a good fit it doesn't need sealing?
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 enough. ;-)
Christian.
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. :-)
.andy
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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...Christian.
I would say that a few _drops_ of the sealant is faster and neater (no possibility of a stray peice of tape hanging out).
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.
Roger
No. Been there tried that.....
Steve
I always use PTFE tapes, sounds much simpler. Just wind a good pile on so that when you screw it together it tightens not loosens.
Rick
You *do* wind the tape around the thread in the right direction, don't you?
Anyway for tricky ones I find Hylomar is better than hemp.
that when you screw it together it tightens not loosens.
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.
-- John Stumbles
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-+ Women always generalise
Of course !
Never thought of that for domestics.
Steve
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