Replacing a ball valve: how to seal the threads?

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haydude

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I have to replace a 1 and 1/2 inch ball valve (my first time) and I was wondering how should I seal the threads. Since this goes into an underwater seacock I cannot afford it to leak after relaunch.

Should I use just PTFE/Teflon tape round the threads or can I add sikaflex for extra security?

Thank you in advance.
 
There has been a recent lengthy thread (haha) about this, may be worth following it up. It seems HR use a thread lock compound for it but to many of us that seems to be somewhat OTT. Either PTFE or Sikaflex 291 on the threads would be fine but I would not use both. The likelihood of a significant leak is very low but it is well worth preventing small seeps, especially on a toilet discharge.
 
Thank you again Vyv, I will follow your advice.

One more question, what if in the tightened position the handle does not face the right way? Is it safe to screw back a bit for an adjustment?
 
I used PTFE tape on a household 3/4 inch fitting many years ago when installing my domestic central heating and it leaked. I consulted the resident plumber in the building in which I worked and he told me never to use PTFE on anything over 1/2 inch fittings and to use plumbers white and hemp. I used this on all threaded joints on the system and thirty odd years later the system is still watertight.

I am not sure that you can get the plumbers hemp anymore but if you can it is well worth using. Do not however use it on gas fittings.

Tiddler.
 
nigelmercier said:
I wouldn't use PTFE, you want it to lock up, not glide.
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With a 1.5 inch thread the friction is far higher than a bit of PTFE can overcome, so I doubt it will be an issue. I was assembling 3/8 BSP fittings three days ago using PTFE tape and its effect on friction was negligible. I would also say that maintaining the valve in the required position is not an issue for the same reason - it will stop wherever it is wanted.
 
vyv_cox said:
I would also say that maintaining the valve in the required position is not an issue for the same reason - it will stop wherever it is wanted.
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But if you can turn it into that position, surely you can (inadvertently) turn it back out of that position, and potentially unscrew it? I always assume that I might one day be heaving on the handle of a sticky valve; the last thing I want is for the valve to start turning on the skin fitting.

When we replaced all of Ariam's seacocks I used a backnut on every one. I also trimmed the length down so that there's only a couple of millimetres of thread between the hull nut and the nut that's against the valve.

Pete
 
Loctite grade 577. Seals superbly, locks reasonably firmly in the desired position (forms a semi hard gel) and simply doesn't leak (in my experience). It also allows metal to metal contact within the fitting, which means it is better for effective bonding.
 
vyv_cox said:
With a 1.5 inch thread the friction is far higher than a bit of PTFE can overcome, so I doubt it will be an issue. I was assembling 3/8 BSP fittings three days ago using PTFE tape and its effect on friction was negligible. I would also say that maintaining the valve in the required position is not an issue for the same reason - it will stop wherever it is wanted.
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As far as I can see, from PTFE-taped joints which I have subsequently dismantled, the tape disintegrates in the join, getting out of the way in the places where metal meets metal (and where the friction occurs) and squidging into the gaps elsewhere. If anything it seems to increase friction a bit, presumably by pushing metal bits more firmly together.
 
nigelmercier said:
Loctite recommended their 275. Apparently the over-fast setting that some people had can be avoided by not nipping the joints up until the last minute.
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275 is a high strength thread locker for large bolts see http://www.loctite.co.uk/fullproduct-list-loctite-4995.htm?redDotUID=1000000I9M9

Don't you mean 572 which is a slow cure thread sealant see http://www.loctite.co.uk/fullproduct-list-loctite-4995.htm?redDotUID=1000000IXOY ?

Alternatively 577 as suggested by superheat6k which is much the same as 572 but quicker setting.

There was the same confusion in another recent thread (no pun).
 
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prv said:
But if you can turn it into that position, surely you can (inadvertently) turn it back out of that position, and potentially unscrew it? I always assume that I might one day be heaving on the handle of a sticky valve; the last thing I want is for the valve to start turning on the skin fitting.
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I guess it depends upon the surface condition of the skin fitting but my experience of installing and removing larger valves is that it requires an 18 inch Stilson to turn them. There is no way that operating the valve would cause it to turn. If the threads are looser and turning is a risk then a locknut, or maybe the specialist adhesive is probably the answer, although I would be surprised if Sikaflex did not work just as well.
 
When I replaced mine last year it was impossible on 3 of them to get a decent length spanner on a locknut, so in order to get the handle orientation right I just used a good smear of Sikaflex 291 on the threads: after 24 hours they were absolutely solid. As I had to cut the 8 year old Jeanneau brass ones out (nil access for spanners again) I am not too worried about removing them, as the ones I put in are all-bronze with S/S handles.
 
Troubadour said:
275 is a high strength thread locker for large bolts see http://www.loctite.co.uk/fullproduct-list-loctite-4995.htm?redDotUID=1000000I9M9

Don't you mean 572 which is a slow cure thread sealant see http://www.loctite.co.uk/fullproduct-list-loctite-4995.htm?redDotUID=1000000IXOY ?

Alternatively 577 as suggested by superheat6k which is much the same as 572 but quicker setting.

There was the same confusion in another recent thread (no pun).
Click to expand...

I have been using 577 as a sealant for many years on fridge systems where gas leaks are verboten. These operate up to 600 psi, and 577 neither degrades nor leaks. So a few inches of water head are not an issue.

We also use 243 and 277 as medium and high strength thread lockers. Each has its specific purpose.

I renewed the entire fuel feed system on OB last Winter and applied 577 on every joint as I assembled them, with a PTFE wrap on the olived joints. Not a single leak or weep following assembly nor since. 577 is also good for refreshing tired O rings.

Incidentally PTFE can degrade on fridge systems because the fluorine attacks it. I understand PTFE is made using R22 as the base feed material, not affected by the HCFC ban though.
 
Now that I have removed the leaking (from handle shaft/pin/what is the name?) ball valve I can report that it was fitted using just old plumbers natural fibre.

Eventually I have used sikaflex 291 because I thought that any thread lock like loctite would be overkill for the job and would have made it very difficult to remove the ball valve next time if needed be.
 
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