Sealing large BSP threads

[essayer]

I've looked at pretty much every youtube video out there and I'm still stuck.

I'm connecting a 1.5" male BSP PVC union into a valve (pool multiport) and it weeps even though it's tightened up all the way.

I've tried multiple layers of ptfe, thread sealant, whatever I do it drips. I don't want to go too mad on the ptfe as the female fitting is ABS and will certainly crack if I force it. I can see on the inside that it's touching the base of the valve.

Is there some other trick I need to try? Next step might be to try LS-X on the threads and do it up and wait for it to seal. Seems a lot of the advice out there is US-centric and advice for NPT threads is different to BSP...

[aizvara]

I had a similar problem when fitting an outdoor tap recently. Loctite pipe sealing string helped, in the end: https://www.amazon.co.uk/gp/product/B0083TWKIK

(Though mine was obviously a smaller diameter problem, so may not help quite so much!)

[pquinn]

Are you absolutely sure it's the thread that's leaking and not something else?

If it's definitely the thread maybe try some gas pipe PTFE tape (it's thicker) or jointing compound. If it leaks with jointing compound you really have a problem with it.

[ARHarh]

First are you sure its a BSP fitting and not an NPT fitting, they don't mate every well although they will screw together and even at a quick glance look the same. If both sides are BSP then just put 3 or 4 times the amount of PTFE you think you should use on it and it will seal.

[biggiles]

Pool fittings are a dark art. The abovegroundpool forums are good, but they have funny dimensions and threads over there.

Are you sure it seals using the thread or through an o-ring/washer? You shouldn't need PTFE tape for the latter.

Threads and dimensions are hard to get right. In my experience, theory works so far, then a mixture of brute strength, multiple attempts, plumber's silicone grease on the washer/o-rings and PTFE tape makes it work and then back away carefullyIT! It's low-pressure water, so a tiny leak (if it's an above-ground/Intex) pool is acceptable IMHO.

[Simpo Two]

Hemp takes over when PTFE isn't thick enough: https://www.screwfix.com/p/select-products-hemp-pi...

[Gooose]

Is the thread parallel or tapered? Parallel threads can be a pain in the arse if both male and female threads are parallel, as they don’t end up biting together. Some of them have an o ring type gasket, so you tighten all the way into the valve and it seals in the face.
Loctite 55 sealing cord is great and should seal most things, hemp and boss white is also good.

Double check it’s not a different thread standard as the previous poster mentioned

[shtu]

Simpo Two said:

Hemp takes over when PTFE isn't thick enough: https://www.screwfix.com/p/select-products-hemp-pi...

A mix of hemp plus jointing compound will seal almost anything to anything else.

https://www.screwfix.com/p/fernox-jointing-compoun...


Frenox LSX is good for less extreme stuff.

[b14]

I’ve been through exactly the same thing on our multi port valve. I gave up - it was dripping once a second or so, so I put a can under it and filed it under “try again later”. A few days in, it had slowed. Two weeks later, it’s stopped. Don’t ask me why but it decided to seal itself so I’ve left well alone.

All of the fittings on our system seem to have a mind of their own. Some seal an absolute dream every time and can be done hand-tight with no problems, others are so finicky they will only seal if you do them up at 1401 on a Sunday whilst wearing one flip flop. It’s always fun when you’ve reconnected everything after winter and turn on the pump for the first time to observe how far the pump can spray out of the fittings you forgot to tighten…

As a result all non-urgent maintenance of the pipe work and pump etc is done during winter when the pool is out of commission, as anything I do could end up needing a few weeks of dealing with to get watertight again!

[essayer]

They were both parallel so I reckon need an o ring to seal properly without a bodge

But I bought a replacement union that out the box turned out to be tapered and - after an hour - it appears to have sealed with a bit of slic-tite thread sealant (no ptfe tape) .. fingers crossed!

Next is the filter connections.. that’ll be fun

[JoeRRS]

Sounds like you may be putting a BSP into a NPT fitting even under low pressure will leak. You should never put any sealant on a BSP thread. It may be a BSP-P which going into a female BSP-P barrel needs a dowty seal.

[Baldchap]

I work with a plumber and he always does 14 layers of PTFE tape on a join (cos 13 is unlucky, see).

Put loads on.