How do i seal these threads

[eniacs]

See photos.

 

The gismo is a water flow meter for a heat pump. It has the same fitting as a water meter would do - 1 inch bspp plastic threads. I've bought unions which use a fibre washer and these seem to sit ok and look like it will seal. The problem is the unions came with a 3/4inch bspp male thread. I've bought a BSPP female to 28mm compression fitting, but there doesnt appear to be anywhere for a washer to go, so how on earth can I seal this? 

 

Or have I bought the wrong fitting?

 

Note - I've already destroyed 1 flow meter getting this wrong...

 

Thanks

[markocosic]

 

Generic stuff available at Screwfix

 

https://www.screwfix.com/p/flomasta-pipe-sealing-cord-80m/2272v

[JohnMo]

Wrap the thread in PTFE tape. Do around 15 time around, sounds a lot, but does work.  Wrap clockwise, and run your fingers around the PTFE tape to smooth it off and push it into the threads. Or Screwfix do a liquid PTFE, apply tighten and then leave while you have a coffee to harden.

[markocosic]

Try the string and you'll be a convert away from PTFE I promise!

 

Liquid seal is good if - if - you have the time to wait for it to cure and you don't then disturb the joint. 

 

The waxed string on the other hand can be busted/moved a little bit after fitting (e.g. to realign a fitting) and will still hold pressure.

[Iceverge]

3 hours ago, markocosic said:

Try the string and you'll be a convert away from PTFE I promise!

 

Liquid seal is good if - if - you have the time to wait for it to cure and you don't then disturb the joint. 

 

The waxed string on the other hand can be busted/moved a little bit after fitting (e.g. to realign a fitting) and will still hold pressure.

 

I've had this leak on my UVC after a year. 

 

I prefer Hemp and plumbers compound. It's old school but so long as you roughen the male threads beforehand I've had zero problems. 

 

 

[markocosic]

Loctite 55 leak? After roughing up threads etc? It's effectively hemp and paste, no?

 

Or the pipe seal compound leaking?

[Iceverge]

On 21/12/2023 at 13:07, markocosic said:

Loctite 55 leak? After roughing up threads etc? It's effectively hemp and paste, no?

 

Or the pipe seal compound leaking?

 Don't know yet. Its losing a teaspoon a day. Its on the list of jobs to fix.