Plastic to metal fitting

[davblo]

Hi,

I'm installing a water filter which has plastic inlet and outlet fittings like this...

The suggested way is to go straight to flexible pipe with fibre washer and a 90 degree bend...

...but the pipes supplied have the wrong size at the far end.

I have some other flexible pipes I want to use but they are "straight ended" and I need to start with a 90 degree bend.

So my plan was to use a 90 deg brass fitting before switching to my flexible pipe.
Here is the brass fiting...

I found that sealing plastic into metal isn't so easy. I found out the hard way that PTFE tape doesn't work, and actually damaged the thread on one of the plastic fittings.

The best I could thnk of was to try dry connection just a little tight. But I've heard tha temperature variations can cause such joints to leak.

Are there any suggestions of how to get a good thread seal between a 1" plastic male and a 1" brass female fitting?

 

[Ric2013]

For a start you'd need a parallel female fitting and not, as I suspect you have, a tapered one. And trying to seal plastic on the threads is never going to be easy anyway. Those filter bits are designed to go into what is called a tap connector, and not into a female iron. So the seal is formed on the end, rather than on the thread itself, with a washer as you have described, and as per your angled flexis. So I suspect that brass thing is best kept as a paperweight for now.

But I'm concerned about the water filter itself. Is it WRAS approved? Those connections look like the sort of thing you'd use on a garden hose and may not even be tested to be safe for use with drinking water. Can you tell us more about the filter please? Sadly there are many companies (including Toolstation, to name one) that will happily sell you things that are both (essentially) illegal to connect to the mains, and that you shouldn't be drinking from anyway.

 

[davblo]

Hi, thanks for you comments.
No, the female thread is not tapered. It's G25/1" parallel.
But as you say, and as I realise now, making a seal on the plastic threads is not practical - I'll see what I can sort out with the 90 degree flexi pipe instead.

I see the resemblance to garden hose fittings, but these are much larger fittings, 1" going up to even larger at the head of the filter.

Not the best picture, but this sjows the filter with my original plan (loosly connected)....

 

[WC1]

I don't think the tentacles of w.r.a.s have reached Sweden yet!

WRAS Approvals

WRAS helps prevent contamination of public water and encourages its efficient use by helping with Water Supply Regulations compliance .

www.wrasapprovals.co.uk

 

[Ric2013]

I don't think the tentacles of w.r.a.s have reached Sweden yet!

WRAS Approvals

WRAS helps prevent contamination of public water and encourages its efficient use by helping with Water Supply Regulations compliance .

www.wrasapprovals.co.uk

Fair point. I was just concerned it might have been some kind of Amazon tat!

 

[ShaunCorbs]

My guess is you’ve cross threaded it when the ptfe had been on

Try doing 5-6 wraps of ptfe

 

[Ric2013]

My guess is you’ve cross threaded it when the ptfe had been on

Try doing 5-6 wraps of ptfe

You reckon he'll manage a thread seal (especially if he roughens up the threads a little)?

 

[ShaunCorbs]

I wouldn’t rough them uptoo much just drag a file over them so the ptfe grips

 

[Ric2013]

I wouldn’t rough them uptoo much just drag a file over them so the ptfe grips

Exactly... just a little. No harm in trying, I suppose. If it leaks, it'll be visible and accessible.

 

[Chuck]

I think it's likely you want to use a 3/4" BSP tap connector, i.e. the seal is formed by a fibre washer. 3/4" BSP has a 26.44 mm (1.041") outer diameter and 14 threads per inch. Commonly used on washing machine inlets and some (relatively recent) outside taps.