DCV compression on plastic? I'm not sure...

[Super_Paulie]

Question for a Sunday morning!

 

I need to a DCV here, I can't access it at the other end as it's a wall chase to an external tap. Question is, should I just sack off the compression-to-plastic joint and have a copper stubby from below the DCV and then a 90° elbow at the bottom of this to connect back to my plastic? Downside is that the elbow would be below floor level... 

 

Cheers gents.

[Super_Paulie]

Well looks like everyone is out enjoying the sun, so for info I went with a joint under the floor. It'll be fine, what can ya do eh.

[dpmiller]

better not forget the locking collets on the JG fitting if it's going to be unseen...

[TonyT]

Make sure the flooring is able to lift out 

[Jenki]

Sorry for the lateness. But I prefer the 1st photo🙈 Compression on plastic if you don't overtighten and use a metal insert is fine IMHO. Would prefer a visible compression to a hidden push fit joint.

[Super_Paulie]

1 hour ago, Jenki said:

Sorry for the lateness. But I prefer the 1st photo🙈 Compression on plastic if you don't overtighten and use a metal insert is fine IMHO. Would prefer a visible compression to a hidden push fit joint.

Yeah I was debating it back and forth, everyone was busy today it seemed so I just went ahead and did what I thought best as I needed it done. The bend on the layflat comes in pretty steep so I wasn't 100% on the compression fitting to plastic. Read somewhere that @Nickfromwales suggests compression on copper stubbies, so went with that. Either way, totally suitable I'd imagine.

[Nickfromwales]

15 hours ago, Super_Paulie said:

Yeah I was debating it back and forth, everyone was busy today it seemed so I just went ahead and did what I thought best as I needed it done. The bend on the layflat comes in pretty steep so I wasn't 100% on the compression fitting to plastic. Read somewhere that @Nickfromwales suggests compression on copper stubbies, so went with that. Either way, totally suitable I'd imagine.

1000% the right thing to do! 👍. Tightening metal onto soft plastic is just bonkers. The insert just stops the pipe from caving in, but doesn't stop the nut and olive chewing into the plastic. If you even slightly over-tighten (or tighten as you would with metal / metal) then the olive will start cutting into the plastic of the pipe.

👎

[Jenki]

8 hours ago, Nickfromwales said:

1000% the right thing to do! 👍. Tightening metal onto soft plastic is just bonkers. The insert just stops the pipe from caving in, but doesn't stop the nut and olive chewing into the plastic. If you even slightly over-tighten (or tighten as you would with metal / metal) then the olive will start cutting into the plastic of the pipe.

👎

Curious, @Nickfromwales, if you were to supply a shower valve from a plant room manifold with plastic pipe, would you use stubby copper to the compression on the valve, and then add an additional push fit joint?

So two hidden joints instead of one? Honest question.

[Nickfromwales]

14 minutes ago, Jenki said:

Curious, @Nickfromwales, if you were to supply a shower valve from a plant room manifold with plastic pipe, would you use stubby copper to the compression on the valve, and then add an additional push fit joint?

So two hidden joints instead of one? Honest question.

 

Straight in with these my friend. For showers with a 3/4" entry you just wind a brass reducing bush in first, then these 1/2" fittings wind into those.

 

2 minutes ago, Nickfromwales said:

So two hidden joints instead of one?

If you've travelled the whole length of the building without joints, then don't ever beat yourself up with having a few locally in the room where the supply terminates  You know where these are, can usually pressure test with the live mains before finishing the boarding in that space, and these are bloody bomb-proof anyways!