What is the best jpointing compound I can use

[Mikefromlondon]

I need to join a 1/2"BSF plastic (PVC) adaptor (Socket) to paralell brass adaptor to take on a standard 15mm compression coupling,

So the sequence of joint is like this:

Incoming water 21.5mm PVC/abs pipe to plastic abs/PVC Socket, one end of this socket is glued to the incoming pipe using PVC /abs cement, the other end of this socket is threaded to receive a male 1/2" adaptor, the other end of this brass adaptor will receive a 15mm compression fillting and a 15mm copper pipe onwards.

The plumbing supplier reccomended using PTF tape wrapped on the brass male threads of the adaptor and tightening to a reasonable tightness as overtightening can fracture the plastic adaptor, in one such case when water started to drip I tightened just a little more and the plastic adaptor or socket cracked, but I managed to rescue that socket by tightening a jubilee clip around.

This time, I am thinking if there is a better selant I can use instead of PTF tape, and I don't like the idea of using a jubilee clip to reinforce the socket, though it is probably safe to do so and avoid any flooding if should it crack in future under stress. The sleeve or socket walls are not very thick, barely I would say 2 to 3mm thick and can crack on being stressed.
any recomendations for a decent sealant please suggest.

The incoming pipe is 21.5mm dia dark greay ABS, been plumbed in plastic since the houses were build in the early 60s (Harlow) and Emeregncy water stopcock is very stiff, whilst it is still usable to some extent, any excessive stress applied to its handle can cause the now 30+years old brittle pipes to snap!

I want to add another brass shut off valve upstream as the original one could fail one day and is not easy to replace as it is glued in, (all PVC pipe work,)

My plan is to run some of the pipework in 15mm copper and use standard 1/2"BSF Stopcock, hence the need for plastic to copper adaptor and using a tapered union to plumb the copper pipes with compression coupling.[code:1][/code:1]

 

[APHSLTD]

Sounds like poly-york. Why not use a parallel brass fitting and a washer or a 22mm kuterlite coupling with an imperial ring for the poly-york.

 

[Mikefromlondon]

Thnaks mate, I see what you mean, why my plumber adapted gluing method which is what I followed or am following his method. I had a pipe burst about 5 years ago, and send my plumber to deal with it, he used a plastic socket one end glued in to plastic pipe and the other end a brass adaptor with a compression joint to copper pipe, half of this house is now in copper pipe and half still in plastic pipe, shocking that the plastic pipes can get very brittle over time and snap!

ideally a Kuterlight straight reducer 22mm to 15mm could be used provided the compression fitting can accomodate the incoming 21.5mm outside dia ABS pipe and is rigid enough to take radial pressure from compression of the olive ring.
Or will I need a metal sleeve of about 18mm o/s dia to the inside of the plastic pipe for extra safety?

 

[Mikefromlondon]

I picked up a 22mm to 15mm brass reducer with compression fittings and olive rings, I tried to see how well it would tighten up on a sample plastic pipe of 21.5mm dia external, after tightening it seemed rigid and tight, will it stand mains water pressure of possibly upto 4 bars I don't know, though a quick vacuum test on this section seemed to have held well. I also inserted a plastic rigid sleeve inside the plastic pipe that went in OK and snug fit.