Thermal expansion of shower waste pipe

[Joe90]

I'm about to fit a new shower tray. The bathroom waste pipe, to the drain, is EN-1566 (PVC) but the trap takes EN-1455 (ABS) pipe; both about 40 mm.

I gather that solvent welding PVC to ABS isn't recommended and in any case, the change in length of the 2m waste pipe between (say) 5 and 65 Centigrad e will be about 6 mm so I need some way of stopping it tugging on the showe r trap.

Looking at the Wavin brochure, it seems their push fit "expansion socket" o r "universal connector" would allow some movement. What I'm wondering thou gh is how well they seal. The under-floor gap is going to be really inacce ssible once the floor covering has gone down - can I trust a sliding seal t o handle (say) 10,000 cycles over the next 30 years? Which material is mos t durable - should the seal slide over the ABS pipe or over the PVC pipe? Is one meant to use silicone grease to help it slide?

Ideally I would like a corrugated flexible section with ABS solvent-weld on e end and PVC the other but I don't think anyone makes it!

Thanks Joe

[Charles F]

I gather that solvent welding PVC to ABS isn't recommended and in any case, the change in length of the 2m waste pipe between (say) 5 and 65 Centigrade will be about 6 mm so I need some way of stopping it tugging on the shower trap.

Looking at the Wavin brochure, it seems their push fit "expansion socket" or "universal connector" would allow some movement. What I'm wondering though is how well they seal. The under-floor gap is going to be really inaccessible once the floor covering has gone down - can I trust a sliding seal to handle (say) 10,000 cycles over the next 30 years? Which material is most durable - should the seal slide over the ABS pipe or over the PVC pipe? Is one meant to use silicone grease to help it slide?

Ideally I would like a corrugated flexible section with ABS solvent-weld one end and PVC the other but I don't think anyone makes it!

Thanks Joe

Actually there is such a thing - Heplex flexible waste - which is a semi rigid pipe, smooth on the inside, corrugated on the outside. Available either as preset lengths with rigid ends, or as parts to make your own - see BES

about half way down the page. I used this both for a shower - now very inaccessible, and for a sink with a complicated run. It looks much more long lasting than the standard flex wastes available from Toolstation etc - five years so far - so here's hoping!

Charles F

[Capitol]

I always use a fish tank corrugated long pvc pipe for shower/bath waste connections where I don't have access without removing the bath or shower. I reckon that all these installations will require removing at some point. This method lets this be achieved without disconnection.

[Tim Watts]

I've had the same problem with a 4m run. I used the expansion (slip) connector and it works - but be aware that even if it is greased, it will still tug - there's a moderate amount of friction.

Can you arrange to put some 90 degree bends in so the expansion is absorbed by flexing the perpendicular legs sideways?

[Nightjar]

A common way of dealing with expansion in long runs of pipework is an expansion loop. The simplest to make with waste pipe that you cannot access is probably a horizontal U shape, which can be made with four elbows. The arms of the U should be twice as long as the width of the base and, for your application, a base width of 200mm would probably be about right.

[Joe90]

Thanks, now I know it's possible I have had a look in City Plumbing and they had the MacAlpine equivalent - looks like it will be fine. Has a compression fiting each end so the issue of joining PVC to ABS is avoided too.

Joe

[Joe90]

Thanks Colin, I had wondered about that but I don't have a lot of space for U-pipes. In some ways it's a nicer concept though since it could all be solvent weld - but I would still need some kind of rubber joint at the ABS change point.

Joe

[Nightjar]

There is a transition cement join the two, just like a solvent weld:

They do sell a smaller tin in the USA, but that seems to be the only size I can find on offer in the UK.

I successfully use a general purpose PVC solvent cement to join ABS to PVC, but my application does not need to be watertight, as it is an air vent:

[Charles F]

Hi Joe, I suggested the Heplex because I thought it was a significantly better product than the standard corrugated wastes - which are thin walled and corrugated inside and out - so inclined to collect sludge inside, and possibly crisp up and crack over a long period . Like you, I was plumbing a shower that I really didn't want to have to access for many years, as it would require major surgery to wall and floor tiles. And, all of the cheaper flexible wastes have a shortish length, meaning that there would be another joint under the shower - and I liked the idea of the heplex coming in lengths that would allow me to do the whole run in one flexible pipe.

However, as always with these things - the decision as to what suits you best is yours.

Charles F