Old osma pipe

[Truman]

Could do with some advice from an old hand in plumbing!

Basically, due to some leaks and poor installation in the first place, I need to replace some external pipework, leading from a kitchen sink to a soil stack. The problem I've got is all the existing pipework is Osma 40mm/ 1 1/2 inch BS5255. However, although I bought new push fit 40mm bends and pipework, the existing pipes are too big and do not fit into the new unions! Likewise the new pipe is too small for the existing joins.

I found an old topic here, note the 3rd post down, which suggests that older Osma pipes were actually 43mm outside diameter, whereas new ones are 41.5. This may explain why the existing pipes are too big for my new parts.

Ask The Trades - 43mm or 40mm waste?

So the question is, what is the answer?! The parts I just bought were floplast, but I think even if I could source Osma, the problem would be the same I think, as Osma are now smaller OD than what they used to be. I don't have the option to replace the whole lot as there's too much work involved. I just need to replace an existing section, from the 90 degree bend on the outlet pipe to the existing boss in the soil stack.

 

[rpm]

This is the pipe connection that keeps springing apart due to the load on the 45 elbow yes?

Wont look pretty but a rubber coupling will take up the size difference.

 

[Truman]

Hi, yes it's the 90 degree connection that keeps on springing off due to the 45 degree elbow, but the seals on the 45 degree elbow are knackered as well due to it all being sprung into place rather than done properly. I was going to replace the 2 bends - the springing problem would still exist but the new seals would at least keep it watertight. Where were you suggesting to put the rubber coupling?

 

[rpm]

Hi, yes it's the 90 degree connection that keeps on springing off due to the 45 degree elbow, but the seals on the 45 degree elbow are knackered as well due to it all being sprung into place rather than done properly. I was going to replace the 2 bends - the springing problem would still exist but the new seals would at least keep it watertight. Where were you suggesting to put the rubber coupling?

At the point you want to make the join. It`s only to join pipes of two different sizes.

 

[Truman]

Ah I'm not sure you saw the attachment. Where the old osma pipe exits the wall it's straight onto a 90 degree bend, I need to replace this part so can't fit a rubber coupler here without it protruding way too much. How about a compression fitting? Would a 40mm compression work on a 43mm pipe?

 

[rpm]

Yes I saw the picture, don`t understand why its to much work to replace all the pipe from a kitchen sink but`s that`s another story. There must be somewhere inside you can cut and join then run new pipe to the stack, use two Fernco joints if you must.

 

[Truman]

The hole in the stack accepts a push fit pipe with a diameter of the old pipe, which is 43mm I believe, problem is you can't buy this Osma pipe any more, only the newer 40mm which is obviously too small for a snug push fit into the stack.

 

[rocketmanbkk]

Yes I saw the picture, don`t understand why its to much work to replace all the pipe from a kitchen sink but`s that`s another story. There must be somewhere inside you can cut and join then run new pipe to the stack, use two Fernco joints if you must.

I'd say it's easier & less grief to replace the pipe.

Not sure why it's too much work like you say.

 

[ShaunCorbs]

replace the lot and cap the t in the stack off using one of these

https://www.amazon.co.uk/McAlpine-T23U-Multifit-Universal-Waste/dp/B00LA1800K

and re do the lot and plumb in a new strap on boss

bish bash bosh done

2 x 11/2 45d Black sw
1 x 11/2 90d Black sw
2 x 11/2 clips Black
length of 11/2 Black sw

+ your fittings inside

all in about an hour to hour and half

 

[rpm]

The hole in the stack accepts a push fit pipe with a diameter of the old pipe, which is 43mm I believe, problem is you can't buy this Osma pipe any more, only the newer 40mm which is obviously too small for a snug push fit into the stack.

Then reuse as small section of the old size pipe at the stack end and run the new pipe to a point where you can cut and join.