Water main pipe size query

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I'm doing a major house renovation & have got to the stage where I need to move the incoming water pipe. I've exposed the pipe in question which is black plastic, I can't measure the diameter without cutting it open which I don't want to do until I can reconnect it all back up. I've measured the external circumference of it which is 68mm. I ***think*** that means I need to get 20mm pipe? Or would a house built in '79 ~ '80 era have an imperial plastic pipe?! Also, when they quote pipe sizes is that external diameter or internal? Thanks for any help.
 
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Not sure how you worked out you'll need 20mm pipe if you have 68mm existing? Anyway mdpe pipe is probably 63mm od 51mm Id. You sure it's that big? What you renovating a hospital?
Try 25mm.
 
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He did say circumference, so 21.6mm external diameter.
 
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If your water needs are less then use 25 mm ( the usual size for family home ) but if higher then 32 mm as the cost is only very little more!

Tony
 
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Your existing pipe will be 1/2" internally and that's what will be quoted as the 'size'. Modern MDPE pipe will quote the external diameter.

Considering you've only 13mm ID at the moment I would think 20mm modern equivalent will be fine as its ID is around 16mm. Unless you're replacing the whole run from stopcock to road in which case you may as well put 25mm down. But a short length of that on a pipe made predominantly of 1/2" imperial won't make a blind bit of difference for the extra cost and reduced bending radius you'd have.
 
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I was only going to replace the internal pipe. If I lay a new pipe to the stop cock in the road will the water company be happy to connect that up when I get a water meter fitted? If I do that should I just fit 32mm or is that over kill? What is common for large new build, 20mm or 25mm? Thanks ps. I thought being 79 to early 80's it would be all metric!!
 
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25mm is the standard size but those with longer runs or greater flow needs will fit 32 mm as its little more.

Standard meters are for 25 mm pipe but the 32mm is converted down to 25 mm at the meter.

Contrary to DIY expectations, the flow rate is not dependent on the minimum diameter in the run.

Tony
 
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All done. It was 1/2". Got a new stop cock with reducer and correct olive. No leaks :)

It's a lot of extra work to fit a compete new pipe so I hope we won't have flow issues.
 
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25mm is the standard size but those with longer runs or greater flow needs will fit 32 mm as its little more.

Standard meters are for 25 mm pipe but the 32mm is converted down to 25 mm at the meter.

Contrary to DIY expectations, the flow rate is not dependent on the minimum diameter in the run.

Tony
So would there be any difference in having 22mm instead of 15mm feeding the system?
 

oph

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25mm is the standard size but those with longer runs or greater flow needs will fit 32 mm as its little more.

Standard meters are for 25 mm pipe but the 32mm is converted down to 25 mm at the meter.

Contrary to DIY expectations, the flow rate is not dependent on the minimum diameter in the run.

Tony
So would there be any difference in having 22mm instead of 15mm feeding the system?

Two things. these being flow and pressure which most people cannot differentiate between
 

oph

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they can when it's explained. Takes less than a minute.

Well, what you waiting for then.

At 36,000 plus posts I'd suggest you have a fair bit of time on your hands ;)
 

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