28 or 22mm pipe if 22mm stop cock used on main

[Deansplit]

My home currently has a Lead pipe connected to 15mm to kitchen and then on to 28mm to top of 3 story house (3 showers and a bath plus sinks etc). I'm removing all the copper as the area we're in is reknown for corroding it. A new plastic 25mm pipe will be installed from a new toby.

My query is, if I replace the 28 copper for 28 plastic (plus all branches in relevant descending sizes), do I have to fit a 28mm stop cock co maximise flow? Or will a 22 make much difference? (big difference in price is why I'm asking!)

 

[ismellgas]

I would go to the 28mm mate doesnt make sense to have 28mm pipe both sides of a 22mm stop cock..

 

[kevplumb]

why not use a full bore lever

full bore lever valve

• kevplumb
• 18 Aug 2010
• 1

 

[Deansplit]

good idea, what's the difference? Certainly easier to operate.

 

[Deansplit]

...actually, just asked about these at my plumber's merchant - they only do the ball valve version which as we know restricts the flow, or is this the same (presuming not if it's called a full bore?) Or does a stopcock have the same mechanism anyway?

 

[Perfectionist]

A ball valve is the same.

 

[Perfectionist]

My home currently has a Lead pipe connected to 15mm to kitchen and then on to 28mm to top of 3 story house (3 showers and a bath plus sinks etc). I'm removing all the copper as the area we're in is reknown for corroding it. A new plastic 25mm pipe will be installed from a new toby.

My query is, if I replace the 28 copper for 28 plastic (plus all branches in relevant descending sizes), do I have to fit a 28mm stop cock co maximise flow? Or will a 22 make much difference? (big difference in price is why I'm asking!)

You have a 15mm lead main pipe from the street? Do you have a tank in the loft?

 

[Deansplit]

At the mo yes, but replacing for 25 plastic. No tank, unvented cyl with close CH sys

 

[Perfectionist]

At the mo yes, but replacing for 25 plastic. No tank, unvented cyl with close CH sys

The 25mm will make big difference.

The pipe wall is much thicker than copper. An MDPE pipe of the same diameter as a copper would have much lower flow. Also, as they aren't compatible with copper fittings, it is best not to have the same outside diameter, to prevent the temptation.

20mm MDPE is approximately equivalent to 15mm copper.
25mm MDPE is approximately equivalent to 22mm copper.
32mm MDPE is approximately equivalent to 28mm copper.

By "approximately equivalent to" is meant "slightly better than", especially
for the 15mm 20mm.

There is no need for 28mm plastic. Use 22mm. I don't know why the 28mm was used after a 1/2" lead main. It does make flows better because of less restriction. That may have been the case in using it.

 

[ChrisR]

A ball valve is the same.

Not necessarily.

 

[Deansplit]

There is no need for 28mm plastic. Use 22mm

Oh, so do away with 28 altogether - it's only used for the vertical main to the top floor. I did actually wonder about if it's worth using seeing as it's a lesser volume than the main from the road.

So basically, never use a pipe larger than that from the road?

 

[ChrisR]

So basically, never use a pipe larger than that from the road?

Never say never, it depends on the lengths, but not usually. If you had very low mains pressure you might.

 

[Deansplit]

It's not great- 3 bar max i think.

 

[Perfectionist]

With 3 bar and 25mm from the road use 22mm. The house is not 100 foot high is it?

Have separate feed from the stop cock to the cylinder. Is there a pressure equalisation valve at the cylinder?

 

[Deansplit]

It's 40' to the pitch - 3 story. Oh, separate feed to the cylinder, right, haven't got that - it has the pressure relief valve on main in, is that what you mean