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Dave
 
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Doctor Evil wrote:
"Dave" wrote in message
...


My rising main is black alkathene (I think), the outside diameter is
close to 21.5mm - how can I find out what the bore is without removing
the fittings?



Sounds like LDPE (black) rather than the current metric MDPE (blue) Two main
types were used: Class C and Class D. Class C has a thinner wall than class
D. You may find the type printed on the pipe.

In both 1/2" and 3/4" pipe, internal and external diameters differ.

BES (www.bes.ltd.uk) sell fittings to convert from Class C 1/2" to black or
blue MDPE.

In your case the bore will be 1/2" (15mm). A standard 22mm compression
joint will go over the pipe, as long as you still use the existing pipe
insert. Wrap PTFE tape around the olive before tightening. If replacing a
stop cock use a 2mm compression full-bore valve.


Thanks (and to SimonS). If the bore of the main (about 15m to the
external stopcock) is only 1/2" it seems that there's no advantage
changing the fitting at the house end(?) Currently there's a compression
fitting to a short length (20cm) of 15mm and then into the house
stopcock, I'll just replace the 15mm stopcock with a full bore 22mm
lever valve and run 22mm thereafter - unless someone tells me otherwise.

To estimate the impact of changing pipe bores I'm planning on using an
ohm's law analogy and "series resistance". Can I just say that the
relative "resistance" caused by 22mm and 15mm pipe is directly related
to XSA (a factor of approx 2) of are the surface effects significant?
It's a long time since I did any fluid mechanics, any Bernoulli experts
out there? ;-)

--
Dave S
(The return email address is a dummy)