13mm in other lengths. http://www.bes.ltd.uk , watch the vat + post.
However, I don't think a *short* length of reduced bore makes a lot of
difference, a 30cm length of 13mm will have the same restriction as 70cm
of 22mm; if I calculate correctly. 60cm of 13mm == 1.4m of 22mm.
The hydraulic resistance of a tube is inversely proportional to the FOURTH
power of its radius. 
The bore of 22mm pipe is about 19mm
So the 30cm of 13mm bore is the same as (19/13)^ x 30cm
That's about 136cm of pipe. Not a big problem.
 This is becasue the fluid speed is inversely proportional to the
square of the bore size. The 'back pressrure' is proportional to the square
of the fluid speed.
For viscous fluids and lowish speeds then pressure loss is only
proportional to the speed. Hence resistance only(!) inversely proportional
to the cube of the bore size.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
19mm full bore including the fittings are available on ebay, pictures supplied
on the site. Most of the hoses assemblies throttle down to about 9mm inside the
hose termination so you need to be careful what you fit onto a bath tap. Flexi
pipes are brilliant and very quick, if you have sufficient copper pipe I would
go for JG speed fit adapter 3/4BSP - 22mm speed fit which is full bore (19mm
We started using the smaller sizes from the mid seventies where they
replaced Enots brass compression fittings for a lot of applications.
The first week we had them the store man got a bit sniffy as
following the general style of the Cadburys Smash Martian which was
on the TV at the time we used a hundred or so fittings to build
something similar with a pressure gauge for a face and put it on his
Being a typical miserable bastard store man he complained about the
cost "You've just wasted about £50 pounds of fittings "as he was
oblivious that they could be easily separated without damage.
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