So how do these work ? What's in one ? Having a bit of trouble with the 6
bar inlet pressure relief valve opening intermittently on an unvented water
heater, due to excessive pressure in the rising main, so want to knock it
back some.

E.g. this look any good ?

http://www.plumbworld.co.uk/safeguar...cing-343-21866

I kind of like the pressure gauge on it, and the fact that the through-bore
is 22mm, with reducers to 15mm, which is the size of pipe that it needs to
go on. Currently reduced 'on offer' price looks ok - although a lot of
Plumbworld's prices seem to be permanently on offer - and the couple of
reviews that it has look ok. Only slight thing that's bothering me is that
I'm sure when I've seen pressure reducing kits before, they've had a biggish
sphere like a ball valve size on them. Is that some other design or type? Or
am I thinking of something else ? Advice please ... :-)

TIA

Arfa