In article , Set Square
writes
In an earlier contribution to this discussion,
fred wrote:

.

As to the 28mm valve thing, I think all the valves under a given base
number use the same basic internals with just a different size
fitting, so the level of restriction is about the same for 22 & 28mm
models.

I don't think that's right. This range covers 3 sizes of valve - 1/2", 3/4"
(22mm) and 1" (28mm). Honeywell's web site shows 3 different performance
graphs (pressure drop vs flow) - one for each size. For a given flow rate, a
28mm valve definitely has a lower pressure drop than a 22mm valve.

I sit corrected, I had based my assumption on the spares (ball etc) being
the same for all of them (unless I've got that wrong as well , meaning
roughly the same opposition, apparently not . . . .
--
fred