On Sun, 5 Mar 2006 00:17:08 -0000 someone who may be "Dave Baker"
Dave wrote this:-

I'm actually a rather competent engineer

So you claim. However, in my view a competent engineer would have
found out what was going on and then sorted it out at source, rather
then dealing with the symptoms without knowing what they were doing.

Finding out what was going on is fairly simple, as it is an
elementary part of building services engineering. For example in a
library one can find, "Faber and Kell's Heating and Air-conditioning
of Buildings", the book on the subject. In there one should find
some examples of piping layouts.

http://www.foyles.co.uk/foyles/display.asp?K=181613010522833&M=310&WHERE=(keyword +INCLUDES+'heating')&SS=(

Finding out would also involve tracing out the pipes, something you
say you have only just done.

who was hoping for reasoned opinion on the merits of this vent.

From my 1984 edition of the above book, page 190, "In no
circumstances should the feed and expansion pipe be combined with
the system vent pipe as case D. This practice was shown to be
dangerous more than 50 years ago."

The reason why it is dangerous should be obvious. It is to do with
what happens if this one pipe is restricted or blocked, especially
if it is only 15mm. You are living on borrowed time and should sort
it out immediately.

BTW, your one safety valve may have been cleaned and the washer
replaced a few times. What pressure is it set at? How often is the
operation of the valve tested? Can it pass the necessary volume of
hot water/steam?


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54