On Sun, 01 May 2011 13:55:39 +0000, YAPH wrote:

snip

Since the boiler each has its own pump only 2g2w switch required -
standard-ish from elec wholesalers.

snip


Ah... yes... those pumps.

I've just been a-googling and come up with this:
http://www.engineeringtoolbox.com/pu...ial-d_636.html
"Centrifugal pump in series are used to overcome larger system head loss
than one pump can handle alone. For two identical pumps in serie the head
will be twice the head of a single pump at the same flow rate."
"Series operation of single stage pumps is seldom encountered - more
often multistage centrifugal pumps are used."

But:
http://www.mcnallyinstitute.com/05-html/5-12.html
"If you connect the pumps in series, the heads will add together, so the
capacities must be the same or one of them will probably cavitate. You
could also have a problem operating too far to the right of the best
efficiency point with a possible motor "burn out"."


IMHO if the system is currently working ok with either one or both
boilers running (without the noise of pump cavitation) then you should be
ok as you are only changing the control method. However, if the system
doesn't currently run like this (e.g. only one boiler runs at once) then
I should be tempted to leave well alone for the moment. There may well be
a way around this but I'm not qualified to answer.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
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