In an earlier contribution to this discussion,
Andy Hall wrote:

On Tue, 29 Nov 2005 15:00:38 -0000, "Set Square"
wrote:

Yes, I wonder how well they work with automatic by-pass valves.
AIUI, an automatic by-pass only opens on the pressure rise resulting
from low flow through the rads when all the TRVs are closed. If the
Alpha backs off so that the pressure *doesn't* rise, the by-pass may
not open and the boiler may overheat.


You just make sure that the pump is set at a point that it always
overcomes the ABV.

I probably need to educate myself about Alpha pumps. How many parameters can
you change on them?

As we known, a conventional pump operates on a curve (per speed setting)
whose two ends are at max pressure/zero flow and max flow/zero pressure. In
a heating system with TRVs, it would seem to be desirable to have a pump
which provided a constant pressure regardless of flow. Then, when one or
more TRVs closed, the flow through the remaining radiators would be
unaffected. I presume that an Alpha goes some way - but not all the way -
towards this, so that there is still *some* pressure rise to open the ABV
when all the TRVs close?
--
Cheers,
Set Square
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