On Tue, 29 Nov 2005 17:23:31 -0000, "Set Square"
wrote:

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?

This one just has one knob to turn for the setting.

If you look on their web site there is a procedure for setting the
pump and ABVs.

There is a more sophisticated one - UPE 15-60, which has a choice of
two modes of automatic operation plus a head control. You can have a
remote for it if you want....




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?


--

..andy