"Malcolm Reeves" wrote in message
...
On Wed, 22 Sep 2004 22:08:16 +0100, Andy Hall
wrote:

On Wed, 22 Sep 2004 21:52:50 +0100, Malcolm Reeves
wrote:

On Wed, 22 Sep 2004 14:00:09 +0100, Andy Hall
wrote:

With an alpha, as TRVs close the flow falls but the head does not
rise
as in normal pumps.

Not exactly.

Between a certain range of flow/pressure, the Alpha behaves
conventionally. When the flow falls below a certain point, that
is
detected and the power is reduced to reduce the head.

Not according to the alpha data sheet which says:

Electronically controlled, the pump can, by means of a
selector switch located on the terminal box, be set to:
. 2 constant pressure curves
. 2 proportional pressure curves
. 3 fixed speed curves.

No. My one has the 3 fixed speed curves and a pot to adjust the
proportional pressure curve almost infinitesimally. There are some other
models introduced since then though.