"Andy Hall" wrote in message
...
On Wed, 30 Jul 2003 18:25:49 +0100, "IMM" wrote:


"Andy Hall" wrote in message
.. .

BTW, how does the Alpha know when to restart? Does it "poll" at a
certain
frequency to check the resistance?

The Alpha doesn't stop and start of
its own accord, it simply winds
down to a lower power with increasing resistance.

I was informed by a Grundfos rep when they first
came out that it stopped.
Maybe he didn't know too much as it was a
brand new product.

Possibly it did to begin with. I have one for my workshop circuit and
it definitely doesn't stop, although it it does drop power level
considerably. I tested it using the ball valves that I have to
isolate it.

Polyplumb and Speedfit use the Grundfos Alpha in their UFH systems. When
all the zones are closed by electric actuators the pump is still running.
The pump clearly can pump against a total stop when wound down to its
minimum speed without any adverse affects. Having an auto by-pass valve or
a fixed by-pass will make no difference. Just insert a flow switch on the
return and all rads can have TRVs and no electric room stat.



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.488 / Virus Database: 287 - Release Date: 05/06/2003