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 is 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.

One thing that it does do is to pulse a few times when starting.
Apparently this is to help clear any accumulated air.




The purpose of the flow switch would
have to be to detect when TRVs
had closed to a sufficient point that an
automatic valve on a bypass
opens - i.e. flow starts through the bypass
and the switch operates.

An auto by-pass would not be opened by an Alpha. The valve requires pump
pressure to open it.

When the Alpha detects pressure it reduced the speed
thinking TRVs are cloosed down.
I believe it will still deliver enough to open an auto bypass on its
bottom end setting.


A permanent by-pass is the best option.
The flow switch detecting if the TRVs are closed should not be in the
circuit of the by-pass.

The trouble is that flow switches (apart from expensive industrial
process control ones) are not that accurate in terms of operating at a
certain rate. They tend to be either a gravity or spring assisted
mechanism. I have one on the secondary side of my workshop
circuit. The pump is located in the workshop and operated by a
thermostat. When water flows, the flow switch detects it and
operates a 2 port zone valve to the primary side of the heat
exchanger, and of course fires up the boiler. This way, I don't need
any electrical control signals between the locations.



..andy

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