"Michael Askin" <[EMAIL PROTECTED]>
wrote:
>I have never seen the butterfly valves idea in the UK, and
>for good reason, I think, as it looked hard work.
Exactly the opposite IMHO.
Because the water pressure is nearly balanced on the parts of the
butterfly on either side of the vertical shaft, it requires very
little effort to open the paddle, either a little or fully.
However, I've never been able to see a way that theses paddles could
be opened part way. It looks to me like they would either be fully
open or fully closed. I think they would fall closed if left partly
open, as there seemed to me to be no ratchet arrangement to hold them
in an intermediate position.
However, I've never seen a detailed drawing of the mechanism.
Adrian
Adrian Stott
07956-299966
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