It sounds like you've found a solution, but with talk of impellors and
vanes, I wanted to drop one other term into the discussion: nutating disk.
http://www.engineersedge.com/instrumentation/nutating_disk_displacment_mete=
r.htm

Gary

On Thu, Apr 7, 2011 at 6:36 AM, IVP <joecolquitt@clear.net.nz> wrote:

> > This is for an experimental gray water
>
> Martin,
>
> some years ago when the council were to start charging for
> grey water, someone came to me with an impellor fitting
> inside a water pipe. I was meant to do a little PICcing so
> the grey water could be measured but he never followed
> through
>
> ISTR the impellor was either iron or had iron embedded in
> it and the PIC was to record the rpm with a Hall Effect sensor
>
> Although we didn't get to a prototype I don't recall any
> unsolved issues. The impellor had semi-circular vanes, like a
> butterfly valve, so it fitted closely into a round pipe and only a
> very slow trickle was not measurable. I think there was some
> discussion about a reservoir holding such a slow trickle and
> letting it go at a certain weight/volume so it would move the
> impellor
>
> There was also the related question of how full the pipe would
> be at the impellor and what effect that would have on the rpm.
> If memory serves there could have been some sort of vertical
> reservoir which released the water through a hole of smaller
> diameter than the pipe, so that the calculation was based on time
> as well as rpm. ie the water pressure and duration of this 'jet'
>
> Fine on paper theory but we never got to find out how well it
> would have worked. Water volumes and drainage of sink vs
> bath vs shower for example, size of a reservoir etc
>
> Joe
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