Posted by Patrick Fox on December 10, 2002 at 10:47:47 from 141.163.195.189 user pfox.
In Reply to: Re: Tide Mill (Re: Pin Mill and Hamford Water) posted by Andrew Craig-Bennett on December 09, 2002 at 22:37:50:
I was curious at your comment that reversing the wheel would be too much gearing for a millwright. Given that it would only take one more cog, and mills seem full of them, I was unsure if this could be all the story. Having a look at the Eling mill website and reading about how it works I wonder if there's another explanation. The wheel apparently only turns effectively when it is fully out of the water, otherwise there's too much drag. As a result, a sluice is used to hold back the tide pond until the water has fallen enough, then opened to provide a jet of water to power the wheel.
To work the other way, another set of sluices would be needed on the seaward side of the mill to control the flow in the same way in that direction. Additionally, the mill pond would need to be emptied to below the level of the wheel before it began to refill. What I understand of the usual situation is that operating the mill on the ebb produces only a minor change in level of the mill pond, thus maintaining the full head of pressure throughout the working time. Given this, although fitting sluices to allow reverse flow would apparently allow the mill to operate for longer, the need to fully empty the pond first might mean that it operates less efficiently.
Just partly informed speculation on my part!
Cheers
Patrick