MOTHER's MICROHYDROELECTRIC PLANT REVISITED

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At the time, the electronic diverter solved all of our control problems for what seemed a reasonable amount of money, so we have no quibble with the price. But there was the nagging knowledge that whatever it was that made the control work certainly didn't cost more than $100 in parts. Frankly, though, we just didn't have the electronic expertise to design one of these theoretically complicated gadgets. Then in June of 1984 a person with that know-how happened to visit Eco-Village and attend the hydropower workshop. Before heading home, George Ruppert offered to take a stab at designing a control.

Three months later, a package arrived in the mail. A week after that, George drove in to help install and debug the control. The details of his work are reported in the accompanying sidebar, but basically his control consists of about $35 worth of electronics and a circuit simple enough for a hobbyist to understand. The thing works. . . and very well! We're now maintaining constant output within 3 volts, equal to a change in cycling of about one, from no- to full-demand load.

OTHER CHANGES

In January of 1982 a staff member demonstrated the plant to visitors and then shut the gate valve that controls water flow completely when he went home. That night the temperature dropped below zero, and the $900 valve split wide open. The cast iron was too far gone to be welded up, so we were in the market for a new valve. Rather than purchase another high-priced gate valve, we decided to try a butterfly valve. The butterfly is simply a disk that can be turned parallel or perpendicular to the flow, while the gate drops down across the flow by way of a threaded rod.

Because the butterfly can be closed much more quickly than the gate, it increases the possibility of pipe hammer, and its design is inherently weaker than its slower-closing cousin. Still, for $275 (a $625 saving), we figured it was worth a try, and in the three years since it was installed, the butterfly has given us no trouble at all. For our low-head (and therefore low-pressure) installation, the butterfly valve seems to be adequate.

We've also changed our intake screen to a three-foot-square frame covered with 1/2" galvanized hardware cloth. The trash rack's large surface area keeps water moving through slowly enough to prevent debris from plugging the screen. A cleaning after the leaves fall each year is all that's necessary. We did encounter one problem at the intake end: Because our intake opening is simply the end of our 10-inch pipe, without any funnel, we sometimes draw a vortex of air all the way down to the pipe, which is 24 inches underwater. The air that's drawn in seriously hampers performance, but we learned to break up the vortex by floating a piece of 1/4" marine plywood on the surface within the intake screen. The plywood needs to be replaced annually, before it rots, sinks, and is sucked into the pipe.

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