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Posted by Sherman in Idaho [72.47.9.37] on Friday, October 05, 2012 at 23:26:47 :
In Reply to: Re: No pool pump posted by gmharris [71.105.35.169] on Friday, October 05, 2012 at 22:56:35 :
That sounds neat. I do also have a Pelton wheel wheel that came out of the gold country, but I doubt I'll ever have a stream big enough to power it or if I did I'd never get permits for it. Pelton wheels can produce amazing amounts of power in a small space if they have sufficient head. I think there are power plants still in operation on the Feather River with 2000' of head.
In the old days, the mines often ran them flat-out with no regulation, driving air compressors. They'd have a big enough receiver and a steady enough demand for air that they'd just let the water run full bore all the time. As the air pressure builds up, the wheel slows down and it becomes less efficient, so there's a point at which it will simply stop turning. On the other end (receiver empty) an unloaded Pelton wheel will only spin at twice the speed of an optimally-loaded one, so the "runaway" condition is harmless so long as the wheel is strong enough not to fly apart at 2X normal operating speed. The result of both of those things is that in non-critical applications, like compressing air, they could do without all the complication of a speed governor.
I would suppose a machine shop would have some sort of governor, though it wouldn't need to be nearly as precise as that on an AC generator. +/-20% would be fine, versus +/- 1% for even the crudest AC generator. The hydraulic governors on the old power plants are really amazing. I was lucky I got to see the Nooksack Falls plant in operation, disconnected from the grid and regulated by its original fly-ball governor and hydraulic-controlled needle valve. The hydraulic system did not use oil, but used water from the penstock, under natural pressure, to operate the needle valve cylinder. The operator had a digital tachometer on the machine, and it held steady with 3 digits of accuracy (400 RPM I believe) while being governed by a 100 year old control system that contained no electronics. It was interesting to see him use an old synchroscope to switch it back into the grid at the end of the day's work, as well.
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