Hello again,
I put this post where no one might see it so I'm, re posting here, please forgive my repeat.
I went ahead and tried the solenoid valve method, and it did save me from having to make so many trips to the genny for nozzle changes. I used automatic sprinkler valves from the hardware store, two different brands. It was some progress, but it surges the penstock quite a bit during closing, the mechanism clogs very easy thereby not always closing and they don't always open fully. Also there is more pressure drop across the valves, thus lowering the jet pressure and so the electrical output it less than a jet without a sol valve. They also use 10 watts each, so I don't want to use very many of them. They also do require nozzle changes now that the seasonal water flow is rising. It just seems like a crude way to do the job.
I still want to try a needle nozzle. And I would like to develop this into a product since I can't find any for sale anywhere in the size range equivalent to jets of .100 to .375 inches. I think there may be a need for them, I have read a few posts on the yahoo micro hydro web site from folks wanting one. The idea would be to construct an automatically adjustable needle valve using 2 inch stainless steel pipe for the body, a threaded collar containing the nozzle portion on the delivery end and a fixed needle mounted inside. Then by rotating the nozzle collar the distance between the needle and the orifice can be accurately adjusted. Rotating automatically would require some kind of gearmotor and perhaps a small chain or toothed (timing) belt. Then a simple control system to power the gearmotor to open or close the valve as required to maintain a full forebay. Thats my simplest explanation.
I'll see if I can learn how to post some pictures of my little "cricker hydro" which is today operating at an average of 200 watts. The solenoid valves currently in use allow a range of 0 to 280 watts. The genny/turbine with the 36 Hartvigsen bluespoons will provide up to 1000 watts when the water is high.
As always, your ideas will be appreciated.
Nando, is your offer to PM you still good?
Also, I have a Rainbow Power Company epoxy Pelton wheel I want to sell or trade for blue spoons. I bought it new from Australia for $100. USD and it is little used. It is currently mounted on a nearly new 1/2 hp ball bearing 1750 rpm single phase 110/240 volt motor in a "cricker" arrangement with a nozzle. It provided up to 300 watts at 120 volts. The turbine is somewhat noisy and not as efficient as the blue spoon turbine. I will try to post a picture of it if thats OK. I'd sell the whole unit if someone wants that. I'm not much of a salesman, I guess.
Thank you for your interest,
Cricker