How To Build A Greenhouse | Greenhouse Plans

I’ve been using this system for the past 25years and found it more reliable than using batteries or electric power, when I first made them I turned the valves out on a lathe and used magnets to latch the valve on and off. But now use plastic water timers with the clockwork removed and a balance arm on a short up-stand, this operates in the same way as the magnets and gives the arm a definite on and off position when it swings over center.

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