The control for this valve is a rotating crank handle that has to be screwed what feels like a hundred turns to switch from one position to the other.

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The crank-handle drives a dynamo through a clever transmission system, and the resulting electrical energy goes straight into a rechargeable battery.

ECONOMIST: MONITOR

Because some users turn the crank-handle faster and harder than others, a nifty three-stage gearbox and a dynamo based on powerful neodymium-iron-boron magnets is used to ensure that efficiency is largely independent of the torque applied.

ECONOMIST: MONITOR