I've recently visited an old (about 60 years old) micro hydroelectric standalone installation. Total electric power is about 3 kW A/C.

A local told me between generator + fly-wheel and turbine there is a clutch.

Question is: what is the role of a such mechanical part in this system?

NB: local was not an expert.

  • $\begingroup$ How else would you stop the generator (for maintenance, etc) without going outside and messing about with the water supply to stop the turbine? $\endgroup$
    – alephzero
    Commented Jun 28, 2019 at 10:07
  • $\begingroup$ Thus, exactly the same behaviour as clutch in cars? What are the reason why to prefer clutch over choking the water, especially for low flow rate? $\endgroup$
    – mattia.b89
    Commented Jun 28, 2019 at 11:32
  • $\begingroup$ It's to prevent wringing the shaft when something like a golf ball jams the impeller. $\endgroup$
    – Phil Sweet
    Commented Jun 28, 2019 at 17:28

1 Answer 1


The clutch provides an instant disconnect either for scheduled maintenance or in an emergency.

If the water flow is stopped instantly, then the energy of that moving pipeful of water has to be dissipated and can cause a lot of damage. Some systems are fitted with surge pipes for exactly that reason.

On one system I worked with, slowing the flow from max to zero without causing the surge pipe to overflow took 30 seconds and at 30 litres a second that adds up...


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