Maintaining power is a device that keeps a clock or watch running while it is being wound. Without it, some movements would stop during winding. John Harrison fitted one to the fusee around 1726 so that marine chronometers kept going, and the idea was widely taken up.
How does maintaining power work?
In John Harrison’s design, a disc sits between the clock’s driving drum and its great wheel. A spring is fixed to the disc, and that spring turns the great wheel. The spring holds stored energy in reserve. It waits until someone begins winding. Then it keeps the great wheel turning, so the movement carries on. When winding ends, the drum pushes the disc forward again. That loads the maintaining spring back up, ready for the next time the clock is wound. The spring is a short-term source of power only.
Where it comes from
John Harrison came up with his own version in the mid-1720s. He had a practical reason. His clocks used a grasshopper escapement, and it failed if its drive was ever interrupted. A device that kept the drive going during winding solved the problem. Around 1726 Harrison fitted a maintaining spring to the fusee. The aim was to stop marine chronometers from halting while they were wound. The idea was widely taken up.
Which watches have maintaining power?
Good-quality watches include a maintaining spring, and so do many later fusee movements. It is a feature of high-end fusee watches in particular. In fusee pocket watches, the maintaining power is usually a gear mechanism in the base of the fusee. Its job is the same as in Harrison’s clocks. It gives the movement short-term drive while the watch is being wound, so the watch keeps running.
How is it different from a remontoire?
A maintaining power is not a remontoire. A maintaining spring has one narrow task. It keeps the timepiece going during winding and does nothing else. Once winding ends, the spring is loaded back up and returns to waiting in reserve. Its work is limited to the moments when the clock or watch is being wound.
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