triple-expansion

[ trip-uh l-ik-span-shuh n ]
/ ˌtrɪp əl ɪkˈspæn ʃən /
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adjective

noting a power source, especially a steam engine, using the same fluid at three successive stages of expansion to do work in three or more cylinders.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

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