The final step came when steam was introduced into the cylinder to drive the piston backward as well as forward, thereby increasing the speed of the engine and cutting its fuel consumption.

最后一步是将蒸汽引入气缸，使得活塞前后推动，从而提高了发动机的速度，降低了燃料消耗。

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The piston moves by steam pressure.

活塞在蒸汽压力下运动。

《新英汉大辞典》

Filling the cylinder with steam pushes the piston out.

填充汽缸的蒸汽将活塞推出。

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All it means is that the Piston is not the Steam Box that Valve plans to release.

FORBES: Xi3 Is Committed to Piston, While Valve's Steam Box Remains Elusive

The efficiency of his design is further improved by using the moving piston to drive water through a special steam nozzle, which increases the effectiveness of the heat transfer between the inside and outside of the reactor.

ECONOMIST: Nuclear power