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。
2
The piston moves by steam pressure.
活塞在蒸汽压力下运动。
《新英汉大辞典》
3
Filling the cylinder with steam pushes the piston out.