at construction sites, they may use this equipment to transport large and heavy materials and machines from one location to another, or to lift them high in the air, such as to the top of a tall structure. because i don't know this, so i can't go on record and say this, but i think that lyric came from somewhere else that did not get credit. as the steam expands to fill the cylinder, it cools down, loses pressure, and gives up its energy to the piston. that is an area that i enjoy and feel very comfortable with what i am doing and saying. 