The eccentric crank, an odd-looking mechanism attached to the main driver, keeps the valve gear (or motion) a quarter-turn before or after the motion of the main rod (depending on the location of the crosshead and piston). This controls the intake of live steam to the valves from the boiler and exhaust of expanded (spent) steam to the blast pipe and the smokebox.
Quick facts
Best for the job
Peculiar behavior
First use in England
First use in United States