The piston is fixed on top of the vertical shaft. The valving is underneath the base and driven with a small chain from one of the crankshafts.
Steam travels through the vertical shaft to raise the cylinder.
As the cylinder travels up and down it also rotates back and forth. The 3 pins on the cylinder slide through the heim joints on the crankshafts, to rotate the crankshafts. The cylinder is aluminum and the piston ring is Teflon. The Triangle Drive. Built in 1981, it has always drawn attention at shows.