The Double-Acting Cylinder: Push With the Bore, Pull With the Ring

Bramah's press and the hydraulic jack push one way and let the load fall back. Most machines need power in both directions: a digger's arm, a tractor's lift, a press that must open as well as close. The double-acting cylinder has a port at each end, so oil drives the piston out and oil drives it back. The rod makes the two directions unequal. Pushing uses the whole bore; pulling uses only the ring round the rod. That one fact decides a cylinder's forces and speeds, hides a pressure trap that can burst a hose, and — with a long stroke — lets the rod buckle long before the oil runs out of pressure. This rung works all three out and builds a double-acting cylinder from a syringe to measure the difference.