Peterborough Lift Lock, Trent-Severn Waterway
Peterborough, Ontario, Canada
I consider this to be an excellent example of clever design. Because of Archimedes’ principle, the weight of each water tank remains constant whether or not it contains a boat. The two tanks are balanced on hydraulic pistons whose cylinders are connected. Thus when one tank falls, the other rises. As a result, the power required to lift boats is merely that required to overcome a small amount of friction.
However, the best is yet to come. By stopping about four inches short of the extreme, a little water flows into the top tank; and an equal quantity of water flows out of the bottom tank. The resulting imbalance is all that is required to drive the lift lock to the other extreme! And unlike conventional locks, only a tiny amount of precious water is lost.