The Kirkfield lift locks and the larger ones at Peterborough are engineering marvels of the 19th century. Notice the piston under the lock chamber on the right. The high chamber has 1 foot less water than the low one. When the lockmaster wants to raise the other chamber, a bit more than one foot of water is admitted to the high chamber so it weighs more than the lower one. A valve transfers water from the higher to the lower piston forcing it to rise. The valve is run by a 1/4 horsepower motor. Everything else is done hydraulically.