The mechanism was operated from the top level. For a descent, the box was first wound into its upper position using a double rack-and-pinion mechanism, then drawn tightly against the frame of the opening using a ratchet mounted on the top of the wall. The outer door was then drawn up with another rack-and-pinion. At this point the water levels in the top pound and inside the box would have been roughly equal, but as the inner door – the box door – swung outwards horizontally (like a normal single lock gate) it would not open if the outer level was to any extent higher. A small equalising cock was therefore provided. The door was opened, the boat was floated in, the doors closed and the ratchet released. Because the entering boat would displace its weight of water back into the pound, the total weight of the box was always the same and no great endeavour was needed to wind it up and down. However, the operators could release a little water into the box to assist the descent. Water pressure against the outward-opening doors kept them firmly closed and watertight.