 Once the vessels are secured, all gates are closed and the crossover valve in the connecting pipe between the ram shafts is opened.Since the upper caisson weighs more than the lower caisson (1,844 vs 1,700 tons), it pushes down on its ram, forcing out water from its shaft via the connecting pipe into the shaft of the bottom caisson.The force pushes up on the bottom caisson's ram, raising the caisson up to the top position.