 Brownill's innovation was to place wedges ("inclined planes") opposite the upper and lower fixed openings so that as the main caisson moved into place, powered by water being added or released from the counterbalancing caissons, rollers acting against the wedges forced it against a padded frame surrounding the opening.The "conductor" was to have control of a lever to release the rollers when the vertical gates were slid shut for the next ascent or descent.No commercially successful example has ever been built.