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HOW NAVIGATIONAL LOCKS OPERATE ‘These diagrams show how a ship is lowered in a lock—a ship is raised by reversing the operation. No is its own level. With both UPPER GATES losed, UPPER GATES OPENS Lower Gates cose id with the EMPTYING VALVE closed and the FILL- ING VALVE open, The UPPER GATES hav the ship to enter the LOCK CHAMBER, R GATES CLOSED. _ Lower cares c.oseo Now the ship is in the LOCK CHAMBER. The UPPER GATES and the FILLING VALVE have beer! closed, = the the EMPTYING VALVE opened to allow nt to ration from the LOCK HAMBER to the LOWER EL. The water level in the LOCK UPPER GATES CLOSED. LOWER Gates OPEN~ downbound ship. Courtesy U.S. Corp of Engineers mps are used after the close of navigation in order to remove the water, iran the locks. Considerable maintenance work is done during winter, when rea waters are frozen over and steamboat whistles are no longer heard on the busy waterway. 5