How Navigation Locks Operate

These diagrams show how a ship is lowered in a lock. A ship is raised by reversing the operation. No pumps are required; the water is merely allowed to seek its own level.

With both upper gates and lower gates closed, and with the emptying valve closed and the filling valve open, the lock chamber has been filled to the upper level. The upper gates are then opened, allowing the ship to enter the lock chamber.

Now the ship is in the lock chamber. The upper and lower gates and the filling valve are closed. The emptying valve has been opened to allow water to flow from the lock chamber to the lower level.

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With the water level in the lock chamber down to the lower level, the lower gates have been opened, and the ship is leaving the lock chamber. After this, the lock is ready for an upbound ship to come in and be lifted, or may be filled to lower another downbound ship.