The purpose of a lock is to transition a marine vessel from one elevation to another. Following, is a brief description of a ship going from a higher elevation to a lower elevation. (The process is reversed for a ship going from a lower elevation to a higher elevation.)

1. The upper lock gates open, allowing the ship to enter the lock. Simultaneously, a filling valve opens and water from the higher elevation side enters the lock.


2. When the water in the lock and the water on the upper elevation side are somewhat level, the ship enters the lock.


3. After the ship is in the lock, the upper lock gates and the filling valve are closed and an emptying valve opens allowing the water in the lock to be released into the lower elevation side.


4. The lower lock gates are then opened allowing the ship to exit the lock and proceed having been successfully transitioned to the lower elevation side.