The lock has two identical bathtub-like ship caissons in which vessels ascend and descend. Both caissons are enclosed at each end by pivoting gates, and there are pivoting gates at the upper and lower reaches of the canal at the junctions with the caissons. The gates on the caissons fit into slots on the gates on the reaches, so that they open in unison.
Each caisson sits on a ram, the shafts for which are sunk into the ground, are filled with water, and are connected with a pipe that has a crossover control valve. The caissons are guided up and down on either side by rails affixed to concrete towers.
The caissons are 140 ft. (43 m) long, 33 ft. (10 m) wide, and 7 ft. (2.1 m) deep, and when filled with 228,093 imperial gallons (1,036.93 m3; 1,036,930 l) of water, they weigh 1,700 short tons (1,500 t).
No external power is needed: the lift lock functions by gravity alone using the counterweight principle. One caisson always ascends and the other always descends during each locking cycle. When one caisson reaches the top position, it stops 12 inches (30 cm) below the water level of the upper reach, and the control valve is closed; Siemens ultrasonic sensors are used to help determine the differential. The upper reach and top caisson gates open, and water flows into the top caisson until the level equalizes. The weight of the extra foot of water is 144 short tons (131 t), making the total weight of the upper caisson 1,844 short tons (1,673 t). Any vessels that just ascended in the top caisson exit into the upper reach, and any new vessels making a transit of the lock then enter the bottom or top caisson from the lower or upper reach respectively. 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. When the gate of the newly descended top caisson and lower reach gates open at the bottom, the extra foot of water flows out and equalizes with the water level in the lower reach of the canal, and any descended vessels exit, allowing the cycle to start over again.
The Lockmaster took us on a tour of the facility and let us go into the chamber room where the main control valve sits and also the hydraulic cylinders that operate the pan gates on the top side. They were very informative and spent at least an hour telling us about how the lock works, what modifications were made to bring it into the 21st century, and showing us the inner workings of an engineering marvel.
Later this evening, we went onboard Gypsy Spirit with Dash Away and Miss Norma to celebrate a birthday for the admiral of Gypsy Spirit. Bratwursts were cooked on the grill; Texas caviar with a salad and a drinkwere added. Then, to top it off, we heard an amazing story about how the name Miss Norma has become the name of a book, written by the crew of Miss Norma, and can be found on Amazon under the title of Driving Miss Norma. Check it out.
That's the news and here are some views:
Bike trail to Lift Lock
Riding along the Levy toward the Lock
Topside of Lock 21
The right side "bathtub"
Great view from on top of the Lock
Looking down from above
Left Pan Up, Right Pan Down
Here is a time lapse video of today's locking from the top
View from the bottom
Lock Control Station
Back at the Marina
Fellow Loopers
Chill'n -n-grill'n onboard Gypsy Spirit
Birthday Girl
Telling Tall Tales
Bedtime for puppy
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