Talk:Caisson lock

More detail please
What an amazing piece of engineering. One thing that is not clear from the article is how water is retained in the cistern. Clearly the caisson decends to the bottom of the cistern. I assume that there is a door at the bottom of cistern to match the door in the caisson. Is this true? How does the caisson seal against the cistern to prevent water escaping? 203.23.210.116 22:25, 10 October 2006 (UTC)

Diagram
Is the diagram right? AFAIK the caisson couldn't be lifted above the water level, because of the weight of the ballast. Instead, the chamber wall was built higher than the water level in the top pound, and filled right up. There was an opening, normally closed by a guillotine-style door to keep the water in, into the top pound. Only when the caisson was in place tightly against the frame of the outer door, and a little air pumped into the space between them to equalize the pressures, was the door wound up to admit the descending boat. The same thing happened at the bottom: the increased water pressure improved the seal between the caisson and the door frame but the doors were forced solidly closed until air was pumped between them (at a higher pressure, of course). The pump was in the caisson and operated by the boat crew. Does any of this make sense? I can't draw, otherwise I'd try to fix it  ––Old Moonraker

Well the one existing diagram is a little unclear but looking at it again It appears you are right. I'll fix the diagram.Geni 11:03, 13 October 2006 (UTC)
 * Added the above information, but disregarding the stuff about air pressure: Equalisation was achieved just by opening and closing taps/faucets.  ––Old Moonraker 15:24, 13 October 2006 (UTC)
 * I've managed a tweak on Geni's caisson lock diagram to show the full-height cistern, as suggested. I've also simplified the labelling. May I upload it and try it in the article (full attribution to the original source, licensing as before, of course)? If it doesn't work I'll take it out Old Moonraker 11:22, 28 October 2006 (UTC)
 * Fine by me - I've left a note on User:Geni's talk page as the original creator.&mdash; Rod talk 11:28, 28 October 2006 (UTC)

Caisson/cistern
I had to check on this as I was confused as well (see edit history). Originally "caisson" meant a water-tight box and "cistern" was a underground water storage chamber (not in the loft, as now). To our minds today this seems strange, but only because of the modern engineering use of "caisson" to mean a vertical, water-tight tower used underwater for excavations, concrete-pouring etc. It's the vertical, water-tight tower bit which would cause anyone a bit of doubt! Old Moonraker 19:11, 13 October 2006 (UTC)


 * The names make more sense if you think of this as an underwater boat lift.Geni 01:27, 14 October 2006 (UTC)

Unmanned?
Although the article does not state anything on the subject I take it all the tests and also if the plan had gone ahead would have been an unmanned vessel? I know I wouldn't want to be entombed in water with the chance of mechanical or structural failure, not quite the same as getting stuck in a lift. Boothferry (talk) 15:57, 1 January 2011 (UTC)
 * As it's currently written, the penultimate test had the vessel carrying 60 people, and the final failed test (see the Abandonment section) was with a boat carrying a group of investors. So, it seems the vessel was manned, and I presume that was the intention had the project proceeded. (I would imagine it's easier to get the boat out of the caisson if it's already got someone aboard.) --David Edgar (talk) 19:30, 1 January 2011 (UTC)


 * Yeah but christ I wouldn't fancy it! I'd get off at the top and back on at the bottom. Barges aren't too hard to drag around with ropes. Who fancies a trip in a massive leaking coffin to the bottom of a 50ft tank? I might imagine investors, who've put a lot of money into the thing, might see the point of demonstrating how reliable it was. And I suppose hydrophobia wears off after enough time working on boats, but that's not a job for me! 188.29.165.134 (talk) 02:47, 27 November 2013 (UTC)

Dubious claim in lead.
The lead section claims, "... a conventional boat lock, which required a volume of water equal to a boat and its cargo weight for each lock used in a flight between levels."

The citation given fails to mention the claim so is an invalid cite. In any case it isn't true. The volume of water required to operate a conventional lock is the difference of the water volume of the chamber between the two water levels less the water displaced by boats and their cargo. Further, in a flight of locks, only one such volume is required regardless of the number of locks in the flight, just as that same water volume operates a series of locks for the same boats. 109.153.242.10 (talk) 17:09, 21 January 2012 (UTC)
 * It's been taken out a couple of times already—striking it once again. --Old Moonraker (talk) 07:50, 22 January 2012 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified one external link on Caisson lock. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added archive https://web.archive.org/web/20061011094639/http://rtjhomepages.users.btopenworld.com/caishist.html to http://rtjhomepages.users.btopenworld.com/caishist.html

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 01:51, 29 July 2017 (UTC)

"Comparison to boat lifts"
I'm not sure why it mentions that boat lifts need engines to lift them, I have never seen a single operating lift-lock that requires an engine to lift the chambers. All the ones I have seen use a counterweight system in which more water is put in at the top than the bottom, and lifting force is provided via hydraulic ram or cables where the heavier of the two chambers pulls/pushes the other up as it descends. I think that section needs to be looked into more deeply. — Preceding unsigned comment added by 70.76.56.93 (talk) 13:33, 1 March 2020 (UTC)

Uncited material in need of citations
I am moving the following uncited material here until it can be properly supported with inline citations of reliable, secondary sources, per WP:V, WP:CS, WP:IRS, WP:PSTS, WP:BLP, WP:NOR, et al. This diff shows where it was in the article. Nightscream (talk) 14:45, 26 April 2022 (UTC)


 * The article now doesn't make sense as the section on abandonment makes reference to content that you've removed. 87.75.117.183 (talk) 01:07, 18 March 2023 (UTC)

History
The proprietors of the Kennet and Avon Canal Company had inspected Weldon's device. The Somerset coal field was opening up, and was to be served by a Somerset Coal Canal feeding into the wider canal system by means of the Kennet and Avon, whose owners would greatly benefit from the development. However, the Somerset Coal Canal suffered from serious water supply problems at Combe Hay; and the Kennet and Avon Company suggested Weldon's innovation as the solution. Three caisson locks were proposed, each to be 80 ft long and 60 ft deep and containing a closed wooden box which could take the boat. This box moved up and down in the 60 ft deep pool of water, which never left the lock.

Method of operation
A vertically sliding outer door sealed the lock chamber from the top pound and kept the water in.

The mechanism was operated from the top level. For a descent, the box was first wound into its upper position using a double rack-and-pinion mechanism, then drawn tightly against the frame of the opening using a ratchet mounted on the top of the wall. The outer door was then drawn up with another rack-and-pinion. At this point the water levels in the top pound and inside the box would have been roughly equal, but as the inner door – the box door – swung outwards horizontally (like a normal single lock gate) it would not open if the outer level was to any extent higher. A small equalising cock was therefore provided. The door was opened, the boat was floated in, the doors closed and the ratchet released. Because the entering boat would displace its weight of water back into the pound, the total weight of the box was always the same and no great endeavour was needed to wind it up and down. However, the operators could release a little water into the box to assist the descent. Water pressure against the outward-opening doors kept them firmly closed and watertight.

At the lower position the process was reversed. Here the water pressure was strong enough to press the box tightly into position against the exit opening. Another rack and pinion (again operated from above) lifted the outer gate, the levels were equalised again, the inner door on the box was swung open and the boat floated out. Apart from the inevitable small leakages, no significant amount of water had been used in the process.

Comparison to boat lifts
The caisson lock may be considered as a submerged form of the boat lift, with which it was approximately contemporaneous. Each has both advantages and disadvantages, for the engineering of this time.

The disadvantages of the caisson lock are the need to provide a sealed, submerged and safe caisson – especially if the crew or even passengers remain on board.

The caisson lock can however be powered, and the caisson lifted, by buoyancy alone. Pumping ballast water in and out of the caisson is enough to float it up or down the lock chamber. The weight of ballast water is approximately that of the canal barge being lifted. The boat lift though needs a mechanical lift system. In most vertical lift systems, this must also lift or lower the weight of the caisson and its water contents as well. This is substantially more than the barge alone, and the power to lift it is supplied mechanically. At the time of their development, the steam engine was in its infancy. Steam engines had been developed as water pumps, but not yet for the supply of mechanical power (see rotative steam engine). Given the engineering constraints of the time, lifting an enclosed caisson by buoyancy was more practical than driving a boat lift.

Small boat lifts could have driven by water supply or pumping between two balanced cars. Practical examples of these though were no bigger than a vertical funicular, used to lift small mine trams.

Dimensions as built

 * height: 20 m
 * width: from 3 to 6 m
 * length: 27 m
 * toothed rack: 14 m
 * rotation: approximately 7 minutes

Tests

 * No 1: February 1798: cracks
 * No 2: June 1798: success
 * No 3: April 1799: success
 * No 4: April 1799: success
 * No 5: April 1799: success, transport of 60 passengers
 * No 6: May 1799: box jammed by a projecting stone

Other installations
No commercially successful example has ever been built.

Is? Or was?
The first paragraph uses present tense suggesting that in some senses such a system is still in operation. I would suggest changing is to was... Lawrence18uk (talk) 05:24, 14 May 2023 (UTC)