Timeline for How to emulate 40ft (12 m) of water?
Current License: CC BY-SA 3.0
19 events
| when toggle format | what | by | license | comment | |
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| Jul 4, 2015 at 5:12 | comment | added | Dr Xorile | That's why it's impressive. The water jet, with some abrasive material, cuts through pretty much anything. | |
| Jul 4, 2015 at 4:20 | comment | added | John Rennie | @DrXorile: compressing water by 20% would require a pressure of over 4,000 atmospheres. For comparison, the pressure at the deepest part of the ocean is only around 1,000 atmospheres. While I'm sure a 20% compression can be achieved, this hardly an everyday phenomenon. | |
| Jul 4, 2015 at 3:44 | comment | added | Dr Xorile | We have a water jet at work, and the pumps compress water by 20%(!) Random thought in response to water being incompressible... | |
| Jul 1, 2015 at 20:01 | review | Suggested edits | |||
| Jul 1, 2015 at 20:25 | |||||
| Jul 1, 2015 at 18:03 | comment | added | supercat | ...then letting go would cause the 1lb weight to accelerate significantly much longer. The acceleration would drop off as the object moved, but even after the weight had moved five feet it would still be accelerating at 25g. Compressing liquids is much safer than compressing gases because, in case of failure, the liquid won't have to expand very much to release all the pressure. | |
| Jul 1, 2015 at 18:01 | comment | added | supercat | To understand the difference between water and air, imagine hanging a one-pound weights from a ten-foot bungee cord and a ten-foot nylon rope, pulling down on those weights with 50 pounds of force, and then releasing them. If the 50lbs of force stretches the nylon rope by an extra inch, then letting to will result in the 1lb weight accelerating upwards at 50g, briefly, but once it has moved an inch the rope will no longer be under tension. If the 50lb of force stretched the bungee cord ten feet, however... | |
| Jul 1, 2015 at 17:14 | comment | added | Phil | This is the process for hydroforming. | |
| Jul 1, 2015 at 14:30 | comment | added | John Rennie | @LightnessRacesinOrbit: in practice there is some compliance in the walls of the tank and that's where most of the pressure is stored. It's like inflating a balloon with water - the water is under pressure even though it hasn't been compressed because you've stretched the walls of the balloon. In effect you would be inflating the metal tank slightly. | |
| Jul 1, 2015 at 12:12 | comment | added | Lightness Races in Orbit | @DavidRicherby: I suppose the force is still there even though (or even "more so since") the water itself doesn't absorb it by compressing? [I'm not a physicist :P] | |
| Jul 1, 2015 at 12:05 | comment | added | Level River St | @paul no he doesn't, he can use a sealed tank like John said, but he should use a water pump not an air compressor to pressurize it, and make sure he eliminates all air. That way he won't kill himself. My job involves testing pressure vessels, I know what I'm talking about. The feasibility of this approach depends on the size of the robot that he would want to put inside the vessel. Hence my comment on the question. Otherwise he might just as well find the nearest dam and dangle the robot off it. | |
| Jul 1, 2015 at 11:59 | comment | added | paul | @steveverrill you completely missed the point about pressure being necessary. To do this without air pressure he needs a 40 foot deep tank, which he says he doesn't have. | |
| Jul 1, 2015 at 11:57 | comment | added | David Richerby | @LightnessRacesinOrbit Pressurized water is exactly what you'd get by, say, being 40ft below the water's surface. | |
| Jul 1, 2015 at 11:52 | comment | added | Level River St | @LightnessRacesinOrbit pressurized water is water under pressure. But with the same density as water that is not under pressure. Unlike air, which when pressurized has the tendency to compress (it reduces its volume and increases its density, which causes it to store a lot of energy.) | |
| Jul 1, 2015 at 11:49 | comment | added | Lightness Races in Orbit | Hang on... if water doesn't compress, then what is "pressurized water"? o.O | |
| Jul 1, 2015 at 10:58 | comment | added | Level River St | John, well edited. @DavidRicherby, using water and eliminating all air (if done properly) massively reduces the (considerable) risks. Some of the first Dehavilland comet aeroplanes suffered explosive decompression due to a design fault with the windows (they were square with sharp corners.) The accident invesigators filled an entire plane fuselage with pressurized water to investigate the problem. This was relatively safe, despite the fact the fuselage was not designed for this, but would have been extremely inadvisable with air. en.wikipedia.org/wiki/BOAC_Flight_781 | |
| Jul 1, 2015 at 10:43 | history | edited | John Rennie | CC BY-SA 3.0 |
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| Jul 1, 2015 at 10:38 | comment | added | Level River St | Air at 1.2 atmospheres =18 psi = 120kPa can store a considerable amount of energy, about 120J (equivalent of dropping a 12kg weight 1m) per litre of air (at a pressure of 12.2 tonnes per square metre!) You could have a significant pressure explosion. An air tank under these conditions in Europe would require certification if sold commercially. Don't use a compressor, use a water pump instead, and eliminate all air from the tank. Water doesn't compress so it doesn't store energy, and doesn't explode when released. Engineers prefer to test pressure vessels with water than air for safety reasons. | |
| Jul 1, 2015 at 10:23 | comment | added | David Richerby | I guess I don't need to mention that working on pressure vessels requires special skills and shouldn't be done unless you know what you're doing. But I'll say it anyway. | |
| Jul 1, 2015 at 8:16 | history | answered | John Rennie | CC BY-SA 3.0 |