How to simulate water pressure at depth

1 yes 2 Only if you already have a boat and live near the water. 3 No
But I would suggest using something more like a dead weight tester
instead of air. That is using a piston to pressurize the paint pot or whatever. The reason is stored energy. Lots of energy with compressed air. Very little stored energy using a piston like a master brake cylinder to pressurize the tank. Also if you have a leak you might be able to realize it sooner.
Dan
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like a dead weight tester instead of air. (clip) The reason is stored energy. Lots of energy with compressed air. (clip) ^^^^^^^^^^^^^^^^^^ If you have air available, and you know how, you can do it safely. Have a small volume of air in contact with the water, connected to the supply through a small orifice, or a nearly closed valve. If you get a rupture in the test vessel, the pressure will drop, and air will only hiss from the supply. (The danger from high pressure gas or steam exists only if there is a substantial volume which can explode.)
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If you keep the chamber full of water, and then pressurise it with air, the only air in the system will be that in the pipe between the chamber and the compressor. The volume will be minimal, and as the stored energy is porpotional the the product of the pressure and volume of the gaseous part only , very little energy will be stored.
Tom
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snipped-for-privacy@hotmail.com wrote:

You could do worse than to look at the leak testers that the watchmakers use. Mostly they test under a vacuum condition while submerged in water. The leak tester has a clear pane or a bell jar that allows the watch to be seen. The watch is submerged and a vacuum is drawn, and the repairman looks for bubbles escaping. If any are seen, they are duly noted and the watch is removed before it can absorb an appreciable amount of water through the venting gaps. Repairs are then made to the seals, etc. Some testers subject the case of the watch to air pressure first, for a period of time, then submerge them and observe for bubbles.
I like the simplicity of the long rope and a lake idea, myself, though it makes it a bit tougher to determine the actual failure mode or point.
Cheers Trevor Jones
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A bit back a friend of mine used to dive, he explained that to test the air bottles they were filled with water (pressurised)the air bottles were placed in a tank full of water to contain any faliures. If you want to test your enclosures this might be a way as you'd fill the enclosure with water under pressure and see if any came out, rather than setting up a 140' tank in your living room to see if any went in.
Just my 2cents (though, I spend pounds!)
Lee
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snipped-for-privacy@hotmail.com wrote:

Normal pressure cookers only go to 15psi, but that is steam so there has to be a good safety margin built in. Just be aware you are overpressurizing the vessel and be prepared for catastrophic rupture.
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Thanks for all the responses. It's nice to get a couple different viewpoints and suggestions.
-M
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snipped-for-privacy@hotmail.com wrote:
[...]

Dunno if this is appropriate to what you're doing, but waterproof watches are tested with vacuum. They suspend the watch in a small container full of water then draw a vacuum and look for bubbles. Has the benefit of keeping the innards dry if there's a failure. Of course, that's backwards from what you're doing, and only puts out a single atmosphere at best, but they certify watches to 100M or so doing it.
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I think the final answer is a 2-1/2 gallon pressure paint tank from Harbor Freight because:
1) It has a good size opening 2) Can take the pressure (80psi) 3) Affordable ($80 US) 4) AND they have a store a one mile away from my house :)
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber7515
Again, thanks for the suggestions.
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snipped-for-privacy@hotmail.com wrote:

The traditional approach is to take a 16" surplus naval shell and make it into a pressure vessel. Doc Edgerton used one to develop all the underwater cameras for Cousteau. He got a good deal on the shells after WWII and his company then sold them for others to use. They have an 8" left hand threaded plug in the back end, and will handle pressures as high as the ocean can deliver. I used his setup for my thesis work on underwater radio.
Doug White
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    I work with underwater vehicles all the time (We do R&D on sonar systems) and the way we check for leaks is to draw a vacuum inside the vehicle and let it sit as long as possible and see if the reading changes. The less obvious advantage of this is that we can back fill with dry nitrogen and not have to worry about condensation when the vehicle hits the cold water.     We do have a fancy pressure test facility that tests for structural integrity, but most of our shells are rated for at least 1200 feet. You might be surprised how little aluminum it takes in a properly designed shell to be rated for 1200 feet. I would think that as long as you design your hull to hold pressure and are just worried about the o-rings and other seals the vacuum test might work.
-Kris
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Yes I used to work with underwater gear and we used to drill and tap and install threaded valve in main housing then pull a vacuum with a handheld pump. Then used to leave it and watch gauge. If its air tight it will certainly be water tight Martin
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Sorry for the delayed reply but I haven't kept up with the newsgroups lately. I had some thoughts of building a tethered or radio control submarine camera setup. The thought I had was to fill the submarine with air pressure equal to or greater than the water pressure. One way would be to build it to handle pressure (PVC pipe?) and air it up to a little more pressure than it needs, perhaps 35 - 50 psi in your case. Another idea would be to have an air tank inside and a pressure sensor. If the external water pressure was greater than the inside pressure, crack a valve to let some air pressure inside the submarine. Good luck!
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I don't think that air would work well. The gas should probably be dry nitrogen to prevent fogging of lenses and condensation on internal parts.
The cases of fish sonars and other equipment is often purged with nitrogen to eliminate the air moisture.
WB .................

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