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# An Improved Gas Cylinder

A gas cylinder stored at a much lower pressure
 (+5, -1) [vote for, against]

Instead of using 2,000 PSI gas cylinder with a very small volume and very thick walls, a bigger volume, smaller pressure cylinder could be used. The cylinder would be split by a moving disk, that seperated the two sections. The bottom section would be filled with R134/propane. The top section would be filled with the product gas. As the product gas was used, the pressure drops. This allows the disk to move upwards in the cylinder. As this happens, R134/propane evaporates, maintaining about 150 psi. By the time the cylinder was empty, it the disk would be at the top and nearly all of the R134/propane would be evaporated. When the cylinder needs to be refilled, just compress the product gas into the top, and the R134/propane will condensate, allowing the disk to drop to the bottom. Using the disk would allow all of the product gas to be used, unlike current high pressure cylinders where the remaining volume of product cannot be used.

The whole cylinder would be constructed of aluminum. The inside diameter would be 10 inches, which would add more stability. With a three foot tall cylinder, there would be 6.5 cubic feet of volume at atmosphereic pressure. If the cylinder was at 10 atm (~150 psi) 65 cubic feet of gas could be stored.

Aside from the improved safety, this gas cylinder would also eliminated the need for expensive high pressure regulators.

 — js_530, Aug 21 2005

Very good. Maybe store the propane in a flexible balloon-like membrane to avoid the complexity of the gas-tight sliding disc.
 — wagster, Aug 21 2005

Okay, lets say you've got an aluminum cylinder at 2000 psi with a 0.43" wall thickness. Drop the pressure to 150 psi, and (keeping the same height and capacity) you now need a diameter 3.65 times that for the high-pressure cylinder. You could probably get away with a 0.12" wall thickness. The result? Both weigh the same, but the low pressure cylinder is much bulkier and prone to damage.
 — ldischler, Aug 21 2005

Surely there would be situations (mainly in permanent installations) where this wouldn't be a problem and a steady 150psi without a regulator would be useful?
 — wagster, Aug 21 2005

// steady 150psi without a regulator //
Another problem is that the pressure is highly dependent on temp.
94 psi @ 60F
175 psi @ 100F
It doubles over a 40 degree range. Very bad!
 — ldischler, Aug 21 2005

? Why would I want a bigger gas cylinder? Surely the whole point of the gas cylinder is that it is compact, and thus is easy to transport and store and (by virtue of being pressurized) has a lot of gas in it. Can you give me some application where your cylinder would be better than a normal one?
 — moomintroll, Aug 21 2005

//Why would I want a bigger gas cylinder?// Maybe it would look more impressive that way.
 — wagster, Aug 21 2005

That's pretty amazing stuff [Pa`ve]. I'd have never suspected what was inside those tanks, and hearing it from you saves me the trouble of cutting one open. :-)
 — reensure, Aug 22 2005

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