Where can I buy a small pressure vessel under $200?

[stuffandthings]

I'm doing a science fair to investigate the effect of air pressure on the efficiency of a Stirling engine. Since it is extremely difficult to built a pressurized engine, I want to increase pressure by operating the Stirling engine in a pressure vessel; the pressure vessel must be five inches in diameter and ten inches tall. I would either increase the temperature by heating the vessel or by increasing the amount of gas in the vessel. (I will do whichever seems easier, as I can adjust other variables to compensate for increasing ambient temperature.)

So far, I haven't been able to find many pressure vessels for sale, and the ones I did find were out of my budget. Where could I buy a small pressure vessel?

[rmarz]

stuffandthings - Some things were left out of your requirements. What kind of pressure are we talking about? Ten PSI, a hundred PSI? Also your description seems to suggest that you want your Sterling engine "inside the pressure vessel". I guess that is the reason for the unique size, and it suggests that you must have a 5" opening to access the inside of the vessel. This automatically rules out compressed gas cylinders as candidates. A large cooking "pressure cooker" may work. These could cost up to $50. You might have to do some modification like the addition of a Schrader type valve to hook it to a bicycle pump or compressor. These cooking pressure vessels typically are protected to between 10-15 PSI above ambient pressure (also referred to as gauge pressure, or PSIG).

Always a caution, you are working with potentially high pneumatic pressures and could be exposed to explosive forces if limits are exceeded.

Rick Marz

[stuffandthings]

rmarz
I forgot to mention, I'm looking for close to 100 psi. I would need a bare minimum of 50 psi.
I managed to find many gas cylinders with diameters of greater than 5". Is it possible to "open" a gas cylinder (after depressurizing it of course)?

Thanks for the response.

[rmarz]

stuffandthings - You can consider something like schedule 80 PVC pipe that is available in 4" and 6" diameters. Specifications rate it around 290 PSI at room temperature. There may be end caps and threaded fittings and plugs that might work for you. I'm a bit leery of using something like this at high pneumatic pressures (as opposed to hydrostatic applications), but you might check with a supplier about your application.

Rick Marz

[stuffandthings]

I researched into that, and I don't want to take the safety risk.
I found a "pressure closure only" for $89. Would it work?

Here's a screenshot from the file the supplier gave me:
http://postimg.org/image/tkzayg3yp/

[rmarz]

stuffandthings - I believe this is just the closure fitting for a standard pressure vessel like a "Cornelius" tank used by carbonated beverage systems. See attached photos and research "Cornelius tanks". I use these frequently and they would be much safer than trying to assemble a PVC tank, but your physical entrance is limited to the roughly 3"x4" oval opening. The tanks are rated for 100 PSI working pressure and burst limits are much higher. I have stored them for weeks at a time pressurized at 100 PSI, but I wouldn't go any higher than that. The tanks are manufactured of stainless steel and quite rugged. They are about 8" in diameter and 30" tall. You can purchase proprietary pressure connectors (usually specified as Coke or Pepsi) and can be connected to plastic tubing to attach to air compressors or other air sources. I have bought them, used, on eBay for between $25-50 each, but you might call a local supplier of beverage distribution systems for a used tank and material. Also check local suppliers to home beer and winemakers. Good luck. Use safety glasses, gloves and an abundance of caution when working with this kind of equipment.

Rick Marz

[rmarz]

stuffandthings - Forgot to add a photo or link. Here is a typical ad for this kind of equipment.

Rick Marz

http://www.homebrewing.org/5-Gallon-Cor ... _p_70.html

[stuffandthings]

Thanks!

[stuffandthings]

Is the 100 psi limit absolute pressure or is it 100 psi relative to the atmosphere (114.5 psi in absolute pressure)?

[rmarz]

stuffandthings - Working pressure is 100 PSIG, relative to 1 atmosphere, so absolute pressure is 114.5.

Rick Marz

[stuffandthings]

I know I'm reviving a dead post here, but I've been getting mixed response to taking a Corny keg that high. I've already decided to take it no higher than 6 bar, but even that seems controversial.
I'm using an AEB keg, and I've heard these are better quality than the Chinese ones.
In any case, it would be completely safe if the relief valve was functioning, so I've decided to test the relief valve by pressurizing the keg until the valve (hopefully) opens.

I'll be standing far away inside a building while I do this.

[rmarz]

stuffandthings - The problem with testing the pressure relief valve to the point of it releasing is that you don't know if the keg will fail before that point or if excessive pressure will weaken or damage the vessel. The working pressure is 100 psi, so you should be OK in that the manufacturer certainly has tested the design with a margin above that. If you want to take it to say 110 psi, (above working pressure, but below max rated pressure) do the test somewhat hydrostatically. By that I mean, fill the keg with water so that the high pressure air is a relatively small volume and if you burst a seam or other part of the keg, the energy of the small volume of high pressure air will cause very little damage. This is the way very high pressure tanks (3000 psi tanks for welding and industrial purposes) are tested. A gas is not used, a liquid, which is not very compressible is taken to very high pressure and if the tank fails, it is just a small spray of liquid for a short time. Be safe, be careful and try to operate at a pressure below the operating pressure for an extra measure of caution.

Rick Marz

[stuffandthings]

The high cost and the potential safety hazard of the experiment caused me to change my topic.