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Why have I not seen this, yet?

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Why have I not seen this, yet?

Unread postAuthor: Hubb » Thu Jul 31, 2008 8:27 am

Recently, I've been planning a new project. Initially, I was going to build another combustion but I'm past due for a pneumatic. Last night, I thought of a way to use CO2 with PVC AND without a regulator.

Propane is usually ran through a meter to obtain the correct mix. Why not build a meter similar for CO2?

By using ideal gas law formula (P1V1=P2V2), it should be fairly simple to calculate the needed meter volume to fill a certain chamber to a certain pressure. Make sense?

Here is an example:
Chamber size - 2" Sch40, 24" long (75.36 in^3)
Desired pressure - 100psi
Meter Pressure - ~850psi
Meter pipe - 1"

100(75.36)=850V
7536=850V
8.8659 in^3

8.8659/(3.14*.5^2)
8.8659/.785
Meter length - 11.295"

Note: Appropriate safety precautions not included. Also, I've not taken into consideration the exact maths, such as atmospheric pressure, volume combinations, etc, either. This is just very basic.

Any thoughts?
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Last edited by Hubb on Thu Jul 31, 2008 8:40 am, edited 1 time in total.
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Unread postAuthor: CasinoVanart » Thu Jul 31, 2008 8:30 am

Sounds great. Why limit it to c02 though, its heavy right? Could the same idea be used for other gases?
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Unread postAuthor: Hubb » Thu Jul 31, 2008 8:38 am

Yes it could. HPA, propane (pneumatic), whatever. I just used CO2 because...well, it's CO2.
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Unread postAuthor: CasinoVanart » Thu Jul 31, 2008 8:43 am

hubb017 wrote:Yes it could. HPA, propane (pneumatic), whatever. I just used CO2 because...well, it's CO2.


Cheap, plentiful and easy to obtain... Gotcha :D
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Unread postAuthor: Hubb » Thu Jul 31, 2008 8:47 am

Not only that, but this may be an answer for all those shock pumps. You fill the low volume meter pipe to high pressure, then dump it into the chamber, cutting down on the pump strokes.
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Unread postAuthor: iknowmy3tables » Thu Jul 31, 2008 8:51 am

It's been mentioned before, but were are very concerned about the safety because if the first valve were accidentally left open when you were opening the second valve, this and the fact that the meter has to be made to take all the pressure of co2, it's just easier to buy a regulator
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Unread postAuthor: Hubb » Thu Jul 31, 2008 9:21 am

Finding a pipe to hold the pressure should not be a problem.

As far as safety goes, I've thought about this but did not mention it in the original post. A small burst disk would suffice. It can be set to rupture (say, 150psi) in case the first valve is left open.

A popoff valve may be an option, but it may not release pressure fast enough. It could be a primary safety, regulating the chamber pressure to 125psi (in case it's a little warm outside) and the burst disk a secondary safety, in case the valve is left open.

What about using the meter with shock pumps? It should be ideal for that situation.
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Unread postAuthor: DYI » Thu Jul 31, 2008 9:40 am

Sounds like a good way to get around buying expensive regulators to me. But if you're only filling a pneumatic and don't need such precision, wouldn't it be easier to just crack open the cylinder valve on the gas bottle, and close it when the chamber pressure reaches the right level? You'd need a safety either way, due to the use of an unsuitable chamber material, so why not skip the meter altogether?
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Unread postAuthor: Hubb » Thu Jul 31, 2008 9:45 am

Sounds like a good way to get around buying expensive regulators to me. But if you're only filling a pneumatic and don't need such precision, wouldn't it be easier to just crack open the cylinder valve on the gas bottle, and close it when the chamber pressure reaches the right level? You'd need a safety either way, due to the use of an unsuitable chamber material, so why not skip the meter altogether?


I considered that, as well, but, there would be a bigger chance of liquid getting into the chamber. This meter design will work as an expansion chamber to keep this from occurring. Not only that, but PVC tends to get brittle (even more so) when it's cold.
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Unread postAuthor: POLAND_SPUD » Thu Jul 31, 2008 12:27 pm

hmmm.. I think DYI is right.. of course it has some advantages but they are not good enough (esspecially if you are going to use PVC and 100psi)
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Unread postAuthor: Coodude26 » Thu Jul 31, 2008 1:36 pm

I think this would work, but it could be pretty dangerous. And a burst disk wouldn't make a difference, it's where the pressure is being released, not how much (although that also has a factor).

Out of curiosity, does anyone know how much PSI those little 12g cartridges are loaded to?
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Unread postAuthor: DYI » Thu Jul 31, 2008 1:43 pm

Out of curiosity, does anyone know how much PSI those little 12g cartridges are loaded to?


They're filled with liquid CO<sub>2</sub>, so the pressure they're at varies significantly depending on the temperature. They could get over 1000psi on a hot day.
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Unread postAuthor: Hubb » Thu Jul 31, 2008 2:43 pm

I don't think I follow, Coodude. The pressure is distributed evenly throughout the chamber. The addition of a safety burst disk (like the ones found on a common paintball CO2 tank) will cause it to rupture at a certain pressure, taking the stress off the chamber walls.

I guess a better term for it would be rupture disk.

As far as those 12 grams. They have just as much psi as any other CO2 tank. Generally, it varies between 800 and 1000 psi, but, like DYI said, that is solely dependent on the temperature (that would be the bottle temp and not the atmospheric temp, although they usually are one and the same).
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Unread postAuthor: psycix » Fri Aug 01, 2008 5:02 am

Besides a popoff and/or rupture disk, make sure the PVC does not freeze up.

Also, It may be a good thing if you used one 3-way ballvalve instead of two normal BV's (use the L-type, not the T-type). It not only saves time of opening/closing BV's, it it also makes sure the CO2 tank can never directly be connected to the PVC chamber.
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Unread postAuthor: Coodude26 » Fri Aug 01, 2008 2:47 pm

Sorry hubb, I meant "wouldn't" not "would". I fixed it.
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