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TheHow7zer 02-09-2013 12:25 PM

What volume of gas does a 12 gram put out?
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I have this expansion chamber from a vm68 and was wondering how much air it can hold at a time. I want to use it as a compact semi-air source, my plan is to have the expansion chamber in the marker with a one way valve of some sort (check valve?) between it and a 12g changer.

My hope is that with the expansion chamber I will be able to hold more than 30 shots worth of air while being able to pop in a new 12g before running out of air without dumping what is in the ex chamber.

Skibbo 02-09-2013 12:51 PM

Quick google search brought this up:

"12g CO2 x 1mole CO2/44gCO2= 0.2727mole CO2

V=[(0.2727mole)(0.0822)(293)]/1atm = 6.57LCO2"

TheHow7zer 02-09-2013 01:38 PM

That still doesn't help me figure out if it could hold a 12g. I don't know what its volume is

dano_____ 02-09-2013 02:00 PM

I am sure it can hold a 12 gram, however it can't hold a 12 gram at the same pressure as it would coming straight from the 12 gram. The pressures will equalize between the two causing a drop in pressure in the 12 gram. So a one way valve will hold some pressure in. However, since the pressures will be equal in the 12 gram and chamber, you will lose some of your volume when you unscrew the 12 gram. Basically you will never be able to utilize more than an extra half of a 12 gram with the gun provided you install and shoot an entire 12 gram with the chamber.

big jim 02-09-2013 02:03 PM

The problem is that you don't push the CO2 from the 12 gram to the ex chamber. When you open the 12 gram to the chamber the gas simply spreads out to provide an equal pressure in both reservoirs and results in a lower overall pressure in both places. By using the exp chamber you will be able to have a few shots when the 12 gram is removed but you will lower your overall efficiency and have fewer shots in the long run. How much depends on the volume of the exp chamber.

Dang you Dano, I type to slow.

agentSmith 02-09-2013 03:49 PM

So, instead of equalizing it from a 12gram, you should use a larger co2 tank like a 7 or 9oz.
If you screwed the expansion chamber into a tee from the gun and put a quick disconnect fill nipple on the last port, it should work fine and give you more shots.
Then you could use a short fill whip hose to charge it.

The check valve to keep the gun gassed is in the fill nipple in this case.

In a pinch you could leave the hose on and shoot from the tank.


TheHow7zer 02-10-2013 10:03 AM

Using a larger co2 tank would kind of defeat the purpose of using the expansion chamber. My plan is to use it as a compact tank. At that point I might as well just use my 13cu tank

Manning 02-13-2013 01:08 PM

I think he means fill your expansion chamber from a larger tank rather than trying it from a 12g.

GoatBoy 02-20-2013 07:18 PM

Couldn't help but LOL at this one. LOL@SCIENCE.

Back-of-envelope calculation: if your gun consumed 0.25g of CO2 per shot, you would need 7.5g of CO2 for a 30-shot reserve. Might work, assuming your expansion chamber does what an expansion chamber isn't supposed to do -- and that is, pool up CO2. Otherwise, you have to go with straight volume of CO2 compressed that's still gas and not the liquid, and for 30 shots, I'm reasonably sure you're not going to like the answer.

Ignoring that, once the two go online, your shots will draw from them both the expansion-chamber-that-isn't-behaving-like-an-expansion-chamber and the 12g equally, if not from the expansion chamber slightly first thanks to the check valve.

So the fun begins: how do you know when it's time to change a 12g? Just because you took 30 shots didn't mean you took 30 shots out of the 12g. Half of those shots may have come from your reserve expansion chamber (probably more), and half from your 12g, so if you change, did you just waste half the 12g?

Manning 02-20-2013 07:38 PM

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