Checking a C02 Build, looking for input

[gungecko]

Looking to start designing a first Co2 sourced cannon.

attached is a drawing(poorly) roughly of what I am thinking of doing.

Right now I expect to utilize a 3 way valve to facilitate the Primer section of the QEV which will fill to a reservoir under the Atmosphere from a larger (10lb) regulated co2 tank at 200-300psi. prior to making this jump I referenced the awesome chart on the 12g co2 guide to build a ball valve prototype but I understand that is currently filling a 2Ci expansion chamber at closer to 800psi. this has helped me be a little more familiar with the properties of Co2. while the 12g carts are great and easy to work with they produce a lot of waste for the amount of use I would like to put this through, not to mention expensive since I plan to put 50+ shots through it in a weekend. yes this is for paintball and similar applications.
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My concerns are the following, and here is where my inexperience in more complicated builds comes in :

1. Are there going to be issues using a electric 3 way valve or QEV with a C02 source. this will be triggered using a reed switch so it is a 12V Dc switch.

2. is my reservoir too small at the 10Ci to launch tennis ball sized/mass objects, I am thinking of utilizing a 24" barrel.

3. I would really like it if the reservoir would stop filling when the pressure is equal between the fill line and itself. what do i need to incorporate to fulfill that condition?
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Previously I have done a few LPA builds with modified sprinkler and electric solenoid 2 way valves. but 3 way feels like a good jump up to allow me to fill from the 3 way and also trigger the primer. in my research I probably need to incorporate a check valve on the fill line.

As always Proper Planning Prevents Poor Performance

What am I missing or overlooking?

Thanks,

[quinn whitsitt]

that is great quick question does it work with air too