Chamber & Barrel length

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Postby bigfoot42 » Wed Jul 30, 2003 12:10 am

I have never built a pneumatic gun before and I was wondering what lenght of chamber works well. I already have 9' of 4" pipe left from my combustion gun so I am going to use that for my chamber but how long should it be. Also, how long of a barrel should I use.
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Postby boogieman » Wed Jul 30, 2003 12:14 am

ok, answer these quesions:
1. what type of compressor/pump do you have?
2. do you want it powerfull as heck, or how powerful?
3. what do you want to shoot?
4. do you know what type of valve you will be using?

this info will help us help you with the chamber length.
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Postby PCGUY » Wed Jul 30, 2003 12:15 am

^^ What he said ^^
Site Admin
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Postby bigfoot42 » Wed Jul 30, 2003 8:07 am

1. air compressor with over 100 psi
2. not overly super powerful but impressive
3. potatoes and anything else that fits in a 2" barrel
4. i am going to order a Watermaster form home depot unless somebody can tell me a better valve for around the same price
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Postby mta » Wed Jul 30, 2003 8:42 am

Bigger is better. Make it with the longest barrel you care to handle. With a one inch sprinkler valve, you won't have to worry about it being overly super powerful.

Running the numbers thru GGDT

We get:

(Air 100 psi, Valve Cv = 6.8, projectile = 125g)

6' barrel 1' chamber 268 fps
6' barrel 2' chamber 283 fps

8' barrel 1' chamber 282 fps
8' barrel 2' chamber 302 fps
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Postby someguynamedchris » Wed Jul 30, 2003 9:18 am

it all depends if you are going to buy a supa or not. or a sprinkler valve or two. If you go with the sprinkler vavle then the chamber couldnot be aslong if you were going with a supah. Or you could go witha home made piston valve ( if go there don't bother on going to the plans because you have to buythem just scole down abit.

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Postby andeh » Wed Jul 30, 2003 10:05 am

You could build a floating diaphragm valve for that price or less, I'm pretty sure. A square YARD of 1/8" 70 durometer commercial grade neoprene on mcmaster is around 10 bucks, and I think that's enough for something like 81 4" discs. You could get a smaller piece of it for less. A square foot would be plenty, I think its something like 3 bucks for that. Then get a square foot of 1/32", that's more like 2 bucks. Then a small section of 16 gauge sheet metal... totals to around 10 bucks probably. BUT, it involves a lot more time and effort to making your first homemade valve.. believe me, been there, done that.

Actually, after going through typing all that I'd go with the watermaster, at least to start out. Mod it to be pneumatically actuated. Pushbutton or blowgun, either way.

edit: Also, what is the cfm on the "air compressor"? They vary greatly, from the 12v emergency compressors you plug into a car, to small electrical oil-recycling ones like I have(around 1.3 cfm), to compressors with tanks. They also have some that you put gas in and they work anywhere, but I doubt you have one... its something crazy like a thousand bucks.
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Postby OJHSPyro89 » Wed Jul 30, 2003 10:15 am

Ok this is my theory just make the barrel and the chamber about the same length cause that would make the ratio pretty good. Also look at the theory page on spudtech.
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Postby andeh » Wed Jul 30, 2003 10:41 am

ratios don't matter on pneumatics. Hangover from combustions... forget about it here. There is no explosion, only air. Or some type of gas anyway.
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Postby bigfoot42 » Wed Jul 30, 2003 11:37 am

so if i went with 1.5 - 2 feet of 4 inch pipe and a sprinkler valve would it be able to take 90-100 psi. i dont think i could make a home made piston untill i learn more about how they work. i also dont have a lot of money to spend on a supavalve. if i did decide to make a home made valve would it work any better than a sprinkler valve and would it be able to withstand more psi:?:
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