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Little help for a semi noob

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: potatoflinger » Mon Mar 17, 2008 8:31 pm

rcman50166 wrote: They also don't sell tennis ball sized PVC. (2.5in)

Try looking for 2.5" electrical conduit, it's that gray-looking pipe. The Home Depot near me sells 2.5" electrical conduit, which works perfectly for tennis balls.
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Unread postAuthor: enginerd » Mon Mar 17, 2008 8:43 pm

Has any one tried using a butterfly valve?
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Unread postAuthor: D_Hall » Mon Mar 17, 2008 9:25 pm

rcman50166 wrote:It seems that people on this site have very short tempers. Sarcasm, cold shoulder, or just plain insults. Not calling anyone out but does anyone else think the community can be a bit "nippy" at times?

To me his first post could be summed up thus: "I'm smarter than ya'll, but I'm too lazy to do any homework so I want you to do my homework for me."

No, I don't respond well to such requests. If that defines me as one with a short temper I guess I'll live with the lable.
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Unread postAuthor: D_Hall » Mon Mar 17, 2008 9:25 pm

enginerd wrote:Has any one tried using a butterfly valve?

Mythbusters used one for their chicken gun.
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Unread postAuthor: TurboSuper » Mon Mar 17, 2008 9:52 pm

On the subject or sprinkler valves, do you really need more than 1" porting for a golf ball launcher?

You can get one easily enough off the internet for like $15.
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Unread postAuthor: D_Hall » Mon Mar 17, 2008 10:00 pm

TurboSuper wrote:On the subject or sprinkler valves, do you really need more than 1" porting for a golf ball launcher?

Depends on how far/fast you want to fling a golf ball. I've got a 2" sprinkler valve based gun that has been chrono'ed at 500 fps. Drop it down to a 1" valve and GGDT indicates I'll be in the 330 fps range. So yeah, it matters.
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Unread postAuthor: enginerd » Tue Mar 18, 2008 11:04 am

i was going for more of

i'm not an idiot know how these systems work but you guys have more practical experience.

i knew the mythbusters used one but if any one here has maybe they could compare how it flows compared to a sprinkler valve even though the butterfly would be manually opened
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Unread postAuthor: MaxuS the 2nd » Tue Mar 18, 2008 11:44 am

Butterfly valves are more likely to cost more than your average sprinkler valve. I don't understand the problem with a sprinkler valve?

It's considered good manners if you search for answers yourself first, then if by some random chance, you are unable to find the answer you seek, then feel free to ask.

People on here don't have to reply you know..
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Unread postAuthor: jimmy101 » Tue Mar 18, 2008 2:31 pm

enginerd wrote:To Jimmy: Correct i am not an english major, i do not care if i have bad grammar.

Every REAL engineer I've ever known (at least a couple dozen) DID care if they had bad grammar. If you can't lucidly explain what you are trying to do then ya ain't much of an engineer. REAL engineers are very picky about their use of words and their grammar since a misunderstanding often results in either a heck of a lot of wasted money or people dying.

enginerd wrote:To D_Hall- A ball valve with a strong rotary solenoid would work better then any other valve out there because it would be a straight shot from tank to barrel with no losses from corners or reductions.

How fast do you think the valve needs to open? (Hint: how long does the projectile take to move through the barrel given a reasonable estimate of the muzzle velocity.) How far does the lever on the valve have to move for a 1/4 rotation? How much force does the valve take to open? How fast will the lever have to be moving to get the valve to open in less time than it takes for the projectile to transit the barrel? How much kinetic energy will be in the lever when it slams into it's stop?
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Unread postAuthor: Pilgrimman » Tue Mar 18, 2008 4:55 pm

Well, I was about to reply angrily, but enginerd seems more contrite in his last post.

Anyway, for your purposes, a large QEV (Quick Exhaust Valve in case you haven't heard of one) or a piston valve are likely your best options for optimal performance. I personally would choose a 1 1/2" QEV, as it is commercially manufactured, and optimized. However, I don't know what the price range is on QEVs of that size. If you would like to create a coaxial design, a diaphragm valve might suit your needs better.

A butterfly valve has massive flow, but the opening speed is simply too slow for this application. Unless your barrel is very long, on the order of 10 feet or more, a fast opening valve is almost always preferable to a slow-opening-high-flow-valve (To an extent). Additionally, piston and diaphragm valves are more elegant to operate, because the pilot can be set up to fit the gun better and make it easier to aim.
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