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Second Pnuematic Launcher

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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Second Pnuematic Launcher

Unread postAuthor: Mr.Tallahassee » Sun Jul 10, 2011 4:24 am

This isn't my first attempt at a pneumatic launcher but my first one was only half as powerful. The chamber is 24'' long 1.5'' schedule 40 PVC, the barrel is 1/2'' schedule 80 sold as 48'' risers for spigots at Lowe's, and a quick disconnect in a pressure rated cap on the end. The valve is a lawn genie with flow control. I removed the flow control knob and used the hole left as my pilot vent. I typically run this gun around 80-90 psi but I have made frequent shots up to 100psi. I used GGDT to get a good estimate on power. It says that, with a marble, I'm shooting upwards of 747fps. Any feedback?
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Unread postAuthor: Alster370 » Sun Jul 10, 2011 4:38 am

Did you calculate the dead volume in your pneumatic?
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 10, 2011 4:48 am

Alster370 wrote:Did you calculate the dead volume in your pneumatic?


Dead volume and valve characteristics seem GGDT default so the result isn't as accurate as it could be.

Had a play myself, still a good result ;)
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Unread postAuthor: Mr.Tallahassee » Sun Jul 10, 2011 4:49 am

I did the best measurements that I could. I'm not 100% certain but that actually seems about correct. The valve is a 1'' Lawn Genie. It was the only one I could get. If anyone knows the actual specs of this valve it would help greatly.
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Unread postAuthor: Mr.Tallahassee » Sun Jul 10, 2011 4:54 am

jackssmirkingrevenge wrote:Dead volume and valve characteristics seem GGDT default so the result isn't as accurate as it could be.

Had a play myself, still a good result ;)


I actually went and did some measuring and the default dead volume seems to be accurate so i left it. the flow coefficient was in percent on my go. I went on the low end at 30% which I got from searching the forums. I actually used my camera as a makeshift chronograph by counting frames at 60 frames/sec. I calculated the projectile speed with the precise distance at 24'. I calculated between 750 and 800 fps to leave some room for error. It happened to be just over 3 and a half frames. I had to play with it a little to get reasonable results.
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Unread postAuthor: Alster370 » Sun Jul 10, 2011 4:56 am

I just noticed you had originally modelled it on a piston valve, which would explain the unusually high results. The gun itself is very good, clean too. A piston valve could be your next upgrade. You will definitely notice an improvement in performance.

dead space is the air volume between the valve and the projectile, correct?
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Unread postAuthor: Mr.Tallahassee » Sun Jul 10, 2011 5:05 am

Alster370 wrote:I just noticed you had originally modelled it on a piston valve, which would explain the unusually high results. The gun itself is very good, clean too. A piston valve could be your next upgrade. You will definitely notice an improvement in performance.

dead space is the air volume between the valve and the projectile, correct?

I believe that is what the dead space is.

Isn't a sprinkler valve a very inefficient chamber sealing piston valve? Of course, it's technically a diaphragm valve. However, it should be that great a difference, right? I'm still trying to figure a few things out. :?:

My next upgrade is definitely a piston valve! :D
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Unread postAuthor: Alster370 » Sun Jul 10, 2011 5:09 am

Sort of, but you still model them as a generic type valve in GGDT. A piston valve will make a big difference in power due to the increased flow and speed at which the air is released.
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Unread postAuthor: Mr.Tallahassee » Mon Jul 11, 2011 4:42 pm

Action shots! :D No distinguishable damage shots YET. I still need to find suitable targets.
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Unread postAuthor: Mr.Tallahassee » Thu Jul 14, 2011 4:48 am

I recently went to the GGDT page and found the specs that are supposed to closely resemble the 1'' sprinkler valve. I input these and got the same result as previously BEFORE I found these specs. Also, this IS with a very light glass marble as ammo. I recalculated the shot with a AA battery at 302fps which seems VERY accurate. I can watch the battery in flight across my backyard(it's a very large yard)
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