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Portable Semi Auto

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Portable Semi Auto

Unread postAuthor: palanit » Thu Jul 05, 2012 1:18 pm

I have been researching semi auto pneumatic guns diligently the past two weeks. I have found that aquiring semi auto is not the hard part, but aquiring portability is. I have been exploring the options of co2 and propane as my power source. I like how co2 is more consistent and yields higher psi, but I also like how propane is cheap and easy to come by. I have heard mixed reviews about propane. Most of the complaints about propane are about how LP (liquid propane) freezes valves and other components of the gun. Some people have installed expansion chambers and hoses. This is where I am confused. I understand the purpose of an expansion chamber, but don't fully understand how to make an effective one that works with my design. My semi auto design consists of a 3 way direct control valve that pilots a qev that is connected to a small chamber (I did not make up this design I got it from Poland_Spud and Jor2daje):
http://www.spudfiles.com/forums/i-too-has-semi-auto-t21039.html
http://www.spudfiles.com/forums/directional-control-valves-3way-valves-and-stuff-like-that-t20438.html
Poland Spud and Sgort87 have alreadly started helping me, which I really appreciated.
Once again, I did not come up with these designs and take no credit for them. I got them by looking through Spud Files.
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semi auto plan with out covers.png
The propane fills up the chamber, which is attached to an air cylinder. The Air Cylinder (with a magnet on the end of the rod) pushes a bb into firing position. The The 3 way valve is then triggered, which pilots the QEV. When the QEV is piloted, air is released into the barrel.
semi auto plan with out covers.png (15.88 KiB) Viewed 1339 times

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Unread postAuthor: POLAND_SPUD » Thu Jul 05, 2012 1:22 pm

Most of the complaints about propane are about how LP (liquid propane) freezes valves and other components of the gun. Some people have installed expansion chambers and hoses. This is where I am confused
Co2 can freeze valves.. it's not limited to LP
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Unread postAuthor: palanit » Thu Jul 05, 2012 1:24 pm

yes. does it look like this design would be vulnerable to freezing.
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Unread postAuthor: palanit » Thu Jul 05, 2012 1:41 pm

would it significantly help freezing if I connect like 5 ft of coiled hose inbetween the propane tank and the 3 way valve or would it be better to build an expansion chamber.
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Unread postAuthor: POLAND_SPUD » Thu Jul 05, 2012 1:46 pm

you should try to keep liquid propane from entering the valve
it wouldn't hurt to have a lenght of air line between the tank and the 3 way valve

plus it would be nice if there was a short lenght of iron pipe to act as an expansion chamber... anything that helps to absorb heat from suroundings will help... you might even put coiled copper tubing between the tank and the valve


I understand that the gun hasn't been built yet ? well then just build it using threaded fittings and see for yourself how well it works... if it doesn't perform well you can rebuild it in a few minutes

EDIT
yeah coiled hose sounds ok... copper would be better as it's a better heat conductor, but it's semi rigid
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Unread postAuthor: palanit » Thu Jul 05, 2012 1:51 pm

thanks for the suggestions. should i use math calculations to figure out how big my chamber should be to be most effective. I am going to be firing 4.5mm bb's and my propane tank will probalby be the 14 oz size
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Unread postAuthor: palanit » Thu Jul 05, 2012 1:57 pm

how does this look. Does it matter how big the expansion chamber is, I would imagine the bigger the better, but after a certain size does it become less efficient.
Edit:
Sorry for the double posts, I didn't know it was not allowed. Won't let it happen again.
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Unread postAuthor: sagthegreat » Thu Jul 05, 2012 5:07 pm

HPA, nuff said :P


but seriously get yourself a ninja paintball tank

http://www.amazon.com/Ninja-Aluminum-N2 ... B001RQRXJW

they are adjustable without a separate regulator.
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Unread postAuthor: palanit » Thu Jul 05, 2012 5:53 pm

The only thing I don't like about that tank is that I don't know where I could refill it or how much it would be to refill. How low can you regulate the psi down to.
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Unread postAuthor: palanit » Thu Jul 05, 2012 6:02 pm

The only thing I don't like about that tank is that I don't know where I could refill it or how much it would be to refill. How low can you regulate the psi down to.
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Unread postAuthor: ramses » Thu Jul 05, 2012 9:06 pm

I have a palmer regulator that I use down to about 120 PSI on a CO2 tank. It's pretty unstable. you'd be lucky to maintain maybe +-20psi

From there, I use a standard air compressor regulator.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 06, 2012 12:01 am

palanit wrote:The only thing I don't like about that tank is that I don't know where I could refill it or how much it would be to refill. How low can you regulate the psi down to.


You can get yourself a fridge compressor for free if you look in the right places, and converting it to an HPA pump costs very little time and effort, there are plenty of examples and tutorials on the forum.

It will not give you the 3000/4500 psi that paintball tanks are normally filled to, but with some encouragement it will go to 500 plus psi.

A container designed for CO<sub>2</sub> will take at least 1000 psi safely, something like a fire extinguisher for example, or even a used paintball tank.

If you're "time rich,money poor", an effective HPA system can be made this way with a little effort.

If you have a paintball or dive shop nearby that refills tanks and have a few quid to spare, go directly for a paintball bottle and think about having a SCUBA tank you can keep at home to refill the bottle yourself.
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Unread postAuthor: palanit » Fri Jul 06, 2012 10:21 am

The hpa regulators say they only regulate down to around 500 psi. That sounds like way too much. Maybe I'm just not understanding them correctly. Could someone clear it up for me.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 06, 2012 12:17 pm

palanit wrote:The hpa regulators say they only regulate down to around 500 psi. That sounds like way too much


Is it though? Small calibres need high pressure for decent power.

If you want more than 500 feet per second and a couple of foot pounds for steel BBs, you need to up the pressure, because even with a fast valve, big chamber and long barrel, there isn't much you can go with 150 psi for 0.177".

For a range of regulators that can go down to lower pressures, look here: http://palmer-pursuit.com/cart/index.ph ... th=8_25_27

not cheap but very good quality and reputation.
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Unread postAuthor: palanit » Fri Jul 06, 2012 12:45 pm

The hpa tank says paintball users get over 500 shots per tank. But if it is releasing over 500 psi per shot, it seems like you would only get 6 shots or so. Is there something I am not getting?
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