Portable Semi Auto

[palanit]

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-h ... 21039.html
http://www.spudfiles.com/forums/directi ... 20438.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.

[POLAND_SPUD]

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

[palanit]

yes. does it look like this design would be vulnerable to freezing.

[palanit]

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.

[POLAND_SPUD]

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

[palanit]

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

[palanit]

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.

[sagthegreat]

HPA, nuff said


but seriously get yourself a ninja paintball tank



they are adjustable without a separate regulator.

[palanit]

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.

[palanit]

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.

[ramses]

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.

[jackssmirkingrevenge]

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 CO₂ 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.

[palanit]

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.

[jackssmirkingrevenge]

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.

[palanit]

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?