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Some newbie questions

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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Some newbie questions

Unread postAuthor: stklp06 » Fri Jul 12, 2013 11:10 am

Im going to be starting my first build but i have some questions. Im attempting to build a semi automatic pneumatic rifle with a qev and a slide valve. First question is im wondering if there is a better option than the slide valve because from what it looks like im going to have to reset the slide manually every time i pull the trigger which is something im trying to avoid also i wanted to be able to use at a higher pressure prob around 300 psi and im wondering if that much pressure will make the trigger pull very hard. Next i was wondering about the qev from what i have been reading around this site even though most qev max psi is 150 i shouldn't have a problem pushing it to 300, ive seen people say they can go up to 600 but i wanted to make sure i didnt have to make any modifications to the qev and if i did what would i have to do. To anyone who can help me out i would greatly appreciate it also im fairly new so the more you can explain the better it will help me.
Thanks
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Unread postAuthor: Major Collins » Fri Jul 12, 2013 12:32 pm

you can use anything that can pilot a qev , eg blowgun or ballvalve.
The differnce is the slide valve is convenient because it stops the incoming
air when it exaust.(i personally don't like slide valves either)

I think there are 2 ways around this
1.add a spring or springs to the slide valve so it resets or
2.move the incoming air to: in front of the exaust but behind the qev.(i dont know if stock qevs have a spring in them. If they do, they can be filled in through the air chamber)
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Unread postAuthor: stklp06 » Fri Jul 12, 2013 1:38 pm

thanks major collins i have a another question. do i need to release the pressure from the incoming air in order to trigger the qev? ive never done this before, i am under the impression that you do but from what your suggestion it sounds like you dont.
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Unread postAuthor: Major Collins » Fri Jul 12, 2013 2:29 pm

Well im assuming it will be attached from a external air supply eg compressor or hpa tank, and it will be a constant air flow filling up the air chamber.
You will need something to cut off the air supply manually-like a ball valve.If you decied to use anything but a slide. Becuase a slide valve cuts off air and pilots the exaust at the same time.
Eg the blowgun exaust would be like: fill > close air supply > shoot.
Then repeat and you got a semi auto.
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Unread postAuthor: stklp06 » Fri Jul 12, 2013 2:45 pm

ok so you saying that the "exaust" from the slide valve is not necessary just the cut off from the constant air flow. i could attach a blowgun before the qev and it would work pulling the trigger having the chamber fill with air then releasing the trigger cutting off the air and it would cause the qev move its piston and fire. again i really appreciate the help i just want to make sure i have the right idea before i start
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Unread postAuthor: Major Collins » Fri Jul 12, 2013 3:53 pm

This theory http://www.youtube.com/watch?v=HIRr5n-x7TI
Just get high pressures from the other tank for a decent amount of shots.
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Unread postAuthor: stklp06 » Fri Jul 12, 2013 4:01 pm

thanks major collins
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Unread postAuthor: Major Collins » Sat Jul 13, 2013 2:17 am

wait i sent you the wrong video, silly me but the video is a good example of how a qev/piston works

anywho heres the one i ment to link
http://www.youtube.com/watch?v=88PaX91wjbw
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Unread postAuthor: budabob07 » Fri Jul 26, 2013 4:20 pm

Instead of a slide valve, get a normally open push button 3-way DCV. Like something from here but a bigger size if you need better airflow.
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