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Maximum QEV Pressure

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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Maximum QEV Pressure

Unread postAuthor: jssizzle » Fri Aug 31, 2007 2:00 pm

Hi! I've been away doing other things but I'm trying to start a "Kinetic Science" club (I know, a blatant euphemism) at my High School, and feel like making a new cannon just to help advertise, etc.

My basic plan was a small, rifle-like high pressure steel gun. After doing some snooping on Mcmaster, I decided on schedule 80 black steel for pipe, but couldn't decide on a valve. I was thinking of making a spring loaded ball valve (I saw it on a cannon . . . forget the name) because I knew it could handle the pressures (hopefully around 300 psi), but it will be alot easier to just use a QEV. Unfortunately, on Mcmaster, the QEVs are rated only to 125 psi.

Would it be safe (at least a 2:1 safety margin) to use a QEV around 300 psi? Or do I have to use the ball valve.

Thanks in advance.
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Unread postAuthor: Pete Zaria » Fri Aug 31, 2007 2:17 pm

The usual answer on this site when someone inquires about a high-pressure valve is "build a metal piston valve in a T". Look around this site, there's tons of great info on how to do exactly that.

Otherwise, try to fin done of these: http://www.sigmavalves.com/catalog/quic ... sindex.php Ebay would be a good resource here.

Best of luck with your "Kinetic Science Club". I hope the school administration is OK with that. Consider also building a small-scale coil gun using a modified camera flash circuit (with several caps), and some other goodies.

Peace,
Pete Zara.
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Unread postAuthor: iPaintball » Fri Aug 31, 2007 2:20 pm

I wouldn't. The diaphragm would most likely rupture, so unless you plan on replacing it after every shot, you should use another valve. If ti's performance you want, build a small piston valve. They can easily hold pressures in excess of 300 psi.
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Unread postAuthor: jssizzle » Fri Aug 31, 2007 2:29 pm

Wow that was fast.

Yeah thats about what I figured.

I'll look into a metal piston valve . . . and eventually post the cannon.

Thanks!
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Unread postAuthor: Velocity » Fri Aug 31, 2007 3:12 pm

Dude... copper piston valve! If I wasn't afraid of liability and such, I would build you one.
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Unread postAuthor: jssizzle » Fri Aug 31, 2007 9:35 pm

Hmmm. . .

Don't have any experience with copper but anything requiring a torch is out, sadly. Parents.

Well as of now I'm thinking a 1" ball valve w/ spring trigger. Lots of flow and hopefully the spring will make the opening time a little quicker.

Eventually I'll make a metal piston valve, but for short term the ball valve will be fine.

Thanks again to everyone that responded.
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Unread postAuthor: Dave_424 » Sun Sep 09, 2007 8:24 am

by the way
my QEV can hold 300psi easily
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Unread postAuthor: Infernal Maveric » Sun Sep 09, 2007 11:19 am

I have taken my Detrol 1/2 up to 400PSI and my face is still intact.

However, if you feel uneasy about pumping a QEV upto that preasure, then don't.
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Unread postAuthor: frankrede » Sun Sep 09, 2007 3:09 pm

The reason QEV's are rated at a relatively low pressure is because if it were to fail some one could be seriously injured.
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Unread postAuthor: Infernal Maveric » Sun Sep 09, 2007 3:27 pm

"If" is the word here. If a car could fly it would be a plane.

I see no real reason why a QEV wouldn't be safe at 300PSI, as long as it was a "piston" type, not a diaphragm QEV. However, if you do feel uneasy about using a QEV at pressures above 300PSI, then build a barrel sealing piston gun.
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Unread postAuthor: frankrede » Sun Sep 09, 2007 3:32 pm

Infernal Maveric wrote:"If" is the word here. If a car could fly it would be a plane.

I see no real reason why a QEV wouldn't be safe at 300PSI, as long as it was a "piston" type, not a diaphragm QEV. However, if you do feel uneasy about using a QEV at pressures above 300PSI, then build a barrel sealing piston gun.
Ok, I still don't see why its a good idea to put 300psi into a object that is rated for only 150psi.
It is rated for that pressure for a reason.
I'm sure that abs dwv could hold air fine, but does that make it suitable for use in a pneumatic?
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Unread postAuthor: Hotwired » Sun Sep 09, 2007 6:26 pm

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