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QEV Difficulties

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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QEV Difficulties

Unread postAuthor: noname » Fri Aug 14, 2009 7:55 pm

My new 1/4" QEV came in the mail today and it has been confusing me. I know on most QEVs there should be ports labeled In, Out, and Exhaust. Mine has Out and Exhaust but no In is labeled. I couldn't figure out the valve configuration by looking at it so I hooked it up to my old hybrid. I hooked up the hybrid to one port and a blowgun to another, leaving one empty as the barrel. I did this in all 6 possible configurations. The only time it held pressure, when I vented the blowgun it all came out the blowgun and none out the "barrel." I can't figure it out.
It's <a href="http://airinc.thomasnet.com/viewitems/specialty-valves-acc-/super-quick-exhaust-valves?&forward=1">this</a> valve by the way.
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Unread postAuthor: POLAND_SPUD » Fri Aug 14, 2009 8:22 pm

I've never heard of one faulty QEV... every time someone said he had problems with them it turned out it was because of leaks
use way more Teflon tape and check all the parts for leaks

I am not familiar with that particular model but the port that's at the right angle to the other two is almost certainly 'chamber'

one of the other two is where your fill/pilot valve should be

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corrected
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Last edited by POLAND_SPUD on Sat Aug 15, 2009 7:26 am, edited 2 times in total.
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Unread postAuthor: dewey-1 » Fri Aug 14, 2009 8:34 pm

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Unread postAuthor: noname » Fri Aug 14, 2009 11:21 pm

Poland Spud, are you saying it is necessary to fill from the pilot port? Because that would be a problem.
Dewey, I would read that if my computer could read PDF files. But it can't.
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Unread postAuthor: FORE!!!! » Fri Aug 14, 2009 11:32 pm

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Unread postAuthor: noname » Fri Aug 14, 2009 11:48 pm

Alright thanks, so I guess by the diagram that I have to fill from the In (pilot?) port.
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Unread postAuthor: MrCrowley » Sat Aug 15, 2009 12:49 am

Yeah looks that way, is that the configuration that half worked?
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Unread postAuthor: noname » Sat Aug 15, 2009 1:09 am

I think it probably is. Either that or I just need to flip the chamber and pilot and figure out a way to fill through the pilot. More complications for my design. :?
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Unread postAuthor: Brian the brain » Sat Aug 15, 2009 5:03 pm

A spring and a tiny equalisation hole will fix this..


That's how I modify my QEV's to accept filling from the chamber side..

The hole must connect the chamber side to the pilot side.
So don;t mess with the sealing surface or it will be FORKED...for like...ever... :D
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: noname » Sat Aug 15, 2009 5:20 pm

Thanks for the suggestion BtB, but I'd honestly rather risk the gun's aesthetic appeal than the valve. If it's extremely necessary I think I might just run a hose from the chamber to the pilot with either a check valve or a tiny equalization hole in between.
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Unread postAuthor: Brian the brain » Sat Aug 15, 2009 5:26 pm

If you know what you're doing...it shouldn't be an issue.

I've never screwed up a QEV by modding it yet...
And I've just turned one into a chamber sealer for crying out loud.
(oh.. whatever..I'm not going to enter the competition anywho)
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: noname » Sat Aug 15, 2009 5:33 pm

I know it's not difficult and it shouldn't be a problem, but I really don't feel up to the small risk right now.
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Unread postAuthor: Technician1002 » Sat Aug 15, 2009 7:26 pm

If you don't wish to modify the valve and have an old fridge to tear apart, the capillary tube can be coupled between the chamber and pilot to provide external equalization.
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Unread postAuthor: noname » Sat Aug 15, 2009 7:47 pm

Key word if. I don't know what the capillary tube is but I sure wish I had one.

EDIT: I did some pressure testing and I have the QEV working fine. Unfortunately, it is necessary to fill from the pilot. But that won't be an issue because I have a simple way to connect the pilot side to the chamber. I will give the connection very low flow so the pilot doesn't drain the chamber.
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Unread postAuthor: noname » Tue Aug 18, 2009 1:12 am

I've been screwing around with the gun and found some more annoying things. I connected a hose from the firing chamber to the pilot chamber to make the QEV seal. But then of course all of the gas came out of the blowgun instead of the QEV. So I blocked the hose to make it almost airtight. And the QEV wouldn't seal. So I unblocked it a little. The QEV would fire but most gas was still being dumped by the blowgun. I reblocked it and screwed on a ball valve. It fired as it should. But then the QEV refused to fire again. So I gave up on semi auto.
I placed a 1/4" ball valve in between the firing and pilot chambers and reconnected the blowgun as a trigger. I have yet to test it but the times it fired properly it shot the BB around 400-450 fps (guesstimation) at 100 psi.
In the morning I will test again to make sure it fires consistently using the breech loading barrel I have set up. After that I will just have to crack down and finish the blow forward assembly and figure out a way to make a frame for the gun instead of having parts hanging around all over.
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