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QEV sealing question

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 sealing question

Unread postAuthor: Eddbot » Wed Jun 11, 2008 11:17 pm

Ok, i bought a qev one ebay, and once i got it, i tested by blowing on the chamber side and sealing the pilot side with my hand. As i expected, when i moved my hand i could blow through the valve. I do it again, and it turns out when i blow into it, the valve hasn't sealed, and have to blow into the plot to get t to seal. Then i can do the test i first did. So, my question is, should it be sealing without me having to blow pressure back into the pilot side? The only thing I could think to do that would fix this, would be to put a spring between the piston and the pilot hole. Does anyone understand what i'm saying, or did i miss a day of QEV school?

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Unread postAuthor: Hotwired » Thu Jun 12, 2008 5:15 am

What?

Blowing manually though any port does not = valve testing. It needs more pressure than that to work properly.

Also, you're blowing air in from the chamber. It's not meant to be like that.

You pump air in through the pilot and that seals the valve as the chamber fills up.
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Unread postAuthor: Lentamentalisk » Thu Jun 12, 2008 8:57 pm

I had the exact same problem as you. My pump doesn't have enough flow to get it to seal, so I made my own spring for it. Just a little bit of wire, coiled in on its self(like a battery spring, so it takes minimal space.) I just had like one wrap, with the minimum spring, so as to have the least force necessary holding it closed, so that it will still open easily.
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Unread postAuthor: psycix » Fri Jun 13, 2008 4:59 am

A QEV needs to be filled from the pilot side. When your airflow is not big enough to get it seal, a spring can do the job.
Also, when you use a spring and puncture the piston (equalisation hole) it is possible to fill it from the chamber side. (BTB made a gun like that)
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Unread postAuthor: POLAND_SPUD » Fri Jun 13, 2008 9:40 am

lol edbot did you blow a valve ? I know that I had made a comment sometime ago http://www.spudfiles.com/forums/you-mig ... rt,30.html - but what you did is sick... :D

anyway.... you have to fill and pilot QEVs form the pilot side that's it... you would have to make a small hole in the piston/diagraph to fill from the chamber side
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Unread postAuthor: Eddbot » Fri Jun 13, 2008 12:51 pm

yeah, i've been looking at all the QEV guns on here for a while, i guess i never realized you fill from the pilot side...

@poland, lol, i never saw yours on the "you might be" thread
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Unread postAuthor: POLAND_SPUD » Fri Jun 13, 2008 1:50 pm

I write it just in case ) -->if your QEV leaks there is a 99% chance that there is not enough PTFE tape on the threads and/or the threads are not tightened strong enough
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Unread postAuthor: Lentamentalisk » Fri Jun 13, 2008 2:08 pm

no, that is not what we are talking about at all. that would be a minor leak around the threads. What we are referring to is the piston not setting, so all of the air flows out the tube.
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Unread postAuthor: POLAND_SPUD » Fri Jun 13, 2008 2:48 pm

ehm yes I know what are we talking about... I just mentioned it because quite a lot of people who bought their first QEV start new threads asking 'why does my qev leaks??'

so it was not refering to the question asked by the eddbot. I provided him some additional information on what problems he may come across

sorry I should have explained that more precisely
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