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Will this QEV set-up work? Please leave your opinion below.

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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Will this QEV set-up work? Please leave your opinion below.

Unread postAuthor: ham_machine » Sun Sep 28, 2014 4:15 pm

Thought I would start a new topic on this subject. So I can get as many opinions as possible if this would work or not before I begin buying materials and parts.

diagram, sliding valve converted.jpg
Regular shop brought QEV


What if I was to put a sliding hand valve as the pilot valve. One end is connected to port P, and the other connects up with port A and the chamber. My theory is that the pressure in both chamber P and A will be the same while the sliding valve is in position A. This is what will happen anyway if i were to fill the pressure from behind the pilot, or if I was to modify it. So with the sliding valve in position A, the pressure will be the same in the pilot chamber, as it is in the main chamber. By sliding it into position B (as illustrated) the sliding valve will seal the two chambers, and instantaneously eject the pressure from the pilot chamber through the holes - and so activating the QEV.

My major concern is as follows -

As we all know - if the pressure is greater at port A than it is at Port P, the pressure difference will pull back the piston and activate the QEV. I am going to have a ball valve (in the location of the schrader valve) which will connect this system to a large storage vessel.

What I am worried about is - when I release the pressure from the large storage vessel (using the ball valve) into this system I have illustrated above. Lets say the ball valve is located very close to Port A - like it is in the diagram. The pressure released will reach Port A first before it gets to Port P, and the pressure difference may activate the QEV (because it takes longer for the pressure to reach Port P than it does Port A)- it has to go round a bend!

My design requires the ball valve to be closer to Port A..

Or perhaps Pressure doesn't work anything like I think it does.. What does anybody think?
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Re: Will this QEV set-up work? Please leave your opinion bel

Unread postAuthor: Baldyforks » Mon Sep 29, 2014 1:44 am

I'm not an expert, but id be thinking it should work but wont reset the qev when you try to fill it, if you put a spring in the qev to reset it(closing port R) after firing it could work, I think you'd be better putting the fill valve behind the slide valve and not connected to the port A chamber, like everyone else does, im not seeing what advantage you'd get by doing it your way?

As I said, Im not an expert though :)
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Re: Will this QEV set-up work? Please leave your opinion bel

Unread postAuthor: ham_machine » Mon Sep 29, 2014 10:59 am

"Baldyforks"


Thanks for the feedback. I see where you are coming from with the spring! I might do what everyone else has done (with the storage vessel behind the pilot) then It will be quicker to reload. But my design I have made won't give me much room for that to work!
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Re: Will this QEV set-up work? Please leave your opinion bel

Unread postAuthor: mulderscully911 » Mon Sep 29, 2014 12:58 pm

I think your gun designs are amazing! Bravoooo! QEVs are very good for spud guns
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