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Help Making A QEV - English

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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Unread postAuthor: jackssmirkingrevenge » Thu Jan 19, 2012 1:25 pm

josephlys wrote:Does the piston have to act as a divider to separate the high pressure air at the pilot end and the main air-chamber?


If it doesn't, the thing will never work, you will just dump all the air through the pilot and the piston will not budge.

Read up: http://www.spudfiles.com/forums/piston- ... t8157.html
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Unread postAuthor: josephlys » Fri Jan 20, 2012 1:55 am

That's what I thought, but you have grooves on the piston to allow air to get to the main tank. So that means the air from the pilot side can get to the main air-chamber and vice versa. Right, so if there isn't a perfect seal as a divider it shouldn't be a problem right? 99% of the hpa will gush out the barrel end first, right? Sorry for so many 'rights?' Haha
Thanks for the link.
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Unread postAuthor: jackssmirkingrevenge » Fri Jan 20, 2012 2:00 am

Right.

:D

Unless the piston has o-rings or similar, there's no need to cut grooves or holes in it, the air will flow though anyway.

Even with my cast epoxy pistons I never needed to cut grooves.
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Unread postAuthor: josephlys » Mon Jan 23, 2012 12:50 am

If I want to use a spring at the back of the piston, what type of spring and how strong/weak should it be. I can't seem to find a good compression spring. Any ideas where I can scavenge them from?
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 23, 2012 1:32 am

It just needs to be strong enough to overcome piston friction. A small one from a clicky top ball point pen should suffice for small piston applications.
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Unread postAuthor: josephlys » Mon Jan 23, 2012 2:19 am

What do you mean by piston friction? I thought the spring serves the function as to prevent the piston from going backwards to the pilot side when you pump air through the air-chamber. It's job is to close the piston valve right? and the hpa will seal it off.

But when fired, wouldn't a small spring bend/get stuck/easily move outta place? It wouldn't compress in-line, it would bend like crazy? Or would putting a bunch of small springs at the back of the piston do the trick of holding it against the valve and acting like a shock absorbent.
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