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QEV or piston valve

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: Hotwired » Sun Dec 30, 2007 8:32 pm

A 1" QEV has the opening speed and flow advantage. No competition.

At equal porting a piston QEV still has an advantage in the same areas over a homemade piston valve.

They cap out at 1" though and cost too much over 3/4" until an industrial demand appears for larger ones.

Still, they're not quite as specific as a homemade one, they are meant to be generic screw on and go devices, not to have a convenient layout for a launcher.

Would be nice to have a side piloting piston QEV...
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Unread postAuthor: Ragnarok » Sun Dec 30, 2007 8:48 pm

I use piston valves because I can get more flow out of a piston valve for a given size than a QEV, because I can use relatively larger porting.

Taking HEAL as an example, the main piston valve can give 3 to 4 times the flow of the 1/2" QEV that pilots it, but in a space barely larger than the QEV would take if it were the main valve (if you include the fittings to go from 1/2" BSP to the various pipe sizes as well)

Still, QEVs have their advantages.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: Hotwired » Sun Dec 30, 2007 8:57 pm

A QEV is that fat because it is meant for low-medium pressure use, you can get away with a skinny homemade piston valve with a small actuating area because it is meant for higher pressure :P

Still, thats what I meant by less personalised.
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Unread postAuthor: ALIHISGREAT » Sun Dec 30, 2007 9:34 pm

Hotwired wrote:A QEV is that fat because it is meant for low-medium pressure use, you can get away with a skinny homemade piston valve with a small actuating area because it is meant for higher pressure :P

Still, thats what I meant by less personalised.


yes a qev is meant for low pressure use but they are often used at relitivly high pressures in the 300psi region...
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Unread postAuthor: Ragnarok » Sun Dec 30, 2007 9:36 pm

HEAL's valve will seal just fine at slightly over 0.5 bar, and it'll still actuate well at only 1 bar... doesn't make the same ungodly thud it does at 22 bar, but the very low area doesn't seem to limit the lower end of pressures much.

It will affect things at high pressure though, the huge area exposed when the piston starts to move back creates a net force of over 800 Newtons (180 lbf.) on the piston, which I'm carefully lightening as part of my mods to get opening times even lower.

When I go up to 30 bar (which I will do pretty soon), and with the modifications, the valve will be opening in well under a millisecond, which is the same sort of time as a QEV. That levels the playing field a bit.
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Unread postAuthor: ALIHISGREAT » Sun Dec 30, 2007 9:45 pm

:shock: 30bar *goes to online conversion thingy to convert* :shock: thats over 400psi :shock: will soldered joints take that?

on a slightly related note i'm flirting with the idea of a 400psi marble gun that will use a super awesome piston valve probably 1" with a ridiculously tiny pilot volume, super light piston and a massive flow (hopefully) and it will be do able with off the shelf parts and no special tools like a lathe (hopefully) i will try and get some diagrams up tomorow morning and get some advice on a few things :)
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Unread postAuthor: Hawkeye » Sun Dec 30, 2007 9:57 pm

I recently soldered together a copper gun with a small calibre brass barrel. I took it to 350 without trouble. I admit that I was more nervous about the blowgun pilot blowing up than the copper or brass fittings. I'm going to put together a trigger exhaust that is of higher strength materials and try a bit higher pressure. I might go with a slimmer pump for those pressures and perhaps make a smaller chambered gun.
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Unread postAuthor: ALIHISGREAT » Sun Dec 30, 2007 10:04 pm

Hawkeye wrote:I recently soldered together a copper gun with a small calibre brass barrel. I took it to 350 without trouble. I admit that I was more nervous about the blowgun pilot blowing up than the copper or brass fittings. I'm going to put together a trigger exhaust that is of higher strength materials and try a bit higher pressure. I might go with a slimmer pump for those pressures and perhaps make a smaller chambered gun.


hmm interesting... if i was going for those pressures i would use JFC (just for copper- do you guys have that in the us?) because i wouldn't trust my soldering :lol: and i'm glad you didn't have any blowgun trouble because thats what i'm planning to use for my 6mm 'sniper'

p.s. if you want 400psi the best way to go is a shock pump unless you want to make a pump yourself?
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