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Idea: Piston actuated ball 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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Idea: Piston actuated ball valve

Unread postAuthor: aEx155 » Sat Jul 30, 2011 12:24 am

Just a thought:

It seems like you could buy a 1/4" QEV for a lot less than a 1" QEV. But a 1/4" valve doesn't help if you have a 1" barrel. (just looking at mcmaster, a 1/4" QEV is $10 cheaper than a 3/4" QEV)

Ball valves are much cheaper than QEVs, but they're slow, and spring loading only gets you so far. They do have the most ideal flow, though; no right angles or turbulence.

Why not combine the best of both worlds? Making a small, single acting piston doesn't seem too hard. A 1/4" QEV should flow enough to move a small piston enough to open a ball valve. No need to reset any springs.

I admit it's a little cumbersome or unnecessary, but it's just a thought, and I hadn't seen it done before.

I wonder what the theoretical fastest opening time for a ball valve is.
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Unread postAuthor: jackssmirkingrevenge » Sat Jul 30, 2011 1:25 am

It's been done before, can't find the bloody link but I remember the cannon was a horrid shade of blue.

Why stop there, have a double acting cylinder and a three way ball valve et voila, semi/full auto!
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Unread postAuthor: aEx155 » Sat Jul 30, 2011 1:50 am

You certainly could use a 3-way ball valve to do fill/fire. Semi-auto with a 1" barrel does sound pretty interesting, although it would use up so much air...

It would be interesting to find out what chamber, barrel, and pressure results in launching a tennis ball at reasonable serving speed, and the highest-flow regulator you can get (maybe multiple in parallel)...intense tennis practice anyone?
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Unread postAuthor: jackssmirkingrevenge » Sat Jul 30, 2011 1:52 am

aEx155 wrote:You certainly could use a 3-way ball valve to do fill/fire. Semi-auto with a 1" barrel does sound pretty interesting, although it would use up so much air...


In theory with a three way valve, the inner volume of the ball valve itself could be the "chamber"... if you're using high pressure this would still result in worthwhile performance.
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Unread postAuthor: POLAND_SPUD » Sat Jul 30, 2011 4:00 am

I don't think it's a good idea.... yeah I know it involves 3 way valves :-D but still it isn't a good idea

a 1/4" QEV is $10 cheaper than a 3/4" QEV
that's not much you know?
if you don't want to buy a QEV then just build a QDV
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Unread postAuthor: aEx155 » Sat Jul 30, 2011 4:12 am

@POLAND_SPUD
What is the difference between a 1/4" QEV and a 2" QEV then? Because this would theoretically work in that application too. It seems like a small air cylinder and a ball valve is much easier to manage than figuring out o-rings and a piston on a QDV. (I had the worst time fitting o-rings for inside 1-1/4" PVC; I ended up just cutting some larger ones down and gluing them and that resulted in some small leaks but it barely worked)

On a slightly related note:

Would a QDV function similarly if you use a small valve to feed air from the chamber to the space between the projectile and the piston?

I would think that would allow for higher performance, as it equates to pulling on the piston using an air cylinder; you might need a really tight fit on the projectile though.
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Unread postAuthor: POLAND_SPUD » Sat Jul 30, 2011 4:30 am

my point is... if you're no good at building stuff as I am just get a 3/4" QEV - they are fairly cheap and will offer higher performance than a 2" BV

yeah finding the right o-rings is a PITA
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Unread postAuthor: al-xg » Sat Jul 30, 2011 4:55 am

A ball valve gives the "ideal flow" when it is fully opened but in most cases the projectile will have left the barrel before the valve is fully opened.

A pneumatic ram will mean you can open a larger valve faster but I think the opening time won't be much smaller than a good spring set up.

I'm pretty sure I recorded an opening time of 25ms on my 1/2 BV rifle and the spring tension isn't particularly high. But most projectiles with any decent amount of pressure will have left the barrel in less than 10ms.

I remember quite a nice air ram canon on USKGC, reasonably large bore too.
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Unread postAuthor: jackssmirkingrevenge » Sat Jul 30, 2011 5:57 am

After some digging through the bowels of the interwebs, found it!

Website is dead but dug up some pictures though mark's site:
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Re: Idea: Piston actuated ball valve

Unread postAuthor: velocity3x » Sat Jul 30, 2011 6:18 am

aEx155 wrote: A 1/4" QEV should flow enough to move a small piston enough to open a ball valve. No need to reset any springs.


Why not delete the QEV as it seems a bit redundant? The ball valve on the gun below is actuated by pneumatic cylinder and controlled by a 3-way solenoid valve. You could use a push button valve for a trigger rather than a solenoid.
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