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Measuring valve opening speed

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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Measuring valve opening speed

Unread postAuthor: dilweed » Mon Oct 06, 2008 1:22 pm

Is it possible to measure the speed of a spring and hook activated ball valve opening. Could you record an audio file, open the valve by pulling the hook (you hear a click), then measure the time between the bang when it shoots? Im not shure if this ould work, and if it did do you recomend any software. Thanks.
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 06, 2008 1:40 pm

Using an audio program (audacity for example) would probably not work out as I doubt the release "click" would be loud enough to show a distinct peak. However, there's only one way to find out and all you need is a PC, microphone and free software so what are you waiting for ;)
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Unread postAuthor: dilweed » Mon Oct 06, 2008 1:43 pm

SWEET...Ill scurry to my pitifull money stash (not telling you, it's mine mine mine all mine, all that lovely measly £15 poundsworth!) and get the equipement. Also whats a good opening speed? sorry with all the questions, i guess its quite annoying, but im learning.
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Unread postAuthor: Hotwired » Mon Oct 06, 2008 1:48 pm

The "bang" you refer to would be the noise of the air escaping the moment the ball valve openings provide a path from chamber to barrel.

You would in fact end up with the time it took for the ball valve to rotate enough to just open.

There is a difference between that and the moment it is completely open.

If you wanted to measure the time it took for the ball valve to totally open then you don't need compressed gas in there.

One click for the ball valve to be released and a clunk when the arm hits its stopper which is also when it is completely opened.
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 06, 2008 1:49 pm

Some useful advice on audacity can be found -->here<--

Also whats a good opening speed?


zero ;) but that is the preserve of valveless launchers :D

As little as possible, but of course it depends on your launcher how much of a factor it will be. For example with a very long barrel and large chamber, opening speed is less important than flow. The simple equation however is less time = better performance.
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Unread postAuthor: Ragnarok » Mon Oct 06, 2008 2:23 pm

jackssmirkingrevenge wrote:As little as possible, but of course it depends on your launcher how much of a factor it will be.

Less than a couple of milliseconds on an average launcher is practically indistinguishable from perfect 0 millisecond opening in muzzle velocity, so endeavouring to get it much faster becomes fairly moot past that point.
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Unread postAuthor: dilweed » Mon Oct 06, 2008 2:32 pm

Okay. Im planing on getting those valve speeds. I think I can. I have a ballvalve which can cover the whole barrel so i dont have to worry about air volume being dumped. Right now my chamber is the stock, and the barrel to chamber ratio is an estimated 1(B)-1.7(C). I plan on replacing it like a pistol grip, downgradeing the ratio to about 1(B)-.5(C). My marbles wiegh 5-7 grams. They already travel pretty darn fast but i want it more compact and sturdy. I take it on a averafe of 80-100 psi, you cant see the marbles and they can penetrate wood. My chanber is a threaded 1/4" width copper pipe, which will be upgraded to a 1/2" or a 3/4" threaded bronze pipe.
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Unread postAuthor: ALIHISGREAT » Mon Oct 06, 2008 2:57 pm

well i could possibly use audicity with my copper coax and the piston makes a satisfying ping as it opens... and i could use the QEV piloting as the start.... but i can;t be bothered :D
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Unread postAuthor: jimmy101 » Mon Oct 06, 2008 4:10 pm

Use the MIC input to a PC. Connect the tip of the MIC plug to the metal handle of the valve. Connect the ground wire to each of two temporary contacts (tin foil on wood would be fine). Set the contacts up so when the valve is closed the metal handle touches one. The other contact is positioned so that when the valve is 100% open it is contacted. Use Audacity (or whatever) to record how long it takes to get the valve open.

Or, instead of the MIC input use a 1.5V battery and the LINE input to the PC.

Opening a valve in a millisecond or less means you have to get the handle moving pretty darn fast. If the end of the handle swings through a 4" arc (90 degree rotation) in 1 mS then the handle's end is moving at 4/12/0.001=333 feet per second. That's a bit faster then the speed of a BB from a cheap BB gun. I doubt you can get the handle moving that fast with your hand.

How fast do you want to get the valve open? You can calculate that easy enough based on the barrel length and the expected muzzle velocity. If you have a 5' barrel and hope to get a muzzle velocity of 500 FPS ...

Time for ammo to move through barrel = 2*(barrel length)/(muzzle velocity) = (2)(5)/500 = 0.02 seconds. So, you want the valve to open in significantly less than 0.02 seconds. Figure 0.002 seconds. In that time the ammo will not have moved significantly. 0.01 seconds would probably start to show significant drop in the muzzle velocity. (GGDT will calculate a much more accurate estimate of the affect of changing the valve opening time on the muzzle velocity.)
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Unread postAuthor: psycix » Tue Oct 07, 2008 11:54 am

When measuring the opening time of a specific valve, you should have no barrel connected.
That way you do not have to compensate for the time that the projectile travels.
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Unread postAuthor: D_Hall » Tue Oct 07, 2008 5:12 pm

dilweed wrote:Okay. Im planing on getting those valve speeds.

You plan on opening a ball valve in a couple milliseconds?

[/stifles laughter]

Good luck with that.
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Unread postAuthor: DYI » Tue Oct 07, 2008 6:35 pm

You plan on opening a ball valve in a couple milliseconds?

[/stifles laughter]

Good luck with that.


You could open a ball valve that fast... once.

If you want a decent opening time, use a pressure actuated valve (barrel/chamber sealing piston valve, diaphragm valve) or a burst disk.
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