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Pneumatic copper pistol having odd issue at 400+ psi.

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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Pneumatic copper pistol having odd issue at 400+ psi.

Unread postAuthor: air_dannon » Tue Oct 01, 2013 8:38 pm

Hi All,

I built Gippeto's "stirrup hand-pump" and love it.

I'm having an odd occurrence happen when I pump the copper pistol to 400+ psi range? I'll pull the trigger and there will be around a 250-400 millisecond delay, then the expulsion of air, but it's very weak :? It's like, What the heck happened to that pressure in there? Now, pumping it to around 260-300 psi area, this odd delay does not occur... good release of pressure.

So, what is going on at high pressures? I really want to take advantage of using the stirrup pump and copper gun at full potential, but maybe my pistol's design is the culprit?
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Unread postAuthor: Gippeto » Tue Oct 01, 2013 9:21 pm

Ball valve gun...shouldn't be any issues with the valve if it's opening. Higher pressure may be increasing friction enough that it's opening slowly???

Any strange behavior when pumping to higher pressures? Leaking check valve in the pistol or the pump maybe, but that should be fairly obvious.

Nice job on the pump...glad you like it. :)
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 02, 2013 6:56 am

Gippeto wrote:Ball valve gun...shouldn't be any issues with the valve if it's opening. Higher pressure may be increasing friction enough that it's opening slowly???


Could be... maybe film it firing at low and high pressure and compare the footage in slow motion?
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Unread postAuthor: wyz2285 » Wed Oct 02, 2013 7:10 am

Ball valves gets harder to open at high pressure because the "ball" is pushed against the nylon/whatever washers that creates the seal. Even a 1/4 ball valve can be very hard to open at 400 psi.
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Unread postAuthor: air_dannon » Wed Oct 02, 2013 1:16 pm

Well, further analysis does indeed show my spring is not strong enough to pop that valve open as fast as it needs to at high psi. Thought I'd make a video for the fun of it.

http://youtu.be/qbxvambocyo

Thanks for the comments. Time to upgrade.
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 02, 2013 2:07 pm

[youtube]http://www.youtube.com/watch?v=qbxvambocyo[/youtube]

Excellent analysis and well presented, that's the way :D

Looks like you need a spring with bigger huevos, or an exhaust valve of some description is in order...
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Unread postAuthor: dart guy » Wed Oct 02, 2013 2:48 pm

i am going to pint this out, the longer the lever the more tork is put on with same amount of force
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when life gives you lemons... make root beer and leave the world wondering how you did that :D
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 02, 2013 2:51 pm

... but a greater distance is travelled, so it will happen slower.
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Unread postAuthor: dart guy » Wed Oct 02, 2013 2:53 pm

yeah i kind forgot im losing my mind
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when life gives you lemons... make root beer and leave the world wondering how you did that :D
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