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pilot venting

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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pilot venting

Unread postAuthor: mexthatcan » Fri Jun 13, 2008 6:07 pm

For a barrel sealing piston, with ~6.6 cubic inches of pilot, will a blowgun (either modified or standard) be enough to quickly actuate the valve? Or would something like this pop-off safety valve be better?
McMaster part #48435K72

A sprinkler valve is out of the question because it needs to be small, 1/4" or maybe 3/8".

Thanks in advance for your help.
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Unread postAuthor: MrCrowley » Fri Jun 13, 2008 6:25 pm

It could work, it depends on your piston also. Though I would not recommend it, you'll be losing A LOT of power with a blow gun. I'd recommend a 1/2" ball valve, at the minimum a 3/8" ball valve.
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Unread postAuthor: mexthatcan » Fri Jun 13, 2008 6:27 pm

the piston is fairly light, just a endcap thats been shaved down with some washers on it. I have no scale so i cant say exactly, probably a little more than a 1 1/4" endcap unmodified.

And even though the ball valve opens slower, it would be better than the others?
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Unread postAuthor: jrrdw » Fri Jun 13, 2008 6:32 pm

Members have spring loaded ball valves to make them work/open fast and swear by them.
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Unread postAuthor: MrCrowley » Fri Jun 13, 2008 6:46 pm

A 3/8" ball valve will offer probably somewhere around 4x as much flow as a blow gun. I can't be bothered doing the math, but the larger flow will easily out do the quicker opening of the blow gun.
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Unread postAuthor: pizlo » Fri Jun 13, 2008 6:57 pm

definatly go with a metal, 1/2 ball valve.
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Unread postAuthor: hyldgaard » Fri Jun 13, 2008 7:12 pm

I have had great experience with using a small qev as exhaust, and with that you can use your blowgun without problems.
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Unread postAuthor: mexthatcan » Fri Jun 13, 2008 7:12 pm

If a quick connect is at the venting end of the ball valve, will that 1/4" hole restrict as well? And if so, can that hole me machined larger without compromising the integrity of the quick connect? Or since there is no pressure without it being inside the female adaptor, there is no issue
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Unread postAuthor: MrCrowley » Fri Jun 13, 2008 7:16 pm

No it should be fine having a 1/4" QC on a 3/8" or 1/2" ball valve.
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Unread postAuthor: mexthatcan » Fri Jun 13, 2008 7:25 pm

Alright thanks again for all the advice everyone gave. Using just a ball valve actually simplifies my original design.
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Unread postAuthor: Carlman » Sat Jun 14, 2008 2:46 am

or use a qev then a blowgun or BV
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Unread postAuthor: Gippeto » Sat Jun 14, 2008 9:25 am

I used a modified blowgun on my first. Check the video and see if you think it pilots quickly enough for you.

http://www.youtube.com/watch?v=NgYKn3GsSFA

The thread is here;

http://www.spudfiles.com/forums/my-firs ... 12796.html
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