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Pilot valve help for piston guns

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 valve help for piston guns

Unread postAuthor: Engineererrrr » Tue Feb 28, 2012 4:03 pm

I was just wondering about pilot valves and how much air can they pilot for there size. Im calling on anyones great expertise to explain the required valve size for a particular amount of chamber volume. Does the amount of psi effect the valve size?
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Unread postAuthor: sharpshooter11000 » Tue Feb 28, 2012 4:10 pm

It depends what type and size of valve you use as a pilot and how big the pilot volume is. For most pistons a ball valve should do.
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Unread postAuthor: Engineererrrr » Tue Feb 28, 2012 4:13 pm

thats what in trying to figure out

What chamber size will be piloted by what valve
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Unread postAuthor: jsefcik » Tue Feb 28, 2012 4:19 pm

sprinkler valves work fine
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Unread postAuthor: sharpshooter11000 » Tue Feb 28, 2012 4:32 pm

It's not the chamber being vented out by the pilot, it's the pilot volume that gets released. If you think about it, people use ball valves and sprinkler valves as main valves to fire a, let's say 2l chamber. Which means that either of those would work as a pilot for even a large pilot volume as generally a pilot volume is quite small.
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Unread postAuthor: Engineererrrr » Tue Feb 28, 2012 4:44 pm

i see, so lets say the pilot volume is in a 1" pipe, what valve would pilot that, non sprinkler? does the length of volume matter, Ex. 1"*x Will the x of the equation effect pilot?[/i]
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Unread postAuthor: sharpshooter11000 » Tue Feb 28, 2012 4:48 pm

Well it's the pilot volume so yeah the length does matter :wink:
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Unread postAuthor: Engineererrrr » Tue Feb 28, 2012 5:01 pm

alright so would a blowgun pilot 1"squared of air volume?
1" of 1 inch pipe is 1" squared right?
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Unread postAuthor: sharpshooter11000 » Tue Feb 28, 2012 5:20 pm

No, to find the volume it's pi multiplied by the radius squared, then multiply that by the length. JSR is a whole lot better at this than me (he figured out the pilot volume etc for my co ax) so I think it would probably be better if he answered this :oops:
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Unread postAuthor: jrrdw » Tue Feb 28, 2012 5:23 pm

It depends on how well your main valve is set up. If you have a air tight piston, only the pilot volume will vent. You need to do some more reading in the Wiki and forums. 1 x 1 = 1, right...
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Unread postAuthor: sharpshooter11000 » Tue Feb 28, 2012 5:28 pm

jrrdw wrote:You need to do some more reading in the Wiki and forums.


Who? Me or him?
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Unread postAuthor: jrrdw » Tue Feb 28, 2012 5:31 pm

I was talking to Engineererrrr, but you have to ask then both of you! :P
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Unread postAuthor: sharpshooter11000 » Tue Feb 28, 2012 5:36 pm

Haha I was wondering if there was something terribly wrong with my maths :D
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Unread postAuthor: dewey-1 » Tue Feb 28, 2012 6:31 pm

1 inch ID by 1 inch long has a volume of .5 x .5 x 3.1459=.785 cubic inches.
Volume of a cylinder is: (Pi x r square x length).
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Unread postAuthor: Technician1002 » Tue Feb 28, 2012 7:54 pm

It may sound strange, but the larger chamber the smaller the required pilot valve. To prevent the piston from re-closing, the pilot pressure must be low in relation to the chamber pressure. A smaller chamber drops in pressure faster with all else being equal. This requires a faster pilot vent rate to keep up. Otherwise the pilot pressure could become higher than the diminished chamber pressure and close the valve.
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