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Blowgun ggdt numbers

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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Blowgun ggdt numbers

Unread postAuthor: jon_89 » Fri Jan 30, 2009 7:49 pm

What numbers would you put in ggdt if you were to use a blowgun as the valve? Ie: flow cof, seat diameter, etc.
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Unread postAuthor: maggotman » Fri Jan 30, 2009 7:51 pm

it depends how fast you open it most blow guns are different if i were you i would dissemble it and measure them
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Last edited by maggotman on Fri Jan 30, 2009 7:55 pm, edited 1 time in total.

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Unread postAuthor: jon_89 » Fri Jan 30, 2009 7:54 pm

Lets just say I open it as fast as possiblr.
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Unread postAuthor: btrettel » Fri Jan 30, 2009 10:45 pm

Short of using the flow coefficient calculator in GGDT (which requires measured data), you could use the information the manufacturer provided to get an idea of what the flow coefficient is.

Scroll down on this page to find "Flow Coefficient - Cv - for Air and other Gases". You can use the calculator there to find the Cv flow coefficient.

As a test I entered the numbers for McMaster-Carr part number 5650K13 and got a Cv of 0.19. While that blow gun does seem to be generic, it may not be like yours, so don't just enter this value. Find the data on your valve as I mentioned earlier.

Be aware that the provided flow figures often are optimistic, so you might want to devalue the result of this calculation. Also note that manufacturers often give flows in cubic feet per minute, not hour as the website requests. Multiply by 60 to convert to per hour.

Using the generic valve option, you should measure everything else from the valve. For seat diameter put in the ID of the blowgun exit. For open time something like 20ms is probably a decent start.
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