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valve coef in ggdt?

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valve coef in ggdt?

Unread postAuthor: A-98 » Thu Jul 06, 2006 10:52 pm

what is it? is it the same as flow coef?and what does it do?

im making a mini mega-launcher using a barel sealing piston and a 9/32"barrel that is 12 inches long and 2, 1 or 2 in by 6 in chambers.
it is designed as a mini airsoft gun and can shoot .2g bbs at 570feet per second or about 630 miles per hour. when i have the flow coef set to 1 its fine but only comes out at 480-520 fps . however when i set it from 2-35 its says barrel is constricting flow, valve coef is imposibly large(btu fps goes up).

thanks alot.

ps is there an instructions page forr ggdt?(oh how i loath pc's)
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Unread postAuthor: Urban Ninja » Fri Jul 07, 2006 12:01 am

If you go to the original website there are instructions on how to use it and a guide through what everything means.

http://www.thehalls-in-bfe.com/GGDT/index.html.
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Unread postAuthor: LucyInTheSky » Fri Jul 07, 2006 11:30 am

if it says vlave coef impossibly large then dont used that amount/
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Unread postAuthor: frogy » Fri Jul 07, 2006 12:46 pm

"570feet per second or about 630 miles per hour"

Um.... 570fps is about 400 mph, not 630.... :roll:

GGDT says
"Valve -> Flow Coefficient
Typically, valve performance is specified by a valve manufacturer in one of two ways: (1) by Cv or (2) by Kv. GGDT allows for either of these methods and a third; efficiency. Which method is used is defined in the configuration dialog box. For those who may not be familiar with these nomenclatures, a few words are in order. A valve that has a Cv of 1.0 will allow one gallon of water to flow through it per minute with a one psi pressure drop. If I remember correctly, a valve that has a KV of one will allow one liter of water flow through it per minute with a one bar pressure drop. In general, these two parameters will be listed in the manufacturer's literature. If it is not, I suggest using efficiency (30-50% would be typical values)."

You can't know the CV or KV of a homeade valve until you've made a gun with that same exact valve before, if it's a Barrel Sealing Tee i'd use about 50% with the efficiency setting...
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Unread postAuthor: A-98 » Fri Jul 07, 2006 3:24 pm

whoops srry bout that i think i put ina wrong # in my conversion. i figured that out at work today (whichis where im typeing this fom) and i was wondering if anyone would get that.

any way im making a valve that will fit inside a .4 metal pipe that ia about 1-1.5 inches long and i have never made this so i have no idea what to put in, so is there some # that is pretty general?. also how do i change it from cv to %.

also is there any difference between flow coef and valve coef?
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