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 Post subject: Hmm...
 Post Posted: Tue Jul 15, 2003 10:00 pm 
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Originaly posted by Freefall,
Those numbers are a bit off. First off, with a piston valve built into a tee (3 inch comes to mind), the air can flow up around the sides as well as straight into the barrel, so it does have the benefit of the full circumference of the barrel. As for the required travel for full open, assuming flow isn't affected by turning (which it is, to a huge degree), the choke area is:

(barrel dia) x (pi) x (piston travel)

Notice I used barrel dia instead of coupler dia. So, to get fully open, you need a travel of .494 inches. If you've been designing your guns with .223 travel, you may want to consider shaving an extra quarter inch off the breech end of your barrel. (how you'd do that on an assembled gun is up to you...)


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 Post Posted: Wed Jul 16, 2003 7:00 am 
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Originaly posted by mta,
I inexplicably used 4.5" for the barrel OD. A 2" barrel has an OD of 2.375" This is also the ID of the coupler/valve seat. So a movement of .442" will fully open the valve. The non-coaxial piston must travel about 5 times further and 5 times as much air behind the piston must be dumped.

Notice I used the coupler ID to figure the circumference. The coupler extends a ways past the end of the barrel and was put there to (among other things) increase air flow by providind a larger ID.

The breech can be seen here:

http://w3.mivlmd.cablespeed.com/~mta/spud/breech2.jpg




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