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piston valve barrel sealer

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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piston valve barrel sealer

Unread postAuthor: far_cry » Sat May 09, 2009 5:32 pm

i had asked a while ago for my old uncompleted coax , that how much piston have to open, <a href="http://www.spudfiles.com/forums/how-far-the-piston-must-open-t15999.html" target="_new">this is the old topic </a>

so my question is , is this same role of opening gap (d/4 of the barrel) also for a barrel sealer ? or is dos not matter
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Unread postAuthor: Gaderelguitarist » Sat May 09, 2009 8:26 pm

Logically it would be the same ratio.

Coaxial and Tee based piston valves work upon the same principal more or less. You don't want too large of a gap because of air expansion and the setbacks of a larger pilot volume, and you don't want it too small because it will choke the flow.
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Unread postAuthor: spudtyrrant » Sun May 10, 2009 9:02 am

i usually get better results when i use the radius when trying to figure out optimum piston movement so to awnser you question 1cm
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Unread postAuthor: far_cry » Sun May 10, 2009 1:04 pm

theseat diameter is 9mm in side
i make it 5 mm and the piston workk great
how can i know if this shock the flow
thank you
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Unread postAuthor: Gaderelguitarist » Sun May 10, 2009 4:40 pm

To see if your gap size is choking flow, you could either download GGDT and punch in the figures, or test by adjusting the gap size and firing with each difference. Then just use a chronograph or a box of truth to figure the power.

Sorry chronographs are for speed, not power. but you get the idea
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Unread postAuthor: Technician1002 » Sun May 10, 2009 4:55 pm

Gaderelguitarist wrote:Sorry chronographs are for speed, not power. but you get the idea


Chronographs are for speed. Knowing speed and mass, power can be calculated.

For instance, the amount of kinetic energy KE of an object in translational motion is equal to one-half the product of its mass m and the square of its velocity v, or KE = 1/2mv2, provided the speed is low relative to the speed of light.


clipped from here;
http://www.answers.com/topic/kinetic-energy

With scales and a chronograph, energy can be calculated.
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Unread postAuthor: Gaderelguitarist » Sun May 10, 2009 5:04 pm

Chronographs are for speed. Knowing speed and mass, power can be calculated.


I don't know what I was thinking! :oops:
Face-palm-smash-into-wall-jumps-out-of-window combo...


Back to the topic at hand...

Have you posted your cannon on the site yet? I'd like to see it with a couple shots of the piston.
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Unread postAuthor: far_cry » Sun May 10, 2009 5:31 pm

Gaderelguitarist wrote:Have you posted your cannon on the site yet? I'd like to see it with a couple shots of the piston.


actual is an air gun not a canon ,8mm barrel
but it's not completed , he need's some work the stock mostly, and i building a stirrup pump to get 800-1000 psi
then i will post the air gun and the pump

i will post a video for the valve how he works at 100 psi tomorrow
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Unread postAuthor: psycix » Sun May 10, 2009 5:53 pm

so my question is , is this same role of opening gap (d/4 of the barrel) also for a barrel sealer ? or is dos not matter

D/4 only counts if:
-Air comes from all sides (like a coaxial)
-The edges are perfectly smoothed
-The piston does not bounce back at all

For those last two points: it will always be better to have a little bit more.
For the first part, note that in a barrel sealing piston valve built inside a T piece, the air only comes from one side, so you will at least need D/2.
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Unread postAuthor: Technician1002 » Sun May 10, 2009 7:55 pm

psycix wrote:
so my question is , is this same role of opening gap (d/4 of the barrel) also for a barrel sealer ? or is dos not matter

D/4 only counts if:
-Air comes from all sides (like a coaxial)
-The edges are perfectly smoothed
-The piston does not bounce back at all

For those last two points: it will always be better to have a little bit more.
For the first part, note that in a barrel sealing piston valve built inside a T piece, the air only comes from one side, so you will at least need D/2.


In my cannons I have used the piston radius plus more in the bumper zone assuming it needs a deceleration zone to prevent hammering itself to bits. The free flight distance before landing on the bumper in mine is about the piston radius.
Another 1/2 that or more is the deceleration zone where it compresses the bumper.
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