Finding volume

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SpudFiles Forum Index » Pneumatic Cannon Discussion » Finding volume

Finding volume

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no-limit

Posted: 06/23/2008 13:07 PM Post subject: Finding volume

Sergeant

Joined: 10 Apr 2008
Posts: 92
186.92 Spud Bux

I was told this is the formula for finding cylinder volume. pi*r*r*length but these calculations don't make sense.

1" by 60" = 47.12
2" by 30" = 94.24
4" by 15" = 188.49

Sems to me they would all be the same. What am I doing wrong? I'm am trying to figure the C:B ratio and by this my 1" by 60" barrel would only require a chamber of 2" by 30". I am using 2 sprinkler valves using 2 chambers at a 1:1 ratio for each chamber making it 2:1 for the total chamber volume.

Gippeto

Posted: 06/23/2008 13:20 PM Post subject:

Colonel

Joined: 19 Jan 2008
Posts: 505
1134.83 Spud Bux

Your not doing anything wrong.

When you double the diameter of a circle (pi*r*r) the area increase by a factor of 4.

Example:

1" circle area =3.14*.5*.5 =.785in2

2" circle area =3.14*1*1 = 3.14in2

3.14/.785 = 4

For a pneumatic, I wouldn't recommend any more than 1:1. (unless you just want the work out. Wink

)

And just to satisfy my curiosity, why 2 sprinkler valves on a 1" barrel? Are you planning on firing the chambers one at a time?

no-limit

Posted: 06/23/2008 13:30 PM Post subject:

Sergeant

Joined: 10 Apr 2008
Posts: 92
186.92 Spud Bux

Someone once said that having 2 sprinkler valves would give twice the speed since they only have to open up halfway to achive full volume.

Someone also once said "c:b ratio's are mostly important with combustions. with a pneumatic, more air and/or higher pressure equates to more power. The larger the chamber (if pressure is held constant) will give you more even force on the ammo as the compressed air expands down the barrel."

MrCrowley

Posted: 06/23/2008 14:04 PM Post subject:

Blizzard of Ozz
<b>Moderator</b>

Joined: 23 Jun 2006
Posts: 5949
2657.43 Spud Bux

no-limit wrote:

Someone once said that having 2 sprinkler valves would give twice the speed since they only have to open up halfway to achive full volume.

Not true. I remember reading that and I also remember posting a lengthy reply saying why it's not so.

It'll improve performance but wont even come close to doubling.

Pilgrimman

Posted: 06/23/2008 14:06 PM Post subject:

Major

Joined: 28 Jun 2007
Posts: 373
778.89 Spud Bux

You mean 2 valves in parallel right? It will not necessarily give double the speed, but it will help with a longer barrel as the flow is improved by having 2 valves. With a pneumatic, a C:B of 1:1 is more than enough to get as much power as possible without diminishing returns. .2:1 is (roughly) a perfect C:B ratio in terms of efficiency, but 1:1 should be good for power.

no-limit

Posted: 06/23/2008 14:14 PM Post subject:

Sergeant

Joined: 10 Apr 2008
Posts: 92
186.92 Spud Bux

Yes they are running parallel. I'm launching rockets and a 60" would qualify as a longer barrel I think. Most of my launchers have a bigger chamber volume (more than 2:1) because it needs to stand up. This one will be less than a 2:1 ratio because of the design using 2 valves.

Improved performace is good.

psycix

Posted: 06/23/2008 14:34 PM Post subject:

Major General

Joined: 25 Jun 2007
Posts: 1591
86.93 Spud Bux

That is true on one hand, and also you've got double flow. The downsides are that you've also got yourself a double as large pilot volume, and that it might become rather costly, you might be better of building a simple piston valve.

no-limit

Posted: 06/23/2008 16:33 PM Post subject:

Sergeant

Joined: 10 Apr 2008
Posts: 92
186.92 Spud Bux

For me there is no such thing as a "simple piston valve". The inside of a pvc pipe is way to filled with bumps to get a good seal. After my 4th attempt I have stopped that nonsense.

iisthemuffin

Posted: 06/23/2008 18:22 PM Post subject:

Major

Joined: 11 May 2008
Posts: 387
504.10 Spud Bux

Im sorry to steer away from the conversation but will someone please tell me the formula for finding volume of the pipe? I currectly have a simple sprinkler valve cannon with a 2 inch by 1 foot chamber and a 1/2 inch by 3 foot barrel. I want to know the formula to find the volume of my pipes to see if this is efficient.

DYI

Posted: 06/23/2008 18:30 PM Post subject:

Rear Brigadier
Major General

Joined: 07 Jul 2007
Posts: 2215
1323.29 Spud Bux

Quote:

The formula for volume of a cylinder is given in both the first and second posts of this thread. Would it really kill you to read the thread first?

iisthemuffin

Posted: 06/23/2008 18:33 PM Post subject:

Major

Joined: 11 May 2008
Posts: 387
504.10 Spud Bux

I read though the entire thread. But i thought that both of those were given for just a circle. I wasnt aware it was for a cylinder.

DYI

Posted: 06/23/2008 18:37 PM Post subject:

Rear Brigadier
Major General

Joined: 07 Jul 2007
Posts: 2215
1323.29 Spud Bux

Circle area is pi*r²
Cylinder volume is pi*r²*length

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