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How To calculate spring specs? Please help!

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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How To calculate spring specs? Please help!

Unread postAuthor: BigBang J » Tue Aug 17, 2010 4:33 pm

Hi, I need some help here I am working a hybrid with a mix of 7x.
I was wodering how to calculate spring specs for the valve I am building.I mean if I want the valve to start opening around 500 psi, do I need a spring that is rated at 500lbs? Please help me out here.
Thanks in advance
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 17, 2010 4:45 pm

You need to calculate the exposed area of the piston:

(pi x piston radius x piston radius) - (pi x barrel external radius x barrel external radius)

Do that with all dimenstions in inches, and multiply the result by 500
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Unread postAuthor: Heimo » Tue Aug 17, 2010 4:50 pm

Here are a couple of calculators I found that might help you answer your own question just cause I don't really know how to help you

this one seemed to be the best and easiest to use
http://www.msdspring.com/springcalculator/compression/Input_round_cyl.asp

and here are some others that looked good

http://www.engineersedge.com/spring_comp_calc.htm
http://www.tribology-abc.com/calculators/t14_1.htm
http://www.calculatoredge.com/mech/hspring.htm
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Unread postAuthor: Lockednloaded » Tue Aug 17, 2010 5:04 pm

to calculate the forces on the piston you also have to account for surface area of your piston that it showing pre-explosion
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Unread postAuthor: lozz08 » Tue Aug 17, 2010 6:16 pm

Rip out your calculator, and do this:
enter the diameter of the hole that the air goes through to push the piston.
divide that number by two.
times the answer to that by itself.
times the answer to that by the number 3.142.

the result of all that is the area. now you times the area by whatever pressure you are using, and the answer to that will be the spring force.
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Unread postAuthor: D_Hall » Tue Aug 17, 2010 8:37 pm

1) Hooke's Law
2) Pascal's Law
3) Wikipedia
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