# Calculating PSI, bore, and load values on props



## SkeletalRemains (Jan 14, 2006)

I did a search for 'PSI Calculation' on the forum and couldn't find this info (I know I've seen it here buried in a few threads though in years past, just can't seem to find them now). So I thought this might be handy for someone trying to figure out some basic values regarding pneumatic cylinders and loads, PSI, etc...

I figured this was OK for the 'How-To' section, please move if it is not.

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I have seen so many questions about what to do with specific cylinder sizes, bores, lengths, what PSI to use, etc. Hopefully this will help anyone who has a question regarding this.

A LOT of pneumatic props are 'third-class levers'. This is where you have the force between the load and the fulcrum. The fulcrum is typically a hinge on one end, the load is the prop on the other end, and the force is the cylinder mount somewhere in between.

If you are moving 100 pounds at the end of this lever, and you connect the cylinder rod to the middle of that lever, you are effectively moving 200 pounds (based on the physics of a third-class lever). In order to move that kind of weight, you need a pretty heavy duty cylinder. For every pound you want to lift per a single psi of air pressure, you need 1 sq. inch of area of cylinder bore. Using a 2" cylinder at 75 psi, you would use A=(3.14 x r^2), or 3.1 sq. in. of bore surface area. Then multiply that times the amount of air pressure to get 235 pounds of force at the rod end, more than enough to push your load of 200 pounds. All you would do is tweak the air pressure to get it jumping the way you want it...

One thing to think about though, do not assume that two 1" cylinders will do the work of a single 2" cylinder, doesn't work that way. The key element here is surface area of the bore. the surface area of a 2" bore cylinder is 3.14 sq. inches. The surface area of a 1" bore cylinder is only .785 sq. inches. That means it would take the power of four (4) 1" cylinders to do the work of a single 2" bore cylinder. 

If anyone wants more info on this, I will put together a 'How-To' with illustrations and formulas to further explain.


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## Garage-of-Evil (Feb 24, 2008)

This site has helped me in the past:

Pneumatic Calculators


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## SkeletalRemains (Jan 14, 2006)

Very cool website! Thanks for the post! This makes everything a lot easier!


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## David Rosenblatt (Jan 23, 2013)

I would love to learn More.

Thanks

David Rosenblatt


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