# Need some help with pneumatic math



## trex (Feb 28, 2010)

Hello, I need some help with this math,, I really cant grasp this! I've been trying on my own and really just cant seem to get anywhere, can someone please help? Here are a few of the problems i need help with. What would be the minimum bore size for a cylinder if it needed to devolp 550 pounds of force and operate from a pressure of 110 psig? Another one,, what torque is produced by a 2.5 hp air motor that operates at 1800 rpm with 80 psig air pressure?


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## niblique71 (Dec 2, 2009)

There are several force calculators out there. Here's one. I came up with 2.5" bore at 110psi

http://www.stearnsonline.com/calc.htm

As far as your air motor, torque and HP aren't always related. Same thing with rpm. If the motor has a nameplate with a model number, you might be able to get the specs on the net. Otherwise there is a pretty simple test you can try. Attach a 1' bar (lightweight aluminum) to the air motor, Securely mount it to a very solid surface, hang a known weight (say 1'lb) at exactly 1' from the center of rotation. If you have a good regulator with a guage I would start at 0 pressure and VERY slowly raise the pressure untill the bar lifts the weight from vertical (hanging straight down) to horizontal (Parralell to the ground). Make sure you make some kind of safety stop JUST above the vertical position on BOTH sides of the motor since you might not know the direction of rotation. This will prevent full rotation and a potentially dangerous situation. Once you find the pressure needed to get the bar at exactly horizontal, that will give you "foot lbs" at a certain pressure. let say it takes 15 psi to lift a 1lb weight that would be 1-ftlbs at 15psi. Torque is measured in ft-lbs or inch-lbs. There are people in here that can help extrapolate what kind of pressure you might need to achieve a certain torque base on your results. If you double the air pressure you might triple or quadrouple the torque you achieve. Obviously this method doesn't account for the weight of the bar but it should get you close. Hope this helps. Anyone with more knowlege please chime in.


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