What is the best approach to choosing a pneumatic linear actuator for a specific job? I know that force is equal to pressure times area. I beleive that stroke is simply a matter of the distance the load is required to be actuated, is this correct?
If I know the pressure range available to me is anywhere between 0 and 90 PSI, then by determining the amount of force required to move the load can’t I determine the required piston area? What about the annular area?
I think you’ve answered your own question. You are correct that pressure times piston cross section area (Pi*R[sup]2[/sup]). Stroke is determined by what is available in whatever piston you use, presuming of course your hydraulic pump can deliver the volume of oil required without losing pressure.
Are you going to use this on the Moon?
One of the primary reasons for the use of air, along with its many inherent problems is it is cheep and kind of easy to come by(around here).
Now sizing of prime mover/actuator/work is a very necessary thing in Hydraulics.
What are you trying to do?
I mis-read your Q
My experience with pneumatics is, Its only good quality is the expense of the medium. With its compressibility, mostly low power(however we use air lift bags lifting 10 tons and more but dangerous to work with) and many other faults. If you need to move a 1,000 lbs. load a pneumatic system will have to be capable of moving a 2,000lbs system, then flow controls, are used to regulate speed. USE non-compressables.
Output force is area times pressure. If you are extending the actuator, you use the “head end” area, which is pi(D^2)/4 (where D is the diameter of the bore). If you are retracting the actuator, you have to subtract the cross-sectional area of the rod from that–i.e, area is pi(Dbore^2 - Drod^2)/4.
You might want to add orifices or a needle valve to control actuator rate. If the load is opposing the direction of motion, it’s best to restrict the flow into the actuator; if it is in the direction of motion, it’s best to restrict flow out of the actuator.
You might also consider some kind of snubbing at the end of stroke, especially if the load is more than a few pounds or if the mechanism you’re moving is massive.
I agree with dbrohman that with high loads (greater that 100 pounds or so), hydraulics is the way to go.
And if you need a good calculator for those circle cross-sections, go to
www.1728.com/diam.htm
It also has cylinder volume calculations which is something I think you won’t need though.
As usual I would like to thank everyone for taking the time to respond. I love this site.