paper: FRC Pneumatic Cylinder Linear Speed

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FRC Pneumatic Cylinder Linear Speed
by: Deke

This is a calculator that determines the velocity and duration of a pneumatic cylinder extending.

This calculator uses Bernoulli principles to calculate the volumetric flow for pneumatic cylinders. The volumetric flow is then used to calculate cylinder velocity and extension duration.

For latest file, see FRC Calculator: paper: FRC Calculator - CD-Media: Papers - Chief Delphi

FRC Pneumatic Cylinder Linear Speed.xlsx (11.7 KB)

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Hey Deke (and other CD people),

I am working on a system that requires certain cycle times of pneumatic cylinders. This spreadsheet is very helpful but I am finding it a bit difficult to understand exactly what is going on having little to no formal training in real-life pneumatic systems myself.

My questions primarily deal with your first set of calculations, that being the effective area of the tube and solenoid. Do you have any literature I can find to help me understand these calculations and where you are pulling the constants and equations from?

Thank you very much.

-Phil

Hey Phil,

I missed the original post, but here is some information if you haven’t found it already.

Here is a good site reviewing Cv and it’s constants: http://kb.eng-software.com/display/ESKB/Relationship+Between+Flow+Coefficient+and+Discharge+Coefficient

Basically Cv = 27.66 * A * Cd

Since we are only told the Cv of the solenoid valves and not Cd, I set Cd to 1 and solve for area. This gets us close to where we need to be for the calculations.

For the tube effective areas, I simply calculated the area from the tube inner diameter and applied a .7 discharge coefficient (Cd). A .7 Cd is a fairly common starting point for discharge coefficients. Now this ignores the length of the tube, so you can adjust the Cd to account for that if needed.

Whenever we do hand calculations like this at my place of work, we do extensive testing to validate our calculations. Air flow and fluid flows are very sensitive to edge conditions (Cd) and need to be validated. We can get in the ball park, and the testing gets us zeroed in.

Hope that helps.

-Deke