Don't take this wrong but you cannot calculate suction. A vacuum does not pull. I know the word conveys the idea in a short simple term, but the idea is incorrect. Even in a vacuum chamber the particle pressure empties the chamber.
I understood engineering much better when I didn't think: suction, cold, vacuum, etc.
If you already do this my apologies, I am just trying to keep you from the faults I have learned to avoid (most of the time).
Brad
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(Larrabee's Law) Half of everything you hear in a classroom is crap. Education is figuring out which half is which.