Thanks for the replies. I did do some searches, and found no useful help. It seems simple issue. I know the volume of the tank. I can give times to any pressure,or the time between any two pressures. I can even put an orifice of a known size in the discharge line with the compressor running, and time what happens then.
I can even find the ideal gas formula. I just don't know how to use that to tell what I want to know.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags