Hi Cas,
I'm pretty sure I'm not looking for an "industrial" compressor, but I can't get a clear picture from my internet seaching for a small high(ish) pressure compressor.  All I need to do fill an air line in a water well to measure water depth - 1 psi of air pressure displaces 2.31 vertical feet of water.  So to fill a 600' vertical air pipe in the well I need almost 300psi (less than 10 gal of volume in pipe, but the bottom of pipe is open ended so air bubbles out bottom, and small volume of air needs to keep flowing to maintain enough pressure to keep air bubbling out the bottom of the pipe as the water level above changes.  Some $20 portable car tire inflator pumps are marketing 300 psi.  Shortish run times.  (Don't know why they'd need 300psi for a car tire).  and one hand pump bicycle pump is saying 260psi, (impractical to keep pumping and also record data)  I need to monitor recovery rate of well when well pump is turned off, so air pump need to keep going.  Most residential construction compressors are max psi of up to 175PSI.  There appears to be a new residential construction movement to "high" pressure compressors in the 400psi range (the units appear overkill for my application when a bicycle pump could do if if I could just keep pumping...)  Is there some sort of technological threshold that limits compressors to around 150psi? (before they get to industrial sizes).  Tips on what I should be looking for?