-> But how does the oil return to the tank? The reed valves in the
-> outlet line will prevent back flow, so you'd have to add some sort of
-> small bypass, no?
Nah.  Those valves don't seal all that well and the oil gets shoved back
through as it condenses and runs back.
-> What happens to all the water from compression? How much can you
-> allow to accumulate with the oil?
THe water doesn't stay IN there all that good.  You DO need to get rid
of that highly hygroscopic compressor oil though.  I use 10w-30 and it
lasts for years.  I've not checked mine in five years.
-> I've tested these and very seldom do the open below 500 lbs. Way too
-> high.
No, No, I mislead you.  I meant the pressure control switch.  I use
popoff valves off water heaters.  Feel free to BUY an appropriate one if
you're concerned that your pressure control switch might malfunction.
-> them. It doesn't take a lot of volume to be terribly dangerous.
Nope, but shatterproof tanks generally just go ONE direction!  
The blowout plugs in the freon bottles will sent the tank UP!  WAY up!
 ^..^
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