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Message: [QUOTE="juniort444e, post: 95280, member: 797"] [I][FONT=Verdana][COLOR=lemonchiffon]25psig (psi gauge) is 39.7psia (psi absolute), 25psi + 14.7psi of atmosphere. Since the gauge is set to zero at 14.7psi, a reading of 25 tells us we actually have 39.7psi.[/COLOR][/FONT][/I] [I][FONT=Verdana][COLOR=lemonchiffon]This represents a pressure ratio across that compressor of 2.7:1, 39.7psia / 14.7psia. The meaning of this is that the compressor is taking in air at 14.7psia and compressing it 2.7 times such that it is discharging air at a pressure of 39.7psia. That is the pressure ratio. It is technically described as P2/P1 where P2 is the outgoing and P1 the incoming pressure.[/COLOR][/FONT][/I] [I][FONT=Verdana][COLOR=lemonchiffon]From here the easiest way to see this might be to simply take a ride through the system.[/COLOR][/FONT][/I] [I][FONT=Verdana][COLOR=lemonchiffon]The first stage takes in air at 14.7psia at sea level. If it's producing a pressure ratio of 2.7, then it is compressing that air from 14.7psia to 39.7psia on it's outlet. [/COLOR][/FONT][/I] [I][FONT=Verdana][COLOR=lemonchiffon]The second stage compressor then takes in this air at 39.7psia and compresses it another 2.7 times such that it takes the air from 39.7psia and compresses it to 107.21psia.[/COLOR][/FONT][/I] [I][FONT=Verdana][COLOR=lemonchiffon]Ok. Here i took charles post a did some math by putting in my numbers. [/COLOR][/FONT][/I] [I][FONT=Verdana][COLOR=lemonchiffon]Im guessing the first stage would be the atmosphere and the second stage is the primary. [/COLOR][/FONT][/I] [I][FONT=Verdana][COLOR=lemonchiffon]I figured 25psi from the atmosphere would be a good guess. Let me know what you think.[/COLOR][/FONT][/I] [I][COLOR=lemonchiffon]And those last numbers are absolute so it would read on the gauges... atmosphere 25psi....primary 92.5psi[/COLOR][/I] [/QUOTE]