I know that the average PSI at sea level is 14.7 PSI, I just don’t understand why gauges and other PSI measuring equipment dont account for outside atmospheric conditions.
For example, if you were filling a scuba tank at sea level, the gauge would say 0 PSI instead of 14.7. And when you do fill the tank up by 100 PSI (I don’t know how much a scuba tank holds), it would say 100, not 114.7.
It’s the same with vacuum chamber gauges. Instead of going from 14.7-0, they go from 0 to around -30 PSI. Where is the extra 15.3 PSI coming from? I assume that it is just standard to start at 0 PSI for all gauges, but it’s a bit confusing. Because if you were were on top of a mountain then the gauge wouldn’t be accurate.
In: Physics
The gauges are measuring against the outside air, since that’s generally what you care about. You don’t really care how much air is in your tire, you care how hard that air is pressing out, and that varies depending on how much air is outside the tire. A balloon with the same amount of air might be regular size at your house, very tiny at the bottom of your pool, and pop at the top of a mountain.
The gauges are essentially using a balloon to measure relative pressure, which will tell you how much more the air on one side is pressing than the air on the other side.
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