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
It’s all relative to the ambient atmosphere. If you fill your tires at sea level (or below) to 35 psi, then take it to the peak of Mt. Everest, the internal pressure will have increased, even though no air has been added to the tire. In most cases, you’re not going to care how much *actual* air you have in the tire, but whether the tire can withstand the *relative* pressure. Plus, to calibrate an absolute gauge, you’d need a perfect vacuum for reference. It’s much easier just to calibrate to the ambient atmosphere.
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