Difference between PSI, PSIA and PSIG
This article will help you understand the difference between PSI, PSIA, and PSIG - how compressed air is measured.
PSI, PSIA and PSIG: What’s the difference?
If you’re an avid user of compressed air for industrial use - you must be well-aware about the term PSI. But if you’re relatively early in your compressed air journey, we’ve got you covered. Air compressors supply the air pressurized air to various industrial functions and requirements. Pressure is measured in PSI - which indicates the maximum pressure produced by an air compressor in conjunction with supply metric - CFM (Cubic Feet per Minute).
Let’s take a closer look at Compressed Air Measurements:
As we mentioned earlier, PSI indicates how the compressor functions. Though, there are multiple factors that come into play while considering the air pressure measurements of an air compressor like the altitude and geographic location you’re at. We suggest it’s best to take expert advice before trying things out on your own to assure best output.
PSI - Pounds per square inch
PSI is used to measure the amount of pressure imposed on a single square inch of space. It measures the force in an area specific to one square inch. The force of air is the driver of power while producing compressed air. For example, an air compressor’s output rated at 500 psi means that it provides 500 pounds of pressure per square inch.
It is particularly specific to non-SI industrial and technical purposes such as tire pressure, fuel storage & distribution, waste water management among others.
PSIA - Pounds per square inch absolute
Also referred to as total pressure, PSIA refers to pressure relative to zero or a perfect vacuum.
For example - In a vacuum, if the tire in our example were completely empty of air, 0 PSIA would be the measurement.
PSIG - Pounds per square gauge
It is also referred to as pressure relative to ambient atmospheric pressure. A vessel completely void of any air molecules (at sea level) would be roughly -14.7 PSIG, and ambient air pressure is always measured as 0 PSIG
PSIG is always lower than PSIA. The formulas used to describe the relationship are:
PSIA = PSIG + 1 atm
PSIG = PSIA - 1 atm
(where atm is atmospheric pressure)
You can easily calculate the PSIA, PSIG or even convert between the two - if you know the actual atmospheric pressure value for your location, you can use that number in the above formulas. Alternatively, you can use 14.7psi - the approximate atmospheric pressure value at sea level.
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