Introduction to the PSI System
The pound per square inch or, more precisely, pound-force per square inch is known as a unit of pressure or stress based on avoirdupois units. The pressure arising from a force of one pound-force applied to an area of one square inch. In SI units, one psi is nearly equal to 6895 N/m2
What Is The SI System?
- The SI system of units is commonly known as the International System of Units (Système International) determined from the metric system and is based on the metre and the kilogram.
- It is universally accepted and used across the world. The fundamental unit of pressure is pascal, described as the pressure exerted by a force of one newton perpendicularly on an area of 1 square metre.
Understanding The PSI (Pound Per Square Inch)
- Pounds per square inch absolute (PSIA) are used to clarify that the pressure is applied to a vacuum rather than the ambient atmosphere pressure.
- Since atmospheric pressure at sea level is about 14.7 PSI (101 kilopascals), this will be added to any pressure reading made in the air at sea level.
- The opposite is the pounds per square inch gauge (PSIG), intimating that the pressure is relative to the atmospheric pressure.
- For example, a bicycle tire pumped to 65 PSIG in a local atmospheric pressure at sea level will have a pressure of 79.7 psia, i.e., 14.7 psi + 65 psi.
- When the gauge pressure is referenced to something other than the ambient atmospheric pressure, the units will be pounds per square inch differential (PSID).
