2.2 Pressure and Head
There are several bases for measuring pressure as per below:
2.2.1 Atmospheric pressure is the ratio between the weights of the atmosphere per unit area on the earth surface. Thus one atmospheric pressure is equal to 101.325 or 14.7 pound per square inch. Since barometer is used to measure atmospheric pressure, this pressure is often referred to as Barometric pressure, pb
kilo Newton per square meter
psi Pound per square inch
Pressure on a pressure gauge is pressure above atmospheric pressure.
2.2.2 Pressure head() Pressure head is the beight of the liquid that exerts peessure on a surface area. Pressure measuring device measures pressure difference from that of atmospheric pressure. The resulting pressure is called gauge pressure, which can be positive or negative value.