1. ATMOSPHERIC PRESSURE
Atmospheric pressure is the pressure measure on the surface in the atmosphere. However, the difficulty is that it changes with altitude and humidity. Thus, atmospheric pressure may differ from one area or place to another.Atmospheric pressure at sea level is also called barometric pressure.
2. GAUGE PRESSURE
Gauge pressure is the pressure above atmospheric pressure. Hence, the zero of the gauge pressure scale depends on the atmospheric pressure at that point. Sometimes it is called internal pressure.
P gauge = P abs – P atm
3. ABSOLUTE PRESSURE
Absolute pressure is the pressure measured with respect to zero pressure (vacuum).
Absolute pressure = gauge pressure + atmospheric pressure.
4. VACUUM PRESSURE
Vacuum pressure is the pressure less than atmospheric pressure. Vacuum is often measured in inches of water (inH2O) or mercury (inHg).The vacuum scale extend between the absolute zero reference point and atmospheric pressure, thus it is not a positive pressure. It is treated as a sucking force or negative force.
5. DIFFERENTIAL PRESSURE
Differential pressure is the difference in pressure measurement taken at two related points. It is calculating by subtracting the lower port pressure reading from the higher port pressure reading. E.g. Between unknown pressure and a local atmospheric pressure.
6. STATIC PRESSURE
Static pressure is defined as the pressure exerted by fluids at rest. Static pressure is independent of kinetic energy of fluid.