Short Answer
Gauge pressure and absolute pressure are two ways of measuring pressure in a system. Gauge pressure is the pressure measured relative to atmospheric pressure. It does not include the atmospheric pressure around us, meaning a gauge pressure of zero indicates that the pressure inside a system is equal to the surrounding air pressure.
Absolute pressure, on the other hand, is the total pressure measured from absolute zero pressure (a perfect vacuum). It includes atmospheric pressure along with any additional pressure in the system. Absolute pressure is always greater than or equal to gauge pressure and is used in scientific calculations and hydraulic systems where precise measurements are needed.
Detailed Explanation
Gauge Pressure
Gauge pressure is the difference between the measured pressure and atmospheric pressure. It is given by:
Pgauge=Pabsolute−PatmosphericP_{\text{gauge}} = P_{\text{absolute}} – P_{\text{atmospheric}}Pgauge=Pabsolute−Patmospheric
where:
- P_gauge = Gauge pressure
- P_absolute = Absolute pressure
- P_atmospheric = Atmospheric pressure (~101.3 kPa at sea level)
Gauge pressure is widely used in industrial applications, such as measuring tire pressure, pipeline pressure, and hydraulic system pressure, because it directly represents the pressure relative to the environment.
Absolute Pressure
Absolute pressure is the total pressure measured from a perfect vacuum. It is expressed as:
Pabsolute=Pgauge+PatmosphericP_{\text{absolute}} = P_{\text{gauge}} + P_{\text{atmospheric}}Pabsolute=Pgauge+Patmospheric
Since it includes atmospheric pressure, absolute pressure is used in:
- Vacuum systems (where negative pressures are involved).
- Weather and altitude studies (where pressure changes with height).
- Hydraulic and gas systems (where precise pressure control is required).
Conclusion
The main difference between gauge and absolute pressure is that gauge pressure excludes atmospheric pressure, while absolute pressure includes it. Gauge pressure is commonly used in daily applications, while absolute pressure is important for scientific, hydraulic, and aerospace applications. Understanding this difference is essential for accurate pressure measurement and system design.