When measuring pressure, there are two types of pressure measurements: gauge pressure and absolute pressure. Gauge pressure is the measure of relative pressure between two points in a system; while absolute pressure takes into account the atmospheric pressure as well. In order to accurately measure the absolute pressure in a system, you need to know the atmospheric pressure at that location. For example, if you were measuring the absolute water pressure in a pipe at sea level, you would use the atmospheric pressure of 101,325 Pa (Pascals) to calculate the true water pressure. However, if you were measuring the water pressure in a pipe at a high altitude where the air is thinner, you would use a lower atmospheric Pressure such as 84,000 Pa to calculate the correct water pressure
What is Gauge Pressure?
Gauge pressure is a measure of the amount of force per unit area that is exerted on a surface by a fluid. Gauge pressure is often used to describe the pressure of liquids and gases in tanks, pipes, and other closed containers. The term “gauge pressure” comes from the fact that many pressure gauges are designed to measure the difference between atmospheric pressure and the pressure inside a container. Gauge pressure is typically expressed in units of pounds per square inch (psi).
What is Absolute Pressure?
Absolute pressure is a measure of the combined force exerted by the atmospheric pressure and the hydrostatic pressure of a fluid. It is commonly expressed in units of pounds per square inch (psi) or inches of mercury (inHg). Absolute pressure is often used in engineering and scientific calculations, especially in the fields of fluid mechanics and thermodynamics. The absolute pressure at a given point is determined by adding the atmospheric pressure to the hydrostatic pressure exerted by the fluid at that point. Absolute pressure is sometimes referred to as “total pressure” or “pascal’s absolute” pressure. It should not be confused with gage pressure, which is a measure of the hydrostatic pressure only.
Difference between Gauge Pressure and Absolute Pressure
- Gauge pressure is the pressure relative to atmospheric pressure. Gauge pressure is zero in a perfect vacuum. Low pressure in an automobile tire is an example of gauge pressure. Gauge pressure is sometimes also called “relative” pressure.
- Absolute pressure is the actual force per unit area exerted by a fluid against a surface. Absolute pressure is measured relative to a perfect vacuum, making it equal to gauge pressure plus atmospheric pressure. The standard atmospheric pressure at sea level is 14.7 psi (pounds per square inch). This means that, at sea level, the absolute pressure is 14.7 psi higher than Gauge Pressure. A tire with 29 psi would have an absolute pressure of 44.7 psi (14.7+29) measured at sea level. When dealing strictly with liquids, we can use the unit of measure “inches of mercury” (inHg) in place of psi.” Atmospheric pressure at altitude can be found using a barometer.”>p>p class=”c9″>Pressure caused by the weight of the atmosphere is often considered “atmospheric” or “barometric” pressure and is denoted as “P0”.
Gauge pressure is the most common type of pressure measurement. It measures the pressure relative to atmospheric pressure. Absolute pressure, also called total pressure or gauge plus absolute pressure, is the sum of gauge and atmospheric pressures. Differential pressure is the difference between two pressures. Many industrial processes rely on differential pressure measurements for process control.