Pressure
Pressure, abbreviated as p, is one of the most important concepts in piping design. Pressure is a measure of the force exerted per unit area on a surface. It is defined as the force per unit area perpendicular to the surface over which the force is distributed.
Pressure Index
Pressure can be expressed as either absolute pressure or gauge pressure. Absolute pressure is the total pressure measured relative to a perfect vacuum, while gauge pressure is the difference between the absolute pressure and the ambient pressure of the surrounding environment. Pressure is a scalar quantity having magnitude and is independent of any specific direction.
Pressure plays a fundamental role in many areas of science and engineering, including fluid dynamics, thermodynamics, and materials science. It is used to describe and predict the behavior of gases, liquids, and solids under various conditions, and is essential in the design and operation of a wide range of devices, from engines and turbines to pumps and compressors.
Pressure formula |
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\( p \;=\; F \;/\; A \) (Pressure) \( F \;=\; p \; A \) \( A \;=\; F \;/\; p \) |
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Symbol | English | Metric |
\( p \) = Pressure (psi) | \(lbf \;/\; in^2\) | \(Pa\) |
\( F \) = Force Acting on the Surface | \(lbf\) | \(N\) |
\( A \) = Surface Area | \(ft^2\) | \(m^2\) |
Pressure Types
Typical UnitsSome common units for pressure are as follows. For a more complete list, visit the pressure conversion page. | |
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INTERNATIONAL SYSTEM OF UNITS, SI |
ENGLISH UNITS |
Bar | Inches of Mercury |
Centimeter of Mercury | Inches of Water |
Centimeter of Water | Kip per Foot2, KSF |
Pascals, Pa | Kip per Inch2, KSI |
Pound per Foot2, PSF | |
Pound per Inch2, PSI |
Pressure Instruments
In piping design, pressure is measured several different ways. On a Piping & Instrumentation Diagram, the typical instruments are:
Pressure Indicator - It is a mechanical device, that is calibrated to display a pressure.
Pressure Transmitter - This is used to display the pressure in the equipment and send an analog signal to a computer for futher processing. It might be used as an alarm in case the pressure gets outside normal operating conditions.
Pressure Switch - Used to send a digital signal (yes or no, 1 or 0) to a computer for an action to be performed. E.g. send an alarm, turn off a pump, etc.
Tags: Pressure Gas Hydraulic Fluid Pipeline Instrumentation and Controls Drilling