Intuitively, we live in a world where every inch of the human body is under pressure (about 14.7 pounds per square inch at sea level). Evangelista Torricelli realized this fact in the 17th century. He said: "We live in an ocean of elemental air." The pressure exerted by the atmosphere in our gravitational field is also called atmospheric pressure, which is an absolute pressure, which fluctuates with different weather systems. The reason why we do not have such a large pressure is because some incompressible fluids in our body exert equal and opposite pressures.
The pressure in the High Pressure Grease Fitting is the force applied per unit area perpendicular to the surface of the object. Mathematically, it is P = F / A, where P is pressure, F is force, and A is area. Pressure is a scalar quantity with only magnitude and no direction vector characteristics. In a practical sense, we can think of it as a force that acts equally on all surfaces it exposes and is generated by the combined energy of the gas or liquid that touches the surface. There are two basic pressure types-absolute pressure and gauge pressure-which are distinguished by what pressure they are compared to. This is called reference pressure.
The standard terminology used to describe the physical characteristics of a pressurized system may confuse someone new to pressure measurement. Understanding the standard terminology provides a common language to ensure that what you want is what you want when you buy a pressure gauge, pressure controller or calibrator, and pressure transmitter, transmitter or sensor. It will also eliminate the mismatch between the calibration and the calibrator.
The reference for gauge pressure is the ambient atmospheric pressure. The reference for absolute pressure is absolute vacuum. Therefore, in a sense, both are reading the difference between the reference pressure and the applied pressure. However, for gauge pressure, the reference pressure may change according to the current atmospheric pressure.
When our container is under atmospheric pressure, we may want to ensure that the container does not explode or explode. In this case, we can use a gauge pressure sensor to measure the difference between the atmospheric pressure and the pressure in the tank by exposing the reference to atmospheric pressure.
The pressure difference compares two arbitrary pressures. Essentially, all pressure measurements are differential because they compare one pressure to another. Differential pressure is usually measured under elevated pipeline pressure and is used to measure flow, liquid level, density and even temperature in the pipeline.
Like gauge pressure, vacuum pressure is referenced to atmospheric pressure, but it is a measure of pressure below atmospheric pressure and expressed as a positive number.
Bidirectional pressure, like gauge pressure, refers to atmospheric pressure, but the pressure above atmospheric pressure is measured as positive pressure, and the pressure below atmospheric pressure is measured as negative pressure.
This standard terminology can make a big difference when it comes to accurately conveying what is needed for a particular (such as Surface Packers) application.