Basics of pressure measurement
Most industrial measurements are somehow related to pressure in its various forms. For example, current is often measured by determining the pressure at two different points in a system. In a Bourdon system, pressure changes are used to produce mechanical motion of the recording pen. Pressure can also be used to measure temperature in a filled system through changes made by the expansion of a liquid or liquids in a filled system. Pressure measurements are performed more than any other measurement in the process industry. This is the best quick sign for things to be done by pumps and compressors. It is also the most important measure of the condition of tanks under working pressure.
What is pressure?
Pressure is a measure of the force applied to a unit area.
For pressure in a container, it is a measure of the force exerted by a liquid due to its molecular activity. This is a derivative of the above concept, which is combined with the kinetic theory of subjects. For more information, read the article Pressure Gage .
Types of pressures applied by liquids
All liquids (liquids and gases) have a weight, so they put more pressure on the walls of their containers. The pressure caused by a liquid at any particular point or place on the ship depends on the height of the liquid above it. This pressure is independent of the shape of the vessel.
Density is the weight of one cubic meter of material. Different liquids weigh different amounts for the same volume and therefore create different pressures. As we know, the pressure is equal to the force (or weight) of more than one unit, and at any constant volume of the column, the weight of the existing liquid varies with density. So changing the pressure density changes the container.
Pressure produced by gases
To study some of the principles governing the behavior of gases, we will use air as common gases. Because air weighs, it creates static pressure, just like liquids. One cubic foot of air weighs about 0.08 pounds. A room 10 feet wide, 20 feet long and 8 feet high is 1,600 cubic feet of air and weighs about 128 pounds. The deep layer of air that covers the earth exerts as much pressure as water at the bottom of the ocean. This pressure is known as atmospheric pressure and is around 14.7 psi at sea level.
External load pressure
The final or total pressure applied at any point in time on a vessel, pump, line, etc. depends on the head, or the weight of the fluid obtained, plus any external pressure applied to the fluid used. The following figure shows the effect of external pressure.
Tanks are full of water up to 20 feet high and exposed to the atmosphere. The pressure at the bottom will be 0.433 20 20 or 8.66 PSI. If we close the vessel and add 200 psi of compressed gas to the top of the vessel, we find that the floor pressure (PSP) will be (200 + 8.66) psi or 208.66 psi.
There are two reference points for measuring pressure. The most logical zero is absolute – a condition that exists only in a complete vacuum. The pressures measured from this reference point are called absolute pressures. Another reference used is atmospheric pressure. The problem with this reference is that it varies with altitude (reference with sea level) and to some extent with climatic conditions. At or near sea level, this pressure is around 14.7 psia or 29.9 inches or 760 mm Hg.
Absolute pressure is the pressure measured in terms of zero pressure (vacuum).
A barometer (or sometimes called an internal pressure) is the pressure measured by a barometer to reach atmospheric pressure. A barometer shows the pressure difference between a system or ship and the local atmospheric pressure. However, be careful! When reading the sphygmomanometer; Determine whether this is an absolute pressure or a barometer, usually denoted by “a” or “g”, for example. psia or barg.
Atmospheric pressure is a measure of pressure on the surface of the atmosphere. However, the problem is that it varies with altitude and humidity. Therefore, atmospheric pressure may vary from region to region.
Differential pressure is the pressure difference that is measured between two different pressure points at the same pressure reference point. Between unknown pressure and local atmospheric pressure.
Pressure is the pressure exerted by a liquid, which is characterized by an increase in fluid in a liquid column. depends on; 1. The height of the liquid column. 2. Relative density of liquid. Pressure pressure = RD xhx 9.8 kPa where, RD = relative density of liquid, hour = height of liquid g = gravitational force Note: The relative density density of a liquid is relative to the standard reference density (water = 1000 kg / km)
Pressure lower than atmospheric pressure is called a vacuum. Vacuum is the lack of air fluids. The vacuum scale extends between absolute zero reference point and atmospheric pressure, so the pressure is not positive. Treated as a suction force or negative pressure.
Pressure conversion between units
Pressure measurement methods
There are three basic ways to measure pressure. The first method involves the equilibrium of an unknown pressure against the pressure produced by a column of fluid of known density. The second method involves allowing an unknown pressure to act on a known area and measuring the resulting force directly or indirectly. The third method involves applying unknown pressure on the elastic material and measuring the pressure or the resulting pressure. For more information, read the article on pressure transmitter and in case of any ambiguity and questions, contact the industry’s shop.
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