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What Is a Pressure Gauge and When Do You Need One?
Nov 25,2021
In some occurrences, knowing the force of pressure is important to the function of whatever process is in need of this quantification.

For most people, pressure starts and ends as a headache. However, that’s not really what pressure is or means.

In this article, we will cover how pressure is determined in fluids, what a pressure gauge is and its purpose, and some other important faculties of the device.

So keep reading to learn more.

How Is Pressure Determined in Fluid?
Any solid surface is capable of exerting pressure, but liquids and gases also have that ability. This might seem odd if you think of it because it can be hard to imagine hammering a nail in a wall using liquid.

Imagine being submerged at some depth in water. The water above will push down on you because of gravity, therefore it will exert pressure upon you. The deeper you go, the more water is above you, therefore the pressure and weight of the water increases as well.

Not only can the water weight exert pressure, but the weight of gas can do so as well. For instance, the atmospheric air is substantial and we are always at the bottom. The pressure exerted upon our bodies is significant and quite large. The reason you don’t really notice it is because it’s always there.

People only notice changes in pressure below or above normal atmospheric pressure, like swimming underwater or flying in a plane. Our body is able to exert force outward that balances the air pressure inward, so we don’t get injured.

However, this also means that if you are thrown into a vacuum in outer space, the body pressure will continue to push out with excessive force, but no air is there to push in.

What happens after that is a subject for another article, so let’s continue. To measure the pressure of air or water, a pressure gauge is used.

So What Is a Pressure Gauge?
A pressure gauge is a tool that allows a person to mechanically monitor force in a given closed enclosed area. For example, water distribution systems function because air and water within them are pressurized.

A pressure gauge allows you to measure the force of pressure in the air or water, in order to determine if the system is within operational parameters.

What Is Its Purpose?
Gauges are used for many applications across every industry. You will find gauges on pressure regulators to determine set pressure, or a water pump to determine delivery pressure. If you’ve ever seen a firetruck, gauges are everywhere as they determine the flow of water delivered to fight the fire.

And they can be used for reverse osmosis water equipment, as pressure is key to the function of the entirety of the system. And even a simple tire gauge makes sure you travel down the road safely.

When it comes to pressure gauges, there are two distinct types:

Manometer (U-Tube)
The manometer gauges have a U-shaped tube with liquid inside of it. When the pressure is applied to any side of the gauge, the water in the tube is displaced proportionately to the pressure. Pressure is determined by comparing the level of displacement to the markings on the tube. 

Bourdon Tube
The Bourdon gauge is very common in all process industries. It has a reading dial with a needle that points to the appropriate pressure. It consists of a small, sealed tube inside which is connected to a mechanism that moves the needle across a dial.

When the liquid or air enters the gauge, the bourdon tube will try to straighten, and as it does that, it will interact with the gears inside to move the needle.

Is the Pressure Too High or Too Low?
Best industry practices have a bourdon tube gauge operating in the middle arc of its range. By working with engineers in your facility, determine the best operating parameters for your application. If you want to read a maximum of 50 psi, you would want to choose a gauge with a range of 0-100 psi so the gauge operates in the middle of its full range.

Only operators and professional engineers familiar with your application can determine the best and safest range of operation for your process.

Never guess. Your safety and the operation of the process depend on properly specifying critical operating ranges.

How Is a Pressure Gauge Installed?
Most pressure gauges can be mounted directly to the process via a threaded connection, but in instances where the process could clog the

bourdon tube, a diaphragm seal must be used. Connections can be located at the bottom of the gauge, or at the back, mostly determined by how the gauge is to be mounted.

Standing up on a pipe a gauge can be pointed in a direction easily ready by operators. Back connect gauges are typically installed in control panels or in equipment so critical pressures can be monitored.

How Is a Pressure Gauge Calibrated?
Most gauges are installed and forgotten, but in critical applications, annual calibrations are mandatory to maintain accuracy. In general, the smaller the dial the lower the accuracy of the gauge, the larger the dial the higher the accuracy. 4 inch and 6 inch gauges can have accuracies of 0.5% of reading if calibrated correctly and are maintained on an annual basis.

Gauges are calibrated using a known standard usually NIST traceable. This means the standard has been verified to be generating a known pressure at which the gauge can be compared and adjusted accordingly. Only qualified personnel with training should calibrate a gauge in a clean well-maintained environment. Field calibrations for mechanical gauges are not recommended.

Finally, digital gauges must be calibrated in the same way, but usually require a digital interface. In most cases, digital gauges require calibration to specific manufacturers’ standards.