Pressure Gauges – Why You Need Them & How They Work

There is hardly a day I work that I am not talking about the importance of properly installed pressure gauges.  These small devices can often get overlooked or thought of as not necessary on an installation.  When troubleshooting or evaluating the compressed air consumption of an application, this is one of the first items I look for in the installation.

As Russ Bowman shows in the above video discussing proper piping sizes, you can see the importance of properly placed pressure gauges.  This shows the worst-case scenario where the pressure drop due to improper line sizes gives the false sense to the operator that they are achieving full line pressure when in fact they are not.  In order to accurately measure consumption rates, pressure AT THE INLET (within a few feet) to any compressed air product is necessary, rather than upstream at a point where there may be restrictions or pressure drops between the inlet and the gauge. So how exactly do these analog gauges measure the pressure of the compressed air at the installed locations?

Pressure Gauge Model 9011

The video below shows a great example of pressure increasing and decreasing moving the Bourdon tube that is connected to the indicating needle.  The description that follows goes more in-depth with how these internals function.

Most mechanical gauges utilize a Bourdon-tube. The Bourdon-tube was invented in 1849 by a French watchmaker, Eugéne Bourdon.  The movable end of the Bourdon-tube is connected via a pivot pin/link to the lever.  The lever is an extension of the sector gear and movement of the lever results in rotation of the sector gear. The sector gear meshes with spur gear (not visible) on the indicator needle axle which passes through the gauge face and holds the indicator needle.  Lastly, there is a small hairspring in place to put tension on the gear system to eliminate gear lash and hysteresis.

When the pressure inside the Bourdon-tube increases, the Bourdon-tube will straighten. The amount of straightening that occurs is proportional to the pressure inside the tube. As the tube straightens, the movement engages the link, lever, and gear system that results in the indicator needle sweeping across the gauge.

If you would like to discuss pressure gauges, the best locations to install them, or how much compressed air an application is using at a given pressure, give us a call, email, or chat.

Brian Farno
Application Engineer

Air – What Is It?

Air… We all breathe it, we live in it, we even compress it to use it as a utility.  What is it though?  Well, read through the next to learn some valuable points that aren’t easy to see with your eyes, just like air molecules.

Air – It surrounds us – (Yosuke,1)
  1. Air is mostly a gas.
    • Comprised of roughly 78% Nitrogen and 21% Oxygen.  Air also contains a lot of other gases in minute amounts.  Those gases include carbon dioxide, neon, and hydrogen.
  2. Air is more than just gas.
    • While the vast majority is gas, air also holds lots of microscopic particulate.
    • These range from pollen, soot, dust, salt, and debris.
    • All of these items that are not Nitrogen or Oxygen contribute to pollution.
  3. Not all the Carbon Dioxide in the air is bad.
    • Carbon Dioxide as mentioned above is what humans and most animals exhale when they breathe.  This gas is taken in by plants and vegetation to convert their off gas which is oxygen.
    • Think back to elementary school now.   Remember photosynthesis?
      • If you don’t remember that, maybe you remember Billy Madison, “Chlorophyll, more like Bore-a-fil.”
    • Carbon dioxide is however one of the leading causes of global warming.

      Moisture In The Air – (Grant)2
  4. Air holds water.
    • That’s right, high quality H2O gets suspended within the air molecules causing humidity.  This humidity ultimately reaches a point where the air can simply not hold anymore and it starts to rain.  The lack of humidity in the air leads to static, while lots of moisture in the air when it gets compressed causes moisture in compressed air systems.
  5. Air changes relative to altitude.
    • Air all pushes down on the Earth’s surface.  This is known as atmospheric pressure.
    • The closer you are to sea level the higher the level of pressure because the air molecules are more densely placed.
    • The higher you are from sea level the lower the density of air molecules.  This causes the pressure to be less.  This is also why people say the air is getting a little thin.

Hopefully this helps to better explain what air is and give some insight into the gas that is being compressed by an air compressor and then turned into a working utility within a production environment.  If you would like to discuss how any of these items effects the compressed air quality within a facility please reach out to any Application Engineer at EXAIR.

Brian Farno
Application Engineer

1 – Air – Creative Commons – Tsurutea Yosuke –

2 – DSC_0750 – Creative Commons – David Grant –