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

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