What Type Pressure Gauge Should Be Used?
Published:2014-01-15 10:05:57    Text Size:【BIG】【MEDIUM】【SMALL
Pressure gauges come in several different pressure types, and end users need to choose the right one. A basic understanding of what the pressure types are and how they affect the measurement of pressure gauges is helpful. The types include:

    Gauge pressure—is vented to the atmosphere. Therefore, a “gauge” pressure gauge measures all pressures relative to atmospheric pressure, which changes with the weather. It also only measures positive pressure.
    Compound pressure—is also vented to atmosphere. It uses atmospheric pressure as its reference point as well. However, a compound pressure gauge measures both vacuum and positive pressure.
    Vacuum pressure—is also vented. It still uses atmospheric pressure as its reference point. However, vacuum pressure gauges measure only vacuum pressure. At sea level, a vacuum is somewhere between zero and -14.7 psi.
    Sealed pressure—is not vented to the atmosphere. Its reference chamber is sealed at the factory, primarily for dusty, dirty or wet environments to protect the internal electronics. Sealed pressure gauges typically measure positive pressure.
    Absolute pressure—is also not vented. Its reference chamber is sealed at the factory as well, but under a full vacuum. Therefore, it considers even vacuum pressures as positive measurements.

Because pumps deal with vacuum pressure, an accurate pressure gauge must also account for vacuum pressure. For this reason, a compound pressure gauge or an absolute pressure gauge should be used.

Using an absolute pressure gauge on pumps is a good idea, particularly when an end user needs a sealed chamber for protection from dust and moisture ingress. However, because it is not vented to atmosphere, the readings will change along with atmospheric pressure changes. This happens as the weather changes from day to day—resulting in a change of a few psi. Operators will need to be trained to read the pressure gauge. For example, what was zero on the compound gauge is actually the natural pressure of the atmosphere at the application’s elevation. On an absolute pressure gauge, it would read somewhere close to 15 psi, instead of zero. Operators must also understand why the readings will change when compared to a vented reading that automatically adjusts with the atmosphere.
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