Pressure gauges, sometimes known as vacuum gauges, are used for measuring the pressure of various types of fluids and gases, and to give an electrical output of the pressure. These gauges provide visual indication and help to maintain a constant pressure by letting personnel ensure that the pressure does not build up beyond acceptable limits. These types of gauges are used in: pressure vessels, compressors, pumps, vacuum pumps and equipment, process lines, medical gas cylinders, fire extinguishers LPG plants and filling stations.
To properly understand how a pressure gauge works, it helps to understand a little bit about pressure. Air pressure is measured in pounds per square inch (PSI). An object that is one-inch square and one foot long that weighs one pound is equal to 1 psi. There are several types of pressure gauges such as differential pressure gauges, compound pressure gauges, positive pressure and negative pressure gauges. However, the most commonly known type of gauge is the simple tire gauge that is used to tell you the air pressure in your car tires.
When the air from your tire enters the pressure gauge the air is forced against a rod that is marked or engraved with psi readings. A spring that is coiled around the rod and is calibrated to the average maximum car tire pressure pushes against this rod. Since the rod and the spring are calibrated with a known factor, the correct measured air pressure can be determined and shown to you on the gauge.
Other types of common pressure gauges include the following:
- Differential types of gauges provide the relative pressure difference between two tapping points.
- Positive gauges are used to measure the positive pressure (from zero to higher pressure).
- Negative pressure gauges are used to measure the vacuum or negative pressure.
- Compound pressure gauges are used to measure the pressure range from negative to positive.
The pressure readings are can be displayed by using: analog meters, needles in front of a graduated mirror scale, digital readouts, graphical outputs. Units of pressure measurement can include: cm Hg, kg / cm2, kPa, inches H2O, PSI, inches Hg, bars, feet H2O and oz / inch square.