Pressure Gauges

Pressure gauges are used for a variety of industrial and application-specific pressure monitoring applications.  Uses include visual monitoring of air and gas pressure for compressors, vacuum equipment, process lines and specialty tank applications such as medical gas cylinders and fire extinguishers.  In addition to visual indication, some pressure gauges are configured to provide electrical output of indicated pressure and monitoring of other variables such as temperature.

It is important to select a pressure range that accommodates all anticipated pressure swings, and which prevents excessive needle movement. It is recommended to confine normal operating pressure to 25% to 75% of scale. With fluctuating pressure (e.g., pulsation by a pump or compressor) the maximum operating pressure should be lower (50% of the full range).  Choices for pressure gauges measurement ranges include positive pressure, vacuum measurement, compound measurement, differential pressure, absolute pressure, and sealed pressure.  A positive pressure gauge measures a pressure range from zero pressure to a higher, positive pressure.  Vacuum measurement switches measure vacuum pressure (negative pressure).  A compound pressure gauge measures a pressure range from negative pressure (vacuum) to positive pressure.  Differential pressure gauges give the relative pressure between two points. If both operating pressures are the same, the measuring element cannot move and no pressure will be indicated. A differential pressure is indicated when one pressure is higher or lower. Low differential pressures can be measured directly in cases of high static pressures.  Absolute gauges are used where pressures are to be measured independently of the natural fluctuations in atmospheric pressure. The pressure of the media to be measured is compared against a reference pressure of absolute zero (absolute vacuum) in a sealed reference chamber.  Sealed gauge pressure measurement is similar in concept to an Absolute Pressure gauge, except that the pressure of the media to be measured is compared to standard atmospheric pressure (at sea-level).

Display types available for pressure gauges include digital readouts, analog meters and needles, and graphical and video displays.  Pressure range to be measured is an important specification to consider when searching for pressure gauges.  Accuracy of the pressure gauge is measured as a percent of full scale and in cases where the accuracy differs between middle span and the first and last quarters of the scale, the largest % error is reported.  The temperature level to which a gauge will be exposed must be considered. Gauges with welded joints will withstand 750F, with silver brazed joints, 450 F, and soft-soldered joints, 150 F, for short times without rupture. Other parts of the gauge may be destroyed, however, and calibration lost.

On an analog pressure gauge the scale can be single or dual.  A single scale displays one unit only, a dual scale displays in two units on the same face.  Scale units can be PSI, kPa, Bar, inches Hg, cm Hg, feet H₂O, inches H₂O, oz / in², and kg / cm².  Common features of pressure gauges include adjustable pointers, maximum and minimum pointers, adjustable and stationary set hands, throttling devices, and electric contacts.  An adjustable pointer has adjustment to zero the pointer via screw or knob.  A maximum and minimum pointer indicates the maximum or minimum pressure attained.  An adjustable or stationary set hand is a separate pointer (hand) to indicate a specifically set pressure.  A throttling device is used to reduce pressure impact and pointer movement caused by pressure pulsation and/or vibration. Throttling effect is obtained by installing a restricting orifice between the gauge socket connection and the Bourdon tube. Some types of throttling devices are throttling screws, pulsation dampeners, elastomeric bladders, pressure snubbers and needle valves.  Electric contacts are used to turn on signal lights, sound alarms, operate a pump, valve, etc.

• MediaGauge Digital Pressure Gauges Family Overview
  The MediaGauge™ family of digital pressure gauges has four models. The MediaGauge™ models differ in accuracy, pressure ranges, media isolation, supply voltage, user functions and output...
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• Three Process Conditions That Affect Accuracy And Performance Of Pressure Gauges (.pdf)
  This article outlines several factors influencing the accuracy of a pressure gauge, and offers solutions on how to manage those influences for maximum gauge performance. The technology used in today's...
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• Instant Connections for High Pressure Gauge Testing
  FasTest's Type B751 series gauge tester is ideal for testing and calibrating pressure gauges. Engineered for high-volume production use, the pneumatically assisted sliding sleeve creates an instant...
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Part Numbers for Pressure Gauges