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Choosing a Pressure Gauge

When choosing a pressure gauge, it is important to consider the following factors


Pressure Range: A gauge range of twice the working pressure is generally recommended for maximum accuracy, safety, and extended gauge life. Working pressure should always be limited to 75% of the gauge pressure range. When encountering pressure pulsations, the working pressure should be limited to two-thirds of the gauge pressure range.


Temperature Range: The maximum temperature limit for soft soldered general purpose instrumentation is -40oF to 120oF. Silver soldered or soldered process gauges have a maximum temperature limit of -40oF to 190oF, and liquid filled gauges have a maximum temperature limit of 0oF to 140oF.


Conditions affecting system wear: In applications involving severe pressure fluctuations, vibrations and/or pulsations, restrictors or pressure snubbers are recommended. In addition, liquid-filled meters should also be considered. The filling fluid will lubricate the movement and reduce friction and wear. Liquid filling also prevents moisture or corrosive atmospheres from affecting the inside of the meter. The most common filling fluid is glycerin, although we supply several others at the factory. Silicones can be used in applications with large temperature extremes. In applications where liquid filling is not feasible.


Pressure fluid composition: Since the sensing element of the pressure gauge may be directly exposed to the measured medium, the characteristics of this medium should be considered. It may be corrosive, it may be a gas or liquid, it may cure at different temperatures, or it may contain solids that can leave deposits inside the sensing element. For pressurized fluids that do not solidify or leave deposits under normal conditions, a Bourdon tube pressure gauge can be used. When the wetted parts of the pressure gauge are not compatible with the measured medium, the use of a diaphragm chemical seal should be considered. Please refer to the Chemical Compatibility Charts in this section to help you select the appropriate sensing element material.


Pressure Range: A gauge range of twice the working pressure is generally recommended for maximum accuracy, safety, and extended gauge life. Working pressure should always be limited to 75% of the gauge pressure range. When encountering pressure pulsations, the working pressure should be limited to two-thirds of the gauge pressure range.


Pressure Fluid Temperatures: Steam and other hot media can raise the temperature of instrument components above the safe operating limit of the sealed joint. In these cases, it is recommended to use a siphon or chemical diaphragm seal with the pressure gauge. Chemical diaphragm seals and remote armored capillaries may also be considered for use with meters that withstand very low or very high ambient temperatures.


Environmental Conditions: Normal ambient temperature range is -40oF to 120oF for general equipment gauges (soft soldering); -40oF to 190oF for process gauges (silver soldering/soldering); 0oF to 140oF for liquid filled gauges. The error due to temperature change is approximately ±1% per 50oF change. The reference temperature is 75oF. Remote mounting of pressure gauges using chemical diaphragm seals and capillary lines is an alternative for applications involving extreme ambient temperatures. Moisture and weather effects must also be considered. Liquid-filled gauges prevent condensation build-up. For outdoor use, meters with stainless steel, brass or plastic housings are recommended. Mechanical shock, vibration, dust and humidity are some other considerations when choosing a pressure gauge.


Mounting Methods: Most meters offer bottom mount (LM) and center mount or bottom mount (CBM or LBM) connections. The product has a standard variety of threaded connections. Such as metric threads, straight threads, hose barbs and other special fittings are available as special order. Pressure gauges are calibrated in a vertical, upright position and should be installed as such. For applications where the meter is mounted laterally, horizontally or upside down, the meter should be recalibrated at the end-use location.


Required Accuracy: Gauge accuracy is ±3-2-3% of full scale (ASME Class B) to ±.25% (ASME Class 3A). Generally, more accurate gauges have larger dial diameters and are more expensive.


Case Vent: Liquid filled gauges have a resilient vent/fill plug tip that can be easily cut (after installation) to allow case venting. Recommended for all fluid filled instruments, especially those with a maximum pressure rating of 100 psi and below. This will compensate for atmospheric changes that may affect the calibration of the fill meter.


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