Correctly selected pressure gauges should act as a reliable tool for accurate measurement of pressure. And while requirements differ across industries, some things just don’t change. Here’s how to pick the right gauge for you;
Accuracy for mechanical pressure gauges is defined as a fraction (%) of the full-scale range. Though the requirements vary across industries, here are general guidelines:
Test Gauges & Standards should have 0.25% through 0.10% full-scale accuracies. Gauges for important Processes should have 0.5% full-scale accuracy while Gauges for General Industrial Processes should be no less than 1.0% accurate. Finally, Gauges for simple commercial Uses should be 2.0% accurate. For further info on accuracy, visit Thermo Fisher Scientific or refer to DIN specifications or the ASME B40.100.
2.The Scale Unit
There are several units for pressure measurements including bar, mbar, Pa, kPa, MPa, psi, mmH2O, inHg and more.
The unit you choose depends on the country where the gauge is manufactured among other factors. Europe prefers the bar or mbar calibration— but the use psi for measurements of 3 to 15 psi. Double-scaled pressure gauges can be very helpful in this case. For instance, you can have a scale with both psi and bar calibrations. Other units like psi and inHg are common in the US while Asia uses the MPa or kg/cm².
3. Size of the Dial
Dial sizes for Pressure gauge vary from 11⁄2˝ to 16˝ in diameter. Factors determining the right dial size include; the amount of space, equipment readability, and the expected gauge accuracy. Gauges with Accuracies of 0.25 or 0.5 percent use size 41⁄2˝ or larger dials because uses require more dial graduations.
4. Pressure Range
The best Gauge range should be two times the working pressure. That way, you can be sure of total safety, accuracy, and prolonged gauge life. The running pressure should always be restricted to 75 percent of the range of the gauge. In situations where you experience pressure pulsations, the working pressure should be controlled to two-thirds of the full gauge range.
General max temperature limits for soft-soldered gauges are -40ºF to 120ºF. Max temperatures for welded or silver gauges are -40ºF to 190ºF, while those of liquid-filled gauges stand at 0ºF to 140ºF.
6. Factors Affecting Wear
When using a gauge for jobs that involve severe vibrations and fluctuations in pressure, it is recommended to use pressure restrictors like snubbers.
For liquid-filled gauges, the fill fluid offers lubrication reducing wear and tear. They can also prevent moisture conditions or corrosion that may affect the internal parts of the gauge. Glycerin is the most common fill fluid; Silicone works well for extremely high-temperature applications. For cases where liquid-filling isn’t practicable, consider the dampened movement design for USG 1981 & 1931 model gauges.
7.The Composition of Pressure Fluid
Because the sensing feature of pressure gauge sometimes gets in direct contact with the medium being measured, it is essential to consider the properties of this medium.
Consider characteristics like corrosiveness, its state (gas or liquid), or whether it may solidify at given temperatures, the presence of solids in it that may leave deposits clogged in your sensing element.
For fluids that won’t solidify even under standard conditions or lead to deposits, consider using a Bourdon tube pressure gauge. Incorporate the use of a Diaphragm chemical seal if the pressure gauge in contact with the fluid is incompatible with media being measured. Remember to double-check the Chemical Compatibility Chart on the gauge to aid in picking the appropriate sensing feature material.
8. The Temperature of the Pressure Fluid
Vapor and other forms of hot media heats up or increases the temp of the parts of the gauge beyond safe working levels of the stuck down joints. In such situations, it’s advisable to use a protective chemical diaphragm or a siphon with your pressure gauge.
These seals also feature remote, reinforced, capillary tubing suitable for use with gauges used under very high or low ambient temperatures.
9. Environmental Factors
The standard ambient temperature range for most soft-soldered gauges is -40ºF to 120ºF; silver-soldered/welded gauges -40ºF to 190ºF; while liquid filled forms stand at 0ºF to 140ºF.
Temperature changes are responsible for errors of roughly ±1% every time the temperature experiences a 50ºF change. 75ºF is the reference temperature.
Mounting you pressure gauge using a chemical diaphragm stopper and the capillary lining is one way to go about uses that require extreme ambient temperatures. You must also look into weather and moisture conditions. Remember, Liquid-gauges hinders the buildup of condensation, so they are your best pick.
If you plan to use your gauge outdoor, consider, brass, stainless steel, or plastic covered gauges. Other factors to inspect include vibration, dust levels, mechanical shock and humidity.
10. Mounting Method
The most common types include the Lower mount, the center back mount or lower back mount. The market has other kinds like the straight threads, metric threads, hose barbs, as well as other special fittings made to special order.
Calibrations in pressure gauges are in an upright position, but the gauge can be recalibrated and placed horizontally, sideways or upside down, depending on which position suits the application.
11. Case Venting
Most fluid gauges more so the liquid filled forms have an elastomeric vent plug tip which is easy to cut after set up to allow for case venting. This feature is must-have for liquid filled gauges, especially those with max pressure ratings of 100 psi and below. The case venting makes up for any atmospheric pressure changes that could interfere with calibration of the gauge.
The Bottom Line
In the end, the best gauge for you will depend on a number of factors. The most important ones being the application or its use along with the surrounding conditions. The goal is to choose what can work for you in the surrounding you are and give you the best results without putting a strain on your body or resources. Also, consider going for popular brands so that you get standard features for things like unit calibration and other essential parts of the gauge.
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