Ashcroft Gauges : A 7 Step Pressure Gauge Selection Guide

Published 16 Jan 2017

By Chris Dodds : estimated reading time 4 minutes

Ashcroft Pressure Gauges – 7 Steps To Choosing The Correct Pressure Gauge

When selecting a mechanical Ashcroft Pressure Gauge with no external power input, there are a number of criteria that must be considered prior to choice and installation.

The 7 points below set out the key steps that must be considered, however there are also further points that must also be considered including the environmental issues, workplace location (safe or hazardous area) and mounting requirements. When considering the main points below and selecting the correct gauge product longevity, performance and reliability will be significantly improved.

The 7 main points to consider when selecting a pressure gauge are:

Step 1 – PRESSURE Gauge Accuracy

The accuracy of mechanical pressure gauges is described as a percentage of the full-scale range and while requirements differ between industries, the general guidelines are:

Test gauges and standards: 0.25% – 0.10% full scale accuracy
Critical processes: 0.5% full scale accuracy
General industry processes: 1.0% accuracy. Less critical commercial uses: 2.0% accuracy: Refer to ASME B40.100 for more information on accuracy.

Step 2 – gauge Dial Size

Pressure gauge dials range in size from less than 1″ to 16″ in diameter and readability requirements, space limitations and required gauge accuracy will determine the dial size chosen. Any accuracies of 0.25% to 0.5% will generally have dial size of 4½” or larger as more dial graduations are required.

Step 3 – Case Style/Material

Prior to choosing and installing a pressure gauge, there are many environmental considerations such as ambient temperature, condensation, humidity, water, chemicals and air-borne particulate.

The ambient temperature can affect the accuracy and integrity of the pressure gauges which are available either temperature compensated or non-temperature compensated and the ambient temperature may require the gauge to be isolated from extreme temperatures.

Where ambient conditions are corrosive and contain a large amount of particulate or if the gauge will be exposed to a wet or humid environment, then a gauge should be specified that is weatherproof/hermetically sealed or liquid filled. The correct case material can prevent corrosion and leaks which will in turn prevent leaks and safety incidents occurring.

Step 4 – Media/Wetted Parts

The gauge process and the wetted parts of the pressure gauge are typically the bourdon tube and socket which must be compatible with the process media. If this not the case, then rust or corrosion can occur and will eventually lead to parts of the gauge failing and potentially cause safety issues.

Step 5 – Pressure Gauge Connection Type

The type of connection and size of connection are available in many varieties including NPT, DIN, JIS, BSP & SAE. Process pressure gauges with 4½” dials or larger are most often supplied with a ½” NPT connection to best support the gauge.

Other factors to consider when selecting a pressure gauge connection include process pressures, gauge size and weight, space limitations, leak integrity, and past experience. In addition, when mounting the pressure gauge, there are a number of options that should be considered including:

Direct stem mount lower connect
Remote wall/surface mount lower connect
Panel surface mount back connect
Panel hole U-clamp flush mount back connect
Panel hole front flange flush mount back connect

Step 6 – Connection Location

The location of the gauge connection is a key consideration as there a number of elements that must be considered prior to installation. These include the stem mount lower connection, wall/surface mount lower connect, panel mount back connect U-clamp and front flange flush mount back connection.

Step 7 – Pressure Ranges

The American Society of Mechanical Engineers (ASME) recommends that normal operating pressure of the gauge should be confined to 25%-75% of the scale. If pulsation is present in the process, maximum operating gauge pressure should not exceed 50% of the full-scale range.

Conclusion

To properly select and specify a pressure gauge prior to purchase the user must consider the pressure gauge process, range, environment, accuracy, dial size, connection and mounting requirements – if in doubt, call T&D.

word of Warning

To prevent misapplication, pressure gauges must be selected considering media and ambient operating conditions. Improper application can be detrimental to the gauge, causing failure and possible personal injury, property damage or death.

The information contained here is offered as a guide to enable the safe and proper selection of a pressure gauge.

Users should become familiar with ASME B40.100 (Gauges – Pressure Indicating Dial Type – Elastic Element) before specifying pressure gauges. The document contains essential information regarding pressure gauge construction, accuracy, safety, selection and testing.

Should you require any further information, technical details or selection support to choose the correct pressure gauge, please do not hesitate to contact us.

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