Selecting a Pressure Gauge

Pressure gauges are integral to a wide range of industries, serving as essential instruments for measuring the pressure of air, gas, or liquid within various systems to ensure safe and efficient operation. To achieve optimal performance, it is crucial to select a pressure gauge with a pressure range that matches the operational requirements of your application, in addition to considering several other critical factors.

When selecting a pressure gauge, evaluate the following parameters: process conditions, pressure range, environmental factors, accuracy requirements, dial size, connection type, and mounting specifications.

Accuracy

For mechanical pressure gauges, accuracy is typically expressed as a percentage of the full-scale range. While accuracy requirements may vary across different sectors, general guidelines are as follows:

Dial Size

Pressure gauge dial sizes typically range from less than 1" to 16". Dial size is determined by readability requirements, space constraints, and the desired gauge accuracy. Gauges with high accuracy (e.g., ±0.25% or ±0.5%) generally require larger dial sizes, typically 4½" or larger, to accommodate more precise increments and ensure legibility.

Case Style/Material

The environmental conditions where the gauge is used must be considered, as these can affect both gauge performance and longevity. Key factors include:

  • Ambient temperature: Extreme temperatures may degrade gauge performance, so gauges should be either temperature-compensated or isolated using flexible lines to avoid exposure to temperature extremes.

  • Environmental exposure: Conditions such as airborne particulates, condensation, humidity, and chemicals can degrade gauge accuracy and lifespan. In such cases, weatherproof, hermetically sealed, or liquid-filled gauges are recommended to protect the instrument from corrosion, particulate ingress, or moisture.

Media/Wetted Parts

The wetted components of the pressure gauge, including the Bourdon tube and socket, must be compatible with the process media to prevent corrosion. Incompatibility between the wetted parts and the media can lead to gauge failure and potential safety hazards. In cases where compatibility is a concern, a diaphragm seal should be considered to isolate the gauge from aggressive or corrosive media.

Connection Size

Pressure gauges are available with various connection types, including NPT, DIN, JIS, BSP, and SAE. Process gauges with dial sizes of 4½" or larger typically feature a ½" NPT connection for optimal support. Factors influencing the selection of connection size and type include:

  • Process pressures

  • Gauge size and weight

  • Space limitations

  • Leak integrity requirements

  • Previous operational experience

Connection Location

Consider the following mounting configurations when selecting a pressure gauge:

  • Stem mount with lower connection

  • Wall or surface mount with lower connection

  • Panel mount with back connection

  • U-clamp flush mount with back connection (for panel mounting)

  • Front flange flush mount with back connection (for panel mounting)

Pressure Ranges

ASME B40.100 recommends that normal operating pressure be within 25% to 75% of the full-scale range of the gauge. In processes with pressure pulsations, it is advised that the maximum operating pressure not exceed 50% of the full-scale range to avoid inaccuracies and potential damage due to rapid pressure fluctuations.