Selecting a pressure gauge correctly means matching seven parameters to the process: range, accuracy class, dial size, process connection, wetted material, element type, and fill fluid.
Get any one wrong and the gauge fails prematurely, reads inaccurately, or becomes a safety hazard.
This guide covers all seven selection factors with practical decision rules, tips from field experience, and a working range checker.
The most common mistake is choosing a range too close to maximum process pressure. A gauge operating continuously above 75% of full scale suffers metal fatigue and zero drift within months. Always keep normal operating pressure between 25% and 75% of the full-scale value.
Pressure Gauge Selection: Why All 7 Factors Must Match
7 Factors for Pressure Gauge Selection
Select a range where normal operating pressure falls between 25% and 75% of full scale. For pulsating applications (pump discharge, compressor outlets), limit to 50%.
For steady-state service with no pulsation, up to 75% is acceptable.
Standard IEC series: 1, 1.6, 2.5, 4, 6, 10, 16, 25, 40, 60, 100, 160, 250, 400, 600 bar. Avoid non-standard ranges: mid-range accuracy is best and over-ranging accelerates Bourdon tube fatigue.
ASME B40.100 defines four accuracy grades for pressure gauges. Most industrial process measurements use Grade 2A (plus or minus 1%). Laboratory and calibration applications use Grade 4A (plus or minus 0.1%). Grade 1A (plus or minus 2%) is acceptable for utility services.
| ASME Grade | Accuracy | Applies To | Typical Application |
|---|---|---|---|
| 4A | ±0.1% | Full scale | Dead weight testers, laboratory reference gauges |
| 3A | ±0.25% | Full scale | Precision process measurement, calibration gauges |
| 2A | ±1% | Middle 80% of scale | Standard industrial process gauges |
| 1A | ±2% | Middle 50% of scale | Utility services, general indication only |
ASME B40.100 recommends: 63 mm dial for viewing within 1 metre, 100 mm for up to 3 metres, 150 mm for up to 6 metres. Larger dials carry more scale graduations and improve reading resolution.
Bottom entry (lower mount) suits panel and bracket installations. Back entry (back mount) is used where the gauge connects directly to a pipe nozzle and the face reads forward.
Common sizes are 1/4 inch and 1/2 inch NPT, and G 1/4 or G 1/2 BSP. Always match thread type and size to the existing fitting. Mixing NPT and BSP causes a leak path even if the fitting physically makes up.
The Bourdon tube (C-type or helical) is standard for 0.5 to over 1000 bar. The diaphragm element suits low pressures (below 6 bar), viscous fluids, and slurries where a Bourdon tube would plug.
Capsule elements suit very low pressures (0 to 25 mbar range) such as gas burner controls and draught measurement.
Wetted materials must be compatible with the process fluid. For compatibility, always cross-check against a chemical resistance chart for the exact fluid at the actual process temperature.
| Material | Compatible With | Avoid For |
|---|---|---|
| Brass (Cu-Zn alloy) | Water, oil, air, non-corrosive gases, steam to 150°C | Ammonia, acetylene, chlorine, strong acids (dezincification risk) |
| 316 Stainless Steel | Most acids, caustic solutions, food fluids, most hydrocarbons | Chloride-rich environments above 60°C (SCC risk), hydrofluoric acid |
| Hastelloy C276 | Oxidising and reducing acids, chlorides, seawater, phosphoric acid | High-temperature strongly oxidising acids |
| Monel (Ni-Cu alloy) | Hydrofluoric acid, alkaline solutions, seawater, fluorine | Oxidising acids, nitric acid |
| Titanium | Wet chlorine, chlorides, seawater, strong oxidising acids | Dry chlorine, red fuming nitric acid, hydrofluoric acid |
A liquid-filled gauge has its case filled with glycerine or silicone oil. Fill fluid dampens pointer oscillation from pulsation and vibration, lubricates the movement, and prevents condensation.
A dry gauge (air-filled case) is used only in clean, vibration-free, temperature-stable environments.
Glycerine (Glycerol)
Mineral-free glycerine is the most common fill fluid. Excellent vibration damping. Compatible with most process fluid leaks. Temperature range: minus 20°C to plus 60°C. Avoid where freezing is possible. Turns milky on water ingress (useful indicator of seal failure).
Silicone Oil (PDMS)
Wider temperature range than glycerine: minus 40°C to plus 200°C. Lower viscosity at low temperatures (better pointer response in cold climates). More expensive. Required for high-temperature or cryogenic service where glycerine would freeze or decompose.
Halocarbon (Fluorolube)
Required for oxygen service and strong oxidising acids (nitric acid, hydrogen peroxide). Silicone and glycerine are flammable in contact with liquid oxygen or concentrated oxidisers. Never use a glycerine-filled gauge on an oxygen line.
Food-Grade (NSF H1)
White mineral oil or food-grade propylene glycol fill. Mandatory for food, beverage, and pharmaceutical applications where incidental contact with the product is possible. Specified to NSF/ANSI 61 or 3-A standards.
Three additional specifications complete the pressure gauge selection for hazardous or demanding environments.
Overpressure protection: Specify a solid-front gauge or blowout-back case for applications where the element might rupture under overpressure. The solid front directs any overpressure blowout away from the operator. Required by many safety standards for pressures above 25 bar or on hazardous services.
IP rating: Specify minimum IP65 for outdoor or wet locations. Liquid-filled sealed-case gauges achieve this naturally. See the zero and span guide for how water ingress causes zero error drift.
ATEX/IECEx: Gauges in Zone 1 or Zone 2 must carry ATEX or IECEx certification. A mechanical gauge has no ignition source, but a stainless steel case can accumulate static charge. Zone 0 or Zone 1 standards may require an earthing provision.
Pressure Gauge Range Selector
Watch: How to Select the Right Pressure Gauge Range
Pressure Gauge Selection Questions
External References
- Pressure Gauge Selection Guide and Product Catalog | WIKA
- Pressure Gauge Selection Guide | Ashcroft (updated 2025)
What We Learn Today
- Select a range where normal operating pressure is 25 to 75% of full scale. Pulsating service: limit to 50%.
- Grade 2A (±1%) is standard for industrial process gauges. Never use glycerine fill on oxygen or oxidiser service.
- Match wetted material to the process fluid: 316 SS for most services, Hastelloy C276 for chlorides and strong acids.