The 7-step selection framework: (1) Pressure range — select 1.25–1.5× maximum working pressure as full scale; (2) Accuracy class — 1.6 for monitoring, 0.6 for control loops; (3) Process medium — determine wetted material requirements (brass for dry air, 316L SS for corrosive/food, Hastelloy for aggressive chemicals); (4) Fill type — dry for stable environments, liquid-fill for vibration/pulsation; (5) Dial size — 63mm for space-constrained, 100mm standard, 160mm for remote reading; (6) Connection — specify size AND type (NPT, BSPP, BSPT, metric); (7) Environment — IP rating, ATEX zone, temperature range.

Specify 316L stainless steel wetted parts for: salt water and marine environments, food and beverage processes, mild chemical service (pH 4–10 with no chloride), steam and condensate systems, hydraulic oil (if chemical compatibility is confirmed), and CO₂/refrigerant systems. Brass wetted parts are acceptable ONLY for compressed air, inert gases, and clean water below 60°C — never for corrosive chemicals, seawater, or food contact applications.

Wetted parts are all gauge components that contact the process medium: the Bourdon tube, the socket (connection body), the socket threads, and any O-rings or seals in the process connection. The case, movement, and dial are not wetted parts and do not require process compatibility. When specifying material for corrosive service, you only need to upgrade the wetted parts, not the entire gauge.

Outdoor installations require: IP65 minimum case protection (EN 60529) for dust and rain; UV-stable case material (ABS or stainless steel — avoid polycarbonate in direct sunlight); operating temperature range covering site minimum (arctic: −40 °C, temperate: −20 °C) and maximum; liquid fill to prevent condensation in the case; and anti-corrosion coating or all-stainless construction in coastal or industrial atmospheres.

Standard industrial: CE marking (EU, PED compliance); ISO 9001 (manufacturing quality). Application-specific: ATEX/IECEx (explosive atmospheres); 3-A or EHEDG (food/dairy); FDA 21 CFR (pharmaceutical); KS (Korea); CRN (Canada); INMETRO (Brazil). For safety instrumented systems, verify the gauge can meet the proof-test interval and PFD requirements of the target SIL level. Request the Declaration of Conformity and test certificates for each required standard.

Gauge pressure (G or PSIG): measures pressure relative to atmospheric pressure — the most common type for industrial processes. Absolute pressure (A or PSIA): measures pressure relative to perfect vacuum — required for gas density calculations, boiling point determination, and vacuum system monitoring. Differential pressure (DP): measures the difference between two pressures — used for flow measurement (orifice plates), filter ΔP monitoring, and level measurement by pressure difference. Specify the measurement type explicitly, as gauges are not interchangeable between types.