A pressure gauge is a mechanical indicator that displays the pressure of a fluid relative to a reference (atmosphere or absolute vacuum). In oil & gas it’s used on utility headers, pump discharge/suction, compressors, steam lines, filters, and manifolds for local indication, commissioning checks, and as a backup to transmitters.

• Types: Bourdon tube (most common), diaphragm, capsule, differential.
• Scale units: bar, kPa/MPa, psig/psia, inH₂O, mmH_g.
• Reference: gauge (g), absolute (a), or differential (d).

• A curved, flattened metal tube tends to straighten when internal pressure rises (elastic deformation).
• The tube tip motion is transmitted through a linkage and sector gear to rotate the pointer.
• Materials: phosphor bronze, 316/316L SS, Monel, Inconel (service dependent).
• Ranges: typically from ~0.6 bar to 1,000+ bar (with suitable tube design).

Pros: wide range, robust, cost-effective. Cons: sensitive to vibration/pulsation without damping.

• Diaphragm gauges: low pressure (few kPa), viscous/slurry/corrosive media (with diaphragm seal), better for pulsation.
• Capsule gauges: very low/微 differential pressures (e.g., HVAC, draft), typically for gases only.
• Choose elastomer/metal diaphragm material for chemical compatibility and temperature.

• Gauge (PG): referenced to atmosphere; reads zero at ambient.
• Absolute (PA): referenced to vacuum; includes atmospheric pressure.
• Differential (PD/DP): measures pressure difference between two points (e.g., across filters/strainers).

Use absolute when atmospheric changes affect the process (e.g., vacuum systems, vapor pressure work).

• Choose a range so normal operating pressure is in the middle third of the scale for readability and longevity.
• For steady pressure: range ≈ 1.5 × maximum operating pressure.
• For pulsating pressure: range ≈ 2 × maximum operating pressure and add damping/snubber.
• Always consider overpressure scenarios (start-up, relief valve lift, water hammer).

• Accuracy class is the maximum permissible error as a % of full scale over specified conditions.
• Typical classes: ±0.5%, ±1.0%, ±1.6%, ±2.5% of full scale (per common industry practice and EN-style classes).
• Higher accuracy (“test gauges”) are used for calibration; general service uses ±1.6% to ±2.5%.
• Check the manufacturer’s datasheet for reference standard (e.g., EN 837-1 / ASME B40.100) and test conditions.

It indicates a non-uniform accuracy across the scale (common for general purpose dial gauges):

• ±3% of full scale in the first 10% of the range,
• ±2% in the middle 80%,
• ±3% in the last 10%.

This reflects pointer mechanics near end stops; operate within the mid-scale for best accuracy.

• Benefits: dampens pointer flutter from vibration/pulsation, reduces wear, improves readability.
• Common fills: glycerin (general), silicone (wide temperature), fluorinated fluids (oxygen/chlorine service—check compatibility).
• Considerations: temperature expansion requires a case vent; fill viscosity changes with temperature; avoid chemical attack on window and gaskets.

• Install a snubber (porous orifice) or restrictor screw to limit flow/oscillation.
• Use a needle valve to throttle; open partially to dampen.
• Consider a pulsation damper or accumulator for severe cases.
• Choose a liquid-filled gauge and ensure proper range and safety pattern.

• A siphon (pigtail or U-tube) traps condensate to thermally isolate the gauge from live steam.
• Fill the siphon with water at installation; place a root valve and test connection upstream.
• Use suitable materials (e.g., 316 SS) and ensure blow-down/testing procedures are in place.

• 316/316L SS for many hydrocarbons and utilities; Monel/Hastelloy for chlorides, H₂S, or aggressive media.
• For slurry/plugging: use a diaphragm seal with PTFE, Hastelloy, or compatible elastomer.
• Verify NACE/ISO 15156 requirements for sour service components.

A solid-front safety gauge has a solid wall between the dial and the Bourdon system plus a blow-out back. If the tube fails, pressure vents rearward—away from the operator.

• Recommended for hazardous media, high pressure, and oxygen/chlorine service.
• Often paired with laminated safety glass and a crimped bezel.

• Threads: NPT, BSPP (G), BSPT; confirm male/female type and sealing method (taper vs gasket).
• Sizes: 1/4", 1/2" are typical; select for flow and mechanical strength.
• Use thread sealant compatible with media; avoid over-torque which can distort the Bourdon socket.

• Elevation relative to the tapping creates hydrostatic head (for liquids), shifting the zero.
• Long capillaries or seals add head and delay; specify fill fluid density and capillary length.
• Zero the pointer after installation; some gauges include a front zero adjust.

• Larger dials (100–160 mm / 4–6") improve readability from a distance and allow finer graduation.
• Consider viewing distance, lighting, and operator access; use mirror band dials to minimize parallax.

• Elastic modulus changes cause span and zero shifts; manufacturers specify compensated temperature ranges.
• Use silicone fill for wide temperatures; shield from radiant heat; add siphons/cooling elements on hot media.
• Vent liquid-filled cases in hot sun to prevent window bulging and pointer friction.

• Ingress protection prevents dust/water entry; higher IP (e.g., IP65/66) for outdoor washdown or marine.
• Consider UV resistance of windows (polycarbonate vs glass) and gasket compatibility.

1. Isolate and remove (or use a test tee). Inspect for damage.
2. Use a traceable deadweight tester or pressure comparator with a calibrated reference.
3. Exercise the gauge, then perform a 5-point up & down test (0, 25, 50, 75, 100%).
4. Record as-found, adjust zero/span if allowed, then record as-left. Check hysteresis.
5. Affix a calibration sticker with date, due date, and tech signature.

Hysteresis is the difference between the up-scale and down-scale indications at the same applied pressure, due to mechanical friction/elastic effects.

• Measured during the 5-point up/down calibration routine.
• Reduce by exercising the gauge, ensuring proper lubrication, or selecting higher-grade mechanisms.

• Root (block) valve at tapping, plus a test point (mini test valve) for calibration.
• Snubber/restrictor or needle valve for damping; siphon on steam.
• Diaphragm seal for corrosive/plugging media; optional capillary for remote mounting.
• Mounting plate or pipe clamp for visibility and to reduce vibration.

• Used for filter monitoring, flow elements, and seal pots.
• Types: diaphragm-based, piston/segment, and double-Bourdon arrangements with mechanical summation.
• Choose overrange protection for one side, and consider static line pressure rating.

• A seal isolates the gauge via a flexible diaphragm and fill fluid, preventing clogging/corrosion.
• Ideal for slurry, polymerizing, or sanitary services; allows flush or in-line hygienic connections.
• Select diaphragm and fill fluid (e.g., silicone, halocarbon) per temperature and chemistry.

• Specify oil-free cleaning and packaging; avoid hydrocarbon contamination.
• Use compatible materials and non-reactive fill fluids approved for oxygen.
• Prefer solid-front safety pattern and clearly mark “OXYGEN – CLEAN.”

• Flutter: pulsation/vibration → add snubber, needle valve, liquid fill, relocate to a calmer point.
• Sticking: mechanical wear, dirt, bent pointer, window pressing on pointer (case pressurization) → service/replace, vent case.

• EN 837-1/2/3: design & safety requirements for Bourdon/diaphragm/capsule gauges.
• ASME B40.100: pressure gauge performance/accuracy and test methods.
• ISO 15156/NACE MR0175: material requirements for H₂S-containing environments.
• Project specs may mandate safety pattern, window type, dial marking, IP rating, and calibration intervals.

• Use a compound gauge (e.g., −1 to +x bar) or an absolute gauge if needed.
• Ensure the Bourdon tube design tolerates reverse loading; some include overrange stops.
• Check for entrained liquids that may boil under vacuum (erratic readings).

• Glass: good clarity & scratch resistance; laminated safety glass for high-risk areas.
• Polycarbonate: tough/impact-resistant; watch for solvent stress-cracking and UV.
• Acrylic (PMMA): clear, economical; moderate scratch resistance.

• Visual inspection (pointer at zero, window intact, leaks, corrosion).
• Verify damping devices/snubbers and vents are functioning; clean if clogged.
• Periodic calibration based on criticality; replace worn or erratic gauges.
• Keep spare assembly (gauge + root valve + snubber) for quick swap-outs.

• Use one primary unit (e.g., bar) with a secondary smaller scale if necessary.
• Mark red zones for overpressure/relief settings; show tag number and service fluid if required.
• Avoid clutter; ensure adequate graduation spacing for the chosen accuracy and dial size.

1. Confirm model, range, materials, and pressure test certificates against the datasheet.
2. Install root valve, snubber/needle, and test point; add siphon on steam.
3. Use correct thread engagement/sealant; support to minimize vibration.
4. Open valves slowly during pressurization; check for leaks; verify zero and operation.
5. Record baseline reading, set maintenance/calibration interval based on criticality.