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Pressure Gauges — Selection, Design, and Safe Application in Production

Pressure gauges measure pressure in gaseous and liquid media, providing clear status data for plant operation and quality assurance, and are indispensable in production, test benches, and supply networks. Decisions regarding design, measuring range, connection, and materials determine measurement reliability, maintenance effort, and service life. The following text focuses on technical criteria, installation situations, material compatibility, and concrete practical applications to help you select the appropriate pressure gauge for industrial requirements and operate it safely and reliably in the long term.

Measuring Principles and Designs

Bourdon tube pressure gauges are the standard solution for general applications typically up to 0–1000 bar; the change in elasticity of a bent tube is mechanically transmitted to a pointer. Diaphragm pressure gauges are suitable for low pressures, aggressive or viscous media, as the measuring element is separated by a membrane. Capsule pressure gauges offer high sensitivity in vacuum and very low positive pressure ranges. For dynamic or pulsating pressures, liquid-filled cases (e.g., with glycerin) are preferable as they dampen pointer fluctuations and reduce mechanical stress.

Materials and Wetted Parts

The choice of materials depends on corrosivity, temperature, particle content, and hygiene requirements. Measuring tubes and cases made of stainless steel (e.g., 1.4301/304L or 1.4404/316L) offer broad chemical resistance and are the first choice in the food and pharmaceutical industries, as well as for chloride-containing media. Measuring elements made of brass are cost-effective, suitable for neutral gases and non-aggressive liquids, but are unsuitable for chlorides and aggressive chemicals. Diaphragms and seals are typically made of NBR (nitrile rubber) for oils, EPDM for water and steam, FKM/Viton for aggressive chemicals, and PTFE for highest chemical resistance. Pay attention to the compatibility of sealing material and medium, as well as the temperature limits of the elastomers.

Connection Sizes, Cases, and Mounting Options

Typical process connections are G1/4, G1/2, 1/4 NPT or 1/2 NPT, as well as special flange or weld-in connections for pipelines. For vibrations or high temperatures, the variant with a Bourdon tube and/or bayonet connection is recommended. Case designs range from panel mounting with a mounting ring to screw-in variants and pipeline connections with an angled fitting. For mobile test equipment, shock-resistant plastic versions or rubberized frames are available as protective housings. Pay attention to blow-out back protection in case of overpressure events and to anti-reflective safety glass or safety plastic to prevent glass splinters in case of breakage.

Measuring Range, Accuracy, and Calibration

Select the measuring range so that the operating pressure ideally lies between 25% and 75% of the scale to maximize reading accuracy and service life. Accuracy classes are usually specified as Class 1.6, 1.0, or 0.6; lower values mean higher precision. Applications with legal or safety-relevant requirements necessitate regular calibration according to DIN EN ISO/IEC 17025 standards and documented traceability. For control technology, electronic pressure gauges with analog output (4–20 mA) or digital interfaces (Modbus, CANopen) may be required to automatically record and archive measured values.

Temperature Conditions and Pressure Surges

Ambient and measuring medium temperature influence accuracy and material selection. Standard pressure gauges are often designed for ambient temperatures from −20 °C to +60 °C; for higher process temperatures, probe extensions or remote sensors are necessary. Pulsating loads reduce the service life of the measuring element; in such cases, pulsation-dampening elements, snubbers, or liquid-filled pressure gauges should be used. For cyclic stress, products with reinforced measuring elements should be chosen and calibrated more frequently.

Seals, Protection Classes, and Maintenance

Sealing systems must be media- and temperature-resistant, as well as tolerant to mounting. Screw connections with PTFE seals, O-rings made of suitable elastomer, or flange gaskets made of graphite/metal are chosen depending on the application. Protection classes according to IEC/EN (e.g., IP65, IP67) provide information about ingress protection; higher protection classes are preferable for wet areas. Maintenance includes visual inspection, leak checks, calibration control, and, for liquid-filled devices, refilling or replacing the filling fluid. A maintenance interval depends on operating conditions, typically annually for critical applications.

Practical Examples from Production

Example 1: In a hydraulic press line, a built-in stainless steel Bourdon tube pressure gauge monitors the hydraulic pressure. The G1/4 connection is located in the immediate vicinity of the control block; the pressure gauge is glycerin-filled to dampen pulsations. The scale is designed for 0–400 bar, with normal operating values between 120 and 220 bar. If an ISO 17025 calibration was performed during commissioning, deviations are recorded during annual maintenance, and exceeding tolerances leads to recalibration or replacement.

Example 2: In a chemical filling plant, a diaphragm pressure gauge with a PTFE membrane measures the pressure in the pump line. The measuring device is designed to be corrosion-resistant, has a flange connection, and a 316L housing for cleaning processes. An electrical switching output signals automatic safety valves in case of overpressure. For cleaning cycles, the pressure gauge was equipped with quick-release couplings so that it can be temporarily removed and checked without system interruption. Details on similar technical solutions can be found on our technology page: https://maku-industrie.de/technik.

Example 3: At compressed air-operated assembly workstations, small capsule pressure gauges are used for precise adjustment from 0–10 bar. They are mounted as panel instruments, easy to read, and calibrated every six months. For documenting test results and evaluating long-term trends, maintenance uses automated data interfaces, and the collection of application examples is centralized at: https://maku-industrie.de/anwendungsbeispiele.

Selection Criteria Summarized

Accurate selection is based on defined requirements for media-compatible materials, suitable measuring principles, appropriate connections, and the correct protection class. Consider pulsations, temperature ranges, necessary accuracy, and calibration cycles. For safety-critical systems, certified designs and documented calibration are indispensable.

• Typical connection sizes: G1/4, G1/2, 1/4 NPT, 1/2 NPT; flange and weld-in connections available; special connections possible for specific applications.

Procurement and Testing Tips

When purchasing, check manufacturer specifications for accuracy class, measuring range, material list (material numbers), temperature range, protection class, and calibration certificate. Request material certificates for wetted parts in corrosive applications. When comparing suppliers, consider life cycle costs, availability of spare parts (pointers, glass, seals), and on-site calibration services. Technical data sheets should reference DIN EN 837 (for mechanical pressure gauges) or corresponding standards for special designs.

Installation Recommendations

Pressure gauges should be installed vibration-free and protected against dirt with shut-off valves and dirt traps. For high process temperatures, the use of capillary remote indication or probe extension is recommended to keep the measuring device within a suitable temperature range. Check sealing interfaces for correct alignment and tightening torque to prevent leaks. When used in hazardous areas, explosion-proof devices must be specified.

Maintenance and Service Life

Regular visual inspections, leak tests, and calibrations are prerequisites for reliable measurement results. For heavily contaminated media, protective filters or drain connections are useful. Replacement intervals depend on stress; in critical processes, annual calibrations are common, while in stable environments, intervals can be extended. Documentation of every maintenance and calibration measure is necessary for audit and quality requirements.

FAQ

1. Which pressure gauge is suitable for aggressive chemicals?

Choose a pressure gauge with wetted parts made of stainless steel 316L or with PTFE-coated measuring elements, as well as PTFE or FKM seals; diaphragm designs offer additional protection against corrosion and fouling.

2. How do I determine the correct measuring range size?

The operating pressure should ideally be between 25% and 75% of the scale. Choose a range that covers short-term peaks without excessively degrading measurement resolution in the operating range; for dynamic processes, buffered or liquid-filled pressure gauges are recommended.

3. Which connection type is most reliable for pipeline integration?

Flange and weld-in connections offer the highest sealing integrity and mechanical stability; for modular systems, G1/4 or G1/2 screw connections are common. For interchangeable applications, use quick-release couplings with suitable seals to minimize downtime.