Use inline pressure indicators for more safety around your compressed air

Pressure Gauges: Precise Pressure Measurement for Industrial Applications

Pressure gauges directly display liquid and gas pressures and are central components in control and monitoring systems within the manufacturing industry. They provide reliable measurement values for process monitoring, incoming goods inspection, test benches, and maintenance. The selection, installation, and specification of pressure gauges directly influence operational safety, measurement accuracy, and maintenance effort. The following text describes designs, materials, connections, seals, typical applications, and selection criteria for integration into industrial systems.

Designs and Operating Principles

Pressure gauges are primarily divided into mechanical and electronic versions. Mechanical pressure gauges (analog) are usually constructed as Bourdon tube, diaphragm, or bellows measuring systems. Bourdon tube gauges convert differences in spring deformation into pointer deflection. Diaphragm and bellows sensors are suitable for low pressures and liquid or contaminated media. Electronic pressure transmitters use piezoresistive, capacitive, or piezoelectric sensors and provide standardized output signals (4–20 mA, 0–10 V, digital fieldbuses) for process control systems.

Key differences concern measuring range, accuracy, long-term drift, temperature compensation, and response time. Mechanical displays are robust, require no electricity, and are often easier to maintain. Electronic pressure transmitters offer higher accuracy, remote signaling, and easy integration into automation architectures.

Materials, Media Compatibility, and Housings

Material selection depends on the measuring medium, environment, and operating conditions. Stainless steel (1.4404 / 316L) is preferred for corrosive media, food, pharmaceuticals, and high hygiene standards. Measuring tubes and diaphragms made of Monel or Hastelloy are required for aggressive chemical media. Measuring systems made of measuring bronze or brass remain an economical choice for non-corrosive gases and oils. Housing materials such as aluminum or stainless steel protect electronics and mechanical parts from environmental influences; painted or powder-coated housings increase corrosion protection in harsh industrial environments. Sight glasses are often made of hardened glass, polycarbonate, or acrylic; for explosion-hazardous areas, shatterproof and grounded versions are necessary.

Connections, Seals, and Process Integration

Connections determine mounting flexibility. Standard threads are G¼, G½ (BSP), NPT, or metric screw-in threads. Flange connections or hygienic Tri-Clamp connections are necessary in food and pharmaceutical applications. For high-pressure applications, compact screw-in measuring devices with reinforcement fittings are used. Sealing materials must be media and temperature resistant: PTFE (Teflon) for aggressive chemicals, Viton (FKM) for high temperatures and oils, NBR for general hydraulic oils. Elastomer seals age depending on temperature and ozone; for continuously high temperatures or UV exposure, metallic sealing systems or graphite seals are preferable.

Measuring Ranges, Accuracy, and Calibration

Measuring ranges are specified in bar, mbar, psi, or Pa and must meet process requirements. Oversizing reduces resolution; too narrow ranges lead to overload. Accuracy classes of mechanical displays typically range from ±1.6% to ±0.5% of the scale; electronic transmitters achieve ±0.1% to ±0.25% in temperature-compensated versions. Regular calibration according to a measurement plan ensures process consistency; test protocols should document manufacturer specifications, calibration intervals, and traceability to national standards.

Environmental Requirements, Protection Classes, and Ex-Protection

Protection classes according to IP (e.g., IP65, IP67) regulate protection against dust and water. In harsh production environments, IP67 or higher rated housings with drip and jet water protection are advisable. For explosion-hazardous areas, Ex-certified pressure transmitters according to ATEX or IECEx are necessary. Manufacturer's temperature range specifications determine use in heating zones, refrigeration systems, or direct sunlight; for extreme temperatures, remote sensors or protective sleeves should be used.

Electrical Interfaces and Communication

Electronic pressure transmitters offer analog interfaces (4–20 mA, 0–10 V), digital outputs (HART, Modbus, PROFIBUS, Ethernet/IP), or IO-Link for decentralized automation concepts. The selection of the interface depends on the control system, cable length, interference immunity, and required diagnostic functionality. Power supply, reverse polarity protection, and overvoltage protection must be considered during installation. For electrical integration, wiring guidelines, PE connection, and shielding of signal and fieldbuses must be strictly observed.

Maintenance, Lifespan, and Replacement Strategies

Maintenance strategies are based on operating hours, temperature cycles, and media exposure. Mechanical displays are less susceptible to electronic errors but show wear on bearings and pointers; moving parts must be kept free of contamination. Electronic devices require protection from condensation; types with encapsulation and vents extend lifespan. Replacement strategies should consider modular design, standard connections, and calibration certificates to minimize response times in case of failure.

Practical Application Examples

Hydraulic Test Bench: Various pressure levels are tested on a hydraulic test bench. An electronic 4–20 mA transmitter with a 0–400 bar range and HART interface provides continuous pressure data to the test control. A mechanical Bourdon tube gauge with 0–500 bar serves as a local visual contact and secondary safety display. Both measuring devices are mounted via G½ connections with PTFE seals. Calibration intervals are documented every 12 months.

Food Production Line: In a filling plant, a hygienic diaphragm pressure gauge made of 316L stainless steel measures low pressures in air filtration. The diaphragm protects against product contamination; a Tri-Clamp connection allows for easy cleaning and quick repair. The pressure gauge has a readable front-facing display and is IP69K certified to withstand cleaning jets and hot steam.

Chemical Reactor Control: In a reactor, a pressure-resistant transmitter made of Hastelloy with a PTFE seal is used to measure aggressive media. The measured values are transmitted via Modbus to the PLC and used in automated safety logics for pressure relief. Additionally, a mechanical overpressure gauge is installed as a redundant safety element to display local alarm thresholds in case of electrical failure.

Selection Criteria for Purchasing

Choose pressure gauges based on measuring range, accuracy, material compatibility, connection type, protection class, and interface compatibility. Pay attention to calibration certificates, test and approval certificates (e.g., ATEX), as well as interchangeability and availability of spare parts. For integration into existing automation systems, compatibility with control interfaces and diagnostic level is crucial. Use manufacturer data sheets for final coordination and check for optional features such as overpressure protection, indicator colors for limit values, and local warning relays.

Related Resources and Further Information

Technical background information on measurement principles, material selection, and installation recommendations can be found on our technology page: https://maku-industrie.de/technik. Practical application examples and case studies on integrating pressure gauges into production lines are available at https://maku-industrie.de/anwendungsbeispiele.

Quick Check Before Ordering

• Measuring range and accuracy class, connection thread, housing material, sealing material, protection class (IP/Ex), interface, and calibration certificate.

FAQs

1. Which sealing materials are suitable for aggressive chemicals?
For aggressive media, PTFE seals are common; for very high temperatures or pungent solvents, metallic seals or special elastomers such as Kalrez (FFKM) are preferable. Selection depends on pH value, solvent types, and temperature profile.

2. When is an electronic transmitter preferable to mechanical displays?
Electronic transmitters are preferable when remote transmission, high measurement accuracy, diagnostic functions, or integration into process control systems are required. Mechanical displays are useful as local, self-sufficient displays without power requirements or as redundant safety displays.

3. How often do pressure gauges need to be calibrated?
Calibration intervals depend on operating conditions and internal quality specifications; typical intervals are between 6 and 24 months. Critical applications with safety-relevant functions require shorter intervals and documented traceability to national calibration standards.