Selecting the Right Pressure Gauge
A Complete Guide for Your Application
In industrial environments where process control and equipment safety are paramount, pressure gauges serve as critical indicators of system health. Whether in oil and gas, chemical processing, pharmaceuticals, power plants, or general manufacturing, selecting the correct pressure gauge ensures reliable readings, minimizes downtime, and extends the life of your instrumentation.
This comprehensive guide explores the selection criteria for pressure gauges based on key parameters such as application type, gauge filling, dial size, material selection, process connection, and mounting design.
1. Understanding the Basics of a Pressure Gauge
A pressure gauge is an instrument used to measure and display pressure in a system. The most commonly used type is the Bourdon tube pressure gauge, where pressure is converted into mechanical movement. Other types include diaphragm and capsule gauges, used for specific low-pressure or corrosive service conditions.
Key Parameters Displayed:
- Gauge pressure (relative to atmospheric pressure)
- Absolute pressure (relative to a vacuum)
- Differential pressure (difference between two points)
Essential Process Conditions to Define:
- Medium (gas, liquid, or vapor)
- Pressure range & Temperature
- Environmental exposure
- Presence of vibrations or pulsations
- Hazardous area classification
2. Liquid Filling: Dry vs. Liquid-Filled Gauges
Dry Pressure Gauges
Best For: General-purpose indoor applications with minimal vibration and pulsation.
Advantages: Cost-effective, simple, suitable for non-corrosive and stable pressure systems.
Disadvantages: Can fog up due to internal moisture condensation; less suitable for harsh environments.
Liquid-Filled Gauges
Best For: Outdoor, vibrating, pulsating, and corrosive environments (e.g., pumps, compressors).
Common Fill Liquids: Glycerin, silicone oil, mineral oil.
Advantages: Dampens needle vibrations, reduces wear, extends gauge life, and prevents fogging.
| Application | Recommended Gauge Type | Fill Fluid |
|---|---|---|
| Hydraulic systems | Liquid-filled | Glycerin |
| High temperature (>60°C) | Liquid-filled | Silicone oil |
| Food & Pharma | Liquid-filled with diaphragm | Non-toxic oil |
| Low vibration, indoor | Dry type | Not applicable |
3. Dial Size Selection
Dial size affects readability and the physical space required for mounting. Standard sizes range from 40 mm to 250 mm (1.5” to 10”).
| Dial Size | Typical Application | Mounting Location |
|---|---|---|
| 40–50 mm | Panel mounted, lab instruments | Local/close viewing |
| 63 mm | General-purpose process measurement | Close monitoring |
| 100 mm | Field service (oil & gas, chemical) | Remote/local |
| 150 mm | High-precision and remote readings | Remote field viewing |
| 250 mm | Large-scale industries | Tank farms, control towers |
4. Material Selection for Wetted and Non-Wetted Parts
Choosing appropriate materials ensures gauge longevity, accuracy, and safety in corrosive or hazardous environments.
Wetted Parts (Contact with Process Fluid)
| Process Medium | Recommended Wetted Material |
|---|---|
| Air, Water, Oil | Brass |
| Corrosive Chemicals | 316 Stainless Steel or Monel |
| Acids, Chlorides | PTFE lining, Tantalum, Hastelloy |
| Oxygen | Degreased SS, oil-free systems |
| Steam | SS with siphon or pigtail loop |
Case Materials (External Parts)
| Environment | Case Material | Window Material |
|---|---|---|
| General indoor use | Painted steel | Glass |
| Corrosive atmosphere | SS 304/316 | Laminated safety glass |
| Explosion-proof areas | SS with flameproof enclosure | Glass/polycarbonate |
| Vibration-heavy zones | SS with rubber-sealed window | Acrylic |
5. Pressure Range and Overpressure Protection
Selection Rule
Set the pressure range to 1.5 to 2 times the system's normal operating pressure for optimal life and performance.
Example: If your system runs at 5 bar, choose a gauge with a 0–10 bar range.
6. Accuracy Class Selection
Accuracy is the permissible deviation from the actual value, expressed as a percentage of the full-scale range. Always refer to EN 837, ASME B40.100, or ISA S40 standards.
| Accuracy Class (EN 837-1) | Typical Application |
|---|---|
| ±2.5% | General industrial usage (small dial) |
| ±1.6% | Field instruments |
| ±1.0% | Process instruments |
| ±0.6% to ±0.25% | Laboratory and calibration gauges |
7. Process Connection and Mounting Design
Process connections must match the system configuration in terms of thread type, size, and orientation.
Connection Orientation
- Bottom Entry (Radial): Common for panel or direct inline connections.
- Back Entry (Axial): Preferred for panel or flush mounting.
- Lower Back Entry: For vertical installations.
Mounting Types
- Stem Mount (Bottom): Threaded directly into process pipe.
- Surface Mount (Back): Panel-mounted with a back flange.
- U-Clamp Mount: For instrument panels.
- Flush Panel Mount: For control rooms or cleanrooms.
8. Special Applications and Custom Features
Diaphragm Seals
Used when process fluid is highly viscous, crystallizing, hot, corrosive, or contains solids. They isolate the gauge from the process.
Snubbers and Pulsation Dampeners
Recommended for systems with reciprocating pumps, compressors, water hammer, or pressure surges to reduce wear and improve stability.
Pressure Gauge with Electric Contacts
Used to initiate alarms or control actions (e.g., compressor cut-off) when pressure reaches set points.
Conclusion: A Safeguard for Your Operation
A pressure gauge may seem like a small component, but its role in system integrity and process control is huge. By understanding the operational demands of your system and the properties of available gauges, you can make informed decisions that enhance safety, accuracy, and equipment life.
Take time to assess your process conditions and consult manufacturer datasheets or instrumentation engineers before making a final selection. The right pressure gauge is not just a measurement tool—it’s a safeguard for your entire operation.