Choosing the Right Pressure Gauge for Every Application
Pressure gauges are everywhere in industry: on pumps, compressors, boilers, tanks, filters and process lines. They are often the first instrument an operator checks and, in many systems, the only local indication of whether equipment is running safely. Yet pressure gauges are also among the most frequently replaced instruments, usually because the wrong type, range or material was chosen for the job.
This guide explains how pressure gauges work and takes you step by step through choosing the right gauge, so it gives accurate readings and a long, trouble-free service life.
What Is a Pressure Gauge and How Does It Work?
A mechanical pressure gauge converts pressure into the mechanical movement of a pointer over a calibrated dial. A pressure-sensing element deforms elastically when pressure is applied; a movement (linkage and gear mechanism) amplifies that small deflection into pointer rotation. Most gauges measure gauge pressure, relative to atmosphere. Variants measure absolute pressure, relative to vacuum, or differential pressure between two points.
Types of Pressure Gauge Sensing Elements
Bourdon Tube Gauges
The Bourdon tube is a curved, flattened tube sealed at one end. As pressure rises, the tube tries to straighten, moving the pointer. C-shaped tubes are used for ranges from about 0.6 bar to 60 bar; helical and spiral tubes are used for higher pressures up to around 1,000 bar or more. Bourdon tube gauges are the most common and economical choice for liquids and gases that will not clog or corrode the tube. Bliss Flow offers the Bourdon sensing pressure gauge for general and process service.
Diaphragm Gauges
A diaphragm gauge uses a flexible circular membrane clamped between two flanges. Diaphragms are robust, can be made from corrosion-resistant materials or coated with PTFE, and have a large wetted area that resists clogging. They are well suited to low pressures, viscous or crystallising media and high overload protection.
Capsule Gauges
A capsule consists of two diaphragms welded together. Capsule gauges measure very low pressures, typically in millibars, and are used for gases such as air, fuel gas and inert gas, as well as for draft and filter differential pressure.
Differential and Specialty Gauges
Differential pressure gauges measure the difference between two pressures, for example across a filter or strainer. Other variants include safety pattern gauges with solid-front cases and blow-out backs, contact gauges with electrical switches, and digital gauges for higher accuracy.
Step-by-Step Pressure Gauge Selection
1. Choose the Right Range
Select a full-scale range of about twice the normal operating pressure. The normal reading should fall in the middle third of the dial, typically between 25 and 75 percent of full scale. This keeps the element away from its stress limit, gives better readability and leaves margin for pressure surges. If the gauge will see vacuum, choose a compound range.
2. Specify the Accuracy Class
Accuracy is expressed as a percentage of full scale. Under EN 837-1, common classes are 0.1, 0.25 and 0.6 for test gauges, 1.0 for process gauges and 1.6 or 2.5 for general utility gauges. ASME B40.100 uses grades such as 4A (0.1%), 3A (0.25%), 2A (0.5%), 1A (1%) and A (1-2-1%). Match accuracy to the purpose; higher accuracy costs more.
3. Select Dial Size
Dial sizes range from about 40 mm to 250 mm. Larger dials are easier to read from a distance and give finer graduations. 100 mm and 150 mm dials are the most common for process plants.
4. Choose Wetted Materials
- Brass / bronze: Water, air, oil and non-corrosive media at moderate temperatures.
- Stainless steel 316: Corrosive media, process industry and higher temperatures. Also needed where soldered brass elements could fail, above about 60 °C.
- Monel, Hastelloy, tantalum or PTFE-coated: Aggressive acids, chlorides and specialty chemicals.
5. Decide on Dry or Liquid-Filled
Liquid-filled gauges, usually glycerine or silicone oil, dampen pointer vibration and pulsation, protect the movement from wear and corrosion and prevent condensation. They are strongly recommended on pumps, compressors and vibrating equipment. Use silicone for low temperatures and inert fluorinated fills for oxygen or strong oxidisers.
6. Case and Safety Design
Stainless steel cases resist corrosion in harsh environments. For high pressure or hazardous gases, choose a safety pattern gauge with a solid front and a blow-out back so that, in the unlikely event of element failure, energy is released away from the operator.
7. Process Connection and Mounting
Common connections are 1/4 inch and 1/2 inch NPT or BSP, and G threads in many international markets. Choose bottom (lower) mounting for direct line mounting and back mounting for panels, with optional front or back flanges.
8. Temperature
Process temperature affects both accuracy and life. For hot media such as steam, use a siphon to keep live steam away from the element. For very high temperatures, use a capillary-mounted diaphragm seal or a cooling element.
Essential Pressure Gauge Accessories
- Diaphragm seals: Isolate the gauge from corrosive, viscous, slurry, hot or hygienic media using a flexible diaphragm and fill fluid. A diaphragm seal extends gauge life in difficult services.
- Snubbers and restrictors: Dampen pressure pulsations and spikes from pumps and compressors.
- Siphons (pigtails): Protect gauges from steam and high-temperature vapour by forming a condensate barrier.
- Gauge cocks and needle valves: Allow isolation and venting for safe replacement and calibration.
- Overpressure protectors: Close automatically to protect the gauge from pressures above its range.
- Flushing rings: Allow the diaphragm seal to be flushed in clogging services.
Bliss Flow supplies matching flushing rings, gauge cocks and snubbers so the complete gauge assembly is engineered as one package.
Matching Gauges to Common Applications
- Pumps and compressors: Liquid-filled Bourdon tube gauge with snubber; stainless steel wetted parts.
- Steam lines and boilers: Bourdon gauge with siphon and isolation valve; correct temperature rating.
- Corrosive chemicals: Stainless steel or exotic alloy gauge, often with a diaphragm seal.
- Slurries and viscous media: Diaphragm gauge or gauge with a flushable diaphragm seal.
- Low-pressure gas and draft: Capsule gauge with mbar range.
- Filters and strainers: Differential pressure gauge to show clogging.
- Food and pharmaceutical: Hygienic gauge with sanitary diaphragm seal and tri-clamp connection.
- Oxygen service: Specially cleaned gauge marked ‘Oxygen – Use No Oil’.
Common Causes of Pressure Gauge Failure
- Overpressure: Exceeding the gauge range permanently stretches the element and causes a zero shift. Choose a higher range or fit an overpressure protector.
- Pulsation and vibration: Wear the movement teeth and loosen the pointer. Use liquid filling and a snubber.
- Corrosion: Attacks the element and solder joints. Upgrade wetted materials or add a diaphragm seal.
- Clogging: Viscous, crystallising or dirty media block the element. Use a diaphragm gauge or flushable seal.
- Excessive temperature: Weakens solder joints and causes errors. Use a siphon, cooling tower or capillary seal.
- Freezing: Water trapped in the element can freeze and burst it. Use a diaphragm seal with suitable fill fluid or heat tracing.
Installation and Maintenance Tips
- Always install an isolation valve or gauge cock so the gauge can be removed safely.
- Tighten using the wrench flats on the socket, never by turning the case.
- Mount the gauge vertically and away from heat sources where possible.
- Check zero regularly and calibrate against a reference according to the criticality of the measurement.
- Replace gauges that show a permanent offset, sticking pointer, cracked window or leaking fill fluid.
Pressure Measurement Solutions from Bliss Flow Systems
Bliss Flow Systems supplies a complete range of pressure gauges, including Bourdon tube, diaphragm, capsule and safety pattern solid-front gauges, along with diaphragm seals and accessories, for oil and gas, chemical, power, water and general industrial applications.
Frequently Asked Questions
What range should I choose for a pressure gauge?
Choose a full-scale range about twice the normal operating pressure so the reading normally falls in the middle third of the dial.
When should I use a liquid-filled pressure gauge?
Use a liquid-filled gauge where there is vibration or pressure pulsation, such as on pumps and compressors, or where condensation and corrosion of the movement are a concern.
What is the difference between a Bourdon tube and a diaphragm gauge?
A Bourdon tube gauge uses a curved tube and suits most clean liquids and gases at medium to high pressures. A diaphragm gauge uses a flexible membrane and is better for low pressures, corrosive, viscous or clogging media.
Why use a diaphragm seal with a pressure gauge?
A diaphragm seal isolates the gauge from corrosive, hot, viscous or hygienic process media, protecting the gauge and preventing clogging.
What accuracy class is used for process gauges?
Process gauges are commonly Class 1.0 under EN 837-1 or Grade 1A under ASME B40.100, while test gauges use Class 0.25 or better.
How often should pressure gauges be calibrated?
Most process gauges are checked annually, while gauges on safety-critical, custody transfer or quality-critical duties may be checked every three to six months. Gauges exposed to overpressure, pulsation or impact should be checked immediately, and any gauge that does not return to zero should be recalibrated or replaced.
Conclusion
The right pressure gauge depends on the pressure range, accuracy needed, process media, temperature, vibration and installation conditions. Taking a few minutes to specify the correct sensing element, materials, filling and accessories will deliver reliable readings, improve safety and reduce the cost of frequent replacement.
Contact Bliss Flow Systems
For product selection, technical datasheets or a quotation, reach our engineering sales team at the office nearest to you, or send an enquiry through our contact page.