Baumer Capsule Pressure Gauges: How to Select the Right Gauge for Low Pressure Measurement
Low pressure measurement is one of those applications where choosing a pressure gauge only by dial size and connection can cause trouble.
A plant may need to monitor clean air pressure, low pressure draft, a gaseous line or a low viscosity process medium. The pressure may be only a few millibars, so the instrument has to provide useful indication in a range where a conventional high pressure gauge would not be the logical choice.
This is where a Baumer Capsule Pressure Gauge fits.
The Baumer capsule gauge range in the supplied datasheets is designed around low pressure measurement, with available ranges from 25 mbar to 600 mbar, pressure, vacuum and compound scale possibilities, several mounting styles and two useful construction choices: the AX SS Case Brass Pressure Gauge and the AF All SS Pressure Gauge.
The important part is deciding which construction is right for your process. The AX and AF may look similar from the front, but the materials, temperature capability, ingress protection and overpressure capability are not the same.
What is a Capsule Pressure Gauge?
A capsule pressure gauge is intended for measuring relatively low pressures where a more sensitive measuring element is required.
In general engineering terms, the pressure acts on a capsule sensing element. Small movement of this element is transferred through the mechanical movement to the pointer, giving a direct local reading on the dial.
For the Baumer models covered here, there is no electrical output specified in the supplied datasheets. These are mechanical indicating instruments intended for local pressure indication.
That distinction matters. If your requirement is only to see the pressure locally at a duct, vessel, utility line or process point, a capsule gauge may be suitable. If you need the pressure value inside a PLC, SCADA, BMS or remote control system, you would normally need an appropriate pressure transmitter or electronic measurement solution as well.
Why Capsule Gauges Matter in Actual Plant Conditions
When pressure is low, range selection becomes especially important.
Suppose the normal process pressure is around 150 mmWC. Installing a gauge designed for much higher pressure may technically give a reading, but the useful movement of the pointer can become too small for practical monitoring.
A properly selected capsule gauge gives the operator a scale that is actually useful for the process.
Baumer lists these gauges for applications including:
- Low pressure draft measurement
- Food and beverage plants
- Pharmaceutical applications
- Breweries
- Conventional power plants
- Nuclear power plants
- Clean air
- Gaseous media
- Low viscosity, non corrosive media that will not obstruct the pressure system
The datasheets specify ±1.6% of full scale accuracy for both AX and AF models.
For a maintenance engineer, this means the first question should not be "Which pressure gauge is cheapest?" It should be "What is the actual operating pressure, what media touches the instrument and what range gives me a useful reading?"
Baumer Capsule Pressure Gauge Range
The uploaded datasheets give two main constructions worth comparing.
Baumer AX Capsule Pressure Gauge
The Baumer AX is an SS case pressure gauge with copper alloy pressure components. It is a practical option where the process medium is compatible with copper alloy wetted parts and the application does not require an all stainless steel pressure system.
It also comes in four dial sizes, making it possible to choose a compact local gauge or a larger dial for easier reading from a distance.
Technical points to note:
- Available range: 25 mbar to 600 mbar
- Accuracy: ±1.6% of full scale
- Nominal sizes: 63, 100, 125 and 150 mm
- Case and bezel: AISI 304 stainless steel, bayonet type
- Capsule: copper alloy
- Socket: copper alloy
- Movement: copper alloy
- Joints: tin soldering
- Protection: IP55
- Ambient temperature: minus 25°C to plus 65°C
- Maximum process temperature: 100°C
- Recommended operating pressure: 75% of scale value
- Overpressure: listed as not suitable
- Zero adjustment provision
- General standard reference: EN 837-3
Where it is commonly suited:
- Low pressure air lines
- Draft measurement
- Clean gas service
- Utility monitoring
- HVAC related low pressure points
- Suitable brewery and food process utilities
- General plant low pressure monitoring
Baumer AF All Stainless Steel Capsule Pressure Gauge
The Baumer AF is the better option when stainless steel wetted parts, a higher process temperature limit or stronger ingress protection are required.
Its maximum listed process temperature is 150°C, compared with 100°C for the AX.
Technical points to note:
- Available range: 25 mbar to 600 mbar
- Accuracy: ±1.6% of full scale
- Nominal sizes: 63, 100, 125 and 150 mm
- Case and bezel: AISI 304 stainless steel
- Capsule: AISI 316 stainless steel
- Socket: AISI 316L stainless steel
- Movement: AISI 304 stainless steel
- Joints: TIG argon arc welding
- Protection: IP65, with IP55 for the 63 mm size
- Ambient temperature: minus 25°C to plus 65°C
- Maximum process temperature: 150°C
- Recommended operating pressure: 75% of scale value
- Overpressure: 130% of maximum scale value
- Zero adjustment provision
- General standard reference: EN 837-3
Where it is commonly suited:
- Pharmaceutical utility applications
- Food and beverage processing
- Breweries
- Clean air systems
- Suitable gas applications
- Process plant low pressure monitoring
- Applications requiring stainless steel wetted components
Baumer AX vs AF Capsule Pressure Gauge
| Selection Point | Baumer AX | Baumer AF |
|---|---|---|
| Construction | SS case with copper alloy pressure components | Stainless steel construction with SS wetted components |
| Capsule | Copper alloy | AISI 316 SS |
| Socket | Copper alloy | AISI 316L SS |
| Maximum process temperature | 100°C | 150°C |
| Protection | IP55 | IP65, except 63 mm at IP55 |
| Overpressure capability | Not suitable | 130% of maximum scale |
| Accuracy | ±1.6% F.S. | ±1.6% F.S. |
| Dial sizes | 63, 100, 125, 150 mm | 63, 100, 125, 150 mm |
| Main selection reason | General compatible low pressure service | Stainless wetted parts and more demanding installation requirements |
The practical decision is straightforward. If the process is compatible with copper alloy components and the environmental conditions fit the AX specifications, AX may be sufficient. If stainless steel wetted parts, higher process temperature capability or better enclosure protection are important, AF becomes the stronger choice.
Pressure, Vacuum and Compound Ranges
Range selection deserves more attention than most buyers give it.
The Baumer datasheets show pressure scales such as:
- 0 to 250 mmWC
- 0 to 400 mmWC
- 0 to 600 mmWC
- 0 to 1000 mmWC
- 0 to 1600 mmWC
- 0 to 2000 mmWC
- 0 to 2500 mmWC
- 0 to 4000 mmWC
- 0 to 6000 mmWC
Vacuum and compound ranges are also listed.
Baumer notes that other national and international scales such as mbar, kPa, inWC, MWC, inHg and mmHg, along with dual or equivalent scales, can be provided according to requirement.
The selection lesson is important: do not choose the largest available range "for safety." A range that is unnecessarily high makes a low pressure process harder to read.
Mounting Options Matter More Than They Look
A replacement gauge can have the correct pressure range and still be wrong for the installation if the connection and mounting arrangement do not match.
The Baumer capsule range includes several configurations, depending on nominal size:
- Wall, surface or projection mounting with bottom entry
- Direct bottom entry
- Direct lower back entry
- Direct center back entry
- Lower back entry with front flange
- Lower back entry with mounting bracket
- Center back entry with mounting bracket
The dimensional drawings on pages 2 and 3 of the AX and AF datasheets show that the body depth, flange arrangement and mounting dimensions change with nominal size and mounting type. That is particularly important when replacing a gauge in an existing panel or machine.
Before ordering a replacement, check the old gauge from the side and rear, not just from the front.
Process Connections
The ordering tables provide connection options including:
- 1/4 inch BSP male
- 1/4 inch NPT male
- 3/8 inch BSP male
- 3/8 inch NPT male
- 1/2 inch BSP male
- 1/2 inch NPT male
- M20 x 1.5 male
The datasheets also note that other connection types can be provided on request, and that some connections for the 63 mm size are achieved through adaptors.
This is one of the easiest purchasing mistakes to avoid. Confirm the thread before placing the order.
Key Selection Factors for a Baumer Capsule Pressure Gauge
1. Actual working pressure
Start with the normal operating pressure, not only the maximum possible pressure. Both datasheets specify operating pressure at 75% of scale value.
2. Media compatibility
For AX, check compatibility with the copper alloy capsule and socket.
For AF, check compatibility with the AISI 316 capsule and AISI 316L socket.
3. Overpressure possibility
This is a major difference between the two models. AX is listed as not suitable for overpressure, while AF specifies 130% of maximum scale value.
4. Process temperature
AX has a maximum process temperature of 100°C.
AF extends this to 150°C.
5. Ambient condition and enclosure
Both models list an ambient range from minus 25°C to plus 65°C. For protection, AX is IP55, while AF is IP65 for the larger sizes and IP55 for 63 mm.
6. Dial size
Choose 63 mm where space is tight. Consider 100, 125 or 150 mm where the operator needs to read the gauge from farther away.
7. Mounting and connection
Confirm bottom entry, back entry, panel arrangement, flange or bracket requirement before ordering.
8. Required scale
Confirm whether your plant standard uses mbar, mmWC, kPa, inWC or another unit. Dual scales can also be requested according to the datasheet.
Common Mistakes to Avoid
| Common Mistake | Why It Causes Problems |
|---|---|
| Selecting only by pressure range | Material, connection and mounting may still be wrong |
| Assuming every stainless case gauge has SS wetted parts | AX uses copper alloy capsule and socket |
| Selecting an unnecessarily large range | Low pressure changes become harder to read |
| Ignoring overpressure | AX is specifically listed as not suitable for it |
| Forgetting process temperature | AX and AF have different temperature limits |
| Ordering only from a front photo | Rear connection and mounting may not match |
| Assuming all four dial sizes have identical IP protection | AF 63 mm is IP55 while larger AF sizes are IP65 |
| Forgetting the thread standard | BSP, NPT and M20 options are not interchangeable |
Do This, Not That
| Do This | Not This |
|---|---|
| Select the range around the actual operating condition | Buy the highest range available |
| Check capsule and socket material against the media | Select based only on stainless case appearance |
| Confirm bottom or rear connection | Assume the new gauge will fit the old installation |
| Check overpressure conditions | Ignore pressure spikes |
| Match dial size to reading distance | Choose the smallest dial only to reduce cost |
| Confirm BSP, NPT or metric thread | Identify the connection only by approximate size |
| Compare AX and AF by process requirement | Assume AF is required for every application |
Quick Selection Checklist
Before asking for a Baumer Capsule Pressure Gauge quotation, confirm:
- Normal operating pressure
- Required pressure, vacuum or compound range
- Preferred engineering unit
- Process media
- Maximum process temperature
- Possibility of pressure spikes or overpressure
- Required dial size
- Bottom or back connection
- Mounting flange or bracket requirement
- BSP, NPT or metric process connection
- Required IP protection
- Whether copper alloy or stainless steel wetted parts are acceptable
- Calibration certificate requirement
- Any custom dial or tag requirement
Optional Features Worth Confirming
The Baumer ordering tables also list options such as calibration certificates, traceable calibration certificates, plexiglass, safety glass, toughened glass, custom dial marking and stainless steel tag plates.
For the AF version, the datasheet also lists options such as material test certificates and an AISI 316 case and bezel for nominal sizes of 100 mm and above.
These options are worth discussing at quotation stage rather than after the gauge has already arrived.
Why Buy Baumer Capsule Pressure Gauges from Radical TechMart?
A low pressure gauge inquiry often begins with something simple such as "Need 100 mm capsule gauge, 0 to 600 mmWC."
But that is not always enough information to select the correct instrument.
At Radical TechMart, the focus is to help buyers check the application before finalizing the gauge, including pressure range, media, wetted material, dial size, mounting type, process connection and installation condition.
This is particularly useful for OEMs, plant maintenance teams, instrumentation engineers, EPC contractors and purchase departments that need a correct replacement or project specification rather than simply another gauge with a similar dial.
Final Thoughts
A Baumer Capsule Pressure Gauge makes sense when the application involves low pressure measurement and clear local indication.
The real selection decision is not AX versus AF based on price alone. It is about what touches the process, how hot the process can become, whether overpressure can occur, what protection level is required and how the gauge has to fit into the existing installation.
For compatible general service, the AX offers a stainless case with copper alloy pressure components. For applications needing stainless steel wetted parts, higher process temperature capability and stronger protection in larger sizes, the AF provides the more appropriate construction.
In low pressure measurement, choosing the correct range and construction is what makes the gauge useful after installation, not simply choosing a familiar model number.
FAQs
1. What is a Baumer capsule pressure gauge used for?
It is used for low pressure measurement in applications such as draft measurement, clean air, gaseous media and suitable low viscosity, non corrosive process media.
2. What pressure ranges are available for Baumer capsule gauges?
The datasheets state an available range from 25 mbar to 600 mbar. Example mmWC pressure, vacuum and compound ranges are also provided.
3. What is the difference between Baumer AX and AF capsule gauges?
AX uses a stainless steel case with copper alloy capsule and socket. AF uses an AISI 316 stainless steel capsule and AISI 316L socket, provides a higher listed process temperature and has IP65 protection for 100 mm and larger versions.
4. Is the Baumer AX suitable for pressure spikes?
The AX datasheet lists its overpressure limit as "Not Suitable." If pressure spikes are expected, this must be considered during selection.
5. What is the accuracy of Baumer capsule pressure gauges?
Both AX and AF datasheets specify accuracy of ±1.6% of full scale.
6. Which dial sizes are available?
Both models are available in standard nominal sizes of 63, 100, 125 and 150 mm.
7. Can I order the gauge in mmWC, mbar or kPa?
Yes. The datasheets reference scales including mbar, kPa, inWC, MWC, inHg and mmHg, along with dual or equivalent scales on request.
8. Can Baumer AX or AF connect directly to a PLC?
The supplied AX and AF datasheets describe mechanical indicating gauges and do not specify an electrical output. For PLC or SCADA pressure monitoring, an appropriate pressure transmitter or electronic pressure instrument should be selected separately.
