What Is the BGN All-Metal Armored Flow Meter?
The KOBOLD BGN is an all-metal armored variable area flow meter that measures liquids, gases, and steam in processes requiring high pressure capability, high temperature operation, or low pressure loss. Engineered for conditions up to 580 PSIG standard — 8,700 PSIG (600 bar) on request — and process temperatures reaching 660°F (350°C), it delivers precision flow measurement where other instruments fail.
Unlike conventional rotameters limited by pressure and temperature constraints, the BGN's armored construction withstands severe process conditions while maintaining ±1.6% of full scale accuracy for liquids and ±1.8% for gases. The direct-reading scales come factory-calibrated for your specific media viscosity, density, operating pressure, and temperature, eliminating field calibration requirements and reducing installation time.
View the sizing guide and app tool
Pressure, Temperature, and Accuracy Specifications
According to specifications, standard BGN-S/H meters are rated 580 PSIG (ASME Class 150/300), with special designs available up to 8,700 PSIG (600 bar) for severe applications. Process temperatures span -40°F to 392°F (-40°C to 200°C) as standard and reach 660°F (350°C) with the high-temperature option.
- Accuracy: liquids ±1.6% of full scale (BGN-S/H), ±2.0% for the PTFE-lined version; gases ±1.8% (BGN-S/H), ±2.2% (PTFE-lined)
- Repeatability: ±0.5% of full scale for consistent process control
- Flow ranges: 0.0022–0.022 GPM to 57.24–572.2 GPM (water); 0.0088–0.088 SCFM to 64.74–647.4 SCFM (air)
- Line sizes: ½" to 6" ASME B16.5 flanges (Class 150 or 300) or ¼" to 2" NPT threaded connections
- Protection rating: IP65 (aluminum housing) or IP67 (stainless steel housing)
Advanced Material Options for Chemical Compatibility
Process compatibility drives flow meter reliability. The BGN offers three wetted material configurations: 316L/316-Ti stainless steel for general industrial service, PTFE-lined stainless steel for aggressive chemicals at temperatures up to 257°F (125°C), and Hastelloy C-22 construction for extreme corrosion resistance. Special materials including Monel, Tantalum, and other exotic alloys accommodate unique process requirements on request.
Every material selection undergoes rigorous testing to ensure long-term chemical compatibility under specified operating conditions.
Comprehensive Hazardous Area Certifications
The BGN delivers easy safety compliance through globally recognized certifications: ATEX, IECEx, and CE Pressure Equipment Directive compliance. The meter carries ATEX approval for Zone 1 and Zone 2 installations, supporting both gas and dust atmospheres with II 2G Ex h IIC T1…T6 Gb and II 2D Ex h IIIC T85°C/T350°C Db markings, according to specifications.
The intrinsically safe electronic options feature certification for II 2G Ex ia IIC T6 Gb protection, enabling installation in the most stringent hazardous locations. The BGN is also available with optional SIL-capable limit switches for integration into Safety Instrumented Systems, with SIL 1 and SIL 2 conformity examined by EXIDA according to IEC 61508-2.
Intelligent Electronic Integration Options
Electronic options transform mechanical indication into actionable process data. The ES transmitter provides 4-20 mA output with HART protocol, enabling remote monitoring and configuration while maintaining local indication; Profibus-PA and Foundation Fieldbus interfaces are available as alternatives, according to specifications.
Configure up to two NAMUR-compliant limit switches for critical process alarms, or combine one switch with a pulse output for totalization applications. The transmitter electronics operate from 14-30 VDC with galvanically isolated outputs, ensuring signal integrity in electrically noisy industrial environments.
Sample Applications Across Demanding Industries
From chemical processing plants to power generation facilities, the BGN provides reliable flow measurement where accuracy matters. In refineries, it monitors catalyst injection and additive dosing systems at elevated temperatures. Chemical manufacturers rely on its corrosion resistance for acid and solvent service. Power plants utilize the high-pressure capability for boiler feedwater and steam applications up to 8,700 PSI.
The low-pressure-loss design particularly benefits gas measurement applications where maintaining system pressure is critical. The mechanical simplicity ensures reliable operation without external power, making it ideal for remote installations and emergency shutdown systems.
Installation Flexibility and Maintenance Simplicity
The BGN installs vertically with bottom-to-top flow direction for optimal float response and measurement accuracy, and typically requires no straight pipe runs where the medium has a linear flow profile. For non-standard orientations, the companion BGF model offers spring-return mechanisms enabling horizontal or angled mounting.
Maintenance requirements remain minimal throughout the service life. The all-welded metal construction eliminates gaskets and seals in the flow path, preventing leakage and reducing failure points. When maintenance is required, the removable cone-and-float assembly on flanged versions allows thorough inspection or easy replacement; float removal is not available on NPT-threaded models, according to specifications.
Why Choose the BGN for Your Application
When process conditions exceed the capabilities of standard instrumentation, the BGN delivers where others fail: extreme temperature and pressure ratings, comprehensive material options, and hazardous area certifications compatible with both legacy systems and modern digital infrastructure.
Contact KOBOLD USA's application engineers for sizing calculations, material compatibility assessments, and configuration recommendations, with local support from our Pittsburgh facility.
Common Questions for All-Metal Armored Flow Meters
The BGN is a rotameter-type instrument in which a conical float rises inside a sharp-edged measuring ring as flow increases; a permanent magnet in the float transmits that position to the indicator scale. Its all-metal construction withstands process conditions that limit conventional rotameters while measuring liquids, gases, and steam.
Pressure ratings start at 580 PSIG for standard BGN-S/H meters on ASME Class 150/300 connections and extend to 8,700 PSIG (600 bar) through special designs, according to specifications. Temperature limits are -40°F to 392°F (-40°C to 200°C) standard, 660°F (350°C) with the high-temperature option, and 257°F (125°C) for PTFE-lined versions.
Water-service ranges run from 0.0022–0.022 GPM at the low end up to 57.24–572.2 GPM, while air-service ranges run from 0.0088–0.088 SCFM up to 64.74–647.4 SCFM, according to specifications. Every meter ships with a scale matched at the factory to the stated media properties, and each range spans 10–100% of its upper value.
Buyers can specify measuring tubes in 316L/316-Ti stainless steel, in stainless steel with a PTFE lining rated to 257°F (125°C) for aggressive chemicals, or in Hastelloy C-22 where corrosion resistance is paramount. Monel, Tantalum, and other special materials can be quoted on request for unusual process media.
Yes. For explosive atmospheres the mechanical device is marked II 2G Ex h IIC T1…T6 Gb (gas) and II 2D Ex h IIIC T85°C/T350°C Db (dust), according to specifications. Adding the intrinsically safe ES transmitter keeps the assembly hazardous-area capable, with certification II 2G Ex ia IIC T6 Gb under ATEX and IECEx.
Yes. When ordered with the appropriate limit switches, the BGN can serve in Safety Instrumented Systems: EXIDA has examined SIL 1 conformity to IEC 61508-2:2010 and SIL 2 conformity to IEC 61508-2:2000, according to specifications. An EXIDA SIL conformity assessment (ordering option SK) is available for qualifying switch configurations.
A passive, galvanically isolated 4-20 mA signal with HART protocol is standard on the ES transmitter, which runs on 14-30 VDC. Buyers can instead specify Profibus-PA or Foundation Fieldbus versions. Switching options cover as many as two NAMUR limit switches, or a single switch paired with a pulse output that feeds totalization.
No. The basic BGN indicates flow through a purely mechanical magnet-and-pointer system, so no power supply is needed for local measurement. Electrical power comes into play only if the optional ES transmitter or limit switches are added for remote monitoring, alarms, or totalization functions, according to specifications.
Mount the meter in a vertical pipe run so the medium flows upward through it. Extra straight piping is generally unnecessary; only when fittings converge directly upstream should you allow 5xD before and 3xD after the meter, per the manual. Where a vertical run is impossible, KOBOLD's spring-loaded BGF handles horizontal or inclined lines.
None on a routine basis when the meter is used as intended, according to the manual. There are no gaskets or seals to service in the welded flow path. Should cleaning become necessary, flanged versions allow the cone and float to be withdrawn, and a magnetic filter accessory protects against ferrous particles in the media.