All-Metal Armored Flow Meter for Liquids/Gas – BGF

What Is the KOBOLD BGF All-Metal Armored Flow Meter?

The KOBOLD BGF is an all-metal armored variable area flow meter for liquids and gases that uses a guided float and spring return mechanism, allowing installation in both horizontal and vertical pipes. It is designed for difficult applications requiring high-pressure or high-temperature operation or low pressure loss, in line sizes up to 3 inches.

In standard configuration, the BGF is a purely mechanical meter suited for water and compressed gases. Its armored design is available in stainless steel (BGF-S) or PTFE-lined stainless steel (BGF-P), and custom designs for high-pressure operation, special fittings and special materials of construction are available upon request.

How Does the BGF Transmit Its Flow Reading?

The position of the measuring body inside the measuring ring serves as the measure of flow. A permanent magnet embedded in the measuring body converts that position into rotary motion through a magnetic coupling, which is transmitted to the scale and to any additional electrical equipment mounted in the indicator unit.

The indicator is an analog display with a pointer that travels approximately 90°. Customized scales are possible when process data is provided.

BGF Flow Ranges, Accuracy and Pressure Ratings

According to specifications, BGF water ranges start at 0.044 to 0.44 GPM (0.01 to 0.1 m³/h) and extend to 26.4 to 264 GPM (6 to 60 m³/h). Air ranges start at 0.176 to 1.76 SCFM (0.3 to 3 m³/h) and extend to 100 to 1,000 SCFM (170 to 1,699 m³/h). Accuracy is ±2% of full scale.

Repeatability: ±0.8% of full scale; additional inaccuracy with the ES transmitter: ±0.2%
Nominal pressure: 580 PSIG (40 bar) for the BGF-S, ASME Class 150/300; 230 PSIG (15.9 bar) for the BGF-P, ASME Class 150
Higher pressures upon request, up to 5,800 PSIG (400 bar)

Materials, Connections and Temperature Limits

The BGF-S wetted parts are 316L/316-Ti stainless steel with a 316-Ti spring. The BGF-P uses a PTFE-lined stainless steel measuring tube with Hastelloy C-22® and PTFE wetted parts. Process connections are ASME B16.5 flanges from 1/2 to 3 inches or NPT threads from 1/4 to 2 inches, with other connections on request.

Process temperature, BGF-S with electrical output: -40 to 300°F (-40 to 149°C)
Process temperature, BGF-S without electrical output, or with a display assembled at a distance (options V, H or W): -40 to 390°F (-40 to 199°C)
Process temperature, BGF-P: -40 to 257°F (-40 to 125°C)
Ambient temperature: -40 to 176°F (-40 to 80°C) without switch; -40 to 150°F (-40 to 66°C) with switch
Display housing: stove-enameled aluminum (IP65) or optional stainless steel (IP67)

Mounting Orientation and Installation

The BGF is installed vertically or horizontally according to the flow direction specified in the order: top to bottom, bottom to top, left to right or right to left.

No straight runs are needed upstream or downstream with a linear flow profile; with an extremely non-linear profile, a 9.84 in (250 mm) inlet section is recommended
Recommended minimum lateral distance: 11.81 in (300 mm) between adjacent meters and 7.87 in (200 mm) from interfering steel parts
A magnetic filter accessory is recommended ahead of the meter when ferromagnetic solids cannot be excluded
Face-to-face length: 9.84 in (250 mm) for flanged models, 11.81 in (300 mm) for NPT models

Limit Switches, Transmitters and Hazardous Area Options

Electronic limit switches and/or an analog flow transmitter may be added to the BGF. Analog output is supplied standard with HART® protocol, and FOUNDATION® Fieldbus™ is available as an option. Available switches and analog outputs include intrinsically safe versions that may be used in hazardous areas where intrinsically safe installations are permitted.

Switch options: inductive (standard), inductive safety design, 3-wire inductive and microswitch, in single or dual versions
ES transmitter: 14 to 30 VDC supply, passive and galvanically isolated 4-20 mA output
Mechanical device Ex marking: II 2G Ex h IIC T1...T6 Gb and II 2D Ex h IIIC T85°C/T350°C Db
ES transmitter: DMT 00 ATEX E 075 / IECEx BVS 16.0072, marked II 2G Ex ia IIC T6 Gb
EXIDA-examined SIL 1 or SIL 2 conformity per IEC 61508-2 for selected switch and transmitter options

Common Questions about BGF - All-Metal Armored Flow Meters

Process flow passes through a sharp-edged measuring ring and pushes a conical measuring body against a compression spring. The body moves until the flow force and the spring tension reach equilibrium, and its resulting position corresponds to the volume flow, which the manual lists as the measured variable.

The largest water range for each size is: DN15, 0.264 to 2.64 GPM (0.06 to 0.6 m³/h); DN25, 1.76 to 17.6 GPM (0.4 to 4 m³/h); DN40, 4.4 to 44 GPM (1 to 10 m³/h); DN50, 11 to 110 GPM (2.5 to 25 m³/h); DN80, 26.4 to 264.2 GPM (6 to 60 m³/h). Smaller ranges are offered within each size.

The stainless steel BGF-S carries a standard nominal pressure of 580 PSIG (40 bar) with ASME Class 150 or 300 connections. The PTFE-lined BGF-P is rated 230 PSIG (15.9 bar) standard with ASME Class 150 connections. Custom designs rated as high as 5,800 PSIG (400 bar) are available upon request.

Without an electrical output, the BGF-S handles process temperatures from -40 to 390°F (-40 to 199°C), and the same limit applies when the display is mounted at a distance. Adding an electrical output limits the BGF-S to 300°F (149°C). The PTFE-lined BGF-P is rated from -40 to 257°F (-40 to 125°C).

Yes. Its guided float and spring return let the BGF operate in horizontal lines as well as vertical ones, with flow running left to right, right to left, top to bottom or bottom to top as specified when ordering. When mounted horizontally, keep the indicator unit from facing upward.

Options include inductive limit switches (standard, safety design or 3-wire), microswitches and the ES electronic transmitter. The ES delivers a 4-20 mA signal with HART® protocol from a 14 to 30 VDC supply, with versions adding two NAMUR switches or one NAMUR switch and a pulse output. A FOUNDATION® Fieldbus™ version is also offered.

It has ATEX and IECEx certification. The mechanical BGF is marked II 2G Ex h IIC T1...T6 Gb and II 2D Ex h IIIC T85°C/T350°C Db. The ES transmitter is certified under DMT 00 ATEX E 075 and IECEx BVS 16.0072, and selected options carry SIL 1 or SIL 2 conformity examined by EXIDA.

According to the manual, inlet and outlet sections are not required when the fluid has a linear flow profile. For an extremely non-linear profile, such as when shut-off or control valves sit in front of the meter, an inlet section of 9.84 in (250 mm) is recommended. Pipe and meter nominal sizes must match.

KOBOLD requires a completed BGF application guide with each order. For liquids, it asks for the liquid type, normal operating temperature, viscosity, specific gravity and desired range. For gases, it also asks for the normal pressure at the outlet fitting, because the calibration pressure is the pressure the meter sees at its outlet.