The KDS is an all-metal, low-volume variable area flow meter, also known as a rotameter, that measures liquid flows from 0.026 to 52.8 GPH (0.1 to 200 l/h, water) and gas flows from 0.11 to 212 ft³/h (3 to 6,000 Nl/h, air) in a compact 316 stainless steel body with ¼" NPT female connections. Accuracy is ±3% of full scale, and pressure ratings reach 6,092 psi (420 bar) on the optional high-pressure KDS-S. Designed as a rugged mechanical system with a low rate of wear, the KDS is available with inductive limit contacts and a 4-20 mA output.
How the KDS Variable Area Flow Meter Works
Fluid enters at the bottom and rises through a conical stainless steel measuring tube, lifting a float until the annular gap between float and cone matches the flow rate. A permanent magnet in the float transmits its height through a magnetic tracking system to the pointer of the analog indicator, which reads volume or mass flow. The KDS-K and KDS-C include a built-in flow-setting valve.
KDS Flow Ranges for Liquids and Gases
Eleven standard ranges run from 0.026 to 0.26 GPH (0.1 to 1.0 l/h) up to 5.28 to 52.8 GPH (20 to 200 l/h) for water, and from 0.11 to 1.06 ft³/h (3 to 30 Nl/h) up to 21.2 to 212 ft³/h (600 to 6,000 Nl/h) for air, each spanning 10 to 100% of its upper value.
The two largest ranges are KDS-S only; the KDS-K and KDS-C top out at 2.64 to 26.4 GPH (10 to 100 l/h). Air values are referenced to 14.7 psia (1.013 bar absolute) and 68 °F (20 °C).
Pressure, Temperature, and Accuracy Ratings
The KDS-K and KDS-C are rated PN 40 (580 psi, 40 bar); the KDS-S is rated PN 63 (914 psi, 63 bar), with an option up to 6,092 psi (420 bar). Accuracy is ±3% of full scale per VDI/VDE 3513, with repeatability of ±1% of the upper range value.
Process temperature limits depend on the fitted electronics: -40 to 266 °F (-40 to 130 °C) without switches or electronics, -13 to 212 °F (-25 to 100 °C) with the standard NJ 1.5-6.5 N contact, and -40 to 212 °F (-40 to 100 °C) with the NJ 2-11 SN contact or 4-20 mA electronics. Ambient temperature is -13 to 158 °F (-25 to 70 °C); the indicator is rated IP 65.
KDS Model Variants: KDS-K, KDS-C, and KDS-S
Three versions differ in connection orientation and mounting. The KDS-K has horizontal process connections toward the rear with a 3.54 in (90 mm) mounting dimension, the KDS-C adds a bolt for panel or wall mounting, and the KDS-S has vertical connections at top and bottom with a 7.09 in (180 mm) mounting dimension.
The KDS-S carries the high-pressure option and SIL conformity. Weight is 1.43 lb (0.65 kg).
Materials and Process Connections
Wetted parts (measuring cone, float, and armature) are 316 stainless steel, with PTFE sealing as standard and other materials on request. The process connection is ¼" NPT female; adapters for Ermeto and Swagelok tube fittings, G ¼" and G ½" male threads, and ¼" hose can change the mounting length.
Limit Switches and 4-20 mA Output Options
The KDS accepts one or two inductive NAMUR limit contacts (Pepperl+Fuchs NJ 1.5-6.5 N, 8.2 V) or one NJ 2-11 SN safety contact, connected through an M12 plug. The KDS-E version adds a passive 2-wire 4-20 mA loop output powered at 14 to 30 V DC with a 500 Ω maximum load.
Installation Requirements
Install the KDS vertically with flow from bottom to top, in a line whose size matches the ¼" NPT connection. Keep at least 11.8 in (300 mm) between adjacent meters and at least 7.9 in (200 mm) from solenoid valves, steel brackets, and other ferromagnetic parts.
No inlet section is needed for a linear flow profile; a non-linear profile calls for 5.9 in (150 mm). Fit a magnetic filter where ferromagnetic particles may be present and raise gas inlet pressure slowly. The KDS is intended for non-viscous liquids free of solids and for gases with linear flow behavior and adequate inlet pressure.
Common Questions about KDS - All-Metal, Low-Volume Variable Area Flow Meter
The lowest standard range is 0.026 to 0.26 GPH (0.1 to 1.0 l/h) for water and 0.11 to 1.06 ft³/h (3 to 30 Nl/h) for air. Every KDS scale reads from one tenth of full scale up to full scale, so the smallest readable flow on any range is 10% of its top value.
All three use the same float measuring principle. The KDS-K connects horizontally toward the rear, the KDS-C is the same meter with a bolt for panel mounting, and the KDS-S connects vertically. Only the KDS-S reaches 52.8 GPH (200 l/h), carries the PN 63 rating, and offers the 6,092 psi (420 bar) and SIL options.
Nominal pressure is PN 40, equal to 580 psi (40 bar), for the KDS-K and KDS-C, and PN 63, equal to 914 psi (63 bar), for the KDS-S. A high-pressure KDS-S version is available on request for operating pressures up to 6,092 psi (420 bar).
Without electronics, the fluid may run from -40 to 266 °F (-40 to 130 °C). Fitting the standard NJ 1.5-6.5 N switch narrows that to -13 to 212 °F (-25 to 100 °C); the NJ 2-11 SN contact and 4-20 mA electronics allow -40 to 212 °F (-40 to 100 °C). Ambient limits are -13 to 158 °F (-25 to 70 °C).
Yes. Options are one or two NAMUR inductive limit contacts, a single NJ 2-11 SN contact for safety circuits, or the KDS-E transmitter with a 4-20 mA signal (14 to 30 V DC, 500 Ω maximum load). Default switch points are 10% on falling flow and 90% on rising flow, and every version connects through an A-coded 4-pin M12 plug.
Pressure loss rises with the measuring range. For 68 °F (20 °C) water through a fully open valve, range A is 0.087 psi (6 mbar) on every model, while range I reaches 1.38 psi (95 mbar) on the KDS-K and KDS-C but only 0.22 psi (15 mbar) on the KDS-S. The largest KDS-S range, K, is 0.41 psi (28 mbar).
Mount it upright so flow travels upward, with piping that matches the ¼" NPT connection size and flanges aligned to avoid stress. Allow 11.8 in (300 mm) between neighboring meters and 7.9 in (200 mm) from steel parts or solenoid valves. If in doubt, move the meter about 7.9 in (200 mm) and check whether the pointer shifts.
None when used as intended. If dirt collects on the measuring cone or float, depressurize, drain, and cool the line before removing the meter, then clean the parts with a brush and a suitable agent. If the pointer does not respond to changing flow, a stuck float or pointer is the usual cause; magnetic contaminants call for a magnetic filter.
KOBOLD USA requires a completed KDS Application Guide before specifying or quoting a new KDS, even when a part number has already been identified; only repeat orders of a previously specified product are exempt. Provide fluid data, specific gravity, temperature, pressure, viscosity, materials, connection size, measuring range, accessories, required approvals, and material certificates. Send the form to customerservice@koboldusa.com.
Product Specifications
Measuring Range Liquid
0.1...1 L/h to 20...200 L/h
Measuring Range Gas
3...30 Nl/h to 600...6000 Nl/h
Wetted Material
316 St. Steel
Max. Pressure
40 Bar (Higher pressures available upon request)
Max. Temperature
-40...130 °C (-25..100 °C w/Contact)
Media Categories
Liquid or Gas
Product Features
For Measurement of Low Flow Rates
Optional Switches, Analog Transmitter
Certificates/Approvals: ATEX, IECEx, SIL
Documents
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