The KOBOLD KSM is an all-plastic variable area flow meter and switch that measures liquids and gases with no metal parts in contact with the fluid. Also commonly known as a rotameter, it provides the same reliable measurement principle as expensive metal or glass rotameters at a fraction of the cost, making it ideal for budget-conscious projects requiring multiple measuring points or applications where plastic construction offers an economic advantage.
Measuring flow rates from 0.06...0.66 to 35...264 GPM for liquids and 0.5...3 to 50...400 SCFM for air, the KSM maintains ±4% full scale accuracy across the entire measurement range, with repeatability of 1% or better according to specifications. The transparent measuring tube provides direct visual flow indication without external power, and optional reed switches add alarm capability at minimal cost.
How the KSM Variable Area Rotameter Works
Flowing fluid lifts a float within a tapered tube to indicate flow rate, one of the most economical technologies for visual flow indication. This simple principle makes rotameters the preferred choice for applications requiring reliable indication without complex electronics or external power. Two adjustable markers allow the user to designate desired flow conditions for instant verification.
Made in USA Rotameter, BABA Compliant Without Premium Pricing
Manufactured in Pittsburgh, Pennsylvania, the KSM meets Build America, Buy America (BABA) compliance requirements while maintaining competitive pricing. Domestic manufacturing streamlines procurement for federally funded projects, including municipal water systems, wastewater facilities, and industrial infrastructure upgrades, delivering compliant variable area flow measurement without the premium cost typical of domestic instrumentation.
KOBOLD's Pittsburgh facility combines American quality and competitive pricing with efficient production, and readily available domestic inventory helps accelerate project completion. Engineering support assists with application evaluation, ensuring proper model selection for economic and technical requirements.
All-Plastic Construction for Corrosive and Standard Media
Plastic construction provides dual benefits: significant cost savings compared to metal or glass rotameters for standard applications, and inherent corrosion resistance for aggressive media. Measuring tubes come in Trogamid or Polysulfone, with other wetted parts of PVDF, PVC, and EPDM, so these meters offer excellent resistance and reliability.
The Trogamid option handles general water or air service at reduced cost versus other variable area meters. The Polysulfone version accommodates aggressive acids and chemicals, providing one platform for diverse requirements. Both tube options are rugged and shock resistant.
Optional Reed Switches for Automated Monitoring
Up to two optional bistable reed switches add automated monitoring to this economical rotameter, enabling high/low alarms or flow setpoint indication at minimal cost and transforming the visual indicator into a control device suitable for integration with common automation infrastructures.
The optional switch is a normally open reed contact activated by increasing flow, rated for up to 230 VAC, with mechanical switching that requires no external power. An IP65 housing provides suitable protection from dust and water ingress in industrial environments. This simple approach helps reduce installation costs versus powered variable area instrumentation.
Installation Flexibility and Connection Options
Multiple sizes ranging from 1" to 2-1/2" accommodate a variety of pipe diameters and flow rates. Standard PVC glue socket connections provide economical permanent installation, and optional female NPT threaded connections are also available. The meter mounts vertically with media flowing from bottom to top, according to specifications.
Direct Reading Scales for Water and Air
Water scales provide direct GPM readings and air scales offer SCFM readings. The flow meter has large, clear scales with contrasting floats to ensure easy reading from a distance, and percentage scales enable quick flow verification relative to system capacity, so operators can confirm conditions at a glance without conversion tables.
KSM Technical Specifications
The specifications below summarize the KSM's documented ratings: measuring ranges for water and air, pressure and temperature limits by construction, wetted materials, connection options, and switch ratings, all according to the current KOBOLD datasheet. Ranges are model-dependent; the datasheet ordering table lists the exact range for each size and tube material.
- Accuracy: ±4% of full scale; repeatability 1% or better
- Liquid range: 0.06...0.66 to 35...264 GPM (water)
- Air range: 0.5...3 to 50...400 SCFM
- Maximum pressure: 145 PSI (10 bar)
- Maximum temperature: 140°F (60°C) with Trogamid tube or PVC fittings; 212°F (100°C) with Polysulfone tube; 185°F (85°C) with reed contact
- Wetted materials: Trogamid or Polysulfone tube; PVDF float and float stops; PVC fittings; EPDM O-rings (others upon request)
- Connections: 1" to 2-1/2" PVC glue socket (standard) or female NPT (optional)
- Mounting: vertical, media flow bottom to top
- Pressure drop: 0.26 to 0.48 PSI maximum
- Switch option: bistable normally open reed contact, up to 230 VAC, 10 W/12 VA, 0.5 A, IP65
Common Questions about KSM - All-Plastic Flow Meter and Switch for Liquids or Gases
Flow lifts a float that moves freely, without friction, inside the measuring tube; the reading edge at the float's largest diameter shows the value on the scale. Standard units include a water scale, a percentage scale, and two adjustable set point indicators, and switch-capable versions carry a float with an integral magnet.
Water models span 0.06...0.66 GPM on the smallest 1" size up to 35...264 GPM on the 2-1/2" size, according to specifications. Air models run from 0.5...3 SCFM up to 50...400 SCFM. Pressure drop is low, between 0.26 and 0.48 PSI maximum depending on model.
Maximum operating pressure is 145 PSI (10 bar). Temperature limits depend on construction: 140°F (60°C) applies to Trogamid tubes and PVC fittings, 212°F (100°C) to the Polysulfone tube, and 185°F (85°C) when a reed contact is fitted, according to specifications.
Wetted components are the Trogamid or Polysulfone measuring tube, a float and float stops made of PVDF, PVC glue socket or optional NPT fittings, and EPDM O-rings, with other O-ring materials available upon request. On 2-1/2" models, the float guide rod is PVDF-clad stainless steel, keeping the cladding against the fluid.
Yes, BABA compliant models are available, and the meter is produced at KOBOLD's Pittsburgh, Pennsylvania facility. This supports procurement on federally funded municipal water, wastewater, and infrastructure work, and readily stocked domestic inventory supports quick delivery when project schedules are tight.
The contact is a bistable, normally open reed switch actuated by rising flow, rated for a maximum of 230 VAC, 10 W/12 VA, and 0.5 A, with IP65 protection, an ambient range of 32...130°F (0...54°C), and approximately 0.12 to 0.47 in (3 to 12 mm) of float travel hysteresis, according to specifications.
Yes. To retrofit an instrument with a contact, the float must be replaced with a float with an integral magnet, per the datasheet. Switch-ready models KSM-5... and KSM-6... accept the contacts, and ordering suffix R adds an extra switch so one meter can signal two alarm points.
Mount the meter in a vertical pipe run so the medium enters at the bottom and exits at the top. Remove transport packing first, verify system pressure and temperature against the ratings, avoid mechanical stress on the plastic body (brace the piping if needed), protect the tube from impact and pressure surges, and check for leaks immediately after assembly.
Minimal maintenance is needed when the medium is clean. If deposits build up on the tube or float, remove the unit and clean it with suitable agents or an ultrasonic bath. On switch-equipped versions, magnetic filtration in the line helps protect the magnet-equipped float from ferritic contamination.
The Polysulfone measuring tube is suited for very corrosive media, while the Trogamid tube is available for less aggressive media; both are rugged and shock resistant. Polysulfone also carries the higher 212°F (100°C) rating, whereas Trogamid is rated to 140°F (60°C).
Product Specifications
Measuring Range
0.06...0.66 to 35...264 GPM / 0.5...3 SCFM to 50...400 SCFM
Fittings
1"...2½" Glue Socket or NPT Thread
Body Material
Polyamide, Polysulfone
Max. Temperature
140 °F (60 °C) (w/PVC Connections)
Accuracy
± 4% of Full Scale
Contact
Optional Reed Switch
Media Categories
Liquid or Gas
Product Features
Shock and Corrosion Resistant
Direct Reading Scales for Water or Air
Large, Easy-To-Read Scale
BABA (Build America, Buy America) compliant models available
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