The KOBOLD KAL-L is an economical insertion-style thermal air flow switch that monitors non-hazardous gas and air flows in HVAC, ventilation, and industrial systems. It detects flow-rate changes across a switching range of 3.3 to 66 ft/sec (1 to 20 m/s) at 68 °F (20 °C) and 14.5 PSIG, with no moving parts and negligible pressure loss.
The switch is rated for media temperatures from -10 °F to 250 °F (-23 °C to 121 °C), ambient temperatures from 14 °F to 140 °F (-10 °C to 60 °C), and operating pressures up to 120 PSIG (8.3 bar); according to specifications, the switching span is restricted at conditions other than the stated reference temperature and pressure.
How the KAL-L Works: Calorimetric Measurement Principle
The KAL-L operates on the calorimetric principle: one RTD sensor is heated a few degrees above the gas temperature while a second RTD measures the actual media temperature. Flowing air draws heat away from the heated sensor, cooling it in proportion to velocity, and the electronics compare both sensor resistances through a Wheatstone bridge circuit.
When the flow velocity drops below the adjustable setpoint, an SPDT relay switches to provide a control or alarm contact. Because the second RTD tracks the medium's temperature, this "smart" compensation minimizes erroneous switching caused by thermal changes in the surroundings, such as weather. Response time is adjustable from 1 to 60 seconds, and maximum warm-up time is 30 seconds according to specifications. An 8-digit LED bar graph displays the current flow trend with a flashing LED marking the switch point, while a two-color LED shows relay status.
Key Features and Specifications
The KAL-L combines rapid flow detection, temperature compensation, and simple insertion installation in a maintenance-free electronic design. It is powered by 24 VAC/VDC (-15%, +10%), draws a maximum of 4 VA, and features an IP65-rated, glass-fiber reinforced polyamide housing with a nickel-plated brass sensor.
- Negligible pressure loss and no moving parts — the electronic design eliminates wear-prone mechanical components
- Adjustable response time (1 to 60 seconds) via potentiometer
- Compensated for temperature to reduce false switching
- Switching accuracy of ±10% of reading with ± 1% repeatability, according to specifications
- SPDT relay output rated max. 250 VAC / 1000 VA / 4 A (option M12: max. 24 VAC/VDC, 3 A)
- Documented flow ranges from 344 SCFM in a 4-inch duct to 34,357 SCFM in a 40-inch duct
Installation and Setup
The KAL-L mounts through a ½" NPT fitting or 2-bolt flange so the sensing elements contact the flowing medium — the probe tip projects a minimum of 0.39 in (10 mm), ideally more than 0.59 in (15 mm), into the pipe. Straight runs of 10 pipe diameters upstream and 5 downstream help avoid incorrect readings.
Because almost any conceivable pipe size can be accommodated by the insertion design, the KAL-L is designed for pipes from 0.79 in (20 mm) upward; for pipes larger than 1.97 in (50 mm), the sensor is mounted as far as possible into the pipe. The marking on the hexagon must sit parallel to the flow direction, and knowledge of the flow velocity in your system is all that is needed to put the KAL-L to work.
Industry Applications and Use Cases
Typical application areas include air conditioning systems, ventilation systems, and other non-hazardous gas flow monitoring systems. In commercial and industrial HVAC, the KAL-L monitors supply and return air ducts to verify airflow, detect clogged filters, or confirm fan operation.
In ventilation and exhaust service, it provides low-flow or no-flow alarms for fume hoods, paint booths, and clean rooms. In pneumatic conveying and dust collection systems, it helps ensure carrier air velocity stays within required limits, helping prevent blockages and equipment damage.
Ordering Options and USA Manufacturing
The KAL-L is proudly made in the USA by KOBOLD Instruments in Pittsburgh, PA. Two connection versions are offered: order number KAL-8115 with ½" NPT fitting, and KAL-8115FL with a 2-bolt flange. Suffix "C" adds a ½" conduit hub, and suffix "M12" adds a quick disconnect with 6 ft cable.
Common Questions about KAL-L - Thermal Air Flow Switch
According to specifications, documented air flow ranges run from 344 SCFM for a 4-inch nominal duct up to 34,357 SCFM for a 40-inch duct, with fifteen intermediate duct sizes tabulated on the datasheet. Pipes as small as 0.79 in (20 mm) can also receive the insertion probe.
Media temperatures of -10 °F to 250 °F (-23 °C to 121 °C) are permitted per the datasheet, while the surrounding environment must stay between 14 °F and 140 °F (-10 °C to 60 °C). Pressure is limited to 120 PSIG (8.3 bar) maximum.
A 24 VAC/VDC supply with a -15% to +10% tolerance powers the unit, which draws no more than 4 VA. Polarity does not matter when DC voltage is used, and the device reaches operating readiness within a maximum warm-up of 30 seconds according to specifications.
A single-pole double-throw relay contact — max. 250 VAC / 1000 VA / 4 A per the datasheet — serves as the switching output; units ordered with the M12 plug carry a max. 24 VAC/VDC, 3 A rating instead. A duo-LED reports relay state: red signals alarm, green signals flow.
To avoid incorrect sensor function, the manual recommends 10 pipe inside-diameters of straight run upstream of the probe and 5 downstream. The probe tip must project at least 0.39 in (10 mm) — better more than 0.59 in (15 mm) — and the hexagon marking must be parallel to flow.
Two single-turn potentiometers with roughly 270° of rotation handle adjustment: the left one amplifies the flow range to position the setpoint, which always sits at the third LED from the left, and the right one sets a start-up time delay between 1 and 60 seconds, increasing clockwise.
None on a scheduled basis — the device is maintenance-free per the manual. A periodic visual check of the sensor is advised, with cleaning by air if deposits appear. No spare parts are recommended; a defective unit should be returned to the supplier.
The device is intended for non-hazardous gases only. The manual designates the KAL-L series for monitoring air flow, so it suits air handling and ventilation duct service; any usage exceeding the specified applications is considered non-specified under the manual's regulated-usage terms.
Per its EU Declaration of Conformance, the KAL-L complies with the Low Voltage Directive 2014/35/EU, EMC Directive 2014/30/EU, and RoHS 2011/65/EU, and a separate UK Declaration of Conformity covers S.I. 2016/1091 and S.I. 2012/3032. The enclosure carries an IP65 protection rating.
KOBOLD Instruments produces the KAL-L at its Pittsburgh, PA facility, so the switch ships as a USA-made product. The datasheet lists the company's main office at 1801 Parkway View Drive, Pittsburgh, PA 15205, and Made in USA appears among the approved product features.
Product Specifications
Measuring Range
3.3...66 ft/sec
Max Measuring Range
34,357 SCFM
Fittings
½" NPT Thread, Flange
Output
SPDT Relay, Max. 250 VAC / 1000 VA / 4A
Max. Temperature
250 °F (120 °C)
Switching Accuracy
± 10% of Reading
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