Paddle-Wheel Flow Sensor for Liquids/Water – DF

Economical DF Series Paddle Wheel Flow Meters for Industrial Applications

The KOBOLD DF Series paddle wheel flow meters and sensors provide reliable, cost-effective measurement of low viscosity liquids in a wide range of industrial applications. Manufactured in Pittsburgh, Pennsylvania, these instruments combine a proven paddle wheel sensor with multiple electronics options to meet diverse process requirements. Available in ten flow ranges starting from 0.02…0.14 GPM up to 1.5…36 GPM, the DF Series is designed for water, water-based chemicals, and other compatible low-viscosity media.

Six material combinations support operating pressures of either 145 PSI, 230 PSI, or 1,450 PSI with all versions having a maximum temperature rating of 180°F. These different configurations allow selection based on chemical compatibility and process conditions to fit your application needs. The universal mounting capability and absence of straight pipe run requirements simplify installation in space-constrained or retrofit applications while maintaining ±2.5% of full scale accuracy according to specifications.

How the DF Series Works: Paddle Wheel Measurement Principle

The DF Series operates using a freely rotating paddle wheel with an embedded multipole magnet ring. As liquid flows through the sensor housing, the paddle wheel rotates at a speed directly proportional to flow velocity. The magnets, hermetically separated from the process media, induce a DC signal in a Hall-Effect sensor mounted on the housing. This non-contact design provides a frequency output linearly proportional to flow rate while eliminating wear associated with mechanical sensors. A variety of other output options are available to convert the native signal into a switching or analog output. Advanced electronics provide multiple outputs with LCD displays and provide functionality for continuous rate monitoring, totalizing, or batching.

The internal flow nozzle creates consistent conditions at the paddle wheel, allowing accurate measurement without requiring upstream or downstream straight pipe runs. This installation flexibility distinguishes the DF Series from many competing technologies and supports universal orientation in any mounting position provided the housing remains filled with liquid. Large radial clearance around the paddle wheel provides tolerance to minor debris, while the design maintains low pressure drop across the measurement range.

To learn more about paddle wheel flow technology see Kobold's article Paddle Wheel Flow Meters Explained.

Technical Specifications Overview

Accuracy: ±2.5% of full scale
Flow Range: 0.02 to 36 GPM across ten standard models
Media: Water and low viscosity liquids
Max Operating Pressure: 145 PSI, 230 PSI, or 1,450 PSI depending on material combination
Max Operating Temperature: 180°F (82°C)
Connection Sizes: 1/8" to 1-1/2" NPT female threads
Orientation: Universal (flow must follow arrow direction)
Straight Run Requirement: None
Material Combinations: Six options (polysulfone, nickel-plated brass, 316L stainless steel) with NBR or FKM O-rings and POM or PTFE paddle wheels

Each electronics package shares the same reliable sensor platform while offering specific display, output, and control features tailored to the application.

Selecting the Right DF Material Combination

The DF offers six distinct material combinations available across all models and output options to provide the right flowmeter for an array of applications.

Polysulfone Housing - Lightweight and chemically resistant housing for low-pressure water and chemical service up to 145 PSI. Two versions are available, one with nickel-plated brass connection fittings featuring NBR O-rings and a POM paddle wheel and one with 316-Ti SS connection fittings featuring FKM O-rings and a PTFE paddle wheel. Both come with a polysulfone housing lid that provides a view of the paddle wheel and flow path.
Nickel-Plated Brass Housing – Robust nickel-plated brass construction for higher-pressure general industrial service. The standard version is rated to 230 PSI, and a high pressure design is capable of up to 1,450 PSI. The standard version features nickel-plated brass connection fittings with NBR O-rings, a POM paddle wheel, and a polysulfone housing lid. The high pressure design features the same materials but substitutes the polysulfone housing lid for a nickel-plated brass lid to achieve the higher pressure rating.
Stainless Steel Housing - Corrosion-resistant 316L SS construction for demanding process and high-pressure applications. The standard version is rated to 230 PSI, and a high pressure design is capable of up to 1,450 PSI. The standard version features 316-Ti SS connection fittings with FKM O-rings, a PTFE paddle wheel, and a polysulfone housing lid. The high pressure design features the same materials but substitutes the polysulfone housing lid for a 316L SS lid to achieve the higher pressure rating.

All models incorporate a 316L SS axle, a PTFE axle bushing, and a PTFE orifice regardless of the material combination.

Important Notice: Transitioning to U.S. Manufacturing

Due to the ongoing implementation of EU Directive 2020/2184 that restricts brass materials, product availability is subject to change at any time. We are actively reshoring production of our brass flowmeter models to U.S. facilities to ensure continued supply. Not all products can/will be reshored. During this transition, stock availability may fluctuate between the time of quotation and purchase order placement. We appreciate your patience as we work to establish our domestic supply chain and remain committed to providing you with the same high-quality products made closer to home.

Model Reference Chart

Model	Primary Function	Display	Outputs	Typical Use
DF	Frequency output	None	NPN pulse	PLC/OEM integration
DF-MA	Analog transmitter	None	4-20 mA or 0-10 VDC	PLC/SCADA integration
DF-WM	Flow switch	None	1 SPDT relay	Pump protection/alarms
DF-KL	Digital flow meter	3-digit LED + bar graph	2 relays + analog	Real-time monitoring
DF-ZL	Flow meter with totalizer	Dual 8-digit LED	2 relays + analog	Consumption tracking
DF-DL	Batch controller	Dual 8-digit LED	2 relays + 2 control inputs+ analog	Automated batching

Model DF Sensor

The DF is the most basic model ideal for low cost installations and OEM applications. This version transmits the flow data as a pulse rate output where the signal is linearly proportional to the flow rate. The output is transmitted by a bipolar transistor operating in an open collector configuration. A user supplied pull-up resistor is required to produce an output signal. Power supply is specified between 5 to 24 V_DC.

Model DF-MA Sensor

The DF-MA expands on the standard DF sensor with electronics to convert the native frequency signal to an analog output for precise transmission of flowrate data to indicating devices, PLCs, or process recorders. Output options include 0-20 mA, 4-20 mA, 0-10 V_DC, and 0-5 V_DC signals. Power supply options include 24 V_DC, 24 V_AC, 110 V_AC, or 230 V_AC.

Model DF-WM Sensor

The DF-WM model converts the sensor signal into an adjustable limit contact for flow control, where the switching point can be adjusted via a potentiometer. The changeover contact has a maximum rating of 250 V / 5 A. The ready state is indicated by a green LED and when the flow rate drops below the setpoint a red LED flashes. A push button on the front panel allows for overriding of the alarm switch. Power supply options include 24 V_DC, 24 V_AC, 110 V_AC, or 230 V_AC.

Model DF-KL Sensor

The DF-KL combines the DF sensor with the KOBOLD ZED-K electronics in an integrated package providing an LED display with 3 digit flowrate readout on the top line and a bar graph indicating the flow proportional to the full scale value on the bottom. The device is also equipped with an analog output and two switching outputs. The analog output is available as either a 4-20 mA or a 0-10 V_DC signal. The switches can be set independently via the control keys for the switching points, hysteresis, window point, and switch on/off delay. A red LED for each switch indicates its status. The required power supply is 24 V_DC.

Model DF-ZL Sensor

The DF-ZL combines the DF sensor with the KOBOLD ZED-Z electronics in an integrated package acting as a counting electronic. A 2 row, eight digit LED screen displays a selections of the total volume, partial volume, or the flow rate configurable by the user. The electronics also encompass an analog output and two switching outputs. The analog output is available as either 4-20 mA or 0-10 V_DC. The two switching outputs are freely configurable to monitor the flow rate or partial/total volume set points. The switches can be set independently via the control keys for the switching points, hysteresis, window point, and switch on/off delay. A red LED for each switch indicates its status. The required power supply is 24 V_DC.

Model DF-DL Sensor

The DF-DL combines the DF sensor with the KOBOLD ZED-D electronics in an integrated package acting as a batching electronic. A 2 row, eight digit LED screen displays a selection of either the batch total, volume total, or flow rate configurable by the user. Two control inputs enable batching to start, stop, and reset remotely. Two switches are available as a batching relay and a limit relay. Additionally, the electronics are available with either a 4-20 mA or 0-10 V_DC output signal for the flowrate. The two switching outputs are freely configurable to monitor the flow rate or partial/total volume set points. The switches can be set independently via the control keys for the switching points, hysteresis, window point, and switch on/off delay. A red LED for each switch indicates its status. The required power supply is 24 V_DC.

Industry Applications and Use Cases

In water and wastewater treatment plants the DF Series supports chemical dosing, filter monitoring, and flow verification where accurate, low-maintenance measurement is required. Chemical processing applications benefit from the variety of material combinations that ensure compatibility with a range of process fluids.

Manufacturing facilities rely on the DF-KL and DF-WM models for cooling water and lubrication monitoring to protect pumps and compressors. Hydraulic systems and OEM equipment builders select the DF-MA transmitter or base sensor for integration into automated control systems. The DF-DL batch controller is particularly suitable for automated filling, blending, and dispensing operations across multiple industries.

Build America, Buy America (BABA) Compliance

The entire DF Series is manufactured at KOBOLD Instruments’ facility in Pittsburgh, Pennsylvania. This domestic production qualifies all DF models as Build America, Buy America (BABA) compliant, making them eligible for federally funded infrastructure projects including municipal water treatment plants, wastewater facilities, and public works initiatives. Pittsburgh manufacturing provides direct quality oversight, shorter lead times, and same-time-zone technical support while meeting domestic content requirements for federal procurement.

Common Questions for DF Series Paddle Wheel Flow Meters & Sensors

Liquid moving through the housing spins a paddle wheel whose speed tracks the velocity of the stream. A multipole magnet ring inside the wheel, hermetically isolated from the fluid, triggers a Hall-effect sensor on the body, producing a pulse frequency that rises linearly with flow and feeds the chosen electronics package.

Pick the base DF for pulse output into PLCs or OEM equipment, the DF-MA when you need an analog signal, and the DF-WM for a simple flow-alarm relay. Choose the DF-KL for on-device rate display, the DF-ZL to totalize consumption, and the DF-DL to run automated batching.

No — none upstream or downstream. A built-in nozzle conditions the liquid just before it reaches the wheel, so readings stay accurate even when the meter sits directly after elbows or valves. That makes the series easy to place in retrofits and crowded piping where other technologies demand long straight sections.

Ten standard ranges run from 0.02–0.14 GPM on the smallest model up to 1.5–36 GPM on the largest, with female NPT threads from 1/8" through 1-1/2". That spread lets a single product family cover dosing-level flows and full process lines without changing measurement technology.

Ratings follow the construction: polysulfone-housing versions handle 145 PSI, standard nickel-plated brass and 316L stainless versions handle 230 PSI, and the high-pressure metal-lid designs reach 1,450 PSI. Every version shares the same 180°F (82°C) maximum media temperature, so material choice is driven by pressure and chemistry.

Water, water-based chemicals, and similar thin fluids are the intended media. Six wetted-material combinations — polysulfone, nickel-plated brass, or 316L stainless housings, O-rings in NBR or FKM, and wheels in POM or PTFE — let you match construction to the chemistry, and generous radial clearance gives tolerance to minor debris.

Accuracy is ±2.5% of full scale, according to specifications, and it applies across all ten flow ranges and every electronics version. Because the wheel couples magnetically to the pickup rather than through mechanical linkages, that performance is not degraded by contact wear on the sensing side.

The base sensor delivers an NPN open-collector pulse (supply your own pull-up resistor to generate the signal) and runs on 5 to 24 VDC. Other versions add 0-20 mA, 4-20 mA, 0-10 VDC, or 0-5 VDC analog signals, SPDT relays, and remote control inputs, and can be powered at 24 VDC or VAC, 110 VAC, or 230 VAC by model.

Yes — horizontal, vertical, or angled positions all work, as long as the housing stays completely full of liquid and flow travels in the direction of the arrow on the body. Combined with the zero straight-run requirement, this makes placement in tight or retrofit installations straightforward.

Yes. Every DF model is built at the KOBOLD Instruments plant in Pittsburgh, Pennsylvania, so the whole series qualifies under Build America, Buy America (BABA) — suitable for federally funded work such as municipal water and wastewater projects. Domestic production also shortens lead times and keeps technical support in US time zones.