Paddle-Wheel Flow Meter, Low Pressure Loss - DRB

DRB Paddle Wheel Flow Meter Overview

The KOBOLD DRB is a stainless steel paddle wheel flow meter that measures liquid flow in pipes up to 3 inches in diameter at pressures up to 232 PSIG. Its PVDF impeller is designed to protrude only slightly into the flow stream, which keeps pressure loss low, and it can be ordered with pulse, 4-20 mA, display, or switching electronics.

How the DRB Measures Liquid Flow

Flowing liquid turns an impeller supported on a ceramic bearing with a carbide axle. Permanent magnets embedded in the impeller blades pass a Hall effect sensor, and the sensor output is converted to a linear pulse signal or a 4-20 mA signal. Optional displays and controllers add local flow rate indication, analog outputs, and programmable setpoint switches.

Flow Ranges and Pipe Sizes

Six NPT sizes are offered, each with its own measuring range. Flow volume, pressure, and temperature must stay within the limits of the selected model; over-ranging can cause bearing damage and considerable measurement errors.

DRB-1250, ½" NPT: 1.5...8 GPM
DRB-1255, ¾" NPT: 3...13 GPM
DRB-1260, 1" NPT: 5.5...20 GPM
DRB-1265, 1½" NPT: 6.6...65 GPM
DRB-1270, 2" NPT: 8...90 GPM
DRB-1275, 3" NPT: 15...200 GPM

Pressure, Temperature, and Accuracy Ratings

The DRB is rated for a maximum operating pressure of 232 PSIG at 68 °F (20 °C), a maximum process temperature of 176 °F (80 °C), and a maximum ambient temperature of 176 °F (80 °C). Measuring accuracy is ±3% of full scale, and the housing carries IP65 protection.

Wetted Materials and Pressure Loss

The housing is 316 stainless steel, the seals are FKM, the turbine wheel is PVDF, the axle is carbide, and the bearing is ceramic. This combination is designed to provide long service life and chemical resistance, and the slightly protruding paddle is designed to measure fluids with some small solids content as well as dirty liquids. Maximum pressure loss:

DRB-..50 (½"): 0.73 psi
DRB-..55 and DRB-..60 (¾" and 1"): 0.44 psi
DRB-..65 (1½"): 0.58 psi
DRB-..70 (2"): 0.29 psi
DRB-..75 (3"): 0.15 psi

Output and Display Electronics

Each DRB sensor is ordered with one evaluating electronics option:

Frequency output (..F300): 12-28 VDC, 10 mA, PNP open collector pulse output (max. 25 mA), M12x1 plug connector
Frequency output with divider (..F390): 24 VDC ±20%, 15 mA, PNP open collector pulse output (max. 25 mA), factory-set division ratio 1...1/128, M12x1
Analog output (..L342, ..L343, ..L442): 24 VDC ±20%, 4-20 mA in 2-wire or 3-wire, M12x1 or DIN 43 650 connector; the ..L442 accepts an optional 4-digit LED plug-on display (AUF-1000, or AUF-1001 with an added open collector output)
Compact electronics (..C30R, ..C30M, ..C34P, ..C34N): 3-segment LED display, adjustable 4-20 mA output, one or two PNP or NPN semiconductor switching outputs (N/C or N/O, programmable), 24 VDC ±20% 3-wire, approx. 100 mA, M12x1
ADI-1 electronics (..K042, ..K342): bargraph and 5-digit display, 4...20 mA and 0-10 VDC outputs, two relay changeover contacts rated max. 250 VAC / 5 A resistive or 30 VDC / 5 A, supply 100...240 VAC ±10% or 18...30 VAC and 10...40 VDC, pluggable terminal block via cable gland
ZED totalizing (..E34R) and ZED batching (..G34R): illuminated 2 × 8 digit LCD, adjustable 4...20 mA, two relays max. 250 V / 5 A / 1000 VA, 24 VDC ±20% 3-wire, approx. 170 mA, terminal block via cable gland

Accessory cables: 807.037 (4-pin Micro-DC, 6 ft) for F300, F390, L342, and L343; 807.007 (5-pin Micro-DC, 6 ft) for C3xx electronics.

Installation Requirements

Install the DRB with flow in the direction of the arrow; mounting position is independent. Avoid pressure and tensile loading, secure the inlet and outlet piping mechanically 1.97 in (50 mm) from the connection, and check the sealing of all joints. Upstream straight pipe depends on the disturbance ahead of the meter; allow 5 × D downstream in every case:

Control valve: 50 × D
Two 90° elbows in three dimensions: 40 × D
Two 90° elbows: 25 × D
One 90° elbow or T-piece: 20 × D
Pipe extension: 18 × D
Pipe reduction: 15 × D

Confirm that the supply voltage matches the electronics option before energizing, and use a 0.25 mm² conductor for the supply cable. Units are preset at the factory and ready to operate once wired.

Maintenance

The DRB is maintenance-free when the measured liquid does not deposit impurities; where deposits are possible, installing a KOBOLD MFR magnetic filter upstream is recommended. If the sensor must be cleaned, note the direction the impeller points before removal and reinstall it the same way. Electronics repairs may only be carried out by the supplier.

Common Questions about DRB - Paddle-Wheel Flow Meter

A four-vane paddle wheel sits in the liquid stream and is set in motion by the flowing medium. Magnets hermetically sealed in the ends of the blades generate electrical pulses in a Hall-effect sensor mounted outside the flow area. Various electronics units then display, transmit, or monitor the volumetric flow.

Six models cover threaded pipe from ½" NPT to 3" NPT. The smallest, DRB-1250, measures 1.5 to 8 GPM; the largest, DRB-1275, measures 15 to 200 GPM. Intermediate sizes of ¾", 1", 1½", and 2" NPT span 3 to 13, 5.5 to 20, 6.6 to 65, and 8 to 90 GPM respectively.

Maximum operating pressure is 232 PSIG, referenced to 68 °F (20 °C). Both the process temperature and the ambient temperature are limited to 176 °F (80 °C). Operating beyond these limits, or above the flow range of the model, is outside the specification and can damage the bearing.

Depending on the electronics ordered, the DRB delivers a PNP open collector pulse frequency, a 4-20 mA analog signal, a 0-10 VDC signal (ADI-1 only), semiconductor or relay switching contacts, and a local LED or LCD readout. Frequency, analog, and compact versions use M12x1 or DIN plug connectors.

The ..F300 frequency output runs on 12-28 VDC. The ..F390, analog, compact, and ZED versions run on 24 VDC ±20%. ADI-1 electronics accept 100...240 VAC ±10% (..K042) or 18...30 VAC and 10...40 VDC (..K342). Always verify the supply matches the version before connecting power.

Yes, for any DRB configured with Compact, ADI-1, or ZED electronics. State the flow direction as you face the meter. For horizontal flow the display sits on top of the meter; for vertical flow with ADI-1 or ZED electronics, also indicate whether the display should be on the right or the left.

Allow 5 pipe diameters of straight run downstream in all cases. Upstream, allow 15 diameters after a reduction, 18 after an extension, 20 after a single elbow or tee, 25 after two elbows, 40 after two elbows in three dimensions, and 50 after a control valve.

Wetted parts are 316 stainless steel (housing), FKM (seals), PVDF (turbine wheel), carbide (axle), and ceramic (bearing). All six sizes share this stainless steel threaded construction and the same wetted parts list; no other body material is offered on the US model.

Maximum pressure loss at full scale is 0.73 psi for the ½" model, 0.44 psi for the ¾" and 1" models, 0.58 psi for the 1½" model, 0.29 psi for the 2" model, and 0.15 psi for the 3" model. The impeller only enters the flow stream slightly, which is what keeps these values low.

No scheduled maintenance is required as long as the liquid does not leave deposits inside the meter. A KOBOLD MFR magnet filter is recommended where deposits could form. Cleaning is possible by opening the sensor; electronics repairs are reserved for the supplier, and any access to the electronics voids the warranty.