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Dwyer Turbine Flow Meters: Liquid Turbine Flow Meter Model Sizing Specifications

Quick Answer: Dwyer liquid turbine flow meters provide accurate measurement for low viscosity fluids such as water, diesel, and light chemicals. Model sizing ranges from DN10 to DN200 with flow ranges between 0.02 and 900 m³/h. Match your pipe size, flow velocity, and fluid viscosity using the spec data below or send your parameters to Silver Automation Instruments for a cross-reference quote.

How Dwyer Model Codes Define Size and Output

Dwyer typically uses a prefix like LTF or TF followed by a numeric code that indicates the connection diameter. For example, LTF-25-B-C refers to a DN25 meter with BSPP threads and a pulse output option. The number 25 directly gives the nominal diameter in millimeters. You will also see suffixes for the bearing type, pickup coil, and transmitter configuration. The most common process connections are BSPP male threads up to DN40 and wafer or flanged connections from DN50 upward. A 4-20 mA HART output board is available on most models, and some variants include an integrated PT100 RTD for temperature compensation. If you need a compatible turbine meter with identical form factor, we keep stock of Silver Instruments TM series which closely match Dwyer dimensions.

Actual Flow Ranges for Each Nominal Size

Here are the typical liquid flow ranges Dwyer publishes for water-like fluids with viscosity below 5 cP.

The DN10 model handles 0.02 to 0.5 m³/h. The DN15 covers 0.04 to 1.2 m³/h. For DN25 the range is 0.2 to 5 m³/h. A DN40 meter goes from 0.5 to 15 m³/h. The DN50 unit covers 1 to 40 m³/h. A DN80 model delivers 2.5 to 100 m³/h. The DN100 size moves from 4 to 160 m³/h. The DN150 version spans 10 to 400 m³/h. The largest DN200 unit achieves up to 900 m³/h. These values assume a clean liquid with a kinematic viscosity close to water. If your fluid is heavier (like diesel at 3 cP to 5 cP) you can use the same sizing, but be aware of pressure drop. A paint manufacturer in Thailand once asked us to verify a DN80 turbine meter for a solvent blend at 4.2 cP. The original Dwyer chart overestimated the max flow by about 8%. Always apply a 15% safety margin for fluids above 3 cP.

Viscosity, Pressure Drop, and Real-World Limits

Turbine meters are excellent for low-viscosity fluids, but when you move above 5 cP the meter factors start to shift. In practice most engineers skip this part they assume the vendor chart covers it. We have seen this on customer sites many times. A crude palm oil plant in Indonesia tried to meter oil at 35 cP with a standard turbine meter. The result was a 12% linearity error and the bearings wore out within eight months. You need a positive displacement meter for such viscous service. If your liquid has a viscosity between 5 and 20 cP you can still use a turbine meter but the linear range narrows. A DN50 meter rated for 1 to 40 m³/h at 1 cP may only be accurate from 3 to 30 m³/h when viscosity hits 15 cP. The pressure drop also climbs. Use the Dwyer pressure drop curves and compare with the available pump head. Remember that a 0.5 bar pressure drop at 40 m³/h is typical. Exceeding 1 bar usually triggers vibration issues.

Pipe Straight Run and Installation Dimensions

Upstream straight pipe requirements are crucial. For Dwyer turbine meters plan a minimum of 10D upstream and 5D downstream of straight pipe. If you have a partially open butterfly valve upstream increase the upstream run to 20D. A flow straightener can cut that to 5D. The insertion length and overall dimensions change by model. A DN15 meter is about 130 mm long between threads. A DN50 wafer meter adds only 60 mm of thickness. A flanged DN100 unit is roughly 250 mm face to face. When you replace a Dwyer meter with a Silver Instruments TM series turbine, you must verify the face-to-face dimension. We offer exact dimensional interchange