Natural Gas Roots Flow Meter

A natural gas Roots flow meter is a positive-displacement (PD) volumetric meter. Two twin-lobe rotors turn in mesh inside a sealed casing; each revolution displaces a fixed quantity of gas from inlet to outlet. The rotation count gives totalized volume and the rotation rate gives instantaneous flow. A magnetic pickup on the rotor shaft sends pulses to the integrated flow computer, which displays m³/h actual on the LCD and outputs corrected Nm³/h on the 4-20 mA, RS-485, HART, or 4G channel when temperature and pressure compensation is fitted. Accuracy is ±0.5 % of rate on custody builds, holding across a 1:30 turndown that catches the low-flow billing tail where turbines lose accuracy.

Roots wins the low-flow custody range; LWGQ turbine wins above DN150 and at sustained high flow. Roots is positive-displacement, so accuracy is independent of velocity profile and stays inside ±0.5 % of rate down to the low end of the published range. Turbine is velocity-type and fades at the bottom of its 1:30 turndown. Use Roots on DN25 to DN150 city-gas distribution custody, fence-billing on industrial-park tenants, and town-gas regulator-station accounting where residential and light-commercial demand creates a low-flow tail. Use LWGQ turbine on DN50 to DN300 mains delivery where header flow is steady and high, with HART for DCS integration.

The production range covers ten G-classes from G16 (1 to 25 m³/h on DN25) up to G1000 (15 to 1,000 m³/h on DN150). G16 / G25 on DN25 / DN40 fit residential and small-commercial billing at 0.6 MPa. G40 to G250 cover fence-billing on industrial-park tenants and town-gas regulator stations at 1.0 to 1.6 MPa. G400 / G650 / G1000 handle larger sub-distribution clusters on DN100 to DN150 at 0.6 to 1.6 MPa. DN15 and DN20 are supported through the selection code but ship by-quote, no published flow range. Pressure loss at maximum flow ranges 110 to 600 kPa depending on G-class.

Pick the 3.6 V lithium battery when the install is unmanned residential, light-commercial, or remote-fence with no DC trunk; battery service life is multi-year on standard AMR service (telemetry over 4G or short pulse bursts). Pick 24 VDC when the meter sits on a regulator station or industrial-park skid with a DC trunk already in place, or when the output is a continuous 4-20 mA loop to SCADA / DCS. Hazardous-area certification is Ex ia IIC T6 Ga (intrinsically safe) on both power options, so utility AMR cabinets and Zone 1 regulator stations are both supported without a flameproof housing rework.

Each meter ships with a factory ISO 9001 calibration certificate listing the G-class, calibrated DN, K-factor, and tested flow range. Custody-transfer type approval per the buyer's local gas-meter metrology regime is buyer-arranged with a notified body in the destination market; the factory does not pre-stamp regulatory type-approval marks. The factory provides build documentation and traceable calibration records to support the buyer's type-test submission, and the buyer can arrange witness calibration at a third-party metrology institute (NMi / PTB / NIM equivalent) before shipment. EMC compliance to EU Directive 2014/30/EU ships standard with each meter.

Standard lead time is 5 to 7 business days from order confirmation, factory direct. Each meter is calibrated at the factory on a gravimetric or bell-prover gas rig matched to the ordered G-class, tested across the published flow range, and shipped with a calibration certificate listing K-factor, calibrated DN, tested range, and accuracy class. The 3.6 V lithium battery is fitted before calibration and shipped pre-loaded for multi-year AMR service. For local custody-transfer regimes, the buyer may nominate a third-party witness inspector to attend the calibration run before crating; coordinate that on the order to reserve a slot in the rig schedule.