Gas Roots Flow Meters
Positive-Displacement Custody Billing for Natural Gas, LPG Vapor, Industrial Sub-Distribution, and Small-Skid RNG
Accuracy ±0.5 / 1.0 / 1.5 % of rate options
Pipe DN25 to DN150 across G16 to G1000 flow rates
1:30 turndown; low-flow custody accuracy
- Twin-lobe Roots rotor PD principle; fixed displacement per rotation, independent of velocity profile
- 3.6 V lithium battery option for unmanned AMR billing; 24 VDC for SCADA-integrated
- Ex ia (intrinsically safe) IIC T6 Ga + IP65 + ISO 9001 cal cert with every meter
Roots is the PD custody-billing pick for low-flow gas where turbine loses accuracy and ultrasonic is not warranted. Twin-lobe rotor pair in aluminium casing, fixed displacement per rotation, 1:30 turndown holds accuracy at the low end. DN25 to DN150 across 10 G-classes, ±0.5 % custody, Ex ia IIC T6 Ga, IP65, 3.6 V battery AMR. Lead time 5–7 business days.
Roots gas meter models
Four application-focused models across the Roots range. Each card covers a distinct gas medium + billing scenario; pick the closest match and the configurator inside each model page returns the build code.
Natural Gas Roots Flow Meter
City-gas distribution residential / light-commercial billing + small-industrial fence-billing. 1:30 turndown captures off-peak draw that turbine misses. 3.6 V lithium battery + 4G output for unmanned utility AMR.
View configuration →LPG Vapor Roots Flow Meter
Gas-station LPG vapor return + commercial vaporiser outlet + LPG depot vapor recovery. Vapor-phase service only; liquid LPG goes to a liquid turbine. Pre-pay controller option for retail station service.
View configuration →Industrial Gas Roots Flow Meter
Industrial-park multi-tenant gas sub-billing + chemical-park N2 distribution + low-flow compressed-air ISO 50001 audit. Roots captures the low-flow demand that turbine misses at a site’s gas inlet.
View configuration →Biogas Roots Flow Meter
Small-skid RNG grid-injection + landfill-gas off-taker custody + WWTP biomethane-to-CHP. Post-upgrade biomethane only (raw biogas goes to the swirl meter). Wide turndown captures off-peak production swings.
View configuration →How Roots gas flow meters work
A Roots gas meter counts fixed-volume pockets between a twin-lobe rotor pair sealed in the casing. Gas pressure turns one rotor; synchronized timing gears outside the gas chamber drive the second. Each pair revolution displaces a fixed volume, the meter K-factor.
A magnetic or optical pickup counts the revolutions. Revolution rate gives instantaneous flow; the cumulative count gives totalized volume. Built-in temperature and pressure compensation corrects to reference conditions (Nm³/h) on the 4-20 mA loop, with the totalizer and density on the LCD.
Because the count is positive-displacement, accuracy holds to the low end of the range, independent of velocity profile, gas density, and pulsation. That suits intermittent, residential, and low-pressure sub-billing, where the 1:30 turndown reaches well past the point a turbine falls off (below 10 % of nominal).
The trade-offs: a higher pressure drop than a turbine, a bore ceiling (production caps at DN150), and clean dry gas only.
When to specify Roots
Match your application against the table below. Out-of-range service goes to vortex, turbine, ultrasonic, or Coriolis families.
| Service | Roots Gas (LQ Series) | Alternative |
|---|---|---|
| Residential / light-commercial natural gas billing (low flow) | Standard pick (G16-G65 DN25-DN50) | — |
| Town-gas regulator station to cluster distribution | Standard pick (G100-G650) | LWGQ Gas Turbine for DN200+ high-flow |
| LPG vapor at gas-station return / commercial vaporiser | Standard pick (G40-G250) | — |
| Liquid LPG (tank loading, transport delivery) | Outside the operating range (liquid phase) | LWGY lpg-turbine-flow-meter |
| Industrial-park multi-tenant gas sub-billing | Standard pick (G25-G400) | — |
| Compressed-air audit at low-flow (sub-DN50 idle leakage) | Standard pick (G16-G65) | LWGQ compressed-air-turbine for DN50+ |
| Post-upgrade biomethane / RNG small-skid custody | Standard pick (G40-G250) | LWGQ biogas-turbine for DN50+ grid-injection |
| Raw biogas (wet, >10 ppm H₂S) | Outside the operating range (wet gas not tolerated) | LUXB biogas-swirl-flow-meter |
| High-pressure natural gas (above 1.6 MPa) | Out of range (above rated limit) | LWGQ natural-gas-turbine + fuel-gas turbine |
| Cryogenic LNG (−162 °C) | Outside the operating range | cryogenic-coriolis-flow-meter |
| Pulsating gas service (compressor outlet) | Outside the operating range without accumulator | Vortex + accumulator pre-conditioning |
Which model for your application
Four Roots models cover the range below. Match your service range to a model in the table.
| Service range | G-class & bore | Model page |
|---|---|---|
| City-gas residential billing | G16-G40, DN25-DN40, 0.6 MPa, battery AMR | Natural Gas Roots |
| Town-gas regulator station to cluster distribution | G100-G650, DN80-DN150, 1.0-1.6 MPa | Natural Gas Roots |
| Gas-station LPG vapor return line | G40-G160, DN50-DN80, 0.6-1.0 MPa | LPG Vapor Roots |
| Industrial-park N2 / air tenant sub-billing | G25-G250, DN40-DN100, 0.6-1.6 MPa | Industrial Gas Roots |
| Small-skid RNG biomethane custody | G40-G250, DN50-DN100, 1.0-1.6 MPa | Biogas Roots |
| WWTP biomethane-to-CHP custody | G65-G160, DN50-DN80, 1.0 MPa | Biogas Roots |
All Roots models share the same core: Ex ia IIC T6 Ga, IP65, ±0.5 % custody accuracy option, 1:30 turndown, and the 7-output configurator. Power is 3.6 V battery or 24 VDC; every meter ships EMC 2014/30/EU compliant with an ISO 9001 calibration certificate and 5–7 business day lead time.
Universal Roots install requirements
These install rules apply across all Roots models. Model-specific variations (LPG vapor knockout drum, biogas H₂S pre-conditioning) live on each model page.
- Upstream filter is mandatory Roots is positive-displacement and sensitive to particulate; install a gas filter upstream sized for the service. Never connect the filter directly to the meter inlet flange. Leave one DN of straight pipe between filter and meter to settle any micro-particulate carryover.
- Pressure regulator upstream of the meter For gas-distribution service, install a pressure regulator (or pressure reducer) upstream of the meter to stabilize inlet pressure. Variable upstream pressure drives the meter zero point and biases the reading.
- No pipe-low-point installation Roots cannot tolerate liquid carryover or condensate slugs. Do not install at line low point. Route a condensate trap upstream if condensate is possible (wet upstream gas, ambient cool-down).
- Avoid pulsation source; install accumulator if needed Roots counts volume per rotation; pulsating gas (compressor outlet, regulator hunting) distorts the count. Locate the meter downstream of pressure regulator. On compressor-outlet service, install an accumulator vessel upstream to dampen pulsation.
- Mount with flow-arrow alignment The arrow on the casing must match line flow direction. Both vertical (top-down) and horizontal mounts are supported. The pipe must run full of gas at the meter location.
Frequently asked questions
- bore is DN200+ at steady high flow: gas turbine;
- very-large-bore pipeline custody needs no moving parts: gas ultrasonic;
- low-flow process gas needs direct mass output, not billing: thermal mass.
- natural gas (post-amine-scrubbed, ≤4 ppm H₂S), town / city gas;
- LPG vapor (post-vaporiser, gas phase only);
- compressed air (post-dryer), low-pressure industrial gas distribution;
- post-upgrade biomethane / RNG (≥95 % CH₄, ≤4 ppm H₂S).
- pulse 3-wire for legacy panel counters;
- pulse + battery-card for off-grid AMR;
- 4-20 mA 3-wire and 2-wire for SCADA;
- RS-485 Modbus RTU for plant DCS;
- HART for refinery / petrochem DCS;
- 4G wireless for remote utility AMR.
Need help sizing a Roots gas meter?
Send gas type, DN, P/T, flow, AMR / SCADA need. Reply in 1 day; lead time 5–7 business days.