Roots (waist-wheel) vs oval gear flow meter — what is the difference and how to choose?
Roots rotors are timing-gear driven (no tooth contact, less wear), turndown 1:20+, gas versions available; oval gears are simpler, mostly liquid. Gas → Roots; long life → Roots.
Both are positive displacement meters; the key differences are rotor design and operating characteristics:
1) Rotor structure: Roots rotors are two-lobe, non-meshing, driven by external timing gears — no tooth contact, minimal wear, ideal for long-term high accuracy; oval gears mesh directly and are simpler; 2) Rangeability: Roots meters offer wider turndown (typically 1:20+) and better low-flow performance; 3) Fluid fit: Roots versions exist for gas (fuel gas/biogas), while oval gears are mostly for liquids.
Selection: gas metering → Roots gas type; high-viscosity oils → both work, prefer Roots for long service life.