2026-06-30
A lobe pump looks like a gear pump's cleaner cousin. Two rotors — typically two-, three-, or four-lobed — counter-rotate inside a casing, trapping fluid in the pockets between lobes and the housing wall, then sweeping it from inlet to outlet. The critical difference from a gear pump: the lobes never touch each other. They're held in precise phase by external timing gears in a separate gearbox, so the pumping chamber stays dry-running between the rotors.
That single design choice unlocks the lobe pump's reason for existing. Because nothing rubs in the wetted path, lobe pumps handle:
The tradeoff is slip. Because lobes don't touch and clearances are typically 0.05–0.15 mm, some fluid leaks back from discharge to suction. Slip grows with pressure and falls with viscosity. A lobe pump moving water at 10 bar might lose 30% of its displacement to slip; the same pump moving honey at the same pressure loses almost nothing. Lobe pumps love viscous fluids and hate thin ones at high pressure.
Rule of thumb for sizing: theoretical flow is
Q (L/min) = displacement per rev (L) × RPM × volumetric efficiency
Volumetric efficiency runs ~90–95% on viscous product (>100 cP) at moderate pressure (≤7 bar), dropping to 60–75% on water-like fluids. Typical operating speeds are 200–600 RPM — slower than gear pumps, which keeps shear low and lets larger particles pass.
Concrete example: a yogurt filling line uses a tri-lobe rotary pump with 0.5 L/rev displacement running at 300 RPM. Theoretical flow is 150 L/min; with fruit-on-the-bottom product at 5000 cP, real throughput is about 142 L/min (95% efficient). The same pump on a CIP cycle pushing 80 °C caustic at 3 bar drops to maybe 110 L/min — fine, because CIP doesn't need precision dosing.
Lobe geometry matters: bi-lobe rotors give the largest pockets (best for chunks) but pulsate more; tri-lobe and multi-lobe designs trade pocket size for smoother flow. Helical (twisted) lobes reduce pulsation further at the cost of higher axial loads on the bearings.