WORKING PRINCIPLE OF ROTARY LOBE PUMP
Lobe pumps are similar to external gear pumps in the operation that fluid flows around the interior of the casing. Unlike external gear pumps, however, the lobes do not make contact. Lobe contact is prevented by external timing gears located in the gearbox. Pump shaft support bearings are located in the gearbox, and since the bearings are out of the pumped liquid, pressure is limited by bearing location and shaft deflection.
1. As the lobes come out of mesh, they create expanding volume on the inlet side of the pump. Liquid flows into the cavity and is trapped by the lobes as they rotate.
2. Liquid travels around the interior of the casing in the pockets between the lobes and the casing. It does not pass between the lobes.
3. Finally, the meshing of the lobes forces liquid through the outlet port under pressure.
Lobe pumps are frequently used in food applications because they handle solids without damaging the product. Particle size pumped can be much larger in lobe pumps than in other positive displacement pumps. Since the lobes do not make contact, and clearances are not as close as in other positive displacement pumps, this design handles low viscosity liquids with diminished performance. High-viscosity liquids require reduced speeds to achieve satisfactory performance. Reductions of 25% of rated speed and lower are common with high-viscosity liquids.