Volatile liquids tend to vaporize locally as gear teeth spaces expand rapidly. When the viscosity of pumped liquids rises, torque requirements also rise, and pump shaft strength may not be adequate. Pump manufacturers supply torque limit information when it is a factor. Lobes in lobe pumps do not make contact, because they are driven by external timing gears. This design handles low-viscosity liquids.
Lobe contact is prevented by external timing gears.
Pump shaft support bearings are located in the timing gear case. Since the bearings are out of the pumped liquid, pressure is limited by bearing location and shaft deflection. Use of multiple mechanical seals makes seal construction important. Lobe pumps are frequently used in food applications, because they handle solids without damaging the pump. Particle size pumped can be much larger in lobe pumps than in other PD types.