Rotary lobe pumps are positive displacement (PD) pumps that use rotating lobes to direct flow. They are similar to gear pumps in terms of operation in that fluid flows around the interior of the casing. Because of their different configuration, however, rotary lobe pumps can reduce the shear effects commonly associated with gear pumps. Moreover, unlike gear pumps, the rotary lobes do not make contact because of external timing-gears located in the gearbox.
With rotary lobe pumps, multiple lobes on the rotating elements provide the ability to drive large solids and slurry-laden media. Typically, they are available in double-lobe or triple-lobe configurations. The number of lobes on each rotating element determines this number. Determining which style of pump is better for a given application requires an analysis of the solids size, liquid viscosity, and tolerance of flow pulsation. Rotary lobe pumps with two lobes are suitable for handling larger solids and high-viscosity fluids, but pulsate more than three-lobed devices.
Often, rotary lobe pumps are used in food processing applications because they can handle solids without damaging the product. Because the rotating lobes do not contact each other, these positive displacement pumps can handle products of a larger particle size and are ideal for pushing through low-viscosity media. In fact, rotary lobe pumps may be among the best PD pumps for this type of application. Note, however, that rotary lobe pumps may not be suitable for transporting higher viscosity liquids because their design can lead to foaming and reduced lift unless they are run at a lower speed than their normal rating.
Rotary lobe pumps are used in industries such as pulp and paper, chemical, and food and beverage processing; pharmaceutical applications; and biotechnology. These PD pumps are popular in such diverse industries because they offer superb sanitary qualities, high efficiency, reliability, corrosion resistance, and good clean-in-place and service-in-place (CIP/SIP) characteristics. The design of rotary lobe pumps also eliminate metal-to-metal contact, which can help reduce the amount of impurities within passed media. Note, however, that rotary lobe pumps require frequent service as they require two sets of timing gears and two seals, all of which have a tendency to wear during use.