Lobe Pumps vs. Gear Pumps
Gears or lobes, which is better?
To simplify the confusion that sometimes surrounds selecting the proper pump design, let's view two of the more popular designs and learn about the differences between the designs. While lobe and gear pumps may appear similar, the two designs have different internal structures and active mechanisms. Knowing the similarities and differences of these two popular pump designs may aid your understanding about how different types of pump systems work best for different applications.
Lobe Pump Operation
A lobe pump consists of rounded or triangular-shaped lobes that rotate inside a casing, and external timing gears found within a gearbox that prevent the lobes from coming in contact with any liquid that flows through the pump. During operation, liquid flows through a low pressure inlet around the interior of a casing. The motion developed by the rotating lobes expands the volume on the inlet side of the chamber by trapping the liquid in the pockets between the lobes and the casing of the chamber. As the lobes rotate, the meshing action forces the pressurized liquid through an outlet port.
Gear Pump Operation
In contrast to lobe pumps where the lobes do not contact the liquid, the gears in a gear pump carry the liquid to the outlet side. Gear pumps may have one or two sets of two gears working within a case and may employ spur, helical, or herringbone gears for smooth operation. The action of two rotating gears coming out of mesh at the suction side of the pump develops the vacuum that pulls liquid into the casing.
Fluid on the inlet side flows into the chamber and becomes trapped between the rotating gear teeth and the chamber housing. The spaces between the gear teeth transport the fluid along the outer perimeter of the housing to the discharge side. At that point, the gears re-mesh at the center and discharge the fluid. As the two gears come into and out of mesh, the action develops expanding volume on the inlet side and causes fluid displacement and increases pressure.
Lobe and Gear Pump Applications
Several design features have established lobe pumps as a favorite for the food industry. Lobe pumps have a low-shear, gentle pumping action that minimizes product degradation. If pre-filled or wetted, lobe pumps also have self-priming capabilities. The multipurpose pumps also offer reversible flows. Since the flow remains relatively independent of changes in process pressure, the pumps maintain a constant and continuous output. As a result, lobe pumps have excellent reliability and versatility.
While all rotary lobe pumps are non-contacting, some have large pumping chambers that accommodate whole fruits or vegetables. Moreover, lobe pumps have excellent sanitary qualities, corrosion resistance, and good clean-in-place and sterilize-in-place characteristics. Along with transporting foods, lobe pumps may also carry chemicals, slurries, pastes, beverages, pulp, soap, pharmaceuticals, and liquids for a variety of industries.
Gear pumps work well for hydraulic fluid power pumps and for applications that involve the transfer of liquids. Bearings on both sides of the casing support the gears and allow high discharge pressure capabilities. Since gear pumps have close tolerances and shaft support, the pumps provide a good solution for applications that require medium-to-high pressure and good mechanical efficiency. Examples of gear pumps include applications that control volume flow rate such as mechanical lubrication pumps, and move high-viscosity liquids. Because gear pumps have bearings in the liquid and have close tolerances, the pumps do not work in applications that have high temperatures or transfer abrasive materials.