Geometric clearances at the end and outer diameter of the gears allows leakage and back flow. However sometimes higher clearances help reduce hydrodynamic friction and improve efficiency. Gear backlash: High backlash between gears also allows fluid leakage. However, this aides to reduce wasted energy from trapping the fluid between gear teeth (known as pressure trapping). Applications Petrochemicals: Pure or filled bitumen, pitch, diesel oil, crude oil, lube oil etc. Chemicals: Sodium silicate, acids, plastics, mixed chemicals, isocyanates etc. Paint and ink. Resins and adhesives. Pulp and paper: acid, soap, lye, black liquor, kaolin, lime, latex, sludge etc. Food: Chocolate, cacao butter, fillers, sugar, vegetable fats and oils, molasses, animal food etc. Aviation: Jet engine fuel pumps See also Gerotor Hydraulic pump Vane pump References External links External gear pump description Internal gear pump description Pumps