Gear pump is divided into external gear pump and internal gear pump. Internal gear pump two gears in different shapes, the number of teeth is not the same. One of them is a ring gear, which can float in the pump body. The middle one is a driving gear, which is eccentric to the pump body. The ring gear has one tooth more than the driving gear, the driving gear drives the ring gear to rotate together, and the liquid is transported by the space between two teeth. Another kind of internal gear pump is a ring gear more active gear than two teeth, between the two gear is equipped with a fixed crescent-shaped partition, the suction space was clearly spaced. In the case of the same discharge pressure and flow, the internal gear pump size smaller than the external gear pump. Gear pumps are used to transport viscous liquids such as lube oil and combustion oil. They should not be used to transport liquids with lower viscosity (such as water and gasoline), liquids containing particulate impurities (affect the service life of the pump) Lubrication system pumps and hydraulic system pumps, widely used in engines, steam turbines, centrifugal compressors, machine tools and other equipment. Gear pump high process requirements, not easy to get accurate match. Commonly used gear pumps are: CB-B-type gear pump, a total of 16 kinds of specifications. Model letter CB said gear pump, the latter B pressure level, China Machine Hydraulic system pressure is divided into A, B, C three, the corresponding pressure is 1.0,2.5,6.3 MPa. The CB gear pump for agricultural machinery has high pressure, the rated pressure is 10 MPa, the maximum pressure can reach 13.5 MPa, the speed range is 1300 ~ 1625r / min. CB-F high-pressure gear pump, rated pressure of 14 MPa, the maximum pressure up to 17.5 MPa.