Involute profile of internal gear, in the small gear and internal gear intermediate have a crescent shape of the diaphragm, the purpose is the oil absorption cavity and pressure oil cavity off.
渐开线齿形的内啮合齿轮，在小齿轮和内齿轮中间有一块月牙形状的隔板，目的是把吸油腔和压油腔隔开。
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The tooth profile of gear pump is involute in general. Though the involute profile is easy to design and manufacture, it also brings the inherent problem of oil trapping.