Centered Internal Gear PumpAnother design of internal gear pump isillustrated in figures 4-5 and 4-6. This pumpconsists of a pair of gear-shaped elements, onewithin the other, located in the pump chamber.The inner gear is connected to the drive shaft ofthe power source.The operation of this type of internal gearpump is illustrated in figure 4-6. To simplify theexplanation, the teeth of the inner gear and thespaces between the teeth of the outer gear arenumbered. Note that the inner gear has one lesstooth than the outer gear. The tooth form of eachgear is related to that of the other in such a waythat each tooth of the inner gear is always insliding contact with the surface of the outer gear.Each tooth of the inner gear meshes with the outergear at just one point during each revolution. Inthe illustration, this point is at the X. In view A,tooth 1 of the inner gear is meshed with space 1of the outer gear. As the gears continue to rotatein a clockwise direction and the teeth approachpoint X, tooth 6 of the inner gear will mesh withspace 7 of the outer gear, tooth 5 with space 6,and so on. During this revolution, tooth 1 willmesh with space 2; and during the followingrevolution, tooth 1 will mesh with space 3. As aresult, the outer gear will rotate at just six-seventhsthe speed of the inner gear.At one side of the point of mesh, pockets ofincreasing size are formed as the gears rotate,while on the other side the pockets decrease in size.In figure 4-6, the pockets on the right-hand sideof the drawings are increasing in size toward thebottom of the illustration, while those on theleft-hand side are decreasing in size toward thetop of the illustration. The intake side ofthe pump would therefore be on the right and thedischarge side on the left. In figure 4-5, since theright-hand side of the drawing was turned overto show the ports, the intake and discharge appearFigure 4-5.—Centered internal gear pump.Figure 4-6.—Principles of operation of the internal gearpump.reversed. Actually, A in one drawing covers A inthe other.LOBE PUMPThe lobeoperation aspump uses the same principle ofthe external gear pump described4-6
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