Drawing and inspection of the axial projection view of the centrifugal pump impeller

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Axial projection view
The centrifugal impeller has an axial line. The plane passing through the axis of the impeller is called axial plane or meridian plane, and one impeller has an infinite number of axial planes.
The impeller or the blades are sectioned by several axial planes, and then the axial cross-sectional views are rotated around the impeller axis and then superposed together, so an axial projection drawing of the impeller or the blade is obtained. The points of the exit edge of the blade, the entrance edge and the blade surface are located on three different axial planes. By superimposing the three axial planes together, the structure of different parts of the blade can be represented on one axial planes drawing. The distance on the drawing from one structure of the axial plane to the axis is equal to the true distance from this structure to the axis. This article describes the centrifugal pump impeller.

Drawing principles and methods
After the full geometry parameters (   2  0  2 ) of the impeller are determined, the pattern of the blades should be completed according to these determined dimensions [1][2] . For this purpose, the first work is to draw the axial projection view. The known control dimensions for guiding the axial projection are only four: impeller radius 2 R , impeller inlet diameter 0 D , impeller outlet width 2 b , and hub radius ee . The axial projection drawing of the impeller should meet these four basic dimensions, as shown in Fig.1. In addition, when drawing the axial projection view, the following two points need to be paid attention to: First of all, for the transitional arc portion of the front and rear cover flow lines, due to the arbitrariness of the given circular arc radiuses should be discussed separately when drawing the axial projection view. Secondly, for the low-specific-speed centrifugal pump, in order to improve the hydraulic efficiency of the impeller and ensure that the inlet angle of the cylindrical blade is not too large, the simple treatment is generally performed, that is, the straight portion of the outlet is an isosceles trapezoid, which is symmetrically distributed, as shown the straight lines DG and CH in the figure. The study considers the general case that the quadrilateral CDGH is an arbitrary trapezoid. In particular, for multi-stage multi-suction pumps, for the sake of hydraulic performance and the placement of the blades, the straight portions of the DG and CH should be perpendicular to the axis.

Determination of coordinates
First, a rectangular coordinate system (the axis line of the impeller is taken as the x-axis, and the vertical bisector of 2 b is taken as the y-axis, as shown in Fig. 3-1) is established. Assuming that the center of the arc of the front and rear covers are

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The center of the circle can be obtained in the same way, but it should be noted that for a multi-stage multi-suction centrifugal pump, there is a case where the rear cover flow line is perpendicular to the axis line, which should be discussed separately here.