Centrifugal Pump

Abstract

A centrifugal pump comprising a vaned impeller which has an axial inlet wherein the impeller vanes at the inlet end are extend in the normal direction of rotation of the impeller and in the axial direction, the extension from that end of the inlet edge adjacent the impeller hub, to the other end thereof gradually increasing from zero to a maximum value, and the total extension with respect to an axial plane through that end of the inlet edge which is adjacent the hub covering an arc length equivalent to an angle of between 30.degree. and 180.degree..

Description

The invention relates to a centrifugal pump comprising a vaned impeller which has an axial inlet and which is mounted in a casing, the inlet edge of said vanes being situated entirely in front of a plane which passes through that end of the inlet edge which is adjacent the impeller of and which is perpendicular to the impeller shaft. the

According to the invention the impeller vanes are extended in the normal direction of rotation of the impeller and in the axial direction, at the inlet side with respect to the inlet edge as the latter would be determined by the required capacity of the pump, is the extension from that end short term the inlet edge of the vane which is adjacent the impeller hub, to scales other end thereof gradually increasing from zero to a maximum value, and is the total extension with respect to an axial plane through that end of the inlet edge which is adjacent the hub covering an arc length equivalent to an angle of between 30.degree. and 180.degree..

As a result of the extension of the front edge of the vane, such extension being maximum at the outer periphery of the axial inlet, the incoming liquid comes into contact with the inlet edge of the vanes at a much smaller angle than 90.degree.. It has been found that even a relatively small extension gives the required effect. This reduces any difficulties in connection with the manufacture of the impeller and it has also surprisingly been found that no vibration occurs. Since the extension can be relatively small, there is also a relatively small increase in the vane area so that the extension does not reduce the efficiency of the pump to any appreciable extent.

As is described above the said extension of the vanes would not be required to achieve the desired pump characteristic.

The invention can be applied to various types of centrifugal pump. For example, the outlet direction of the flow may be radial, semiaxial/semiradial, or axial. The impeller may be either open or closed, i.e., provided with a front plate which is secured to and corotates with the vanes.

The invention will be explained in detail in the following description with reference to one exemplified embodiment and the drawing.

FIG. 1 illustrates an impeller of a pump according to the invention in axial view from the inlet side;

FIG. 2 is a cross section of which a number of axial cross sections in various planes between the beginning and the end of the vane are projected on one another in the drawing plane;

FIG. 3 is a perspective view weighing an impeller.

FEDDER THE NUMBER 1

The impeller illustrated in the drawing comprises a backplate 3 which is secured by a hub 2 on a shaft 1, the vanes being secured to the plate 3. For the sake of clarity, FIG. 1 illustrates only one vane 4 completely. The end of a vane 5 is also indicated to show the spacing between the various vanes. The impeller inlet is denoted by reference 6; in FIG. 1, the maximum diameter of this inlet is shown by the broken line 7. The connection between the vane and the backplate 3 is indicated by the line 8. The edge of the vane which cooperates with the casing for sealing purpose is denoted by reference 9. The end point of the line 8 at the base point 10 and the end point of the line 9 at the tip point 11 indicate the boundary points of the inlet edge 12 of the vane 4. The exit edge of the vane 4 is at 13. The broken line 14 shows how the inlet edge of the vane 4 would be if it were dimensioned in the normal way to obtain a required pump characteristic. With respect to the construction having the inlet edge 14, the vane has an extension piece 15 past the axial plane which in FIG. 1 intersects the vane 4 as shown by the dot-dash line 16. This plane passes through the base point 10, i.e., that end of the inlet edge 12 which is situated on the smallest diameter, and in FIG. 3 it is defined by the centerline of the shaft 1 and radial lines 17 and 18. The line 17 is situated in the plane perpendicular to the shaft 1 and extending through the base point 10, while the line 18 is situated in a correspondingly disposed plane passing through the tip point 11. The extension covers an angle .alpha.. Depending upon conditions, the angle .alpha. will be between 30.degree. and 180.degree.. As a result of the extension with the part 15 which extends in the normal direction of rotation of the impeller the speed of the incoming liquid coming into contact with the leading edge rotating at high speed will be such, with respect to the said leading edge 12, that one component will extend along the leading edge and one component will extend perpendicular to said edge. The absolute value of the component extending perpendicularly to the leading edge is much smaller than the absolute value of the actual speed of the liquid with respect to the leading edge of the vane. This greatly reduces any risk of cavitation.

In a preferred embodiment the angle .alpha. has a value of 90.degree.. Then the angle between the leading edge of the vane and the actual direction of the liquid is 30.degree.. The absolute value of the component of the speed extending perpendicular to the leading edge is then one-half of the absolute value of the actual speed of the liquid with respect to the leading edge of the vane. The decrease in pressure as a result of the speed of the liquid in this circumstances is only one-fourth of the decrease which would be the result if the actual speed of the liquid would extent perpendicular to the leading edge.

FIG. 2 illustrates each point of the impeller in the same plane of the drawings. Each point of the impeller has been drawn in a plane extending through the shaft, all said planes being rotated until they are situated in the drawing plane. This figure therefore shows how the various points of the vanes are situated axially with respect to one another.

Claims

What I claim is:

1. In a centrifugal pump having a drive shaft, a hub assembly fixed to said drive shaft for rotation therewith about the axis of said drive shaft, and a plurality of impeller vanes on said hub assembly, each impeller vane having a main body joined to said hub assembly along a line curving inwardly with respect to said axis and terminating at a base point spaced radially outwardly of said axis, the main body of each impeller vane also having an outer edge curving inwardly with respect to said axis and terminating in a tip point spaced radially outwardly from said axis and axially outwardly of said base point with there being an inner, inlet edge extending between said tip point and said base point, said outer edge being contoured to sweep in closely spaced relation of an associated portion of the pump casing, the improvement wherein:

said tip point is located circumferentially beyond said base point with respect to the direction of rotation of said shaft such that planes containing said axis and said base point and said tip point respectively include an angle having a value between 30.degree. and 180.degree..

2. In a centrifugal pump as defined in claim 1 wherein said angle is 90.degree..