Airfoil Vacuum Pump With Tapered Rotor

Abstract

An airfoil vacuum pump of the centrifugal type has a rotor disposed in a conical housing. The rotor has vanes that taper radially inwardly away from the rotor toward the axial inlet of the pump. The leading and trailing edges of the vanes converge in a direction toward the inlet, and the thickness of the vanes decreases in that direction.

Description

The present invention relates to centrifugal pumps, more particularly of the airfoil vacuum type in which a rotor carries a plurality of vanes of airfoil configuration, the inlet to the pump being generally axially disposed and the outlet generally peripherally disposed.

It is an object of the present invention to provide an airfoil pump of the centrifugal type, of greatly increased efficiency.

Another object of the present invention is the provision of such a pump that is free of cavitation.

Still another object of the present invention is the provision of such a pump, in which substantially laminar flow is achieved.

Finally, it is an object of the present invention to provide such a pump, which will be relatively simple and inexpensive to manufacture, easy to operate, maintain and repair, and rugged and durable in use.

Briefly, the objects of this invention are achieved by providing an airfoil pump of the centrifugal type, in which a rotor has a plurality of outwardly extending vanes of generally airfoil configuration, characterized in that the pump casing is tapered toward the axial intake of the pump, and in that the vanes are radially inwardly inclined in the direction away from the rotor and toward the inlet. In this way, the width of the pump casing is at a maximum on its axis and progressively decreases in a radially outward direction, the pitch diameter of the vanes correspondingly increasing in the same direction and the cross-sectional area of the vanes increasing in the same direction, so that the tangential velocity and the pressure of the pumped fluid progressively increase in a direction radially outward from the axis of the pump.

These and other objects, features and advantages of the present invention will become apparent from consideration of the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a view along the axis of the pump of the present invention, taken in the inlet direction, partly in cross section on the line 1--1 of FIG. 2;

FIG. 2 is a cross-sectional view taken on the line 2--2 of FIG. 1;

FIG. 3 is a perspective view of one form of the rotor of the pump of the present invention;

FIG. 4 is a view similar to FIG. 3 but showing another embodiment of the rotor; and

FIG. 5 is a somewhat schematic cross-sectional view of a vane according to the present invention.

Referring now to the drawing in greater detail, there is shown a pump of the centrifugal type according to the present invention, comprising a casing 1 in two portions 3 and 5. Portion 3 is generally in the form of a flat plate, while portion 5 is generally conical and tapers from an axially disposed inlet 7 at the apex of the cone, radially outwardly to a generally tangentially disposed outlet 9 at the outer periphery of the cone. Casing portions 3 and 5 are secured together peripherally and thus define between them a pump chamber 11.

Disposed in chamber 11 coaxially therewith is a rotor 13 comprising a shaft 15 that extends through casing portion 3 and is supported therein by means of a bearing 17. Means (not shown) are provided to rotate shaft 15 to drive the pump. The rotor proper comprises a flat circular plate 19 secured to the left end of shaft 15 as seen in FIG. 2 in spaced relationship to casing portion 3 but parallel thereto.

Plate 19 carries thereon at least one vane 21, on the side plate 19 opposite shaft 15. It is possible to provide only one vane 21 if rotor 13 is appropriately counter-balanced; but it is preferred to provide a plurality of vanes 21 equally peripherally spaced about rotor 13. FIG. 3 shows an embodiment of rotor with four such vanes, while FIG. 4 shows an embodiment of rotor with two such vanes.

Each vane 21 is radially inwardly inclined from its base 23 to its tip 25, preferably along generally conical elements that more or less closely parallel those of casing portion 5. Each vane 21 also has a leading edge 27 and a trailing edge 29 which converge in a direction away from the rotor plate 19. The thickness or depth of each vane 21 at its base is also greater than at its tip. The cross-sectional area of each vane is accordingly greatest at its base and decreases progressively to its tip.

FIG. 5 shows the general cross-sectional configuration of a vane of the present invention, which general configuration remains the same throughout the length of the vane, although, as indicated above, the dimensions of the cross-sectional configuration progressively vary. In FIG. 5, the leading and trailing edges are again seen at 27 and 29, and the intersections of the cross section with that radius that passes through the region of greatest thickness of the blade, locate the element 31 on the outer side of the vane and the element 33 on the inner side. When speaking of "elements" it is of course understood each blade is preferably bounded by an infinite number of straight lines which are the boundary elements of the vane.

With further reference to FIG. 5, it will be noted that the leading edge 27 is about half the radial distance between the radially outermost part of the vane and the radially innermost part thereof. Thus, the outer leading surface of the vane, from 27 to 31, subjects the fluid to pressure in an axially outward direction, while the leading surface of the blade from 27 to 33 imparts an equal and opposite force to another portion of the fluid, so that the influences of the two leading portions of the vane cancel each other.

The portion of the vane from element 31 to the trailing edge 29 is preferably concentric or substantially concentric with the pump, not varying more than a few degrees either way from concentricity. However, the portion of the inner surface of the vane from element 33 to trailing edge 29 traverses the entire radial extent of the vane. Thus, while the surface 31-29 imparts substantially no outward thrust to the fluid, the surface 33 to 29 extends over the full thickness of the vane and hence exerts maximum radial outward force on the fluid.

In operation, a fluid such as water entering chamber 11 from inlet 7 flows into an axially central portion of chamber 11 and initially comes under the influence of the radially innermost tips 25 of the vanes 21. As these tips are disposed relatively close to the axis of rotation of rotor 13, their tangential velocity is lower than the tangential velocity of any other portion of the vanes. Also, as their cross-sectional area is the smallest part of the vane and all their effective surfaces are correspondingly reduced in size, the tips 25 exert the least influence on the fluid of any portion of the vanes.

In other words, fluid entering chamber 11 at inlet pressure and with substantially no speed of rotation, is initially increased in pressure and caused to begin to rotate, by the portion of the vanes 21 which exerts the most gentle action in these respects, by virtue both of the smallest area and of the smallest tangential speed of rotation of the tips of the vanes. This gentlest action of the tips of the blades is augmented by the fact that the fluid at this point is in the widest portion of tapering chamber, that is, nearest the axis of the chamber.

As the fluid begins to circulate in the chamber, it flows radially outwardly in the chamber, and several things simultaneously happen: in the first place, the fluid encounters a portion of the vanes 21 closer to the base 23 thereof and hence radially farther out than the tips of the vanes. The radially farther out portions of the vanes rotate faster than the tips of the vanes, so that the fluid progressively contacts portions of the vanes rotating at progressively higher tangential velocities. At the same time, the cross-sectional configuration of the portion of the vane contacted by the liquid is increasing in size, from the least cross section at the tip 25 to the greatest cross section at the base 23, so that the pressure, or rather the suction, exerted by the vane on the fluid is increasing because the size of the vane is increasing. Also at the same time, as the fluid moves radially outward in the chamber 11, the chamber 11 is becoming progressively narrower, so that the liquid must travel with higher and higher tangential velocity.

All these factors coact to achieve a smooth laminar flow in the pump of the present invention, with greatest efficiency and with least cavitation even when the inlet is substantially closed. These improved results depend not on precision of manufacture and close tolerances, but rather on the factors recited above, so that the pump can be constructed without great attention to precision of manufacture, in other words, inexpensively.

In consideration of the foregoing disclosure, therefore, it will be evident that all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention as defined by the appended claims.

Claims

Having described my invention, I claim:

1. An airfoil pump comprising a casing having an axially disposed inlet and a peripherally disposed outlet and tapering from a greatest axial width adjacent the inlet to a least axial width adjacent the outlet, and a rotor rotatably disposed in the casing, said rotor bearing at least one airfoil vane that extends away from the rotor and is inclined radially relative to the axis of rotation of the rotor, said at least one vane having leading and trailing edges that converge in a radially inward direction.

2. A pump as claimed in claim 1, said casing being conical.

3. A pump as claimed in claim 1, said edges converging in a direction away from the rotor.

4. A pump as claimed in claim 1, said at least one vane having an airfoil cross-sectional configuration whose length and width progressively decrease in the direction away from the rotor.

5. A pump as claimed in claim 1, said rotor comprising a flat plate on which said at least one vane is mounted, said plate being spaced from but closely adjacent a flat plate comprising one side of said casing, said rotor having an axial drive shaft extending through the last-named flat plate.

6. A pump as claimed in claim 1, the radially outer surface of said at least one vane, from the region of greatest thickness of the vane to the trailing edge of the vane, being substantially concentric with said rotor.

7. A pump as claimed in claim 1, said vane having an airfoil cross-sectional configuration characterized by a leading edge and a trailing edge and a region of greatest thickness between said leading and trailing edges, the radially outer surface of said vane between said region of said greatest thickness and said trailing edge being substantially concentric with said rotor.

8. A pump as claimed in claim 1, said inlet and said rotor being disposed on opposite axial sides of said casing.

9. A pump as claimed in claim 8, said casing being conical.

10. A pump as claimed in claim 9, said casing having radially outer side walls that are inclined in substantially the same direction as said at least one vane.