FR2474110A1 - Centrifugal pump with twin 180 degree spiral ducts - has bush in housing as inner wall to channel from first duct to outlet common with second - Google Patents

Abstract

The centrifugal pump with a double spiral housing (1) has each of its two spiral ducts e.g. extending over 180 deg. around the impeller (2) or around the guide vane assembly downstream of the impeller. The pump outlet is at the outer diameter of the housing which is also the diameter of the first spiral duct at the start of the second cut (4). The first duct connects to the common outlet via one or more passages (6,7) arranged to the side of the duct. The passages (6,7) are formed in the housing as channels which are open in radially inward direction and are sealed (13) by insert bushes (9) secured (12) in the housing.

Description

 The present invention relates to a centrifugal pump whose body has two opposite and mechanically similar scrolls in the direction of mechanical similarity.

 For the realization of the working principle of a fluid displacement machine, the body of this machine must delimit the fluid which is there in relation to the ambient medium.

This can take place regardless of the shape of the body concerned, so that over time fundamentally different body shapes have become established to deal with other particular problems.

 In a machine of the type according to the invention, a double scroll body is used, which, in general, fulfills the particular task of producing, over the whole extent of the working range of the machine, a low radial force and as constant as possible.

 This can be achieved by using two opposite and mechanically similar scrolls. Depending on the selected execution force, the double scroll body surrounds the moving wheel or a fixed wheel placed downstream of the moving wheel.

 German patent application DE-OS 26 40 866 describes for example a body with two scrolls offset relative to one another. The first volute develops beyond the start of the second and, thanks to bypass channels, joins the second volute at the point where it opens into a communal outlet pipe. In this body, known in all double volute bodies, the problem is that, owing to its larger outside diameter, its size and its load are greater than those of a single volute body.

 The object of the invention is to produce for centrifugal pumps a double volute body with a small external diameter without this resulting in drawbacks from the hydraulic point of view.

To this end, in the centrifugal pump according to the invention, provision is made to have around the mobile wheel, or a fixed wheel located downstream of the mobile wheel, a body with two volutes which each embrace a maximum angle of 1800, body whose outside diameter is equal to that of the first scroll at the beginning of the second.

Reducing the outside diameter of the body to that of each of the diametrically opposite scrolls allows a saving in material weight which is not negligible.

For double-scroll body pumps in which a common outlet pipe is desired, it is provided, in a more elaborate form of the invention, that the first scroll, from the start of the second scroll, opens through a or several channels which extend alongside the latter, with it, in known manner, in a common outlet orifice.

 In cases where another pump stage is placed downstream of the double-flow moving impeller, it is another form of embodiment of the invention to connect the ends of the volutes to the moving downstream impeller by a or channels placed on one or more diameters smaller than that of the double scroll body.

 To obtain uniform hydraulic conditions in the volutes or the outlet pipe of the pump, another embodiment of the invention provides for ded> nner to the channel or channels a constant or variable section along their length, as the case may be.

 Thanks to the invention, it is possible to produce a double volute body of very small diameter. Although the moldability of this body is also greater than in known pumps of this type, its manufacture by this technique is still an extremely delicate operation.

 An even more elaborate embodiment of the pump according to the invention makes it possible both to further facilitate the molding of the body and to create in the pump optimal flow conditions.

 In this embodiment, the double volute body and its channels have an open profile on the internal face of the body, facing the pump shaft, and inserted pieces of tubular shape, applied against the body tightly , form the inner wall of the body, facing the aforementioned tree.

Thanks to this arrangement, the areas of the double-scroll body in which the fluid circulates are easily accessible, which facilitates manufacturing by molding and makes it possible, for example, to perform polishing operations with a view to reducing the resistance to l flow of volutes and channels.

This free access to the double volute also allows easier control of the surface condition and the elimination of any molding defects. It is also possible to better position the cores which correspond to the shape of the scrolls and channels, which facilitates the obtaining of optimal conditions for the flow of the fluid. This also means a considerable improvement in the machining of such a double scroll.

In any case, the invention will be clearly understood with the aid of the description which follows, with reference to the appended schematic drawings, representing, by way of nonlimiting example, an embodiment of this pump:
Figure 1 is a cross-sectional view of a centrifugal pump with a double volute body, with common outlet pipe
Figure 2 is a sectional view along II-II of Figure 1;
Figure 3 is a sectional view along III-III of Figure 1;
Figure 4 is a sectional view along IV-IV of Figure 1;
Figure 5 is a cross-sectional view of a second embodiment of the pump according to the invention, in which the body is completed by inserted parts
Figures 6 and 7 are sectional views along VI-VII of Figure 5 showing two alternative embodiments of the inserted parts.

Figure 1 shows a double volute body 1, inside which is mounted a movable wheel 2. The first volute 3 embraces a maximum angle of 180th (smaller angles can be chosen) and ends at point 4, which also constitutes the starting point of the second volute 5, which opens into the outlet orifice 6. For better guidance of the fluid stream, a deflecting rib 7 is provided inside the outlet orifice 6.

 It can be seen in FIG. 2 that the fluid leaving the volute 3 is distributed at point 4 between two channels 8, 9. These two channels extend alongside the second volute 5 which begins at point 4 and all three open into the 'common outlet orifice 6. This communicates by other means with the reversing tube of the pump or with the next pump stage, as the case may be.

 FIG. 3, which is a partial section view on the right side of the pump body shown in FIG. 1, shows the movable impeller 2, which sends the fluid to be pumped into the first volute 3.

Figure 4 shows in partial section the left side of the double scroll body 1. We can see the second scroll 5 and, parallel to it, one on each side, the two channels 8, 9, in which the fluid flowing out of the first scroll 3.

The second volute 5 and the two channels 8, 9 open together in the common outlet orifice 6. Depending on the desired flow rate for the centrifugal pump, it is possible to use an embodiment in which the fluid leaving the first volute 3 is directed towards the outlet orifice 6 by a single channel which runs along the second volute 5. The body according to the invention constitutes considerable progress in so far as, compared with known double volute bodies, the ability to mold and to control is greatly improved, while the load on the body could be reduced considerably. The channels can be directed to the next movable wheel by following circles of smaller diameter.

 FIG. 5 shows that tubular-shaped parts 15 are inserted in the body i, next to the inlet orifices of the scrolls 3, 5. In this embodiment, the channels 8 and 9 of the body open onto the internal face thereof, which facilitates molding. The inserted parts 15 here constitute the inner wall of the body 1, facing the shaft 10, which isolates the channels of the second volute 5.

 It can be seen in FIG. 6 that the inserted parts 15, which have the form of sections of tube, can be fixed from the outside to the body 1, for example by means of screws 12.

The seal between these parts 15 and the body 1 is ensured by O-rings 13.

In FIG. 7, the attachment of the inserted parts 15 takes place inside the body 1, on projections 14 of suitable shape that the latter presents. These projections can come from molding or be formed afterwards by removing material. It can be seen that the wheel 2 is here a single wheel, while in FIG. 6, it is a double wheel.

Claims (5)

 1.- Centrifugal pump whose body has two opposite and mechanically similar scrolls in the direction of mechanical similarity, characterized in that around the movable wheel (2) or of a fixed wheel located downstream of this movable wheel is disposed a body (1) with two volutes (3,5) each of which embraces a maximum angle of 180, and in that said body (1) has an outside diameter equal to that of the first volute (3) at the beginning of the second scroll.  2.- centrifugal pump according to claim 1, characterized in that the first volute (3), from the start of the second volute (5), opens through one or more channels (8,9) which extend to side of the latter, with it, in a manner known per se, in a common outlet orifice (6). 3.- centrifugal pump according to claim 1 or claim 2, characterized in that the ends of the scrolls (3,5) are connected to a movable downstream wheel by one or more channels placed on one or diameters smaller than that of the double scroll body (1).  4.- Centrifugal pump according to any one of claims 1 to 3, characterized in that the channel or channels (8,9) have a constant or variable section along their length. 5.- centrifugal pump according to any one of claims 2 to i, characterized in that the double scroll body (1) and its channels (8,9) have an open profile on the internal face of the body, facing towards 'shaft (10) of the pump, and in that inserted parts (15) of tubular shape, applied against the body in a sealed manner (seals 13), form the inner wall of the body, facing the aforementioned shaft.