IMPROVED PUMP CASING FOR CENTRIFUGAL PUMP AND METHOD FOR PRODUCING SAID CASING

Abstract: A pump casing for centrifugal pumps which can be obtained by casting, pressure die-casting or by means of another process for forming a metallic material, comprises an axial suction inlet (3; 3') connected to a pressure chamber (5; 5') shaped as an annular volute. A centrifugal impeller (6; 6') is arranged in the pressure chamber which is provided with a radial discharge outlet (4; 4'). The suction inlet (3; 3') has a substantially radial peripheral passage (9; 9') and an axial channel (18; 18'), at the region where it blends with the pressure chamber (5; 5'). The peripheral passage and the axial channel are connected to the pressure chamber and are obtained by means of a single core (F) which forms both the suction inlet and the pressure chamber. An annular ridge (19, 19') is formed along the edge of the axial opening (18) and forms an axial skimming surface (20; 20') for the non-bladed part of the impeller (6). Together with the impeller the ridge forms an element for separating the suction inlet (3) from the pressure chamber (5). The annular ridge (19') is interrupted by a radial groove (25) to avoid sticking and reduce friction during pickup.

Description: IMPROVED PUMP CASING FOR CENTRIFUGAL PUMP AND METHOD FOR PRODUCING SAID CASING The present invention relates to an improved pump casing for centrifugal pumps with a particularly simplified structure, which can be obtained by casting, pressure die-casting or by other processes for forming metallic materials such as cast iron, steel, brass, bronze and the like. As known, centrifugal or liquid-ring pumps are normally used to raise liquids from shallow wells or to circulate them in small-capacity household systems. Such pumps generally have a casing which is defined by a main portion, provided with an axial suction inlet, an approximately radial discharge outlet and a pressure chamber or volute accommodating an impeller with peripheral blades, which is coupled to a secondary portion for the closure of the pressure chamber and connection to an electric motor or the like. In a known pump casing of this type, schematically illustrated in Figure 1, an accumulation pre-chamber R is defined proximate to the inner end of the suction inlet B; the pre-chamber has a slightly conical toroidal shape and is adjacent to a substantially annular pressure chamber or volute P. The accumulation chamber R has a front wall, or partition S at its inner end. Partition S separates chamber R from the pressure chamber P. A channel C extends between the upper region of the accumulation chamber, externally with respect to the partition, and the pressure chamber or volute, and ensures the continuous filling of the volute. In this pump casing, two distinct and separate cores A-^ and A2 must be prepared in order to form the cavities which define both the portion' provided with the suction inlet and the accumulation chamber and the portion provided with the pressure chamber and the discharge outlet; this entails a considerable expenditure of time and labor for the execution of the cores and for their positioning in the forming dies. In another known pump casing there is a suction inlet which is axially offset with respect to the rotation axis of the impeller and is not provided with a suction pre-chamber. This type of pump has solved some technical problems in casting or pressure die-casting, and has however led to the onset of other problems, especially in installation, because it is not nterchangeable with other pumps provided with an axial suction inlet. It must be furthermore noted that in all these pumps the casing has, in the pressure chamber, annular ridges which define front skimming surfaces for the impeller, with axial plays on the order of a few hundredths of a millimeter. This entails the risk of sticking of the impeller during idle periods, considerable initial separation friction, shorter impeller life and a certain noise. Furthermore, dirt, sand or other matter can penetrate between the skimming surfaces, causing their progressive wear and/or damage . The aim of the present invention is to eliminate, or at least considerably limit, the above described problems by providing a pump casing with simplified structure, obtainable by pressure die-casting or by means of other methods for forming metallic materials, which allows to considerably reduce its manufacturing costs. An object of the present invention is to provide a centrifugal pump casing which is lighter and more compact than conventional ones. Another object is to provide a pump casing which has less risk of impeller sticking and lower initial separation friction and furthermore has a self-cleaning effect on the impeller. Not least object of the present invention is to provide a method for the simplified manufacture of the above described pump casing. This aim, these objects and others which will become apparent hereinafter are achieved by a pump casing for centrifugal pumps which can be obtained by casting, pressure die-casting or by another process for the forming of a metallic material, comprising an axial suction inlet connected to a pressure chamber shaped as an annular volute, a centrifugal impeller being arranged in said pressure chamber, said pressure chamber being provided with a radial discharge outlet, characterized in that said suction inlet has a substantially radial peripheral passage and an axial channel at the region where it is connected to the pressure chamber both said peripheral passage and said axial channel being connected to the pressure chamber and being obtained by means of a single core (F) which forms both said suction inlet and said chamber. In this manner the casing can be produced by using a single forming core instead of two as in the prior art. Preferably, the casing has, along the edge of the axial channel, a first axial ridge which forms a front skimming surface for the impeller and defines, together with the non- bladed surface of the impeller, an element for separating the axial channel from the volute. Said casing furthermore has, on the portion for connection to the motor, a second axial ridge which forms a further front skimming surface for the impeller, at least one of said ridges being interrupted by a radial groove which forms a passage between the suction inlet and the volute. In a further aspect of the invention, a method is provided for the production of castings or pressure die-castings of casings for centrifugal pumps wherein a single core is adapted to define both the suction inlet and the pressure chamber which are mutually connected by means of a substantially radial peripheral passage and an axial channel. The manufacture of semifinished items of the above indicated type requires considerably less equipment and a reduced time for preparations with respect to the prior art, with evident economic and production advantages. For a better understanding of the invention, a few embodiments of the pump casing, according to the invention, are described in detail hereinafter and are illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure ! is a partially sectional side view of a pump casing of the prior art, taken along an axial vertical plane; Figure 2 is a partially sectional front view of a first embodiment, of the pump casing according to the invention, taken along the transverse plane II-II of figure 3; Figure 3 is a sectional side view of the casing of Figure 2, taken along the axial plane III-III; Figure 4 is a partially sectional front, view of a second embodiment of the pump casing according to the invention, taken along a transverse plane IV-IV of Figure 5; Figure 5 is a partially sectional side view of the casing of Figure 4, taken along the axial plane V-V; Figure 6 is a partially sectional general side view of a centrifugal pump which includes the casing of Figures 2 and 3 ; Figure 7 is a partially sectional general side view of a centrifugal pump which includes the casing of Figures 4 and 5. With reference to Figures 2, 3 and 6, a pump casing, according to the invention, has a main portion 1 and a secondary portion 2. The main portion 1 has a suction inlet 3, which is substantially tubular and coaxial to the axis O of the pump, and a discharge outlet 4, whose axis is substantially radial and slightly offset with respect to the axis 0 of the pump. Both the suction inlet 3 and the discharge outlet are internally partially threaded to allow coupling to pipes, respectively for feed and discharge, which are not illustrated in the drawings. The suction inlet 3 and the discharge outlet 4 are both connected to a pressure chamber which is shaped as an annular volute 5, defined inside the main portion 1 and closed by the secondary portion 2. An impeller 6 with peripheral blades is accommodated in the volute 5. The pressure chamber 5 is also connected to a secondary chamber 7. Sensors for measuring flow parameters are arranged in chamber 7 which is provided with a passage 8. Passage 8 is internally threaded and open outwardly. The suction inlet 3 is connected to the pressure chamber 5 through an approximately radial passage 9. Passage 9 is slightly inclined toward the discharge outlet and is suitable to convey the fluid toward the impeller 6. The secondary portion 2 is fixed to a motor 10 by means of bolts 11 and is provided with seats for a mechanical seal 14 and a bearing 12 of the motor shaft 13. The impeller 6 is keyed to shaft 13 and the mechanical seal 14 is arranged within the main portion 1 of the casing. The main portion 1 is connected to the secondary portion 2 by inserting the peripheral edge of main portion 1 in an annular seat 15 of the secondary portion 2, and by means of connecting bolts 16 which are inserted in through holes 17 of the two portions. According to the invention, the suction inlet 3 is provided with an axial channel 18 which is connected to the pressure chamber 5. In this configuration, the radial passage 9 and the axial channel 18 can be obtained by means of a .single core F which extends uninterruptedly from the pressure chamber to the suction inlet and to the discharge outlet and is schematically indicated in broken lines in Figure 3. An annular ridge 19 is provided along the edge of the opening 18 and has a front surface 20. Front surface 20 forms an axial skimming surface for the impeller and cooperates with the non-bladed part thereof to separate the axial channel from the volute-shaped pressure chamber 5. On the opposite side, the connecting portion 2 of the pump body has a similar annular ridge 21. The front surface 22 of ridge 21 also forms a radial skimming surface for the impeller. The coupling between the non-bladed part of the impeller and the two front surfaces 20 and 22 of the ridges 19 and 21, with a play of a few hundredths of a millimeter, forms the pressure chamber 5. Two partially radial curved wings 23 and 24 also extend from both ridges. With respect to pump casingsof the prior art, which is shown in Figure 1, the partition S which separates the accumulation pre-chamber R from the pressure chamber is thus eliminated, with a consequent saving in material and lower weight of the casting. The absence of the accumulation pre-chamber R furthermore makes the shape more compact in an axial direction, with an evident advantage in terms of assembly and overall bulk. A further aspect of the invention is illustrated in the embodiment shown in Figures 4, 5 and 7. For the sake of simplicity, components which are identical or similar to those of the preceding embodiment are designated by the same reference numerals provided with a prime. According to the invention, the two annular ridges 19' and 21' are interrupted by respective radial grooves 25 and 26 which define corresponding passages between the suction duct 3' and the pressure chamber 5' . In practice, the skimming surface 20' and 22" of each ridge 19' and 21' is interrupted at the side of the corresponding wing 23' and 24' which interrupts the continuity of the volute 5. The fluid is then redirected from an axial direction to a radial direction until it enters the volute and is centrifuged by the set of blades until it exits through the discharge duct 4'. The interruption of the skimming surfaces 20' and 22' reduces, in percentage terms, the region of possible impeller sticking. The motor is thus less stressed during startup, and initial separation friction is also smaller. Longer impeller life is thus also obtained. Any particles of dirt, sand or other matter which are drawn inside the pump and become interposed between the impeller and the skimming surfaces 20' and 22' are discharged, at every turn, at the grooves 25 and 26. The pump is thus also self-cleaning. Practical tests have also shown that it is quieter than the pumps of the prior art. In both cases, in order to perform a casting or pressure die- casting of the above described pump casing, and in particular of the main portion 1, it is thus sufficient to insert and coordinate a single core in the die which reproduces the outer surface of said portion. This entails a considerable cost reduction both for the manufacture of the cores and for their positioning inside the dies. Furthermore, since only one core must be provided for each part, the costs for the related forming equipment are correspondingly halved. In the case of the manufacture of the body by casting, because of the simplicity and compactness of the body.it is possible to use a single casting channel for a cluster of castings which comprises for example at least four parts. A plurality of clusters can furthermore be arranged in the same casting box, for example four clusters arranged uniformly so as to optimize the process and reduce preparation and casting times. In practice it has been observed that the pump casing according to the invention achieves the intended aim and objects, and in particular the considerable constructive simplification of the semifinished parts, the significant reduction in the costs for the production of the semifinished parts and of the cores and the better operation and longer life of the pump are stressed. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: CLAIMS 1. Pump casing for centrifugal pumps which can be obtained by casting, pressure die-casting or by another process for the forming of a metallic material, comprising an axial suction inlet (3; 3') connected to a pressure chamber (5; 5') shaped as an annular volute, a centrifugal impeller (6; 6') being arranged in said pressure chamber, said pressure chamber being provided with a radial discharge outlet (4; 4'), characterized in that said suction inlet (3; 3') has a substantially radial peripheral passage (9; 9') and an axial channel (18; 18'), at the region where it is connected to the pressure chamber (5; 5'), both said peripheral passage and said axial channel being connected to the pressure chamber (5; 5') and being obtained by means of a single core (F) which forms both said suction inlet (3; 3') and said chamber (5; 5' ) . 2. Pump casing according to claim 1, characterized in that a first annular ridge (19) is provided along the edge, of said axial opening (18) and forms an axial skimming surface (20) for the non-bladed part of the impeller (6) and forms, together with said impeller, an element for separating the suction inlet (3) from the pressure chamber (5) . 3. Pump casing according to claim 2, characterized in that a second annular ridge (21) is provided on the opposite side with respect to said first annular ridge (19) and forms an axial skimming surface (22) for the impeller, said surface being opposite to the first one. 4. Pump casing according to claims 2 and 3, characterized in that the two opposite annular ridges (19; 21) have respective wings (23; 24) which are slightly curved and partially radial. 5. Pump casing according to claims 2 and 3, characterized in that at least one of said two annular ridges (19'; 21') is interrupted by a substantially radial groove (25; 26) which is adjacent to the respective wing (23'; 24'). 6. Pump casing according to claim 5, characterized in that the radial groove on the side of the suction inlet (3) is aligned with said substantially radial passage (9'). 7. Method for forming, by casting, pressure die-casting or by another equivalent method, a pump casing for centrifugal pumps according to one or more of the preceding claims, characterized in that it comprises the use of a single core to form, both the suction inlet (3) and the pressure chamber (5) , in a main portion of the body (1) said inlet and chamber being mutually connected by means of a substantially radial peripheral channel (9) and a substantially axial opening (18) .

Inventors: CAODURO BRUNO, CAODURO, BRUNO
Applicants: FIP FABB ITAL POMPE, FORAS PUMPS SRL, F.I.P. FABBRICA ITALIANA POMPE S.R.L., FORAS PUMPS S.R.L.
Application year: 1992
Main classification: F04D5
IPC codes: F04D5, F04D29