Sheet metal pump casing

Abstract: A sheet metal casing with differentiated thickness for centrifugal pumps includes a substantially cup-shaped main body (2) formed by a peripheral wall (3) which is continously joined to a transverse end wall (4); the body is coupled to a transverse sealing plate (9) opposite to the end wall (4) so as to define a pressure chamber (13) enclosing an impeller (14); a tangential delivery port (7) and an axial suction port (6). A funnel-shaped reinforcement element (20), has a frusto-conically shape and a transverse end portion (21) arranged inside the main body (2) and a substantially cylindrical longitudinal end portion (22) extending from the body main coaxially to the suction inlet (6). The transverse end portion (21) of the reinforcement element is at least peripherally overlapped and rigidly sealingly coupled to the end wall (4) of the main body so as to thereby define the transverse wall of the casing which is adjacent to the suction port in contact with the pumped liquid.

Description: The present invention relates to a sheet metal casing with differentiated thickness for centrifugal pumps, of the type comprising a substantially cup-shaped main body formed by a peripheral wall which is continuously joined to a transverse end wall, means for connecting the main body to a transverse sealing plate which is arranged opposite to the end wall so as to define a pressure chamber enclosing an impeller, a substantially tangential delivery port and a substantially axial suction port. Many pump bodies of the foregoing type are known which are integrally made of sheet metal; in said pump bodies, the basic problem to be solved resides in the limited resistance to static and dynamic loads acting upon the end wall and on the axial suction port defined in the central portion of the end wall of the main body. Many attempts have been made to solve this problem by providing pump body stiffenings arranged in these overloaded regions, for example providing a suction port of considerable thickness,obtained by casting, and subsequently welding it to the end wall of the pump body by circumferential beads. While this solution provides a suction port of considerable rigidity and fatigue resistance, it cannot impart the same mechanical resistance to the coupling region of the inlet port and the end wall of the pump body. A further attempt to stiffen the suction inlet and the end wall of the pump body consists in providing some box-like annular structures with a more or less complicated shape which are welded or are integrally formed with the coupling flange so as to give rigidity to the entire assembly. These structures, however, are not sufficiently resistant and are also relatively bulky and prevent rusty bolts from being removed owing to the extremely small space available between the flange and the pump body, which is mainly occupied by the reinforcement structures. Other attempts have been made to stiffen the suction inlet and the region of coupling to the end wall of the pump body, by using radial ridges welded to said end wall; this solution allows to stiffen the wall of the pump body but does not give the necessary resistance to the suction ducts if said ducts are made of stamped plate. DE-3517828, for example, discloses a pump casing provided with a reinforcement element having a transverse end portion, arranged at the suction region. The aim of the present invention is to eliminate the aforementioned disadvantages by providing a sheet metal casing for centrifugal pump which has high characteristics of resistance and reliability as well as considerable constructive simplicity and reduced dimensions. Within the scope of the above described aim, a particular object of the present invention is to provide a sheet metal casing with differentiated structure which is capable of easily withstanding, without deformation, both the internal stresses generated by the pressurized fluid and the external ones transmitted through the suction inlet. Not least object of the present invention is to provide a sheet metal casing with differentiated thickness for centrifugal pump which can be easily obtained starting from commonly commercially available elements and materials and which is furthermore advantageous from a merely economical point of view. This aim, the objects mentioned and others which will become apparent hereinafter are achieved by a sheet metal pump casing, with differentiated thickness, as claimed in the appended cliams. In particular, the thickness of the reinforcement element is greater than that of the main body and is such as to integrally withstand, without deformation, both the pressure forces which act inside the chamber in a substantially axial direction and the static and dynamic stresses which act on the suction inlet. By this solution, the sheet metal casing has, at the end wall and at the suction port, a thickness and therefore a resistance which are greater than those of monolithic structures of the prior art, but it preserves the external geometric characteristics thereof, allowing extremely easy and unrestricted assembly and maintenance. Further characteristics and advantages will become apparent from the description of two preferred but not exclusive embodiments of two sheet metal casings with differentiated thickness for centrifugal pump, according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Fig. 1 is a partially sectional side view of a first embodiment of the casing according to the invention, taken along an axial vertical plane; Fig. 2 is a partially sectional side view of a second embodiment of the casing according to the invention, taken along an axial vertical plane. With reference to the cited figures, the same reference numerals have been used for identical or similar elements in the two embodiments. The casing according to the invention, generally indicated by the reference numeral 1, is formed by a main body 2, made of stamped plate, having substantially the shape of a cup, i.e. defined by a substantially cylindrical peripheral side wall 3 and by a transverse end wall 4 which uniformly blends into the wall 3 along the region 5. The casing further comprises a suction port 6 which extends axially from the end wall 4 of the pump body and a pressure port 7 which extends tangentially from the peripheral wall 3 of the body 2. The peripheral wall 3 of the body 2 preferably has a spiral-shaped volute 8 the end portion of which is joined to the discharge outlet 7. A seal-holder plate 9 is provided on the high-pressure side opposite to the suction port 6 and is connected to a flange 10 of the main body 2 by means of a counter-flange 11 and appropriate coupling means, such as bolts, not depicted in the drawings. The seal-holder wall 9 centrally supports a sealing pack 12 which seals a pressure chamber 13 within which an impeller 14, driven by a motor shaft 15, can rotate. Conveniently, according to the invention, a substantially funnel-shaped reinforcement element is arranged at least partially within the main body 2 and is thicker than said main body. In particular, the reinforcement element, generally indicated by the reference numeral 20, comprises a transverse end portion 21 having at least partially a frusto-conical shape, preferably with a slightly curved cross-section, and a longitudinal end portion 22 having a substantially cylindrical or slightly tapered shape. While the transverse portion 21 is located inside the main body 2, the longitudinal portion 22 protrudes from the main body 2 passing through an axial opening 23 of the end wall thereof which defines a folded edge. Advantageously, the transverse wall 21 is at least partially superimposed and rigidly coupled to the inner surface of the end wall 4, proximate to the peripheral edge 24 of the element 20 to provide a liquid-tight seal. To this end, a bead of high-resistance, and perfectly fused welding, accomplished for example by means of a laser beam applied by transparency through the wall 4, is executed in peripheral portions 25. Additionally, the coupling between the transverse portion 21 of the reinforcement element 20 and the end wall 4 of the body 2 may optionally be ensured by traditional spot-welding 16, though these latter are not absolutely necessary. It is noted that the longitudinal portion 22 of the reinforcement element 20 may be nested simply into the folded edge 23 of the end wall 4 without any welded connections. In practice, the folded edge 23 of the apertured end wall 4 might have a diameter which is even greater than the illustrated one, since the wall 4 extends until it completely covers the welding bead 25 to thereby ensure optimum coupling with the transverse wall 21 of the element 20. Thus, the element 20 defines the transverse wall of the sheet metal casing and is so sized to withstand, without deformation, both the pressure forces exerted by the pumped fluid in an axial direction, and the static and dynamic loads transmitted through the suction port 6. In particular, the latter loads are generated by the external piping, not illustrated in the drawings, which is connected to the suction port 6 through a stamped plate flange 27 which is welded at 28 to the end of the longitudinal portion 22 of the element 20. The transverse portion 21 of the element 20 is connected to the longitudinal portion 22 by means of an intermediate portion 20 including an annular corrugation 31 which forms a sealing ring for the impeller 14. In the examplified embodiment represented in figure 1, the longitudinal portion 22 of the element 20 provides the inlet duct of the suction port 6 and needs no further elements to form the inner wall of the inlet. The embodiment illustrated in figure 2 differs from that of figure 1 essentially insofar as the longitudinal portion 22 of the element 20 has a larger diameter than the suction port 6. The inlet duct of the latter element is formed by a sleeve 40 having a partially frusto-conical shape and is inserted inside the longitudinal portion 22 coaxially thereto. The outer end 41 of the sleeve 40 is welded to the flange 27, whereas the inner end has a more complex geometry, comprising a peripheral edge 42 shaped complementarily to the transverse wall 21 of the element 20 and connected thereto at 43 to provide a liquid-tight seal, also in this case, by laser welding. In the vicinity of its inner end, the sleeve 40 has an annular corrugation 44 which forms a sealing ring 45 for the impeller 14. Advantageously, the longitudinal end portion 22 of the stiffening element forms an annular flange 46 which is frontally welded at 47 to the central portion 48 of the flange 27. Also in this case, hermetical sealing with respect to the pumped fluid is ensured at the welding bead 25 and at the welding bead 43, so that the pressure of the fluid to be pumped is integrally acting upon the transverse wall 21 of the reinforcement element 20 and partially on the strongly stiffened annular corrugation 44 of the sleeve 40. In both cases, the resistance of the transverse wall of the casing, as well as that of the suction inlet, are significantly increased, whereas the outer geometry is not substantially altered to facilitate insertion and removal of cut bolts from the flange 27. From the foregoing it can thus be seen that the invention achieves the proposed aim and objects, and in particular the fact is stressed that it provides the maximum reliability and resistance of the casing while keeping unchanged the advantages of the prior art regarding easiness of installation and use. The pump casing according to the invention is susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept. All the details may furthermore be replaced by other technically equivalent elements: in practice, the materials employed, so long as compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to the requirements. 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: Sheet metal casing (1) with differentiated thickness for centrifugal pump, comprising a substantially cup-shaped main body (2) which is formed by a peripheral wall (3) continuously joined to a transverse end wall (4), means (10) for coupling said main body (2) to a transverse sealing plate (9) opposite to said end wall so as to define a pressure chamber (13) enclosing an impeller (14), a substantially tangential delivery port (7) and a substantially axial suction port (6), said casing further comprising a substantially funnel-shaped reinforcement element (20) having a transverse end portion (21) which is at least partially and substantially frusto-conically shaped, characterized in that said end portion (21) is arranged inside said main body (2), and said reinforcement element comprises a substantially cylindrical longitudinal end portion (22) which protrudes from said body coaxially to said suction port, said transverse end portion (21) of said reinforcement element (20) being at least peripherally superimposed and rigidly sealingly coupled, with the end wall (4) of said main body (2) at the junction with the side wall (3) thereof, to thereby define the transverse wall of the casing adjacent to said suction port in contact with the pumped liquid. Casing according to claim 1, characterized in that said substantially cylindrical longitudinal end portion (22) of said reinforcement element is rigidly connected to a sheet metal flange (27) which defines the coupling flange for said suction port (6). Casing according to claim 1, characterized in that said transverse end portion (21) of said reinforcement element comprises at least one peripheral edge (24) which is uniformly in contact with the end wall (4) of said body (2) at a region thereof proximate to the connection (5) between said end wall (4) and said side wall (3), in this contact region there being provided circumferential laser or the like weldings (25) providing liquid-tight and rigid coupling between said body (2) and said reinforcement element (20). Casing according to claim 3, characterized in that said transverse peripheral portion (21) and said longitudinal portion (22) of said reinforcement element (20) are monolithically connected by an intermediate portion (30) provided with a circumferential corrugation (31) adapted to define a sealing ring for the impeller (14). Casing according to claim 3, characterized in that said longitudinal end portion (22) of said reinforcement element defines the inner wall of said suction port (6). Casing according to claim 1, characterized in that said longitudinal end portion (22) of said reinforcement element encloses a coaxial tubular sleeve (40) which defines the inner wall of said suction inlet. Casing according to claim 6, characterized in that said sleeve (40) has an outer end (41) which is welded to the coupling flange (27) of said suction port (6) and an inner end (44) which is welded to the intermediate portion (30) of said reinforcement element. Casing according to claim 7, characterized in that said inner end (44) of said sleeve is partially corrugated so as to define a sealing ring (45) for said impeller and is rigidly sealingly coupled, to said reinforcement element (20) by means of a circumferential laser or the like welding (42). Casing according to claim 8, characterized in that said sleeve (40) is radially spaced from said cylindrical portion (22) of said reinforcement element (20) and said cylindrical portion has, at its outermost end, a substantially annular radial fold (46) which is welded (47) to said coupling flange.

Inventors: GHIOTTO RENZO, PELIZZARO SILVANO, GHIOTTO, RENZO, PELIZZARO, SILVANO
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1990
Main classification: F04D29
IPC codes: F04D29