Case, particularly for centrifugal radial pumps, and method for manufacturing thereof

Abstract: A case (1) for single- or multi-stage pumps having at least one centrifugal radial impeller, and a method for the manufacture of such case with metal plate. The case includes, for each stage and for each impeller, a substantially cylindrical lateral wall (2) and a device (15) for diffusing and directing the flow delivered from the impeller of each stage, which case has, in the lateral wall thereof, at least one volute with a uniformly increasing transverse cross section which is outwardly closed and is formed by an initial portion (17), an intermediate portion (18) and a final portion (19) which are mutually blended in a continuous manner. The initial and intermediate portions extend circumferentially to collect and diffuse the radial flow to the delivery port (4) of the impeller, whereas the end of the final portion is axially offset with respect to the initial and intermediate portions and is directed inwardly of the case to convey the flow toward a central region of the pressure chamber adjacent to the impeller.

Description: The present invention relates to a case, according to the preamble of claim 1 and as known from GB-A612664, particularly for single- or multi-stage pumps with centrifugal radial impeller, which comprises, for each stage and for each impeller, a device for diffusing and directing the flow delivered by the impeller. The invention furthermore relates to a method for the manufacture of said case with metal plate. Italian patent Application no. 85605 A/89 filed on June 7, 1989 in the name of the same Applicant discloses a centrifugal pump incorporating an ejector, which ejector comprises a directing device with at least one approximately radial channel having an annular outlet section which extends peripherally to the diffusion duct of the ejector. By means of said directing device, the flow delivered from the impeller is directed toward a central portion of the case adjacent to the outer wall of the diffusion duct, at such a distance from the discharge outlet to promote separation of the air and its conveyance toward the delivery port. Though said known pump has the above described advantages, in a preferred embodiment it entails the use of a diffuser which, as is known, has the function of converting the kinetic energy imparted to the fluid by the impeller into pressure energy with the best possible efficiency. As is known, diffusers are elements designed to operate in optimum operating conditions beyond which efficiency is lowered considerably. It should be furthermore added that said elements have a relatively complex bladed structure requiring accurate design and rather onerous conventional machining which severely affects the overall cost of the pump. From GB-A-612664 is known a centrifugal multi-stage pump with a case formed by a plurality of identical stator bodies having thick walls with volutes and radial passages formed therein. This case construction is rather heavy and bulky due to thickness of its walls and is furthermore relatively complicate and expensive. The inner surface of volutes and passages are conventionally cast or machined with a relatively high friction factor and lower efficiency. The aim of the present invention is indeed to eliminate the disadvantages described above by providing a stator case with high efficiency and modest cost. Within the scope of the above described aim, a particular object of the present invention is to provide a case incorporating a pressure diffusing and directing device which avoids the use of a conventional bladed diffuser. A further object of the present invention is to provide a method for the manufacture of the above described case by means of short manufacturing times and completely automatic steps. Not least object of the invention is to provide a high-quality product at an economically competitive cost using simplified equipment and commonly commercially available materials. This aim, these objects and others which will become apparent hereinafter are achieved by a stator case in accordance with the enclosed claim 1. In a second aspect of the invention there is provided a method for the manufacture of a stator case in accordance with the enclosed claim 9. Further characteristics and advantages of the invention will become apparent from the description of two preferred but not exclusive embodiments of the stator case according to the invention and of the related method for their manufacture, illustrated only by way of non-limitative example in the accompanying drawings, wherein: figure 1 is a partially sectional side view, taken along an axial plane, of a first embodiment of a stator case according to the invention, inserted in a single-stage centrifugal pump with built-in ejector; figure 2 is a sectional front view of the pump of figure 1, taken along the plane II-II; figure 3 is an external side view of the stator case of figures 1 and 2; figure 4 is a partially sectional side view, taken along an axial plane, of a second embodiment of a stator case according to the invention, inserted in a multi-stage centrifugal pump; figure 5 is an external side view of the stator case of figure 4; figure 6 is a sectional view of an apparatus for the manufacture of the outer casing of the stator case according to the invention starting from a semiworked item made of metal plate. With reference to the above figures, the case according to the invention, generally indicated by the reference numeral 1, is part of a centrifugal pump incorporating an ejector, generally indicated by the reference letter P. The case 1 comprises an approximately cylindrical lateral wall 2 with an axial suction port 3 and a radial delivery port 4. Inside the case there is an impeller 5 keyed on a shaft 7 driven by an electric motor 6. In the pressure chamber 8 of the case 2 there is located an ejector, generally indicated by the reference numeral 9, which comprises a leading nozzle 10, an ejecting chamber 11 connected to the suction port 3 and a diffusion duct 12 connected to the inflow section 13 of the impeller. According to a main aspect of the invention, there is provided a device for directing the delivery flow generated by the impeller 5, which is generally indicated by the reference numeral 15. In particular, the flow directing device is comprising at least one, preferably a plurality of volute formations, generally indicated by the reference numeral 16, which are arranged peripherally of the impeller 5 and extend along the entire circumferential delivery path thereof. In the illustrated embodiment there are provided three mutually independent volutes 16 each having an axis with approximately the shape of a logarithmic spiral and an increasing transverse cross section along the extension thereof. For the sake of clarity, each volute 16 is defining an initial portion 17, an intermediate portion and a final portion 19 which are uniformly blended with each other. In particular, the initial portion 17 and the intermediate portion 18 are aligned along a circular path, and have axes arranged on a perpendicular plane perpendicular to the symmetry axis of the case and approximately coincident with the main plane of the impeller 5. The purpose of said portions 17 and 18 is to collect and diffuse the flow delivered by the peripheral region of the impeller. The final portion 19 is initially aligned with the first two portions 17 and 18 and subsequently has an axial offset s with respect thereto, so as to produce a loop with a curved section 20 and with a oppositely-curved section 21. The value of the axial offset s is approximately equal to the total axial width h of the impeller 5 for reasons which will be exposed hereinafter. The end of the portion 19 is closed by a wall 19′ which is essentially perpendicular to the lateral wall 2 of the case and has the purpose of directing the flow toward the inside of the case in an approximately radial inward direction. For descriptive completeness, inside the stator case 1 there is located an element with a plurality of through passages, which element is formed by a pair of transverse elements 23, 23a substantially parallel to the peripheral portion ring of the impeller and define therebetween an annular space, and by pairs of walls 24, which extend inside of said annular space, transversely to the walls 23, 23a to define a plurality of approximately spiral-shaped directing passages 22 directed toward the axis of the impeller. Said passages 22 merge into a common annular outflow section 25 which extends peripherally to the diffusion duct 12 of the ejector 9. As can be seen in figure 2, the external shape of the case 2 comprises the portions 20 and 21 mutually axially offset by the extent s with an end directed toward the inner region 8 of the case, which region is at a lower pressure and is adjacent to the suction ejector 9. In the stator case embodiment schematically illustrated in figures 4 and 5, the same reference numerals of the preceding figures have been used for the similar components, but said numerals have been referenced by one or more apexed marks. In this second embodiment, which can be expressely used for multi-stage centrifugal pumps, in each stage the outlet section 4' is connected to the suction section 3' of the subsequent stage, with the interposition of a diffusion and re-directing device 15'. In this embodiment, unlike the preceding one, the final portions 19' of the volutes 16' have an axial offset toward the region of the pump where the pressure rises, i.e. in the direction of the suction section of the subsequent stage. Also in this case, the offset s' of the final portions 19' of the volutes 16' is such that the end of each terminal portion 19' is arranged at the side of the initial portion 17' of the subsequent volute. In a further embodiment of the present invention which is not illustrated in the drawings and is suitable for a multi-stage pump with one or more pair of opposite impellers mounted on the same axis, the diffusing and directing device comprises a plurality of suitably shaped and dimensioned volutes falling within the scope of the same general inventive concept. According to a further aspect of the invention, a process is provided for the manufacture of the stator case according to the invention with metal plate, preferably strainless steel or other similar material. The process comprises a first step of blanking a metal plate disk and then of drawing of the blanked disk so as to obtain a hollow partly-finished item 27 with a substantially cylindrical lateral wall 28 which is open at one end, has an outer annular flange 29 and is closed at the opposite end by a substantially planar back wall 10. In the subsequent step, the partly-finished item 27 is stamped so as to assume the external configuration of the finished casing. Figure 6 schematically illustrates an apparatus for the stamping of the above described unfinished item, generally indicated by the reference numeral 28. The partly-finished item 27 is inserted into a cavity 32 of the fixture 33 formed by the segments 33, 34 and 35 which have an approximately cylindrical shape and can be mutually coaxially coupled. The inner walls of the end segment 33 and of the intermediate segment 34 define in negative the overall shape of the casing, whereas the end segment 35 defines the closure element of the fixture and has an annular step suitable for sealingly engaging the annular flange 29 of the party-finished item 27. The segments 33, 34 and 35 are aligned and mutually connected by strong bolts 36 or by other similar securing elements. For descriptive completeness, it is noted that one or more vent holes 40 are provided in the walls of the die 31 to connect its inner cavity 32 with the open atmosphere, in order to allow the free expansion of the partially-finished item inside said cavity. In the central region of the end segment 35 there is a tube 37 connected to inlet and outlet ducts, not illustrated in the figure, with the interposition of a throttle valve schematically indicated at 38. The inlet and outlet ducts can be connected to a central unit for supply pressurized oil or another equivalent technical incompressible fluid in order to introduce and extract the working liquid and exert thereon very high hydrostatic pressures of up to 2000 atmospheres (approximately 201 Mpa). The force exerted by the pressurized liquid on the inner surfaces of the partly-finished item 27 forces them to deform plastically against the inner walls of the cavity 32 until they assume the final external configuration of the finished case. The step of forming the semi-finished item 27 then provides the insertion of the item 31 into the cavity 32 of the fixture 31, the closure of the fixture by means of the bolts 36 so as to provide the tight sealing of the inner wall of the item 27, the insertion of the working liquid into the die from the inner side of the semiworked item 27 as described above, the removal of the liquid from the expanded item, the opening of the die and the extraction of the formed part. The part formed in the fixture 30 can subsequently be drilled and surface-finished so as to obtain the finished pump casing. From the foregoing it can be seen that the process for manufacturing the case according to the invention achieves the cost requirements. In particular, the use of a series of dies with automated opening and closing devices, associated with mechanized systems for automatically feeding and discharging the working liquid and for the automatic insertion and removal of the parts into and from the fixture, can achieve automatized manufacture of large series of items with considerably low production costs. The case as well as the manufacturing method according to the invention are susceptible to numerous modifications and variations, all of which are within the scope of the inventive concept defined in the accompanying claims; all the details may furthermore be replaced with technically equivalent elements. In practice, the materials employed, so long as compatible with the specified use, as well as the dimensions and shapes, may be any according to the requirements and to the state of the art. 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 30 element identified by way of example by such reference signs.

Claims: Stator case, particularly for single- and multi-stage pumps with at least one centrifugal radial impeller, comprising a substantially cylindrical lateral wall (2) and a device (15) for diffusing and directing the delivered flow at the outlet of each stage, said device comprising at least one volute formation (16) which is formed in said lateral wall (2) and has a uniformly increasing transverse cross section, which volute formation is outwardly closed and has an initial portion (17), an intermediate portion (18) and a final portion (19) which are mutually uniformly blended, said initial and intermediate portions (17, 18) extending in an essentially circumferential direction contained in a main plane of the impeller to collect and diffuse the flow delivered thereby, said final portion (19) having an axial offset (s) with respect to both said initial portion (17) and said intermediate portion (18), and being directed toward the inside of said case so as to convey the flow toward a central region of said case adjacent to the impeller (5), characterized in that said at least one volute formation (16) is located in said lateral wall (2) peripherally of at least one substantially spiral-shaped passage (22) which is enclosed by a pair of walls (24) extending inside an annular space formed between a pair of axially spaced disk-like elements (23, 23a) substantially parallel to the peripheral portion of the impeller (5). Stator case according to claim 1, characterized in that said lateral wall (2) is a monolitic item made of metal plate so shaped to define said at least one volute formation (16), and extending from said final portion (19) of each volute formation (16) up to a common annular outflow section (25) located around the axis of the impeller (5). Stator case according to claim 2, characterized in that the final portion (19) of said volute formation (16) has a closure end wall (19') extending substantially perpendicularly to the lateral wall (2) of the case to direct the flow toward a corresponding substantially spiral-shaped passage aligned therewith. Stator case according to claim 1, characterized in that said axial offset (s) of the final portion (19) of said volute (16) is approximately equal to the overall width of said impeller along the axis thereof. Stator case according to claim 1, characterized in that said diffusing and directing device comprises at least two, preferably three, successive and independent volute formations (16) disposed along the entire circumpherential extension of said lateral wall (2). Stator case according to claim 5, characterized in that the final portion (19) of each volute formation (16) comprises a first curved section (20) and a second oppositely curved section (21) which sections define altogether a zigzag path determining said axial offset (s), the end (19) of said second oppositely curved section being arranged side-by-side to the initial portion (17) of the subsequent volute formation (16). Stator case according to claim 1, characterized in that it comprises a single stage with a multiple volute diffusing and directing device (16) formed in said lateral wall (2), wherein the final portions (19) of said volutes (16) are partially located on the suction side of the impeller and said spiral-shaped passages are directed toward the inflow section of the impeller so as to recirculate the flow to a central portion of said case upstream of the impeller. Stator case according to claim 1, characterized in that it comprises a plurality of hydraulically series connected packed stages, wherein the delivery section (4') of each stage is connected to the suction section (3') of the successive stage with the interposition of said diffusion and directing device (15'), the terminal portions of said volute formations (16') being directed axially toward the successive section (3') of the subsequent stage. Method for the manufacture of a stator case of metal plate according to one or more of the preceding claims, comprising the steps of: a) blanking of a circular disk of metal plate; b) drawing of the blanket disk so as to obtain a concave semi-finished item (27) with a substantially cylindrical lateral wall (28) which is open at one end and is closed to the opposite end by a substantially planar transverse back surface (30); c) final forming of the semi-finished item (27) to simultaneously obtain formation of the lateral walls and of the diffusing and directing device in semi-finished conditions; d) execution of the necessary holes and passages; e) surface finishing of the case; characterized in that said final forming step (c) is obtained by placing the semi-finished item (27) inside a hollow openable die (31) which has an open end and internal walls reproducing the outer shape of the finished case, by closing the open end of said die to firmly retain said semi-finished item (27), introducing a pressurized liquid into said die from the inner side of said semi-finished item (27) to expand it against the inner walls of said die, and in that it further comprises the step (f) of forming pairs of substantially spiral-shaped metal plate walls (24) and transverse disk-like elements (23, 23a) suitable to be coupled to provide passages directed toward the center of the case in alignement with said diffusing and directing device. Method according to claim 9, characterized in that said semi-finished item (27) is so shaped to have, at the open end thereof, an annular flange (29) which defines a retention surface suitable to be engages by the inner walls of said die upon closure of the open end thereof. Method according to claim 10, characterized in that said die (31) comprises at least one first end portion (33, 34) which defines the lateral surface of the finished item, and a second end portion which defines a removable back wall which is suitable for coupling longitudinally to said first end portion, said back wall (35) having an engagement surface adapted to cooperate with said annular flange (29) of said semi-finished item (27) to close and retain it during pressuration of the working liquid. Method according to claim 10, characterized in that said openable die (31) is closed by removable securing means (36).

Inventors: CAODURO BRUNO, CAODURO, BRUNO
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1990
Main classification: F04D29
IPC codes: B21D26, F04D29, F04D9, F04D1