CENTRIFUGAL PUMP

Abstract: A centrifugal pump comprising a cylindrical body (10) which contains a plurality of stages, the pump being obtained from the combination of the cylindrical body (10) formed by a segment of metal pipe, of diffusers (15) and impellers (16) obtained by blanking, stamping and welding metal plate, and of heads (12) obtained by precision casting.

Description: CENTRIFUGAL PUMP Technical Field The present invention relates to a centrifugal pump, particularly of the multistage type. Background Art Centrifugal pumps, particularly multistage ones, are constituted by a cylindrical body with two heads, i.e., an intake head and a delivery head. The cylindrical body contains a plurality of stages constituted by an impeller and a diffuser which contains the impeller; the diffuser is rigidly coupled to the cylindrical body and the impeller is rigidly coupled to a motorized central shaft. For these pumps, particularly for those with several stages, the diffuser and the impeller are obtained by blanking and drawing or stamping stainless steel plate, and the individual parts are joined by welding. This manufacturing technology allows to contain costs, but causes several problems linked, in particular, to the low thickness of the metal plate that is used, which does not allow threading or other machining for the coupling of a plurality of stages. For these reasons, the stages, after being inserted in the cylindrical body, are packed by means of tension elements which connect the two heads and the packing load is adjusted by means of torque wrenches during tightening. The packing load is designed to correctly position the diffusers so that they assume an exact position with respect to the corresponding impellers and is also designed to prevent the diffusers from being turned by the flow of water generated by the impellers or, more simply, from moving and causing noise in the pump. In practice, the tightening of the traction elements determines the geometry of the pump, and this is a severe problem for obtaining a standardized and uniform product. For an equal packing load, i.e., for an equal traction element tightening load, there is in fact no assurance that the geometric position assumed by the diffusers is always the same, since the process tolerances linked to the blanking and drawing of the metal plate can be a decisive factor. A solution to this problem might be to provide the diffusers of the various stages by precision casting complemented by machining, but this would entail, particularly for mass-produced pumps, excessively high costs which would render the product unmarketable. Disclosure of the Invention The aim of the present invention is to provide a pump in which the components used for the cylindrical body, the, diffusers and the heads, as well as for the impellers, have a low cost without penalizing the quality of the pump. A consequent primary object of the invention is to reduce to a minimum the components manufactured with expensive technologies such as precision casting. Another object is to provide a pump in which the geometry of the arrangement of the internal elements, and particularly of the diffusers, is not linked to the tension of traction elements or stud bolts. Another object is to provide a pump in which it is possible to disassemble and reassemble the internal pack of stages without losing the correct assembly geometry. Another object is to provide a pump which has a low cost both for small production runs and for large ones. This aim and these and other objects which will become better apparent hereinafter are achieved by a centrifugal pump, comprising a cylindrical body which contains a plurality of stages with diffusers which are rigidly coupled to said cylindrical body and impellers which are rigidly coupled to a motorized shaft, and an intake head which is arranged opposite a delivery head, characterized in that the said cylindrical body is formed by means of a segment of metal pipe, said diffusers and impellers are obtained by blanking and stamping metal plate, and said heads are obtained by precision casting, coupling occurring by means of inserts which act between said cylindrical body and at least one of the heads and are arranged in blind holes in the heads and in through holes in the cylindrical body, said inserts being retained in seats by screws which pass through the inserts and engage the heads. Brief description of the drawings Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred embodiment, given by way of non-limitative example and illustrated in the accompanying drawings, wherein: Figure 1 is a general view of a pump according to the invention in the assembled condition; Figure 2 is a view of the pump of Figure 1, disassembled into its components; Figure 3 is a sectional view of the delivery head and of part of the pump body; Figure 4 is a sectional view of the means for connecting the delivery head to the cylindrical containment body. Ways of carrying out the Invention With reference to the figures, the pump according to the invention is composed of a cylindrical body 10, preferably obtained by means of a segment of stainless steel pipe, which is associated with two heads, respectively an intake head 11 and a delivery head 12, obtained by precision casting of stainless steel. In the pump shown in the figures, the intake head 11 is associated with the cylindrical body 10 by means of a weld 13, while the delivery head 12 is associated with the cylindrical body 10 by means of insert devices, generally designated by the reference numeral 14 in Figure 1, which are described in detail hereinafter. As shown more clearly in Figure 3, the various stages of the pump are accommodated inside the cylindrical body 10; each stage is constituted by a diffuser 15 being rigidly coupled to the cylindrical body 10 and by an impeller 16 being rigidly coupled to a motorized shaft 17 arranged axially inside the body 10. The delivery head 12, obtained as mentioned by precision casting, is composed of two parts 12a and 12b which are mutually coupled by screwing the part 12a onto the part 12b by using a threaded region 17. By inserting the head 12 in the cylindrical body 10 to the intended depth, the part 12a, which is provided with a bearing 18, also acts as a guiding and centering element for the end 19 of the shaft 17. In the part 12a of the head 12 there are conveyance ducts 20 which convey the water into a conveyance chamber 21 being directly connected to the delivery port 22, on which a duct, not shown, is subsequently screwed. A check valve is contained in the conveyance chamber 21 and is constituted by a flow control element 23 having a cylindrical portion 24 which allows guided axial sliding within the chamber 21. The flow control element 23 forms a seal on an O-ring 25 which is accommodated in an annular groove 26 provided in the part 12a of the head 12. Coupling between the head 12 and the cylindrical body 10 occurs by means of the insert devices 14, which are constituted by a cylindrical insert 27 being accommodated in a blind hole 28 formed in the part 12b of the head 12 and in a through hole 29 provided in the cylindrical body 10 in an exactly corresponding region. The insert 27, as shown more clearly in Figure 4, has a central hole 30 whose diameter is larger than the diameter of the shank of a screw 31 which screws into a threaded hole 32 provided in the head 12. The hole 30 is internally threaded so that it is possible to insert therein, after extracting the screw 31, a threaded body which by continuing the screwing action acts as an extractor for the insert 27. In order to provide the coupling between the head 12 and the cylindrical body 10, the head is pushed so as to cause the correct packing of all the diffusers of the various stages and determine their exact positioning when the hole 29 provided in the cylindrical body 10 is perfectly aligned with the hole 28 provided in the head 12, so that the insert 27 can be inserted and locked with the screw 31. This coupling device is particularly advantageous, since correct positioning is no longer determined by the force applied between the head 12 and the cylindrical body 10 but by the alignment of the holes in which the insert is inserted. All problems linked to assembly are thus eliminated, both in the case of first assembly and in the case of reassemblies after disassembling the pump. The advantages of the introduced improvements are considerable. The pump is mostly produced by means of blanking and stamping processes which are particularly advantageous. These processes, which per se do not provide extremely high precision, cause no problems because machining tolerances are compensated by the method for coupling the head to the cylindrical body. It should also be noted that the structure of the head, provided in two parts which are screwed together, allows to contain the water hammer so that the transient mechanical stresses that it produces do not propagate in a possibly destructive manner to the underlying hydraulic stages. From the description and illustrations it is evident that the aim and all the intended objects have been achieved, providing a pump which is simple and inexpensive from the point of view of manufacture but has considerable mechanical and hydraulic characteristics. The disclosures in Italian Patent Application No. PD2000A000039 from which this application claims priority are incorporated herein by reference.

Claims: CLAIMS 1. A centrifugal pump, comprising a cylindrical body which contains a plurality of stages with diffusers which are rigidly coupled to said cylindrical body and impellers which are rigidly coupled to a motorized shaft, and an intake head which is arranged opposite a delivery head, characterized in that said cylindrical body is formed by means of a segment of metal pipe, said diffusers and impellers are obtained by blanking, stamping and welding metal plate, and said heads are obtained by precision casting, coupling occurring by means of inserts which act between said cylindrical body and at least one of the heads and are arranged in blind holes in the heads and in through holes in the cylindrical body, said inserts being retained in seats by screws which pass through the inserts and engage the heads. 2. The centrifugal pump according to claim 1, characterized in that said said metal plate of which said diffusers and said impellers are formed is a stainless steel plate. 3. The centrifugal pump according to claim 1, characterized in that said intake and delivery heads are provided by precision casting, using stainless steel, with subsequent finishing machining. 4. The pump according to claim 1, characterized in that at least said delivery head is locked on said cylindrical body by the action of inserts which pass through gauged holes provided in a wall of said cylindrical body at blind holes which have the same cross-section and are provided in said delivery head, the insertion of said inserts occurring when said delivery head is pushed toward the intake head in order to obtain the alignment of the holes formed in the cylindrical body and in the heads with the simultaneous packing of the diffusers of the individual stages. 5. The pump according to claim 4, characterized in that said inserts are kept in position by a screw which passes through a hole provided in the insert and engages a threaded hole provided in the head. 6. The pump according to claim 5, characterized in that the through hole provided in the insert has a larger diameter than the shank of the screw, with which it does not interact, said hole in the insert having an internal thread. 7. The pump according to claim 5, characterized in that, in order to disassemble the head, a screw is inserted in said threaded hole of the insert, the screwing of said screw causing the extraction of the insert from the blind hole of the head in which it is accommodated. 8. The pump according to claim 1, characterized in that a conveyance chamber for the pumped fluid is provided in said delivery head and is connected to the diffuser of the last stage of the pump. 9. The pump according to claim 8, characterized in that said conveyance chamber contains a check valve, having a flow control element which forms a seal in an annular seat provided in said head by finishing after precision casting, said seat containing an O-ring. 10. The pump according to claim 9, characterized in that said flow control element of the check valve is provided by blanking and stamping metal plate. ]1. The pump according to claim 9, characterized in that said flow control element is shaped like a dome which comprises a cylindrical portion which can slide axially and is guided by protrusions being provided in an internal part of said conveyance chamber.

Inventors: RIGON FLAVIO, RIGON, FLAVIO
Applicants: RIGON FLAVIO, VERTICAL S R L, RIGON, FLAVIO, VERTICAL S.R.L.
Application year: 2001
Main classification: F04D
IPC codes: F04D1, F04D29