The present invention relates to a submersible centrifugal pump.
In particular, the present invention is applied in the sector of extraction of a liquid, usually water, from a well or a tank.
As is known, the pumps currently used generally consist of a cylindrical containment jacket inside which there extends a shaft which can be connected to a motor (normally electric), and at least one stage comprising an impeller and a diffuser. A delivery body and an intake body are located respectively downstream and upstream of the jacket with reference to the direction of the fluid pumped.
The jacket, the delivery body and the intake body have threads on their side surfaces necessary for fixing these components to one another and clamping the hydraulic stages.
A tube is connected to the pump by securely screwing the tube to the delivery body.
In some cases, the delivery body has a non-return valve with the dual purpose of preventing the tube connected to the pump from emptying when the pump is not switched on and of protecting the impellers and the diffusers from possible pressure blowbacks. It is also know that, when pumps operate with a low head, the impellers tend to lift up, carrying the shaft with them. To overcome this disadvantage and, therefore, to prevent the shaft from being subject to excessive axial movements, there are thrust bearing means positioned at the end of the shaft close to the delivery body, so that the resulting forces are discharged mainly on the diffusers.
It is also known from document
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It is also known from document
However, the known submersible centrifugal pumps have significant disadvantages.
Firstly, disadvantageously, the known type of pumps are unable to guarantee suitable internal stiffness due to the screw connection between the jacket and the delivery and intake bodies. With this type of connection adequate clamping of the stages is impossible, and, either the stages can move relative to one another, damaging pump operation, or they are overtightened, with the risk of damaging internal components. Moreover, the threads hydraulic seal and reducing its efficiency.
Secondly, in pumps fitted with a non-return valve, if the valve needs removing (normally during pump installation), the delivery body has to be removed from the containment jacket and this operation is complicated by the fact that subsequent reassembly of the delivery body must be performed in such a way as to guarantee the compactness of the stages and the hydraulic seal again.
Moreover, the shaft thrust bearing means, discharging the forces mainly on the diffusers, may damage the diffusers.
In addition, in the known pumps the tube connected to the delivery body may become unscrewed either during pump use due to the vibrations produced or due to incorrect revolutions by the motor connected to the pump.
Also, for correct pump operation, it is important to maintain the relative position of the various pump components, and in particular the stages, which must not move either longitudinally or transversally, and cannot tolerate relative rotations.
The Applicant has found that several aspects of the pumps of the type described above can be improved, in particular with regard to their stiffness and hydraulic seal.
The aim of the present invention is therefore to propose a pump which can overcome the above-mentioned disadvantages.
In particular the aim of the present invention is to propose a pump which can guarantee optimum compactness of the hydraulic stages and eliminate leaks between the jacket and the intake and delivery bodies.
Another aim of the present invention is to provide a pump which allows the elimination of possible damage to the diffusers caused by the thrust bearing means mounted on the shaft and/or facilitates the removal and refitting of the non-return valve.
These aims and others which are more apparent in the description that follows are achieved by a submersible centrifugal pump with the characteristics described in claim 1 and in the dependent claims.
Further features and the advantages of the present invention are more clearly illustrated in the detailed description which follows of a preferred, non-limiting embodiment of a submersible centrifugal pump according to the present invention.
The description refers to the accompanying drawings, provided by way of example only, without limiting the scope of the inventive concept, in which:
With reference to the accompanying drawings, the numeral 1 denotes as a whole a submersible centrifugal pump according to the present invention. By way of example, the accompanying drawings illustrate a pump with a diameter of approximately 15 cm, or 6 inches.
The pump 1 comprises a containment jacket 2, preferably cylindrical, a shaft 3 with a hexagonal cross-section (usually polygonal so that the various components can be keyed to it) extending inside the containment jacket 2 along a longitudinal axis "X", and which can be connected to a motor, for example an electric motor (not illustrated) .
The pump 1 also comprises a delivery body 4 connected to the containment jacket 2 at its outfeed 2b (with reference to the direction in which the fluid flows) and an intake body 5 which supports a first end 3a of the shaft 3, connected to a jacket 2 infeed 2a.
Inside the jacket 2 close to its outfeed 2b, there is an outfeed sector 6 designed to support a second end 3b of the shaft 3. The sector 6 consists of a tube 7 in contact with the internal walls of the jacket 2 and a domed structure 8 inside the tube 7 to which it is connected by a plurality of tabs 9. The domed structure 8 houses the second end 3b of the shaft 3.
The jacket 2 houses at least one hydraulic stage 10 comprising an impeller 11 keyed to the shaft 3 and a fixed diffuser 12 contained in a supporting tube 13 to which it is attached by tabs 14.
The delivery body 4 is a tubular structure located at the jacket 2 outfeed 2b and is connected to the latter by a circumferential weld. A sleeve 15, which forms a pump 1 outfeed pipe 46 and allows the connection of a threaded tube (not illustrated) to the pump 1, is also present at the top of the delivery body 4 (although in the embodiment illustrated the sleeve 15 is an integral part of the delivery body 4, in other embodiments it may be a separate element). For this reason there is a thread on the inner side surface 16 of the sleeve 15. There is also an opening 17 in the sleeve 15 for a grub screw 17a which prevents the pump 1 from rotating relative to the tube, coming unscrewed and detaching.
Inside the delivery body 4 there is a non-return valve 22 smaller than the outfeed pipe 46 so that it can be inserted in the delivery body 4 through said pipe 46. The non-return valve 22 is then held in position by a supporting element 47 removably attached to the delivery body 4. Moreover, there is preferably a helical spring (not illustrated) acting on the non-return valve to guarantee that it closes with a predetermined force. In the embodiment illustrated (Figures 2 and 3) the supporting element comprises a diffuser 18, having a central hole, which is connected to the delivery body 4 by a plurality of tabs 19 which are connected to a ring nut 20 secured to the delivery body 4 by an elastic stop ring 21 (alternatively, it may be secured by screwing, although this solution is not illustrated). The non-return valve in turn comprises a cylindrical support 23 slidably inserted in the central hole in the diffuser 18, and a closing plate 24 whose centre is fixed to the cylindrical support 23. The plate 24 with the cylindrical support 23 is mobile between an open position, in which the plate 24 is raised and allows the liquid to pass (not illustrated), and a closed position, in which the plate 24 is resting on a projection 25 inside the delivery body 4 (Figures 2 and 3). Said projection 25 is preferably fitted with a seal 26 which, in the valve 22 closed position, is between the projection 25 and the plate 24, guaranteeing the hydraulic seal.
The intake body 5 consists of a tube with, at its first end, a flange 27a needed to connect the pump 1 to a motor and, at its second end, opposite the first, a flange 27b needed to connect the intake body 5 to the jacket 2. The tube also has lateral slits 5a allowing the liquid to enter the pump 1. The intake body 5 is connected to the jacket 2 by clamping means 28 located between the intake body 5 and the jacket 2 which, as well as connecting the two parts, are essential for compressing the hydraulic stages 10 between the intake body 5 and the delivery body 4, thus preventing longitudinal movements by the diffusers 12. Said clamping means 28 comprise at least one screw 29 or one tie rod (not illustrated).
In the embodiment illustrated, there are four screws 29 located around the circumference in a cross shape, having the longitudinal axis "Y" parallel with the axis "X" of the shaft 3. The screws, in particular, are tightened in a ring-shaped structure 30 in turn fixed to the jacket 2. In the embodiment illustrated, (Figure 6), the ring-shaped structure 30 is inserted in the jacket 2 and is held in it by a stop ring 31 inserted in a groove 48 made in the lower end 2a of the jacket 2.
A cup-shaped body 32 covers the lower part of each stage 10, and comprises a tubular structure 33 encompassing the impeller 11 and having an upper edge connected to the diffuser 12, and a ring-shaped surface 34 forming the bottom of the cup-shaped body 32. The ring-shaped surface 34 connects, along its inner edge 49, with the relative impeller 11 to guarantee the hydraulic seal.
The tubular structure 33 guarantees that the hydraulic stages 10 are contained as a pack in the pump 1, whilst the ring-shaped surface 34 prevents the stages 10 from moving transversally and rotating relative to one another. The ring-shaped surface is modelled in such a way that it has on its base three equidistant circular arc protrusions 35 on the same circle, between them delimiting the three seats 36 designed to hold projections 37, 39 on the upstream element (diffuser 12 or closing ring 38). Two hydraulic stages 10 are connected by placing at least one extension 37 of at least one tab 14 in the seats 36 of the next stage. The first stage 10 is connected to the closing ring 38 at the intake body (in particular between the cup-shaped body 32 of the first stage 10 and the flange 27b of the intake body 5) by positioning three of the ring 38 teeth 39 in the seats 36 in the cup-shaped body 32 of the first stage 10.
The outfeed sector 6 also has similar seats 6a delimited by similar protrusions 6b, and designed to receive the extensions 37 of the diffuser 12 of the last stage 10. On the delivery body 4 there is at least one tooth 4a which rests in a seat not illustrated in the accompanying drawings.
Correct positioning of each diffuser 12 relative to the cup-shaped body 32 of the relative hydraulic stage 10 is guaranteed by three small teeth 50 on the inside made in the tubular structure 33 of the cup-shaped body 32 and designed to connect with three recesses 51 made in the diffuser 12 (in particular in the tube 13 which houses it).
The seats 36, 6a, the recesses 51, the extensions 37, the teeth 39, 4a, and the small teeth 50 constitute means designed to prevent the delivery body 4, the outfeed sector 6, the stages 10, the closing ring and the intake body 5 from moving transversally and rotating relative to one another. Tightening the screws 29 brings the intake body 5 and the ring-shaped structure closer together and the latter transfers the action exerted by the screws 29 to the jacket 2 thanks to a shear action applied to the elastic stop ring 31. Moreover, the intake body 5 flange 27b pushes the closing ring 38 against the cup-shaped body 32 (Figure 6) which, by means of its tubular structure 33, transfers the axial action to the relative diffuser, which then transmits it to the subsequent stages as far as the sector 6. In this way, the hydraulic stages 10 are compressed between the intake body 5 and the delivery body 4, eliminating any longitudinal play possible. Finally, thanks to the fact that the extensions 37 and the teeth 39 snap into the seats 36, 6a, immobilisation of the stages in the direction transversal to the axis "X" and prevention of their rotation are also guaranteed.
Advantageously, in the preferred embodiment, the individual parts may be sized in such a way as to guarantee optimum calibrated clamping when the intake body 5 rests against the jacket 2 as illustrated in Figure 6. In this way, the pump can be disassembled and reassembled several times without altering the compactness of the stages 10 which is always kept at the ideal level.
On the first end 3a of the shaft 3 there is a hollow coupling 40 with teeth inside (Figure 7) designed to allow connection of the motor shaft (not illustrated) and the pump 1 shaft 3. Around the coupling 40 there is a thrust bearing washer 41 (advantageously made of anti-friction material) and a support 42 for the washer, both held in place by a metal stop ring 43. These thrust bearing means are inactive and separated from the intake body 5 when the pump 1 operates with a high head (Figure 7), whilst they rest on the intake body 5 when the pump 1 head is low and the shaft 3 with the impellers 11 is raised. In this way, the thrust bearing means prevent excessive axial movements by both the shaft 3 and the impellers 11. The water infeed is at the intake body 5 and is protected by a filter 44 consisting of a cylindrical surface encompassing the side of the intake body and which has many holes in it. Finally, on the outer surface of the delivery body 4, of the jacket 6 and of the intake body 5 there extends a closed channel 45 which houses the motor power cables.
Figures 4 and 5 illustrate an exploded view of several details of an alternative embodiment of the pump 1 with the presence of a single hydraulic stage 10. The delivery body 4, the outfeed sector 6, the diffuser 12, the impeller 11, the cup-shaped structure 32, the ring 38 and the intake body 5 are all visible.
Assembly of the pump 1 involves firstly connection of the delivery body 4 to the jacket 2 by welding. Then, all of the internal parts are assembled on the intake body 5 and all inserted together in the jacket 2. At this point the intake body 5 is removed and the ring-shaped structure 30 and relative elastic stop ring 31 are inserted in the jacket. Then the intake body 5 is fitted again and the first end 3a of the shaft 3, with the coupling 40, is inserted in the body 5. Then the screws 29 are positioned and the entire structure is closed, clamping and compressing the hydraulic stages 10. Finally, the thrust bearing washer 41 and the relative ring-shaped support 42 are placed on the coupling 40 and secured with the elastic ring 43.
The pump 1 is connected to the tube by screwing together a threaded end of the tube with the sleeve 15 and locking the connection with the grub screw 17a positioned in the opening 17.
The non-return valve 22 can be removed by simply removing the supporting element 47, unscrewing the ring nut 20 and taking out the valve 22.
The present invention achieves the preset aims and brings important advantages.
Firstly, the advantages of a pump configured in this way are basically linked to the compactness guaranteed by tightening the four screws which push the intake body 5 against the hydraulic stages, holding them firmly against the delivery body 4. This eliminates the diffuser 12 play, preventing possible faulty operations and vibrations. Moreover, where necessary, the clamping can be given a predetermined optimum intensity.
In the embodiment illustrated, special means prevent unwanted relative transversal movements and relative rotations by the pump 1 components, giving the pump 1 a high level of stiffness.
In addition, the absence of threads on the jacket prevents liquid leaks, avoiding deterioration of pump operation. Moreover, since the delivery body 4 is welded on the pump 1, the connection between the tube and the pump 1 is simply guaranteed by the sleeve 15 thread and the grub screw 17a: this guarantees more simple assembly and does not have a negative affect on the delivery body 4 seal. Another advantage is the simple extraction of the non-return valve 22, which can even be removed by unskilled personnel.
Finally, a significant advantage is provided thanks to the absence of threads on the delivery body 4, on the jacket 2 and on the intake body 5, threads which in conventional pumps reduce the internal working cross-section of the pump and therefore give the pump greater hydraulic losses and less structural stiffness.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.