SUBMERGIBLE MULTISTAGE PUMP

Abstract

 The invention relates to a submergible multistage pump (1) comprising a drive unit (2) having an electric motor (10) and a drive shaft (12), wherein the drive shaft (12) extends in the axial direction, and a hydraulic unit (3) connected to the drive unit (2) and comprising a leading pressure stage, a trailing pressure stage and a top element (19) connected in series, wherein the top element (19) comprises an outlet (5) of the multistage pump (1). The leading pressure stage of the hydraulic unit (3) comprises an axial inlet (29) and an axial outlet (30), a circumferential housing (21), a circumferential internal diffuser (22), and an impeller (20) connected to the drive shaft (12) of the drive unit (2), wherein the housing (21), the diffuser (22) and the impeller (20) of the leading pressure stage define a flow path from the axial inlet (29) to the axial outlet (30), and wherein the diffuser (22) is connected to the housing (21). The pump is characterized in that the leading pressure stage comprises radial play between the housing (21) and the diffuser (22) in the radial direction, and abutment between the housing (21) and the diffuser (22) in the axial direction.

Description

Technical field of the Invention

[0001] The present invention relates generally to the field of pumps configured to pump liquid comprising solid/abrasive matter. Further, the present invention relates specifically to the field of submergible pumps such as dewatering pumps and drainage pumps especially configured for pumping liquid comprising solid matter, such as sand and stone material. The pumped liquid is for instance drilling water in mining/tunneling applications, surface water on construction sites, etc. i.e. transport and dewatering applications. The present invention relates specifically to a submergible multistage pump suitable for said applications, wherein the pump comprises a plurality of pressure stages connected in series. The inventive pump may be entirely wet installed or partly dry installed, and is of submergible type in both installations.

[0002] The present invention relates to a submergible multistage pump comprising a drive unit having an electric motor and a drive shaft, wherein the drive shaft extends in the axial direction, and a hydraulic unit connected to the drive unit and comprising a leading pressure stage, a trailing pressure stage and a top element connected in series, wherein the top element comprises an outlet of the multistage pump. The leading pressure stage of the hydraulic unit comprises an axial inlet, an axial outlet, a circumferential housing, a circumferential internal diffuser, and an impeller connected to the drive shaft of the drive unit, wherein the housing, the diffuser and the impeller of the leading pressure stage define a flow path from the axial inlet to the axial outlet, and wherein the diffuser is connected to the housing.

Background of the Invention

[0003] In mines, tunneling, quarries, on construction sites, and the like applications, there is almost always a need to remove unwanted water in order to secure a dry enough environment at the working site. In mining/tunneling/quarries applications a lot of drilling water is used when preparing for charging before blasting, and water is also used to prevent dust spreading after the blasting, and if the production water is not removed at least the location of the blast and the lower parts of the mine will become flooded. Surface water and groundwater will also add up to accumulation of unwanted water to be removed. It is customary to use drainage/dewatering pumps to lift the water out of the mine to a settling basin located above ground, and the water is lifted stepwise from the lower parts of the mine to different basins/pits located at different depths of the mine. Each step/lift may for instance be in the range 25-50 meters in the vertical direction, and the length of the outlet conduit, i.e. the transport distance, in each step/lift may for instance be in the range 100-300 meters. In mining applications, a considerable amount of sand and stone material is suspended in the water, in some applications as much as 10%. Thus, there are several applications wherein the pumped media is very abrasive and comprises sand, stones, etc. and thereto applications wherein high head/pressure are required.

[0004] Between the stationary diffusor and the rotating impeller there are gaps at which a back flow of liquid will be generated from the downstream side to the upstream side due to pressure differences, i.e. generally speaking higher pressure on the downstream side of the impeller then on the upstream side of the impeller leading to a back flow in the upstream direction. Thereto, like the pumped media/liquid discharged from the pump also the back flow of liquid carries solid/abrasive matter/particles that are suspended in the media, and the abrasive particles will act as grinders on the surfaces of said gaps, and the greater back flow the more wear on the gap and thereby greater backflow and decreased capacity/efficiency of the pump. Thus, back flow creates losses and the smaller gap the smaller back flow and thereby less wear and decreased losses over time.

[0005] However, a multistage pump having a plurality of pressure stages there are long tolerance chains in the construction. According to prior art, the location of the impeller side of the gap, i.e. the location of the impellers, are defined by the position of the drive shaft that is journalled in the housing of the drive unit, and the location of the stationary side of the gap, i.e. the location of the diffusers, are defined by the housing of the hydraulic unit that is connected to the housing of the drive unit. Thus, there are many components between the impeller side of the gap and the stationary side of the gap, i.e. a long tolerance chain, and in order to be able to have a small gap the tolerance range of each dimension/surface of each component has to be decreased/tight resulting in an accelerating increase of manufacturing/machining cost when having a long chain of tolerances.

[0006] A known way to try to provide small gaps is to have a lining of resilient material at the stationary parts, whereby some contact is allowed between the rotating part and the stationary part without entailing wear and risk for damages to the components. However, when/if the lining is lost there will be a huge decrease in capacity/efficiency of the multistage pump. The lining is not as resistive to wear as metal, and the abrasive matter will inevitably provide wear to the lining.

[0007] Generally the site manager, i.e. the process at the working site, requires a constant low liquid level and therefor the drainage pump is in constant operation even though there is only little water/liquid available in the cavity/basins. The water can be constituted by ground water leakage, rain water, and especially process water from drilling, reducing dust, etc. If the water is not removed the production will be negatively affected, which cannot be accepted. Thus, the water is pumped/transported by means of dewatering/drainage pumps. To be on the safe side, in many applications, the drainage pumps are in constant operation, irrespective of water being pumped or not. If the stationary parts and the rotating impeller comes in contact with each other at the gap when no media is pumped or present in the gap, the components are more susceptible for damage/wear. Due to the long tolerance chains and the risk of damage, the gaps of the prior art pumps are wider then optimal considered from a back flow point of view.

[0008] Thus, there is a need to be able to obtain smaller and/or more wear resistant gaps between the stationary parts and the rotating impellers of a submergible multistage pump without being forced to conduct labor-intensive and expensive manufacturing/machining of the components of the submergible multistage pump.

Object of the Invention

[0009] The present invention aims at obviating the aforementioned disadvantages and failings of previously known submergible multistage pumps, and at providing an improved submergible multistage pump. A primary object of the present invention is to provide an improved multistage pump of the initially defined type that comprises a construction that makes it possible to have small gaps between the stationary parts and the rotating impellers of the multistage pump without needing to conduct labor-intensive and expensive manufacturing/machining of the components of the multistage pump.

[0010] It is another object of the present invention to provide an improved multistage pump that is more wear resistant due to decreased back flow at said gaps and thereby longer service interval may be applied. It is another object of the present invention to provide an improved multistage pump that has less decrease in capacity/efficiency over time and thereby longer service interval may be applied. It is another object of the present invention to provide an improved multistage pump that entails that fewer and smaller abrasive particles are passing through the gaps and thereby reduced wear from the back flow of pumped media and thereby longer service interval may be applied. It is another object of the present invention to provide an improved multistage pump that is easier to assemble/mount.

Summary of the Invention

[0011] According to the invention at least the primary object is attained by means of the initially defined submergible multistage pump having the features defined in the independent claim. Preferred embodiments of the present invention are further defined in the dependent claims.

[0012] According to the present invention, the leading pressure stage comprises radial play between the housing and the diffuser in the radial direction, and abutment between the housing and the diffuser in the axial direction.

[0013] Thus, the present invention is based on the insight that by not having the diffuser fixedly connected/bolted to the housing of the hydraulic unit but floating in the radial direction during mounting thanks to the radial play in the radial direction, the location of the diffuser is instead determined directly by the location of the impeller, i.e. the location of the stationary side of the gap is directly dependent on the location of the impeller side of the gap. During mounting the gap may be checked/secured using a thickness gauge, tape, etc. The tolerance chain is made minimal resulting in a possibility to have a small gap without needing to conduct labor-intensive and expensive manufacturing/machining, and thereby less back flow and less wear thereby longer service interval may be applied.

[0014] According to various embodiments of the present invention, the hydraulic unit comprises at least one intermediate pressure stage arranged between and connected in series with the leading pressure stage and the trailing pressure stage, wherein the at least one intermediate pressure stage is configured as the leading pressure stage. Thus, the more pressure stages the greater head will be generated, but the assemblage/mounting of pressure stages of the multistage pump will still be made easy and the small gaps can be secured in each pressure stage thanks to the radial play between the diffuser and the housing in each pressure stage during mounting.

[0015] According to various embodiments of the present invention, each diffuser comprises an upper diffuser element and a lower diffuser element, said upper diffuser element and said lower diffuser element being connected to each other and jointly displaceable in the radial direction in relation to the housing during assembly of the pump. The lower diffuser element is configured to direct the pumped media from the impeller outwards towards the housing, and the upper diffuser element is configured to direct the pumped media from the housing inwards towards the axial outlet of the pressure stage, i.e. towards the axial inlet of the subsequent pressure stage or of the top element.

[0016] According to various embodiments of the present invention, each pressure stage comprises an upper face seal at the interface between the impeller and the diffuser adjacent the axial outlet of the pressure stage. Thereby, increased resistance to wear at the upper gap may be realized without effecting/changing the material of the impeller and/or diffusor.

[0017] According to various embodiments of the present invention, each pressure stage comprises a lower face seal at the interface between the impeller and the diffuser adjacent the axial inlet of the pressure stage. Thereby, increased resistance to wear at the lower gap may be realized without effecting/changing the material of the impeller and/or diffusor.

[0018] According to various embodiments of the present invention, the radial gap width of the upper face seal is equal to or less than the radial gap width of the lower face seal. Thereby, in a situation of deflection of the drive shaft, the upper face seal will experience contact before the lower face seal. The upper face seal is easier to exchange than the lower face seal if damaged.

[0019] Further advantages with and features of the invention will be apparent from the other dependent claims as well as from the following detailed description of preferred embodiments.

Brief description of the drawings

[0020] A more complete understanding of the abovementioned and other features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments in conjunction with the appended drawings, wherein:

Fig 1

is a schematic perspective view from above of an inventive submergible multistage pump comprising three pressure stages,

Fig. 2

is a schematic cross-sectional side view of the multistage pump according to figure 1, disclosing the hydraulic unit and part of the drive unit,

Fig. 3

is a schematic perspective view from above of an impeller of the submergible multistage pump,

Fig. 4

is a schematic perspective view from below of the impeller according to figure 3,

Fig. 5

is a schematic cross-sectional view of the impeller according to figures 3 and 4 together with the diffuser of the multistage pump.

Fig. 6

is a schematic cross-sectional side view of a hydraulic unit of an inventive submergible multistage pump comprising two pressure stages, and

Fig. 7

is a schematic exploded perspective view from above of the hydraulic unit according to figure 6.

Detailed description of preferred embodiments of the invention

[0021] The present invention relates specifically to the field of submergible pumps especially configured for pumping liquid comprising abrasive/solid matter, such as water comprising sand and stone material. The submergible pumps are especially drainage/dewatering pumps. The present invention relates specifically to a submergible multistage pump configured for drainage/dewatering applications.

[0022] Reference is initially made to figures 1 and 2, disclosing an inventive submergible multistage pump, generally designated 1. The submergible multistage pump will hereinbelow also be referred to as pump. Figure 1 disclose a schematic perspective view from above of the pump 1 and figure 2 disclose a schematic illustration of a cross-sectional side view of parts of the pump 1 according to figure 1. The general structural elements of a pump 1 will be described with reference to figures 1 and 2, wherein the pump 1 comprises two major parts, i.e. a drive unit, generally designated 2, and a hydraulic unit, generally designated 3.

[0023] The hydraulic unit 3 of the pump 1 comprises an inlet 4, an outlet 5 and a pump chamber 6 located intermediate said inlet 4 and said outlet 5, i.e. the pump chamber 6 is located downstream the inlet 4 and upstream the outlet 5. In figure 1 the inlet 4 is an axial inlet and the outlet 5 is a radial outlet. In some applications, the outlet 5 of the hydraulic unit 3 also constitutes the outlet of the pump 1 (as disclosed in figures 1 and 2) and in other applications the outlet 5 of the hydraulic unit 3 is connected to a separate outlet of the pump 1, e.g. via a cooling jacket volume. The outlet of the pump 1 is configured to be connected to an outlet conduit (not shown).

[0024] Figure 2 disclose a hydraulic unit 3 of a multistage pump 1 and portions of the drive unit 2. According to the embodiments illustrated in figures 1 and 2, the drive unit 2 is located separated from the hydraulic unit 3 by an inlet volume 7. The inlet volume 7 is delimited by an inlet strainer 8. According to the disclosed embodiment the drive unit 2 is located on the upstream side of the inlet 4 (and the inlet volume 7) of the hydraulic unit 3. The inlet strainer 8 comprises perforations or holes, wherein the inlet strainer 8 is configured to prevent larger objects from reaching the inlet 4 of the hydraulic unit 3.

[0025] According to alternative embodiments, the pump 1 the drive unit 2 is located on the downstream side of the inlet 4 of the hydraulic unit 3, wherein the pump 1 comprises an intermediate wall structure separating the hydraulic unit 3 from the drive unit 2 in a liquid tight manner. The intermediate wall structure may comprise a liquid seal chamber or the like sealing arrangement between the pump chamber 6 of the hydraulic unit 3 and a motor compartment 9 of the drive unit 2. Such pumps 1 still comprise an inlet strainer 8 and an inlet volume 7.

[0026] The drive unit 2 of the pump 1 comprises an electric motor, generally designated 10, arranged in the motor compartment 9 delimited by a liquid tight pump housing 11, The drive unit 2 also comprises a drive shaft 12 extending from the electric motor 10 to the pump chamber 6. In the disclosed embodiment the drive shaft 12 extends from the drive unit 2 through the inlet volume 7 to the hydraulic unit 3. The electric motor 10 comprises a stator 13 and a rotor 14, wherein the drive shaft 12 is connected to the rotor 14 of the electric motor 10 in conventional way.

[0027] According to various embodiments, the pump 1, more precisely the electric motor 10, is operatively connected to a control unit 15, such as an Intelligent Drive comprising a Variable Frequency Drive (VFD). Thus, said pump 1 is configured to be operated at a variable operational speed [rpm], by means of said control unit 15. According to various embodiments, the control unit is located inside the liquid tight pump housing 11, e.g. in an electronics chamber 16 of the drive unit 2, i.e. it is preferred that the control unit 15 is integrated into the pump 1. The electronics/connection chamber 16, is separated from the motor compartment 9 in a liquid tight manner. The control unit 15 is configured to control the operational speed of the pump 1. According to alternative embodiments the control unit is an external control unit, or the control unit is divided into an external sub-unit and an internal sub-unit. The operational speed of the pump 1 is more precisely the rpm of the electric motor 10 and correspond/relate to a control unit output frequency. The control unit 15 is configured and capable of operating the pump 1 in a normal direction of rotation, i.e. forward, in order to pump liquid, and in an opposite direction of rotation, i.e. backwards, in order to clean or unblock the pump chamber 6.

[0028] The electric motor 10 is powered via at least one electric power cable 17 extending from a power supply, and the pump 1 comprises a liquid tight lead-through 18 receiving each electric power cable 17.

[0029] The components of the pump 1 are usually cold down by means of the liquid/water surrounding the pump 1, i.e. when the pump 1 is in a submerged configuration/application. In dry installed applications/configurations the pump 1 comprises dedicated cooling systems. Both configurations comprise a submergible pump 1, i.e. the pump 1 is designed and configured to be able to operate in a submerged configuration/position, i.e. during operation be located entirely under the liquid surface. However, it shall be realized that the submersible pump 1 during operation must not be entirely located under the liquid surface but may continuously or occasionally be fully or partly located above the liquid surface.

[0030] A multistage pump 1 comprises a plurality of pressure stages connected in series with each other, wherein the embodiment disclosed in figures 1 and 2 the pump 1 comprises three pressure stages. The hydraulic unit 3 also comprises a top element 19 comprising the outlet 5 of the hydraulic unit 3 and of the pump 1, wherein the top element 19 is connected in series with the pressure stages. Thus, the outlet of an upstream pressure stage is connected to the inlet of a downstream pressure stage, and the outlet of the last pressure stage is connected to the inlet of the top element 19. According to the disclosed embodiment all inlets of the pressure stages are configured as axial inlets and all outlets of the pressure stages are configured as axial outlets. The outlet 5 of the pump 1 is configured as an axial outlet in the disclosed embodiment, but it shall be realized that the outlet 5 may be configured as a radial outlet in the top element 19.

[0031] Each pressure stage comprises an impeller 20 connected to the drive shaft 12, wherein the impeller 20 is driven in rotation during operation of the pump 1 whereby liquid is sucked into the inlet 4 and pumped out through the outlet 5 by means of the rotating impeller 20 when the pump 1 is active. The impeller 20 is a channel impeller having so-called closed channels. The impeller 20 is concentric to the drive shaft 12.

[0032] Each pressure stage also comprises a circumferential housing 21 and a circumferential internal diffuser 22, wherein the housing 21, the diffuser 22 and the impeller 20 define a flow path from the inlet to the outlet of the pressure stage. The diffuser 22 is connected to the housing 21, wherein the diffuser 22 and the housing 21 are stationary. The pump housing 11, the housing 21, the diffuser 22, the impeller 20, and other essential components, are preferably made of metal, such as aluminum and steel.

[0033] The present invention is based on a new and improved multistage pump 1, that is configured to be used for pumping abrasive media, for instance water comprising sand and stones.

[0034] Between the stationary diffusor 22 and the rotating impeller 20 there are gaps at which a back flow of liquid will be generated from the downstream side to the upstream side due to pressure differences, i.e. generally speaking higher pressure on the downstream side of the impeller 20 then on the upstream side of the impeller 20 leading to a back flow in the upstream direction. Thereto, like the pumped media/liquid discharged from the pump 1 also the back flow carries solid/abrasive matter/particles that are suspended in the media, and the abrasive particles will act as grinders on the surfaces of the gap, and the greater back flow the more wear on the gap and thereby greater back flow and decreased capacity/efficiency of the pump. Thus, back flow creates losses and the smaller gap the smaller back flow and thereby less wear and decreased losses over time.

[0035] Conventionally, in order to be able to have a small gap the tolerance range of each dimension/surface of each component has to be decreased/tight resulting in an accelerating increase of manufacturing/machining cost. Thus, the gaps of the prior art pumps are wider then optimal considered from a back flow point of view, thereby leading to increased wear and service/replacement more often.

[0036] Reference is now made to figures 3-5 disclosing one embodiment of the impeller 20 of the submergible multistage pump 1.

[0037] The impeller 20 comprises a hub 23, an upper cover disc/plate 24 connected to the centrally located hub 23, a lower cover disc/plate 25 and at least one vane 26 extending between and connecting the upper cover disc 24 and the lower cover disc 25. The impeller 20 preferably comprises a plurality of vanes/blades 26 that are equidistantly located around the hub 23. The vane/vanes 26 are preferably spirally swept from an inner leading edge to an outer trailing edge, i.e. in the direction from the hub 23 towards the periphery of the impeller 20, in a direction opposite the direction of rotation of the impeller 20 during normal (liquid pumping) operation of the pump 1.

[0038] Each blade 26 comprises a leading edge 27 adjacent the hub 23 and a trailing edge 28 at the periphery of the impeller 20, wherein two adjacent blades 26 together defines a channel extending from the leading edges 27 to the trailing edges 28. During operation, the leading edges 27 grabs hold of the liquid, the channels accelerate the liquid and the liquid leaves the impeller 20 at the trailing edges 28. Thereafter the liquid is guided by the diffusers 22 and housing 21 towards the outlet. Thus, the liquid is sucked into the impeller 20 and pressed out of the impeller 20. Said channels are also delimited by the upper cover plate 24 and the lower cover plate 25 of the impeller 20. The diameter of the impeller 20 and the shape and configuration of the channels/vanes determines the pressure build up in the liquid and the pumped flow.

[0039] Reference is now also made to figures 6 and 7 disclosing the hydraulic unit 3 of an inventive multistage pump 1 comprising two pressure stages. The hydraulic unit 3 of the inventive multistage pump 1 comprises a leading pressure stage and a trailing pressure stage, wherein the leading pressure stage is the most upstream pressure stage and wherein the trailing pressure stage is the most downstream pressure stage, seen in the flow direction.

[0040] The leading pressure stage of the hydraulic unit 3 comprises an axial inlet 29 and an axial outlet 30. The inlet 29 and the outlet 30 are located around the drive shaft 12 in a concentric manner. According to various embodiments, the inlet 29 of the leading pressure stage is also the inlet 4 of the hydraulic unit 3.

[0041] According to the invention, the leading pressure stage comprises radial play between the housing 21 and the diffuser 22 in the radial direction, and abutment between the housing 21 and the diffuser 22 in the axial direction. Thereby the diffuser 22 is displaceable in the radial direction during mounting/assembly in relation to the housing 21 by having the location of the diffuser 22 adjusted to the location of the impeller 20 by controlling the interface between the impeller 20 and the diffuser 22 adjacent the axial outlet 30 of the leading pressure stage. This adjustment can be made with a tape, a thickness gauge, etc. When the hydraulic unit 3 is fixed, i.e. the top unit 19 is clamped to the housing 21 of the leading pressure stage, using a set of bolts 31, the diffuser 22 is clamped in the axial direction and thereby fixated also in the radial direction. The radial play between the diffuser 22 and the housing 21, i.e. non abutment in the radial direction, is present also when the hydraulic unit 3 is clamped. When the hydraulic unit 3 is clamped the diffuser 22 is concentric to the drive shaft 12 even though the housing 21 might have a small axial misalignment with the drive shaft 12. Thanks to the invention the radial width of the gap between the impeller 20 and the diffuser 22 at the interface adjacent the axial outlet 30 of the leading pressure stage can be made much smaller/tighter than previous solutions.

[0042] According to various embodiments the leading pressure stage comprises an upper face seal at the interface between the impeller 20 and the diffuser 22 adjacent the axial outlet 30 of the leading pressure stage. Such upper face seal comprises an upper seal member 32 connected to at least one of the hub 23 and the upper cover disc 24 of the impeller 20, and an upper seal member 33 of the diffuser 22. The upper seal member 32 of the impeller 20 co-rotates with the impeller and the upper seal member 33 of the diffuser 22 is stationary.

[0043] Thus, the upper face seal has an axially extending gap between an outer diameter of the upper seal member 32 of the impeller 20 and an inner diameter of the upper seal member 33 of the diffuser 22. The upper seal member 32 of the impeller 20 is located in a circumferential upper seat 34 having an envelope surface. The upper seal member 33 of the diffuser 22 is preferably in press fit engagement with the diffuser 22, in order to avoid use of glue/adhesive. The upper seal member/ring 33 of the diffuser 22 is subject to compressive force/strain.

[0044] The upper seal member 32 of the impeller 20 and the upper seal member 33 of the diffuser 22 are made of material that is less affected by wear than the impeller 20 and the diffuser 22. The upper seal member 32 of the impeller 20 and the upper seal member 33 of the diffuser 22 preferably comprises or is made of cemented carbide or the like.

[0045] The inventor has identified that the upper seal member 32 of the impeller 20 shall not be exposed to elevated tensile force, due to the risk of breaking/bursting, and thereby must not be in press fit engagement with the upper seat 34 of the impeller 20. Thus, the inner diameter of the upper seal member 32 is larger than the diameter of the envelope surface of the upper seat 34.

[0046] In order to promote co-rotation of the upper seal member 32 with the impeller 20 and in order to prevent back-flow, the impeller 20 according to various embodiments comprises a resilient member 35 that is located between and separates the upper seal member 32 and the upper seat 34 in the radial direction. The resilient member 35 between the upper seal member 32 and the upper seat 34 is preferably constituted by a rubber O-ring. Thereto, the resilient member 34 works as a damper, i.e. entailing that the upper seal member 32 may be slightly displaced in the radial direction should it be exposed to external force in the radial direction, i.e. due to contact between the upper seal member 32 of the impeller 20 and the upper seal member 33 of the diffusor 22.

[0047] According to various embodiments, the impeller 20 of all pressure stages comprises a lower face seal at the interface between the impeller 20 and the diffuser 22 adjacent the axial inlet of the pressure stage. Such lower face seal comprises a lower seal member 36 connected to the lower cover disc 25, and a lower seal member 37 connected to the diffuser 22. The lower seal member 36 of the impeller 20 co-rotates with the impeller and the lower seal member 37 of the diffuser 22 is stationary.

[0048] Thus, the lower face seal has an axially extending gap between an outer diameter of the lower seal member 36 of the impeller 20 and an inner diameter of the lower seal member 37 of the diffuser 22. The lower seal member 36 of the impeller 20 is located in a circumferential lower seat 38 having an envelope surface. The lower seal member 37 of the diffuser 22 is preferably in press fit engagement with the diffuser 22, in order to avoid use of glue/adhesive. The lower seal member/ring 37 of the diffuser 22 is subject to compressive force/strain.

[0049] The lower seal member 34 of the impeller 20 and the lower seal member 37 of the diffuser 22 are made of material that is less affected by wear than the impeller 20 and the diffuser 22. The lower seal member 34 of the impeller 20 and the lower seal member 37 of the diffuser 22 preferably comprises or is made of cemented carbide or the like.

[0050] The inventor has identified that the lower seal member 36 of the impeller 20 shall not be exposed to elevated tensile force, due to the risk of breaking/bursting during mounting and during operation, and thereby must not be in press fit engagement with the lower seat 38 of the lower cover disc 25. Thus, the inner diameter of the lower seal member 36 of the impeller 20 is greater than the diameter of the envelope surface of the lower seat 38 of the impeller 20. In order to secure that the lower seal member 36 co-rotate with the impeller 20, the impeller 20 comprises a retainer ring 39 that is in press fit connection with the envelope surface of the lower seat 38 of the impeller 20, wherein the retainer ring 39 is configured to retain/clamp the lower seal member 36 in the lower seat 38 of the lower cover disc 25. The retainer ring 39 is made of material that is able to withstand greater tensile forces than the lower seal member 36. The retainer ring 39 is preferably made of duplex stainless steel or the like. Thereto the envelope surface of the lower seat 38 of the lower cover disc 25 may have different diameters for the lower seal member 36 and the retainer ring 39. According to various embodiments there is mechanical engagement, i.e. pin or the like, between the retainer ring 39 and the lower seal member 36 in order to secure co-rotation of the lower seal member 36 and the impeller 20.

[0051] According to various embodiments, the outer diameter of the retainer ring 39 is smaller than the outer diameter of the lower seal member 36. Thereby, it is easier to mount/insert the impeller 20 into the lower seal member 37 of the diffuser 22, thanks to the smaller outer diameter of the retainer ring 39.

[0052] According to various embodiments, a resilient member 40 is located between and separates the lower seal member 36 and the lower seat 38 in the radial direction. The resilient member 40 is preferably constituted by a rubber O-ring. Thereby the lower seal member 36 is centred in relation to the lower seat 38 and thereby in relation to the drive shaft 12. According to various embodiments, the retainer ring 39 abuts the resilient member 40, and the lower seal member 36. Thus, the retainer ring 39 clamps the lower seal member 36 in the axial direction in order to have the lower seal member 36 co-rotate with the impeller 20. The resilient member 40 also promotes co-rotation of the lower seal member 36 and the impeller 20. Thereto, the resilient member 40 works as a damper, i.e. entailing that the lower seal member 36 may be slightly displaced in the radial direction should it be exposed to external force in the radial direction, i.e. due to contact between the lower seal member 36 of the impeller 20 and the lower seal member 37 of the diffusor 22.

[0053] According to various embodiments, the outer diameter of the lower seal member 36 of the impeller 20 is greater than the outer diameter of the upper seal member 32 of the impeller 20. Thereto, the radial gap width of the upper face seal is equal to or less than the radial gap width of the lower face seal, thereby in case of drive shaft 12 deflection the upper face seal will contact before the lower face seal which is preferred since the mutual surface velocity is lower at the upper face seal than at the lower face seal. According to various embodiments, the radial gap width of the upper face seal is equal to or more than 0,05 mm and equal to or less than 0,25 mm, preferably 0,15 mm, and the radial gap width of the lower face seal is equal to or more than 0,1 mm and equal to or less than 0,3 mm, preferably 0,2 mm.

[0054] According to various embodiments, the trailing pressure stage of the hydraulic unit 3 is configured as the leading pressure stage, i.e. comprises the same type of lower face seal and the same type of upper face seal and having an axial inlet and an axial outlet. As disclosed in the various figures.

[0055] Alternatively, the trailing pressure stage does not comprise the upper face seal but instead the diffuser 22 of the trailing pressure stage comprises a stationary cap covering the upper end of the drive shaft 12 and impeller 20, wherein the stationary cap is connected to the diffuser 22 when the location of the diffuser 22 is fixed by clamping the top unit 19 to the housing 21 of the leading pressure stage. IT shall be pointed out that the stationary cap may also be used when the trailing pressure stage comprises an upper face seal. One advantage of having such a stationary cap is that the elevated return pressure from the liquid in the outlet conduit does not act against the drive shaft 12 and thereby the bearing arrangement of the drive shaft 12 is under less stress. Thereto, according to various embodiments (not disclosed) the trailing pressure stage together with the top element 19 comprise a radial outlet.

[0056] According to various embodiments, the hydraulic unit 3 comprises at least one intermediate pressure stage arranged between and connected in series with the leading pressure stage and the trailing pressure stage, wherein the at least one intermediate pressure stage is configured as the leading pressure stage, i.e. comprises the same type of lower face seal and the same type of upper face seal and having an axial inlet and an axial outlet. As disclosed in figure 2.

[0057] When the hydraulic unit 3 comprises two or three pressure stages and the drive unit 2 is located on the upstream side of the inlet 4 of the hydraulic unit3, the drive shaft 12 is journalled in the drive unit 2 and comprises a free end connected to the impeller 20 of the trailing pressure stage. According to various embodiments, then the hydraulic unit 3 comprises four or more pressure stages the drive shaft 12 is journalled also at the upper end in the hydraulic unit 3.

[0058] According to various embodiments, each diffuser 22 comprises an upper diffuser element 41 and a lower diffuser element 42, said upper diffuser element 41 and said lower diffuser element 42 being connected to each other and jointly displaceable in the radial direction in relation to the housing 21 during assembly/mounting of the pump 1. Thus, the location of the lower diffuser element 42 in the radial direction in relation to the housing 21 is determined by the location of the upper diffuser element 41 in the radial direction in relation to the impeller 20 and drive shaft 12. When the hydraulic unit 3 is clamped, the diffuser 22 is concentric to the drive shaft 12.

[0059] According to various embodiments, the lower diffuser element 42 comprises at least one circumferential ridge 43 on the side facing the lower cover disc 25 of the impeller 20, wherein the radial distance between said ridge 43 and the lower seal member 37 of the diffuser 22 is equal to or more than 1/3 and equal to or less than 2/3 of the radial distance between the outer edge of the lower cover disc 25 of the impeller 20 and the lower seal member 37 of the diffuser 22. The circumferential ridge 43 has the purpose to prevent solid matter from reaching the lower face seal. If the abrasive matter is halted at a distance more than 1/3 of the radial distance between the outer edge of the lower cover disc 25 of the impeller 20 and the lower seal member 37 of the diffuser 22, the abrasive matter will follow the surface flow closest to the lower cover disc 25 of the impeller 20 outwards. However, if the abrasive matter is halted at a distance less than 1/3 of the radial distance between the outer edge of the lower cover disc 25 of the impeller 20 and the lower seal member 37 of the diffuser 22, the surface flow is too weak to bring the abrasive matter outwards and the abrasive matter will start grinding holes in the lower diffuser element 42. Thus, if the abrasive matter passes the location of the 1/3 of the distance, it is better to let the abrasive matter reach the lower face seal and be grinded therein and removed through the axial gap.

[0060] According to various embodiments, the hub 23 of the impeller 20 of one pressure stage abuts the hub 23 of the impeller 20 of the adjacent pressure stage. Since all gaps between the impeller 20 and the diffuser 22 are axial, there is no need to have axial trimming of the location of each impeller 20 but the overall configuration/design admit some axial displacement between the drive shaft 12 and impellers 20 in relation to the top element 19 and diffusers 22. Thus, there is axial play between the impeller 20 and the diffuser 22. Thereto the hub 23 of the downstream impeller 20 also retain the upper seal member 32 of the upstream impeller 20 in the upper seat 34.

[0061] Reference is now specially made to figures 6-7 in order to describe the mounting/assembly of the hydraulic unit 3.

[0062] Starting with the leading pressure stage. The housing 21 of the leading pressure stage is connected to the housing 11 of the drive unit 2 such that the housing 21 is as concentric as possible to the drive shaft 12. Then the upper end of the drive shaft 12 is located well above the leading pressure stage. Thereafter the lower diffuser element 42 is inserted into the housing 21 and abuts a seat in the axial direction. The lower diffuser element 42 and/or the housing 21 may comprise means to prevent mutual rotation. Thereafter the impeller 20 is slipped on to the drive shaft 12 and the retainer ring 39 and the lower seal member 36 are inserted into the lower seal member 37. The impeller 20 abuts a radially extending collar 44 or the like on the drive shaft 12. Thereafter the upper diffuser element 41 is lowered over the impeller 20 until the upper seal member 33 of the diffuser 22 is located around the upper seal member 32 of the impeller 20. At the same time the upper diffuser element 41 engage the lower diffuser element 42. The lower diffuser element 42 and/or the upper diffuser element 41 may comprise means to prevent mutual rotation. The lower diffuser element 42 and the upper diffuser element 41 comprise means to prevent mutual displacement in the radial direction. The radial gap width of the upper face seal is adjusted by means of thickness gauge, tape, etc. in order to have concentricity between the drive shaft 12 and the diffuser 22. The drive shaft 12 and impeller 20 is preferably rotated to ensure that there is non-contact between the impeller 20 and diffuser 22. Since the upper diffuser element 41 and the lower diffuser element 42 act as one element, the lower face seal is adjusted at the same time as the upper face seal is adjusted even though the lower face seal is not visible for the operator.

[0063] Any intermediate pressure stage and the trailing pressure stage. The housing 21 of the downstream pressure stage is connected to the housing 21 of the upstream pressure stage, i.e. fixated/guided in the radial direction, and at the same time the housing of the downstream pressure stage abuts the upper diffuser element 41 of the upstream pressure stage. There is still a small gap in the axial direction between the housing 21 of the downstream pressure stage and the housing 21 of the upstream pressure stage. Thereafter the lower diffuser element 42, the impeller 20 and the upper diffuser element 41 are added in the same way as disclosed above. The lower diffuser element 42 of the downstream pressure stage abuts the upper diffuser element 41 of the upstream pressure stage. The hub 23 of the downstream impeller 20 abuts the hub 23 of the upstream impeller 20. The housing 21 of the downstream pressure stage and/or the housing 21 of the upstream pressure stage may comprise means to prevent mutual rotation. The radial gap width of the upper face seal of each pressure stage is adjusted by means of thickness gauge, tape, etc. in order to have concentricity between the drive shaft 12 and the diffuser 22.

[0064] Now all upper face seals and lower face seals of each pressure stage are adjusted/trimmed.

[0065] Thereafter the top element 19 is connected to the housing 21 of the trailing pressure stage, i.e. fixated/guided in the radial direction, and at the same time the top element 19 abuts the upper diffuser element 41 of the trailing pressure stage. There is still a small gap in the axial direction between the top element 19 and the housing 21 of the trailing pressure stage.

[0066] An end member 45 is connected to the free upper end of the drive shaft 12 to secure the impellers 20 to the drive shaft 20. The end member 45 may be added before or after the top element 19.

[0067] Finally the bolts 31 are inserted and tightened whereby the small gaps in the axial direction between the housings 21 and the top element 19 are removed and at the same time the diffuser element 22 are securely clamped/fixated.

Feasible modifications of the Invention

[0068] The invention is not limited only to the embodiments described above and shown in the drawings, which primarily have an illustrative and exemplifying purpose. This patent application is intended to cover all adjustments and variants of the preferred embodiments described herein, thus the present invention is defined by the wording of the appended claims and thus, the equipment may be modified in all kinds of ways within the scope of the appended claims.

[0069] It shall also be pointed out that all information about/concerning terms such as above, under, upper, lower, etc., shall be interpreted/read having the equipment oriented according to the figures, having the drawings oriented such that the references can be properly read. Thus, such terms only indicate mutual relations in the shown embodiments, which relations may be changed if the inventive equipment is provided with another structure/design.

[0070] It shall also be pointed out that even thus it is not explicitly stated that features from a specific embodiment may be combined with features from another embodiment, the combination shall be considered obvious, if the combination is possible.

Claims

1. Submergible multistage pump (1) comprising:

- a drive unit (2) having an electric motor (10) and a drive shaft (12), wherein the drive shaft (12) extends in the axial direction, and

- a hydraulic unit (3) connected to the drive unit (2) and comprising a leading pressure stage, a trailing pressure stage and a top element (19) connected in series, wherein the top element (19) comprises an outlet (5) of the multistage pump (1),

the leading pressure stage of the hydraulic unit (3) comprising:

- an axial inlet (29) and an axial outlet (30),

- a circumferential housing (21),

- a circumferential internal diffuser (22), and

- an impeller (20) connected to the drive shaft (12) of the drive unit (2),

wherein the housing (21), the diffuser (22) and the impeller (20) of the leading pressure stage define a flow path from the axial inlet (29) to the axial outlet (30), and wherein the diffuser (22) is connected to the housing (21),

characterized in that

the leading pressure stage comprises radial play between the housing (21) and the diffuser (22) in the radial direction, and abutment between the housing (21) and the diffuser (22) in the axial direction.

2. The submergible multistage pump (1) according to claim 1, wherein the leading pressure stage comprises an upper face seal at the interface between the impeller (20) and the diffuser (22) adjacent the axial outlet (30) of the leading pressure stage.

3. The submergible multistage pump (1) according to claim 1 or 2, wherein the trailing pressure stage of the hydraulic unit (3) is configured as the leading pressure stage.

4. The submergible multistage pump (1) according to any preceding claim, wherein the hydraulic unit comprises at least one intermediate pressure stage arranged between and connected in series with the leading pressure stage and the trailing pressure stage, wherein the at least one intermediate pressure stage is configured as the leading pressure stage.

5. The submergible multistage pump (1) according to any preceding claim, wherein each diffuser (22) comprises an upper diffuser element (41) and a lower diffuser element (42), said upper diffuser element (41) and said lower diffuser element (42) being connected to each other and jointly displaceable in the radial direction in relation to the housing (21) during assembly of the pump (1).

6. The submergible multistage pump (1) according to any preceding claim, wherein each pressure stage comprises an upper face seal at the interface between the impeller (20) and the diffuser (22) adjacent the axial outlet of the pressure stage.

7. The submergible multistage pump (1) according to any preceding claim, wherein each pressure stage comprises a lower face seal at the interface between the impeller (20) and the diffuser (22) adjacent the axial inlet of the pressure stage.

8. The submergible multistage pump (1) according to any preceding claim, wherein each impeller (20) comprises a hub (23), an upper cover disc (24) connected to the hub (23), a lower cover disc (25) and at least one vane (30) extending between and connecting the upper cover disc (24) and the lower cover disc (25).

9. The submergible multistage pump (1) according to claim 8, wherein each impeller (20) comprises an upper seal member (32) connected to at least one of the hub (23) and the upper cover disc (24).

10. The submergible multistage pump (1) according to claim 9, wherein a rubber O-ring (35) is located between and separates the upper seal member (32) of the impeller (20) and the impeller (20) in the radial direction.

11. The submergible multistage pump (1) according to any of claims 8-10, wherein each impeller (20) comprises a lower seal member (36) connected to the lower cover disc (25).

12. The submergible multistage pump (1) according to claim 11, wherein a rubber O-ring (40) is located between and separates the lower seal member (36) of the impeller (20) and the impeller (20) in the radial direction.

13. The submergible multistage pump (1) according to claim 11 or 12, wherein the outer diameter of the upper seal member (32) of the impeller (20) is less than the outer diameter of the lower seal member (36) of the impeller (20).

14. The submergible multistage pump (1) according to claims 6 and 7, wherein the radial gap width of the upper face seal is equal to or less than the radial gap width of the lower face seal.

15. The submergible multistage pump (1) according to any preceding claim, wherein the drive unit (2) is located upstream the hydraulic unit (3), wherein the drive shaft (12) extends from the electric motor (10) into the axial inlet (29) of the leading pressure stage.

16. The submergible multistage pump (1) according to any preceding claim, wherein the drive shaft (12) is journalled in the drive unit (2) and comprises a free end connected to the impeller (20) of the trailing pressure stage.

Drawing