EP3268616B1 - Self-priming pump - Google Patents

Description

The invention relates to a self-priming pump according to the preamble of claim 1.

Self-priming pumps are known in the art and have been used successfully in the process industry for many years. Process industry means in particular beverage technology, food technology, pharmacy and biochemistry.

Such pumps are designed, for example, as self-priming centrifugal pumps. A first chamber and a second chamber, in each of which an impeller is arranged, can be provided between the inlet and outlet of such a centrifugal pump. Each impeller is part of a pumping stage, with the pumping stage closer to the inlet generating the self-priming property.

A first self-priming centrifugal pump of this type is in the EP 1 191 228 A2 suggested. Another self-priming centrifugal pump is in the DE 10 2007 032 228 A1 shown.

In addition to the centrifugal pump stage, these two centrifugal pumps have a liquid ring pump stage that takes the fluid to be pumped directly from the inlet of the centrifugal pump. With the aid of the liquid ring pump stage, a negative pressure can be generated which sucks in fluid from the line connected to the inlet.

A return line connects the overpressure area of the centrifugal pump stage with the inlet of the liquid ring pump stage. This ensures a reservoir of liquid that is necessary when starting up the centrifugal pump to generate the liquid ring.

The impeller of the centrifugal pump stage is connected to the impeller of the liquid ring pump stage via a shaft section which penetrates an opening in a housing wall. In both cases, the shaft section is designed to be cylindrical up to its shaft end facing the impeller of the centrifugal pump.

Out DE 199 18 286 A1 a centrifugal pump is known, in the housing of which at least one centrifugal pump impeller is arranged, a first impeller is preceded by an auxiliary rotor that rotates together with it, the auxiliary rotor equipped with screw blades being arranged in a housing section for the inflow of the fluid to be pumped and the screw blades being part of a hub of the primary rotor are. The hub of the auxiliary rotor can be provided with a double or multiple flat, with the aid of which a tool can be used to introduce a torque into the auxiliary rotor.

Other self-priming pumps are known from EP 2 894 342 A1 and WO 2015/104137 A1 .

An important parameter of such self-priming centrifugal pumps is the NPSH value. NPSH stands for "Net Positive Suction Head" and is often equated with the term "holding pressure height". This parameter specifies the excess pressure of the fluid to be pumped at the inlet of the pump above the vapor pressure of this fluid in order to avoid cavitation inside the pump. This pressure increase must be generated in the process plant. Therefore, the aim is to have a pump that has the lowest possible NPSH value.

It is therefore the object of the invention to present a self-priming pump with an improved holding pressure level.

This object is achieved by a pump with the features of the first claim. The dependent claims 2 to 10 indicate advantageous developments of this invention.

The self-priming pump has a housing with an inlet and an outlet. A first impeller has a first pumping section which is arranged in a first chamber. A second impeller carries a second pumping section which is arranged in a second chamber. A shaft section is provided between the pump sections, which shaft section comprises a shaft end and penetrates an opening in a housing wall. The flow of the fluid to be pumped, in particular a liquid with gas components, along the shaft section is improved in that the shaft section between a constriction and the shaft end is tapered from the shaft end to the constriction and the first impeller and shaft section form one between the constriction and the first pump section have a smooth course.

A smooth course in the sense of this text is a surface shape of shaft section and impeller, in which steps, kinks, shoulders and similar structures are designed and their number reduced as much as possible so that eddies in the fluid flowing past are kept to a minimum or in an area that is no longer detectable , are reduced.

This design of the pump improves the flow conditions between the pump sections. Due to the tapering of the shaft section, the Reduced flow resistance at the narrow point. The enlarged cross section reduces the flow velocity in the area of the shaft section, which reduces the static pressure loss. The smooth course reduces the risk of turbulence. Both of these work together to lower the risk of cavitation occurring, so that a lower pressure increase is necessary. The NPSH value of the pump is thus improved compared to the prior art. The advantages achieved outweigh the disadvantage with regard to the stability of the second impeller, which results from the constriction and which initially discourages the idea of constricting the shaft.

The flow course between the shaft sections is improved if the thinnest point of the shaft section is arranged in the second chamber.

According to a further development, it is proposed to arrange the thinnest point of the shaft section in the opening. This results in a large passage cross section for fluid, so that a large amount of fluid can flow between the pump stages with a reduced flow velocity and a greatly reduced number of eddies.

The pump has a structurally simple drive if, according to another development, the first impeller and the second impeller are cantilevered together.

According to yet another development, it is provided that the shaft section is formed on the second impeller. This results in the additional advantages of simple production of the pump and the possibility of creating a modular system of self-priming and non-self-priming pumps in which the different types have many identical parts.

Another development relates to the connection of the impellers. The shaft section is accordingly shaped in such a way that it receives a threaded section of a drive shaft carrying the first impeller. This is an advantageously simple structure which also deepens the advantages with regard to a modular system.

A further development of the pump within the scope of this invention is that the first impeller has a first clamping surface which cooperates with a second clamping surface which is formed on the second impeller and via the clamping surfaces a clamping force for clamping the first impeller on a truncated cone which is formed on a drive shaft carrying the first impeller is introduced into the first impeller. This is a simple, inexpensive construction which advantageously causes the fastening of both running wheels at the same time.

The second impeller comprises a blade arranged in the manner of a thread on a cylinder. This means a simple, inexpensive production of the second impeller, for example after the DE 20 2004 013 752 U1 .

The pumping stage with the at least one thread-like blade is additionally improved in its pumping action in that the blade has an extension at its end facing the shaft section.

For the aforementioned applications in the hygienic to aseptic area, it is advantageous to design the pump in such a way that the first impeller is part of a non-self-priming centrifugal pump.

Also with a view to the application and especially in cooperation with a centrifugal pump stage, an advantageous embodiment is a pump in which the second impeller is part of a liquid ring pump stage.

The vortex formation in the pumped fluid is advantageously reduced, whereby the occurrence of cavitation is also reduced if the pump is developed in such a way that an end face which is formed on the second impeller on the side facing the shaft section merges smoothly into the shaft section.

On the basis of an exemplary embodiment and its developments, the invention is to be explained in more detail and the illustration of the effects and advantages are to be deepened.

Fig. 1:

Perspektivischer Blick auf eine selbstansaugende Kreiselpumpe;

Fig. 2:

Längsschnitt durch eine selbstansaugende Kreiselpumpe;

Fig. 3:

Schnitt durch Detailansicht A;

Fig. 4:

Perspektivische Darstellung des zweiten Laufrades.

Show it:

Fig. 1:

Perspective view of a self-priming centrifugal pump;

Fig. 2:

Longitudinal section through a self-priming centrifugal pump;

Fig. 3:

Section through detail view A;

Fig. 4:

Perspective view of the second impeller.

In Fig. 1 a self-priming centrifugal pump 1 is shown in a perspective view. This centrifugal pump 1 comprises a liquid ring pump stage 2 and a non-self-priming centrifugal pump 3. An inlet 4 of the self-priming centrifugal pump 1 is assigned to the liquid ring pump stage 2. Fluid, in particular liquid to which gas may be admixed, enters through the inlet 4 of the centrifugal pump 1 and first reaches the liquid ring pump stage 2.

The fluid is then transferred to the centrifugal pump 3. The fluid ejected from there leaves the self-priming centrifugal pump 1 through the outlet 5. A return line 6 branches off from the centrifugal pump 3. Fluid flows through this return line 6 from the centrifugal pump 1 back into the liquid ring pump stage 2 and is there for the formation of the liquid ring already when the centrifugal pump 1 is started.

The self-priming centrifugal pump 1 rests on feet 7 and has a cover 8 under which the drive and control means are housed, the pumping action of the self-priming centrifugal pump 1 being controllable with these drive and control means.

In Fig. 2 the self-priming centrifugal pump 1 is shown in a longitudinal section.

A housing 9 comprising several individual parts accommodates the liquid ring pump stage 2 and the non-self-priming centrifugal pump 3. The housing 9 is carried by a lantern 10 which connects to a motor 11. This motor 11 is typically designed as an electric motor and is controlled by control electronics 12. Motor 11 and control electronics 12 are arranged under cover 8 and are supported by feet 7.

The motor 11 has a motor shaft 13 to which a drive shaft 14 is detachably and non-rotatably connected. This drive shaft 14 carries a first impeller 15 and a second impeller 16. The impellers 15 and 16 are jointly overhung by means of the motor shaft 13 and drive shaft 14 and are rotatably supported by the bearings of the motor shaft 13.

The first impeller 15 is part of the non-self-priming centrifugal pump 3 and has a first pump section 17. This is arranged in a first chamber 18. When the drive shaft 14 rotates, fluid flows in the area of an axis of rotation Drive shaft 14 and thus of the first impeller 15 and is moved by the first pump section 17 radially outward and there in the circumferential direction and placed under pressure.

The second impeller 16 is part of the liquid ring pumping stage 2 and comprises a second pumping section 19. This second pumping section 19 is arranged in a second chamber 20 and designed so that a liquid ring is generated in this when the drive shaft 14 rotates, with an axis of symmetry of the liquid ring being radial is offset to the axis of rotation of the drive shaft. The liquid ring and the second impeller 16 arranged eccentrically to it create a negative pressure within the liquid ring pump stage 2, which causes fluid to be sucked in through the inlet 3.

Detail A is in Fig. 3 shown enlarged and shows a section of the impellers and the area of the connection between the two impellers.

The drive shaft 14 passes through the housing 9 in the area in which the housing 9 and lantern 10 are connected to one another. The lantern 10 surrounds the drive shaft 14. An interior of the housing 9 is sealed against the atmosphere by means of a mechanical seal. This mechanical seal comprises a rotating sliding ring 21 which is arranged to rotate with the drive shaft 14. The rotating sliding ring 21 is in sliding contact with a stationary sliding ring 22 which is mounted in the housing 9 in such a way that it does not rotate with it. A further development of the mechanical seal is a flushed version according to the DE 203 16 570 U1 .

The first chamber 18 is separated from the second chamber 20 by a housing wall 23. In this housing wall 23 an opening 24 is provided through which a shaft section 25 passes.

The shaft section 25 is designed as part of the second impeller 16 and comprises a shaft end 26 and a constriction 27. The shaft end 26 is in mechanical contact with the first impeller 15. The transition point between the first impeller 15 and shaft section 25 is sealed with the aid of a seal 28 . The seal 28 is designed as an O-ring, which is received in an adapted contour in such a way that there is no gap between it and the recording remains. This is advantageous for hygienic use, since deposits of dirt are prevented.

The shaft section 25 is formed between the constriction 27 and the shaft end 26 to taper from the shaft end 26 to the constriction 27. A diameter of the shaft section 25 decreases from the transition to the first impeller 15 towards the constriction 27. At the same time, the second impeller 15 and the shaft section 25 have a smooth course between the constriction 27 and the first pump section 17. The constriction 27, together with the smooth course, causes a more uniform distribution and reduction of the flow rate in this area of the centrifugal pump. In particular, peaks in the flow velocity are reduced or largely avoided; there is a reduction in velocity over the entire cross section. This will reduce the NPSH value.

The smooth course is given in the mathematical sense if the intersection curve is in Fig. 3 follows a curve with a steady slope. This means that kinks, steps or paragraphs are avoided as far as this is technically feasible. In the context of this invention, smooth is also given when the seal 28 has an exposed section which interrupts the surface of the shaft section 25 and the first impeller 15 and is exposed piece by piece with a curvature. As long as a predominantly laminar flow can be developed along the surface of the shaft section 25 and the first impeller 15, the course is sufficiently smooth.

A further improvement of the flow course is given if, as in the example shown, an end face 29 of the second impeller merges with a hollow groove 30 and thus with a smooth course in the shaft section 25. If the shaft section 25 is made in one piece with the second impeller 16, the hollow fillet 30 can be produced particularly easily and smoothly.

The shaft section reaches its thinnest point in the constriction 27, preferably in the second chamber 20 and / or in the opening 24 in the housing wall 23. As shown, the constriction 27 can extend in the longitudinal direction of the shaft section. This placement and, if necessary, expansion of the constriction 27 makes it possible to keep the opening 24 small with a large flow passage, so that the functions of Liquid ring pump stage 2 and normal suction centrifugal pump 3 are not impaired despite an increase in the cross-sectional area that can be flowed through.

The exemplary embodiment shows a connection of the drive shaft 14 with the first impeller 15 and the second impeller 16, which is very well suited to absorbing the forces resulting from the floating bearing and enables high accuracy and small gaps to the housing 9.

At its end facing away from the motor shaft 13, the drive shaft 14 has a truncated cone 31 which ends in a cylindrical threaded section 32. This threaded section 32 is received in a thread in the shaft section 25 with the formation of a screw connection. The first impeller 15 has a first clamping surface 33, which can be brought into mechanical contact with a second clamping surface 34 formed on the shaft section 25. Establishing the screw connection with the participation of the threaded section 32 brings about clamping forces which are introduced into the first wheel 15 by the second wheel 16 via the first clamping surface 33 and second clamping surface 34 and cause a clamping on the truncated cone 32.

The second impeller has a cylinder 35 as its base body. At least one thread-like rotating blade 36 is provided on this. This blade 36 is used to generate and maintain a ring of liquid in the second chamber 20 and to convey the gas phase helically through the second chamber 20. This at least one blade 36 forms the second pumping section 19. At its end, the blade has an extension 37 which protrudes beyond the end face 29 in the axial direction. This circulates in the gap that exists between the end of the blade 36 and the housing wall 23 and improves the formation of the liquid ring there.

A perspective view of the second impeller 16 shows Fig. 4 . The second impeller 16 has three blades 36 in this figure and each of the blades has extensions 37 at its end which are oriented in the axial direction. Extensions 37 are provided both on the side facing the inlet 4 and on the side of the shaft section 25. The cylinder 35, which is closed with an end disk 38, has a pull-out 39 arranged with it Wrench flats with which the second impeller 16 can be screwed onto the threaded section 32.

List of reference symbols

1

self-priming centrifugal pump

2

Liquid ring pumping stage

3

non-self-priming centrifugal pump

4th

inlet

5

Outlet

6th

Return line

7th

Feet

8th

cover

9

casing

10

Lantern

11

engine

12

Control electronics

13

Motor shaft

14th

drive shaft

15th

first impeller

16

second impeller

17th

first pumping section

18th

first chamber

19th

second pumping section

20th

second chamber

21st

rotating slip ring

22nd

standing slip ring

23

Housing wall

24

opening

25th

Shaft section

26th

Shaft end

27

Constriction

28

Shaft seal

29

Face

30th

Fillet

31

Truncated cone

32

Threaded section

33

first clamping surface

34

second clamping surface

35

cylinder

36

shovel

37

renewal

38

End disk

39

abstract

A.

Detail view

Claims (10)

1. A self-priming pump (1) having a housing (9), an inlet (4) and an outlet (5), having a first impeller (15) with a first pump section (17) that is arranged in a first chamber (18), and a second impeller (16) with a second pump section (19) that is arranged in a second chamber (20), and a shaft section (25) provided between the pump sections (17, 19), which shaft section (25) comprises a shaft end (26) and penetrates an opening (24) in a housing wall (23), wherein the shaft section (25) is formed, between a constriction (27) and the shaft end (26), to taper from the shaft end (26) towards the constriction (27), and the first impeller (15) and shaft section (25) have a smooth contour between the constriction (27) and the first pump section (17), wherein the second impeller (16) comprises a blade (36) arranged in the manner of a thread on a cylinder (35), characterized in that the blade (36) has an extension (37) on its end facing the shaft section (25).
2. The pump according to Claim 1, characterized in that the thinnest point of the shaft section (25) is arranged in the second chamber (20).
3. The pump according to Claim 1, characterized in that the thinnest point of the shaft section (25) is arranged in the opening (24).
4. The pump according to any one of the preceding claims,
   characterized in that the first impeller (15) and the second impeller (16) are jointly mounted in an overhung manner.
5. The pump according to any one of the preceding claims,
   characterized in that the shaft section (25) is configured on the second impeller (16).
6. The pump according to any one of the preceding claims,
   characterized in that the shaft section (25) accommodates a threaded section (32) of a driveshaft (14) that bears the first impeller (15).
7. The pump according to any one of the preceding claims,
   characterized in that the first impeller (15) has a first clamping surface (33) that interacts with a second clamping surface (34) which is configured on the second impeller (16), and a clamping force is introduced into the first impeller (15) via the clamping surfaces (33, 34) to clamp the first impeller (15) on a cone frustrum (31) that is configured on a driveshaft (14) that bears the first impeller (15).
8. The pump according to any one of the preceding claims,
   characterized in that the first impeller (15) is part of a normally priming centrifugal pump.
9. The pump according to any one of the preceding claims,
   characterized in that the second impeller (16) is part of a liquid ring pump stage.
10. The pump according to any one of the preceding claims,
    characterized in that an end face (29) that is configured on the second impeller (16), on the side facing the shaft section (25), transitions smoothly into the shaft section (25) .

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