EP2505842B1 - Multi stage centrifugal pump system - Google Patents

Description

The invention relates to a multi-stage centrifugal pump unit with at least three impellers, d. H. an at least three-stage centrifugal pump unit.

In such multi-stage centrifugal pump units, several impellers are arranged one behind the other in the conveying direction, so that a further pressure increase takes place from stage to stage. The problem with these centrifugal pump units is that they have to be vented and filled with liquid when they are started up. The centrifugal pump units are not self-priming. This is disadvantageous in certain applications, for example in fire extinguishing devices in which constant filling with liquid, in particular water, cannot be guaranteed. In such facilities it is important that the pumps used are self-priming.

EP 0 406 787 A2 discloses a centrifugal pump unit, wherein a return flow channel is provided from the pressure side of the impeller back to the suction side of the impeller in a single-stage embodiment. In a further embodiment, a multi-stage centrifugal pump unit is shown, which, however, has no return from the pressure side to the suction side.

US 5,513,959 A discloses a centrifugal pump unit with a return flow from the pressure side to the suction side with a valve in this return flow. The output side of several pump stages is connected to the input side of the first pump stages.

DE 22 49 883 A1 discloses a self-priming centrifugal pump which has a second blade arrangement on its impeller, which generates an additional flow for suction.

DE 1 703 603 discloses a multi-stage self-priming centrifugal pump.

It is an object of the invention to improve a multi-stage centrifugal pump unit in such a way that its self-priming properties are optimized.

It is therefore an object of the invention to improve a multi-stage centrifugal pump unit so that it is self-priming.

The multi-stage centrifugal pump unit according to the invention has at least three impellers, which are preferably arranged on a common shaft and are driven by a motor, in particular an electric motor, via these.

The multi-stage centrifugal pump unit according to the invention is constructed in such a way that it has two successive impeller groups, ie groups of pump stages, in the direction of flow. The first impeller group in the flow direction is designed in such a way that it enables the centrifugal pump to self-priming. For this purpose, a backflow channel is present in the first impeller group, which connects the output side of the first impeller group with its input side. This backflow channel enables a liquid flow through the backflow channel and through the impeller to be effected within the first impeller group by its at least two impellers. I.e. A limited amount of liquid can be circulated in the first impeller group. This circulating amount of liquid causes a sufficient suction effect in the first impeller group in order to draw in further liquid. This means that the entire centrifugal pump unit can automatically draw in liquid. It is only preferred that a limited amount of liquid is always present in the first impeller group, in particular in the return flow channel, in order to ensure that the circulating flow through the impellers of the first impeller group and the return flow channel can start when the pump is started up.

The return flow channel preferably opens into the suction mouth of a first stage of the first impeller group. This ensures that the liquid flowing through the return flow channel is fed back to the input side of the impeller of the first stage, so that a circulating delivery flow is achieved here.

More preferably, at least one valve for closing the return flow channel is present in the return flow channel. This valve can be used to close the return flow channel when the pump has reached its normal operating state. In the normal operating state, when the pump unit is pumping liquid, an open return flow channel and a constant liquid return would impair the efficiency of the centrifugal pump unit. This can be done by closing the valve be prevented after the pump has started up, so that the pump then works like a conventional multi-stage centrifugal pump.

The valve is preferably designed such that it closes the return flow channel when a predetermined fluid pressure is reached in the return flow channel or on the exit side of the first impeller group. Reaching the predetermined fluid pressure is recognized as a normal operating state or an operating state in which there is already a sufficient delivery flow when further liquid is drawn in. Preferably, the fluid pressure in the return flow channel, i.e.. H. detected on the output side of the first impeller group. The valve is preferably designed as a spring element, wherein it is kept open by spring action against the fluid pressure prevailing in the return flow channel. When the fluid pressure exceeds the spring force, the valve is closed. Thus, an opening can be provided in the return flow channel, in front of which there is a spring plate in the flow direction, which is curved such that the plate is spaced apart from the opening in its rest position. Due to increased fluid pressure, the sheet can be deformed against its spring preload so that it is pressed against the opening and closes it.

According to the invention, the first impeller group is formed at least in two stages with two impellers arranged one behind the other in the flow direction. The return flow channel is arranged such that it leads from the output side of the second impeller to the input side of the first impeller. The two-stage first impeller group enables sufficient flow and suction to be achieved by conveying the liquid in the circuit through the return flow channel in order to generate a sufficient negative pressure overall for suctioning liquid in the suction mouth or suction channel of the centrifugal pump unit.

A separating element, which is designed to separate air and liquid, is preferably arranged on the output side of the first impeller group. Especially when starting up the pump unit when only a little liquid is initially conveyed through the return flow channel, the centrifugal pump unit will also suck in air through its suction line, with air and liquid ideally mixing when entering the first impeller. It is therefore expedient to separate the air from the liquid on the outlet side of the first impeller group, in order to preferably exclusively return liquid through the return channel to the inlet side of the first impeller group. This prevents the backflow channel from running dry.

Therefore, the separating element is further preferably arranged relative to the return flow channel in such a way that the liquid emerging from the separating element enters the return flow channel. This ensures that the liquid flowing from the return flow channel into the first impeller group, when it exits the first impeller group, substantially completely re-enters the return channel in order to create a circuit.

A check valve or a backflow preventer is preferably arranged on the input side of the first impeller group, which prevents liquid from running out of the centrifugal pump unit back into a suction line. This prevents the centrifugal pump unit from running completely dry; rather, the non-return valve keeps liquid inside the centrifugal pump unit even when the centrifugal pump unit is taken out of operation, which fluid enables restarting and renewed suction. The check valve can be integrated directly into the centrifugal pump unit, but can also be attached to the suction port of the centrifugal pump unit as a separate component.

According to a further preferred embodiment, at least one liquid reservoir is arranged between the first and the second impeller group. The liquid reservoir is designed in such a way that it fills with liquid during normal operation of the centrifugal pump unit. When the centrifugal pump unit is taken out of operation or in the event that the centrifugal pump unit should deliver air bubbles, the liquid in the liquid reservoir can ensure that the pumping action of the centrifugal pump unit does not completely stop, but that there is always enough liquid in the centrifugal pump unit to suck in again To allow liquid through the suction nozzle or the suction line of the centrifugal pump unit.

The liquid reservoir preferably has at least one outlet opening which is arranged such that it is opposite an inlet opening of the return flow channel in such a way that liquid can flow from the liquid store into the return flow channel. This ensures that the return flow channel is initially filled or kept filled by the liquid reservoir. The liquid from the return flow channel then flows to the inlet side of the first impeller of the first impeller group and enters it, so that this impeller can immediately achieve a conveying effect and can suck in further liquid through the suction line. Until liquid enters the first impeller from the suction line, the liquid in the return flow channel is then first circulated in the first impeller group, as described above.

The centrifugal pump unit according to the invention is preferably designed such that the axis of rotation of the impellers extends vertically. The liquid reservoir described above is then preferably designed such that its outlet opening is arranged on the underside, so that the liquid emerges from the liquid reservoir downward due to gravity and enters the return flow channel can. The liquid store is preferably filled from above via the liquid flowing to the pump stages arranged behind the liquid store or above the liquid store. The return flow channel preferably has an opening directed upwards, so that the liquid from the liquid reservoir can enter this opening from above.

According to a further preferred embodiment, at least two liquid stores can be arranged such that an outlet opening of the second liquid store opens into an opening of a first liquid store. For example, two or more liquid reservoirs can be arranged one behind the other in the flow or delivery direction between the first impeller group and the second impeller group. The liquid flows from the first or lower liquid reservoir, as described above, preferably into the return channel. The liquid from the second or subsequent liquid store first flows into the first liquid store and from there into the return channel. Accordingly, liquid can pass from a third liquid store into the second liquid store. All liquid stores preferably have an outlet opening on the underside and an inlet opening on the top side.

The at least one liquid reservoir is particularly preferably designed as an annular pot with an open top, which surrounds a shaft driving the impellers. I.e. the pot is ring-shaped or toroidal and has an opening in the middle through which the shaft extends. The opening also serves as a flow path for the conveyed liquid from the first impeller group to the second impeller group. For this purpose, a free space surrounding the shaft is provided in the opening. The top of the pot-shaped liquid reservoir is open, so that the liquid that flows through the central opening over the edge of the opening from above into the Pot-shaped liquid storage can enter. The described at least one outlet opening is preferably formed on the underside. In the case of the arrangement of a plurality of liquid stores, the outlet openings of the subsequent liquid stores are arranged such that they are located above the top of the respective preceding liquid store, so that the liquid runs out of the outlet opening into the preceding liquid store. From the first, that is to say the lowest, liquid reservoir, the liquid runs out of the outlet opening, as described, into the return line. The size of the outlet openings is such that the liquid stores slowly empty. According to a particularly preferred embodiment, the individual impellers of the second impeller group are each arranged in a stepped module, with all the stepped modules having the same axial height, and the at least two impellers of the first impeller group are also arranged in such a stepped module, which has an axial height that the axial height or an integer multiple of the height of a step module of the second impeller group. This modular structure with a fixed grid of the axial heights or lengths of the individual modules has the advantage that centrifugal pump units of different output, in particular different delivery and suction heights, can be realized very easily from the modules. The first self-priming impeller group can also be easily integrated into conventional multi-stage centrifugal pumps, since the parts of the first impeller group have the same grid in their axial length as the modules of the second impeller group. For example, the same tensioning straps can be used to hold the modules together as are used in conventional multi-stage centrifugal pump units. The number of parts required can thus be reduced.

More preferably, the liquid accumulators or spacing elements arranged between the two impeller groups also each have an axial height which corresponds to the axial height or an integer multiple of this height of a step module of the second impeller group. With these components, it is also achieved that the axial height fits into the existing grid of the axial height of the individual pump stages, which are arranged in the second impeller group.

Fig. 1

eine Schnittansicht eines erfindungsgemäßen Pumpenaggregates,

Fig. 2

eine Detailansicht der ersten Laufradgruppe des Pumpenaggregates gemäß Fig. 1,

Fig. 3

in einer teilweise geschnittenen Detailansicht ein Ventil im Rücklaufkanal und

Fig. 4

in einer Schnittansicht die Flüssigkeitsspeicher des Pumpenaggregates gemäß Fig. 1.

The invention is described below by way of example with reference to the attached figures. In these shows:

Fig. 1

2 shows a sectional view of a pump unit according to the invention,

Fig. 2

a detailed view of the first impeller group of the pump unit according to Fig. 1 .

Fig. 3

in a partially sectioned detailed view of a valve in the return duct and

Fig. 4

in a sectional view according to the liquid reservoir of the pump unit Fig. 1 ,

The centrifugal pump unit described by way of example has a total of eight stages, ie eight impellers. Of which two impellers 2 are arranged in a first impeller group 4 and six impellers 6 in a second impeller group 8. The first impeller group 4 faces the inlet or suction port 10 of the pump unit. The second impeller group 8 is connected downstream of the first impeller group in the flow or conveying direction. As with known multi-stage centrifugal pump units, the liquid to be pumped flows through the individual impellers one after the other and becomes the output side of the the individual impellers and the output side of the last impeller 6 is fed to the pressure port 14 via the annular pressure channel 12. All impellers 2 and 6 are driven by a common shaft 16. The shaft 16 is connected at its shaft end 18 to a motor, not shown here, for example an electric motor for driving.

The first impeller group 4 is designed to be self-priming in the manner described below, so that the centrifugal pump can suck in liquid via the suction nozzle 10 even when the suction nozzle 10 and an upstream suction line are not filled with liquid.

The self-priming effect of the first impeller group 4 is determined by the Fig. 2 achieved in more detail. A separating element 20 is arranged on the output side of the second impeller 2 of the first impeller group 4 in the direction of flow. This is designed so that liquid and air are separated from each other. This is done in that the liquid is accelerated radially outward, so that the air in the central area near the shaft 16 and the liquid in the peripheral area near the peripheral wall 22 emerge from the separating element 20. The liquid emerging from the separating element 20 flows over the peripheral wall 22 at its upper edge and enters a return flow channel 24. The return flow channel 24 leads back on the outer circumference of the first impeller group 4 in the direction of the suction port 10. Via openings 26 in a base plate, the return flow channel leads to the suction mouth 28 of the first impeller 2 in the flow direction of the first impeller group 4 of the separating element 20 back through the return flow channel 24 to the suction mouth 28 of the first impeller 2.

To start the pump, a small amount of liquid is sufficient to put the circuit described into operation through the two impellers 2 and the return flow channel 24. As a result, the impellers 2 generate a negative pressure, through which further liquid can then be sucked in through the suction nozzle 10. When commissioning the pump set for the first time, it is necessary to vent the pump set like conventional centrifugal pump sets. H. to fill with a certain amount of liquid.

In order to be able to maintain the described circuit via the return line 24, it is important that the pump in the area of the first impeller group 4 is designed to be as airtight as possible. Various seals are arranged for this. The seals 30 seal the return channel 24 against the pressure channel 12, so that liquid is prevented from flowing over from the pressure side via the return channel 24 to the suction side in normal operation. A bearing 32 is arranged in the interior of the separating element 20 and is in contact with the outer circumference of the shaft 16. This also serves to seal the separating element 20 with respect to the shaft 16 in order to prevent air from flowing out of the separating element 20 back to the impellers 2. The seal 34 seals the axial end of the shaft 16 to prevent air from flowing from the pressure side of the pump over the shaft to the suction side. The seal 36 also serves to separate the pressure side from the suction side, i. H. to seal the pressure port 14 against the suction port 10.

In order to prevent liquid from flowing back via the return flow channel 24 back to the suction side after reaching the normal operating state in which liquid is sucked in through the suction nozzle 10, a valve 38 is arranged in the return flow channel 24. This valve 38 is designed such that when a predetermined pressure is reached, it is on the output side of the second impeller 2, ie on the output side of the separating element 20 and in the return flow channel 24 closes the return flow channel. I.e. after reaching this predetermined pressure, the return flow channel 24 is closed and the liquid flows exclusively to the subsequent impellers 6 of the second impeller group 8.

The configuration of the valve 38 is explained in more detail on the basis of FIG Fig. 3 explained. Fig. 3 shows a detailed view of the separating element 20. The separating element 20 defines, between the outer circumference of the peripheral wall 22 and an annular wall 40 located radially further out, a first section of the return flow channel 24, which forms an entry region of the return flow channel 24. The second portion of the backflow channel 24 is between the outer periphery of the wall 40 and a radially spaced sleeve 42 (see Fig. 2 ) Are defined. A plurality of holes 44 are formed in the wall 40, which enable the passage from the inlet region of the return flow channel 24 into the second section of the return flow channel 24 between the wall 40 and the sleeve 42. Valve elements in the form of spring plates 46 are arranged at the openings 44. These spring plates 46 can assume two positions, namely an open position, which in Fig. 3 is designated by the reference numeral 46 '. In this position, the spring plate 46 'extends in a sinew shape to the inner circumference of the wall 40 and is therefore spaced apart from the opening 44, so that the latter is released. If the pressure now rises in the area of the return flow channel 24, which is located between the peripheral wall 22 and the wall 40, the spring plate 46 'is pressed radially outward and lies against the inside of the wall 40 above the opening 44, so that the Opening 44 is closed.

In order to ensure the safe operation of the centrifugal pump unit even when larger air bubbles pass through the system, three liquid reservoirs 48 are arranged between the first impeller group 4 and the second impeller group 8. These are detailed in Fig. 4 shown. The liquid reservoirs 48 are designed as ring-shaped or toroidal pots which surround the shaft 16. The shaft 16 extends through a central opening 50 of the liquid reservoir 48, the wall of the opening 50 being radially spaced from the outer circumference of the shaft 16. Thus, the opening 50 also serves as a flow path for the liquid conveyed from the first impeller group 4 to the second impeller group 8. The circumferential walls 52 of the openings 50 have a length in the direction of the longitudinal axis X which is shorter than the axial length of the outer walls of the liquid stores 48. The liquid reservoirs 48 are thus opened at their top, so that liquid which flows through the openings 50 can flow over the peripheral walls 52 into the interior of the liquid reservoirs 48. Thus, during normal operation of the pump unit, the liquid reservoirs 48 are filled when liquid flows from the first impeller group 4 to the second impeller group 8.

Each liquid reservoir 48 has an outlet opening 54 with a small diameter on its underside. The outlet openings 54 are spaced radially from the longitudinal axis X to such an extent that they lie above the free space between the peripheral wall 22 and the wall 40 of the separating element 20. Thus, the liquid runs from the first, ie lower, liquid store 48 directly into the return flow channel 24. From the two other liquid stores 48, the liquid first runs through the associated outlet opening 54 into the liquid store 48 located below. The liquid from the liquid stores 48 the small outlet opening 54 runs slowly, even if larger air bubbles or gas bubbles flow through the pump assembly, it can be ensured that the pump assembly still has a sufficient amount of liquid to at least have the starting circuit through the first impeller group 4, ie through the return flow channel 24 in FIG to put into operation again as described above.

In addition to these measures, a check valve or backflow preventer 55 is also arranged on or in the suction nozzle 10. Here, the check valve 55 is arranged directly in the suction nozzle, but it could also be attached to the suction nozzle 10 as a separate component. Such a device can be used to prevent the liquid from the pump unit from running back into the suction line when the suction line adjoining the suction nozzle 10 runs dry. In this way, a certain amount of liquid can always be kept in the pump unit, via which at least the starting circuit in the first impeller group 4 can be put back into operation, in order to then draw in further liquid through the suction nozzle 10. In this way, the entire centrifugal pump unit is designed to be self-priming.

As in Fig. 1 It can be seen that the pump unit is of modular construction overall, this modular construction being based on an axial length grid which is defined by the axial length of the pump stages formed by the impellers 6. These pump stages each have a circumferential jacket 56, which forms the jacket of the individual stage modules. These step modules are placed axially on top of each other. The liquid reservoirs 48 have the same axial length as the jackets 56 of the step modules of the second impeller group 8. In addition, a jacket 58, which surrounds the first impeller 2, also has the same axial length. The separating element 20 has an axial length in the direction of the longitudinal axis X which corresponds to twice the axial length of the jackets 56 and 58. The entire first impeller group 4 thus has an axial length which corresponds to three times the length of a step module of the second impeller group 8. This uniform length grid favors the modular structure, since tensioning straps, which hold the individual step modules together in the axial direction, only in different lengths, which result from this underlying grids are defined, must be kept. A wide variety of pumps can thus be assembled, with different numbers of impellers, liquid stores 48 and possibly the first impeller group 4 in order to ensure the self-priming properties.

LIST OF REFERENCE NUMBERS

2

impellers

4

First wheel group

6

impellers

8th

Second wheel group

10

suction

12

pressure channel

14

pressure port

16

wave

18

shaft end

20

separating element

22

Circumferential wall of the separating element

24

Backflow channel

26

openings

28

saugmund

30

seals

32

camp

34, 36

seals

38

Valve

40

wall

42

shell

44

openings

46

Spring plate / valve

48

liquid storage

50

opening

52

peripheral walls

54

outlet

55

check valve

56, 58

coat

X

longitudinal axis

Claims (13)

1. A multistage centrifugal pump assembly with at least three impellers (2, 6), wherein two impeller groups (4, 8) which are consecutive in the flow direction are present, characterised in that the first impeller group (4) is designed in at least two-stage manner with two impellers (2)which are successively arranged in the flow direction, a backflow channel (24) which connects the exit side of the first impeller group (4) to its entry side is present in a first impeller group (4), and the second impeller group (8) comprises at least one impeller (6).
2. A multistage centrifugal pump assembly according to claim 1, characterised in that the backflow channel (24) runs out into the suction port (28) of a first stage of the first impeller group (4).
3. A multistage centrifugal pump assembly according to claim 1 or 2, characterised in that at least one valve (38) for closing the backflow channel (24) is present in the backflow channel (24).
4. A multistage centrifugal pump assembly according to claim 3, characterised in that the valve (38) is designed in a manner such that on reaching a predefined fluid pressure in the backflow channel (24), it closes this.
5. A multistage centrifugal pump assembly according to one of the preceding claims, characterised in that the first impeller group (4) at its exit side comprises a separating element (20) which is designed for separating air and fluid.
6. A multistage centrifugal pump assembly according to claim 5, characterised in that the separating element (20) is arranged relative to the backflow channel (24) such that the fluid which exits from the separating element (20) enters into the backflow channel (24).
7. A multistage centrifugal pump assembly according to one of the preceding claims, characterised in that a check valve is arranged at the entry side of the first impeller group (4).
8. A multistage centrifugal pump assembly according to one of the preceding claims, characterised in that at least one fluid store (48) is arranged between the first (4) and the second impeller group (8).
9. A multistage centrifugal pump assembly according to claim 8, characterised in that the fluid store (48) comprises at least one exit opening which is arranged in a manner such that it lies opposite an entry opening of the backflow channel (24) in a manner such that fluid can flow out of the fluid store (48) into the backflow channel (24).
10. A multistage centrifugal pump assembly according to claim 8 or 9, characterised in that at least two fluid stores (48) are arranged in a manner such that an exit opening of a second fluid store (48) runs out into an opening of a first fluid store (48).
11. A multistage centrifugal pump assembly according to one of the claims 8 to 10, characterised in that the at least one fluid store (48) is designed as an annular pot with an open upper side which surrounds a shaft (16) which drives the impellers (2, 6).
12. A multistage centrifugal pump assembly according to one of the preceding claims, characterised in that the individual impellers (6) of the second impeller group (8) are each arranged in a stage module, wherein all stage modules have the same axial height, and the at least two impellers (2) of the first impeller group (4) are arranged in a stage module which has an axial height which corresponds to the axial height or an integer multiple of this height, of a stage module of the second impeller group (8).
13. A multistage centrifugal pump assembly according to claim 12 with one of the claims 8 to 11, characterised in that fluid stores (48) or spacer elements, which are arranged between the two impeller groups (4, 8) each have an axial height which corresponds to the axial height or an integer multiple of this height, of a stage module of the second impeller group (8).

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