EP2171279B1 - Naturally-aspirated pump assembly - Google Patents

Description

TECHNICAL AREA

The invention relates to a self-priming pump aggregation, which is a series connection of working as a rotary positive displacement pump liquid ring pump and a normal suction centrifugal pump, wherein the centrifugal pump has a rotatably mounted shaft with an impeller in a provided with an inlet opening and a pressure port housing, one of a housing shell of the Displacement pump limited internal space via the inlet opening with a suction-side interior of the centrifugal pump and in the housing shell, a screw conveyor is mounted, which is fixed to the shaft through the impeller and the housing shell engaging shaft, and wherein a return line is provided, the pressure-side region the centrifugal pump connects directly or indirectly with the interior. In particular, the inner surfaces of the pump aggregation, which are in direct contact with the liquid, meet the hygienic requirements in the fields of food and beverage, pharmaceutical and biotechnology process technology in terms of design and surface quality by smooth and rounded and, are executed without holes, cracks, small elevations, sharp edges and dead spaces.

STATE OF THE ART

It is known, a so-called. Normalsaugende centrifugal pump (centrifugal pump), which is not able to vent their suction and the upstream suction line automatically to vent and thus liquid automatically or to promote existing liquid and gas two-phase flow, with a so-called to combine. Liquid ring pumps work like rotary positive displacement pumps and are able to convey gases or two-phase flows and thus also a suction line of vorg. Kind of venting. As soon as the suction line, the subsequent suction nozzle of the centrifugal pump and thus the latter are self-ventilated and thus the entire system in question is filled with liquid, the centrifugal pump takes over the conveying task alone. A related pump aggregation of normal suction centrifugal pump and liquid ring pump is in the GB 601 516 A or the US 5,711,789 A described. From the GB 601516 A In addition, it is known to connect a device supplying the liquid ring pump with liquid via a switchable liquid return line to the suction nozzle of the centrifugal pump.

One in the DE 79.24 976 U1 described device for improving the Kavitationsverhaltens of centrifugal pumps is characterized in that equipped with suction manifold centrifugal pumps enters a pressure side removed fluid flow in the tangential direction to the suction line and in the direction of rotation of the pump impeller in the suction-side flow space through a plurality of circumferentially distributed openings. The feed of the delivery liquid flow is automatically preferably by means of a arranged in the return line between the pressure and suction sides known control valve at the beginning of part-load operation of the centrifugal pump.

From the DE 7533 458 U1 a centrifugal pump (centrifugal pump, centrifugal pump) is known with a housing containing an impeller having an axial inlet leading to the impeller and a liquid outlet, with a device for pressure release of accumulating in the housing leakage and with the pressure-releasing leakage liquid from the housing dissipating and the inlet-feeding return line. In order to return the leakage liquid into the pump inlet in such a way that the least possible disturbance of the laminar inlet flow takes place, a stabilizing chamber which reduces the velocity of the leakage liquid is provided in the housing in the vicinity of the inlet. The latter has an external inlet for connection to the return line and leads from the stabilization chamber a frusto-conical passage in the immediate vicinity of the impeller inlet. The passage is oriented so that it is the leakage fluid With a small radial component so in the inlet initiates that the disturbance of the incoming flow is kept low.

A self-priming pump aggregation of the generic type is in the EP 1 191228 A2 described. In this known pump aggregation necessary for the aspiration of a liquid evacuation of the suction-side portion of the normal-suction centrifugal pump, as for example from the DE 10314 425 A1 is known, accomplished by one of the centrifugal pump upstream rotary displacement pump. The rotating positive displacement pump embodied as a so-called liquid ring pump is, with sufficient liquid charge in its housing, capable of delivering gas and thus can evacuate an upstream process arrangement and suck and convey liquid or a two-phase flow consisting of liquid and gas. As soon as liquid is sucked in and enters the positive-displacement pump and thus into the downstream centrifugal pump, the centrifugal pump essentially takes over the delivery of the liquid or possibly within limits of the two-phase flow in accordance with its delivery characteristic influenced by the flow losses in the upstream positive displacement pump.

The positive displacement pump always requires the mentioned adequate liquid reservoir for permanent operational readiness before any necessary evacuation of the suction side connected process arrangement, so that the delivery chamber formed by its screw conveyor can ensure the necessary gas transport if necessary. This liquid template is in addition to the supply via the suction line of the pump aggregation also fed and maintained by a in the EP 1 191 228 A2 described return line for liquid, which establishes a connection between the discharge nozzle of the centrifugal pump on the one hand and on the other hand, the housing or the suction nozzle of the positive displacement pump or connected to the latter suction line.

Since the liquid feed of the positive displacement pump to be fed via the return line, it is desirable and advantageous if this return line is primarily applied with liquid. The fluid delivery in the return line However, is necessarily an image of what is available at the junction of the return line to the discharge nozzle of the centrifugal pump to fluid respectively. Depending on the respective process conditions, the pump aggregation and thus also the centrifugal pump in the area of the vorg. Pressure Stutzens of exclusively liquid up to exclusively gas each two-phase flow, formed of liquid and gas in each given proportions, promoted, so that the known return line is also inevitably acted upon by this respective two-phase flow.

It is known that in a pipe flow formed by a two-phase flow, as it begins to form in the discharge nozzle of the centrifugal pump of the known pump aggregation, separation of the gas from the liquid occurs, the gas bubbles preferably being found in the axial region of the pipe flow. However, a sufficient separation in this respect requires a certain residence time of the two-phase flow in the pipeline and thus a certain Mindestströmungsweg. If this minimum flow path available, then it can be successful at the junction of vorg. Return line primarily liquid from the pipe that feeds the return line, branch off.

Since in the known pump aggregation, the return line is connected to the discharge nozzle of the centrifugal pump and this ends relatively short behind the pump housing, in the latter by flow turbulence and turbulent cross exchange rather intensive mixing of gas and liquid is assumed to continue in the discharge nozzle, the Briefly outlined above solution according to the prior art ( EP 1 191 228 A2 ) of the vorg. Separation does not benefit.

Although a shift of the connection point of the return line, seen in the flow direction, beyond the discharge nozzle in the region of a downstream pressure line is in principle readily possible, but this means that this Anschlüssstelle the Rückführieitung only in the course of assembly of the pump aggregation in the process plant on site and no longer by prefabrication at the manufacturer of the pump aggregation can be done, and that the return line under certain circumstances undergoes a corresponding extension, which is fluidically disadvantageous.

It is an object of the present invention to develop a self-priming pump aggregation of the generic type such that the fluidic conditions for the flow of liquid to and in the return line are improved, that the arrangement is compact overall and that a prefabrication of the return line and its connection points is given.

SUMMARY OF THE INVENTION

The object is achieved by a self-priming pump aggregation with the features of claim 1. Advantageous embodiments of the device according to the invention are described in the subclaims.

The fundamental inventive solution idea is to connect the return line Zentrifugalpumpenseitig via a first connection point to a pressure-side interior within the housing of the centrifugal pump, which, seen in the flow direction, downstream of the impeller and thus has a static pressure which is well above the static pressure in Interior of the positive displacement pump is located. This pressure difference ensures fluid transport between the connection point on the centrifugal pump and the connection point on the positive displacement pump. The return line is designed by the proposed measure relatively short, each of the two connection points of the return line can be prefabricated in the course of production of the pump aggregation.

Since all surfaces of the pump aggregation that are in direct contact with the pumped liquid have to be subjected to automatic flow-through cleaning at intervals (so-called CIP cleaning (cieaning in place)), the conditions for cleaning the return line are in accordance with the invention Arrangement particularly favorable, since the turbulence generated by the impeller in the housing of the centrifugal pump intensify the cleaning effect also within the return line.

It has surprisingly been found to be particularly expedient to connect the return line according to the invention to an annular channel which is an integral part of the pressure-side interior, and a related first connection point on a radially or approximately radially oriented annular surface which is part of the rear housing part and the annular channel in the axial Direction frontally limited to provide. In this annular channel, which may be formed as a spiral annular channel or as a vaneless annular space with a constant passage cross-section, the flow is delayed, whereby a part of the kinetic energy of the impeller leaving the flow converts into static pressure, so that the static pressure in the annular channel as a whole increases. The latter is required, in a sufficient amount relative to the static pressure in the positive displacement pump, for liquid transport in the return line. Placement of the first connection point on the above-described radial or approximately radially oriented annular surface makes use of the fact that preferably liquid is located in this area and can be "harvested" there, since gas constituents have this rearmost, frontal wall region, seen in the axial direction avoid the ring channel or vane-free annulus.

A preferred embodiment provides that the first connection point is positioned with respect to the discharge nozzle such that an assembly plane which passes through a radial direction vector which passes through the center of the first connection point is penetrated perpendicularly by the longitudinal axis of the discharge nozzle. The so defined position of the first connection point means that a point in the annular channel is selected immediately before the flow enters the discharge nozzle of the centrifugal pump, at which the maximum possible static pressure within the housing of the centrifugal pump is present. A further increase in static pressure can at best be achieved by a diffuser-like expansion of the pressure port or the downstream pressure line.

A further proposal provides that the return line is connected via a second connection point with the interior of the positive displacement pump, wherein the second connection point is arranged on the housing shell or on a suction nozzle receiving housing cover or on the suction of each positive displacement pump or on a suction line leading to the positive displacement pump. An extremely short return line with correspondingly low flow losses is realized with a further embodiment in which the return line is connected via a second connection point with the interior of the positive displacement pump, wherein the second connection point is arranged on a front housing part of the centrifugal pump and therefore there in the interior the positive displacement pump opens.

Particularly good results are achieved if the second connection point in the arrangement level and laterally next to the suction nozzle or laterally next to the inlet opening to the centrifugal pump, based on the axis of rotation of the pump aggregation, is arranged on the side of the first connection point. As a result, at least in the first variant, an axial component of the flow emerging from the return line is rectified with the axial flow direction of the main flow within the positive displacement pump.

It is further proposed in this context, in order to minimize any influence on the main flow within the positive displacement pump, that the second connection point opens into the displacement area near the wall of the housing shell in the positive displacement pump.

In order to support the rotational component of the main flow within the positive displacement pump, a further proposal provides that the second connection point opens into the positive displacement pump with a tangential directional component and in the direction of rotation of the pump aggregation.

It is known that when conveyed substantially by the centrifugal pump, i. in the operating state of the regular liquid delivery, in which the function of the return line is not required, which has effective via the return line from the centrifugal pump to positive displacement bypass return flow has an adverse effect on the characteristic and thus on the efficiency of the pump aggregation. To avoid this disadvantage to ver, provides a further proposal that in the return line, a shut-off valve is arranged, which is remotely controllable in a preferred embodiment.

In this regard, it is further proposed, in order to automate the closing of the return line, that the remotely controllable shut-off valve is connected via a control line to a signal generator which generates a control signal from a physical quantity characterizing the liquid delivery in the pump aggregation.

The vorg. Signalers can be used in a variety of forms, where he always uses a physical size that significantly represents the change in the gas or two-phase flow promotion for liquid delivery in the pump aggregation. In this context, it is proposed that the signal generator is a pressure sensor in the suction line or in the suction nozzle or in the liquid ring pump or in the discharge nozzle or in the pressure line. But it can also be designed as a differential pressure transducer, which measures the pressure difference between the pressure and suction or between the pressure and suction line. Another possibility is to form it as a flow meter, which is arranged in the suction line or in the pressure line. Also, a liquid sensor at a point between the suction and the pressure line provides the necessary control signal. Finally, the signal generator can also be a power sensor, which detects the drive power of a motor of the pump aggregation.

BRIEF DESCRIPTION OF THE DRAWINGS

Figur 1

in perspektivischer Darstellung die selbstansaugende Pumpenaggregation gemäß der Erfindung;

Figur 2

einen Meridianschnitt durch die Pumpenaggregation gemäß Figur 1 entsprechend einem dort mit A-A gekennzeichneten Schnittverlauf;

Figur 3

eine Ansicht der Pumpenaggregation gemäß Figur 1 entsprechend einer dort mit "Z" gekennzeichneten Blickrichtung und

Figur 4

einen Querschnitt durch die Zentrifugalpumpe der Pumpenaggregation gemäß Figur 1 entsprechend einem in Figur 2 mit B-B gekennzeichneten Schnittverlauf.

An embodiment of the self-priming pump aggregation according to the invention is shown in the drawing and will be described below. Show it

FIG. 1

in perspective view of the self-priming pump aggregation according to the invention;

FIG. 2

a meridian section through the pump aggregation according to FIG. 1 according to a section marked there with AA ;

FIG. 3

a view of the pump aggregation according to FIG. 1 according to a direction of view marked there with "Z" and

FIG. 4

a cross section through the centrifugal pump of the pump aggregation according to FIG. 1 according to one in FIG. 2 with BB marked cutting course.

DETAILED DESCRIPTION

A self-priming pump aggregation 1 ( FIGS. 1 to 3 ) is from a normal suction centrifugal pump (centrifugal pump) 2 and one of these, seen in the flow direction, upstream rotary positive displacement pump 20, which is designed in the embodiment as a so-called. Liquid ring pump is formed. The displacement pump 20 is on the housing side of a housing shell 20.1 ( Figures 2 and 1 ) and a housing cover 20.2 with a centrally arranged on the latter suction nozzle 20.2a limited, wherein the housing shell 20.1 is fixedly connected at its end remote from the housing cover 20.2 end with a front housing part 2.1 of the centrifugal pump 2. The connection between the housing shell 20.1 and the front housing part 2.1 is usually cohesively by welding; a cast construction consisting of the housing shell 20: 1 and the front housing part 2.1 is equally possible.

An axial axis of symmetry a _{2 of} the housing shell 20.1 is opposite a rotational axis a _{1 of} the pump aggregation 1 (see FIGS. 1 and 3 ), based on the drawing position of the pump aggregation 1, which also corresponds to the usual installation position, offset by a vertical eccentricity e down. As a result, located in the positive displacement pump 20 screw conveyor 21, which is arranged on a shaft extension 8b of an impeller 4 of the centrifugal pump 2 bearing shaft 8 to this vertical eccentricity e within the housing shell 20.1 moved upwards. The shaft extension 8b adjoins a hub 8a of the shaft 8, wherein on the hub 8a, the impeller 4 is fixed, and it engages through the front housing part 2.1 and in the housing shell 20.1 a. An inner space 20.3 bounded on the inside by the housing jacket 20.1, the housing cover 20.2 and the front housing part 2.1 is provided via an inlet opening 2.1b ( 2.1b ₎ arranged concentrically in the front housing part 2.1 and thus concentrically with the axis of rotation a1. FIG. 2 ) With a suction-side interior 2.1c of the centrifugal pump 2 fluidly connected.

The expansion of the centrifugal pump 2 is for example from the DE 103 14 425 B4 known. One consisting of the front 2.1 and a rear housing part 2.2 Housing 2.1 / 2.2 of the centrifugal pump 2 is attached via a mounting flange 7 flying on a motor 6 ( FIGS. 1 and 2 ). To the front housing part 2.1, viewed in the direction of the axis of rotation a ₁ , the inlet opening 2.1b and, tangentially opening out circumferentially, a pressure port 5 is connected, which ends via a conical extension 5a in a connecting piece 5b.

From the in FIG. 1 with AA marked cutting curve results in accordance with the meridian section FIG. 2 , The front and the rear housing part 2.1, 2.2 are adapted to the impeller 4 in their radial extension region, each with a narrow annular gap. On the annular circumferential impeller outlet cross-section is followed by a blade-less annular space 3a on the outside, which is bounded in the radial direction initially on both sides of the front and the rear housing part 2.1, 2.2 and then outside bounded by an unnamed transition surface of the front Gehäuseteiis 2.1. This transitional surface is then continued in an outer annular channel housing wall 2.1 a, wherein this example has the shape of a cylinder jacket, ie a constant radius of curvature, an outer radius R _a , has ( FIG. 4 ). The rear housing part 2.2 is formed in the region of the impeller 4 as a radially extending disk. In the outer region of this disc, a mainly axially oriented, from the impeller 4 in the axial direction onward, the axis of rotation a ₁ enclosing inner annular channel housing wall 2.2a connects, the local radius of curvature r _i ( Fig. FIG. 4 ) is variable to realize, for example, a spiral course over the circumference.

The outer and the inner ring channel housing wall 2.1a, 2.2a thus form an annular channel 3 * from between operating at ever-changing type passage cross section (radius of curvature r _i) can be designed as spiral-shaped annular channel 3 **. Nevertheless, with the arrangement shown, an annular channel 3 * with a passage cross section which is constant over the circumference can also be realized. The (spiral) annular channel (3 **), 3 * joins laterally to the vane-less annular space 3a; together they form a pressure-side interior 3 of the centrifugal pump second

FIG. 4 shows how the spiral annular channel 3 **, seen over the circumference, steadily widened. Starting at the rearmost point of penetration of the pressure port 5 with the front housing part 2.1, seen in a direction of rotation n, the passage cross-section of the spiral annular channel 3 ** increases steadily from a minimum cross section to a point where FIG. 4 the horizontal center line forms a vertical with the longitudinal axis of the pressure port 5. Up to this point, the inner annular channel housing wall 2.2a is continuously curved. This is followed by an unillustrated planar wall region, which ensures a passage cross-section in the region of the spiral-shaped annular channel 3 ** which corresponds at least to the passage cross-section of the pressure port 5.

The outer axial limit of the (helical) ring channel (3 **) 3 * is realized via a at the inner annular channel housing wall 2.2a then, moving away from the rotational axis A ₁ in a radial direction radially or approximately radially oriented annular surface 2.2b, which is part of the rear housing part 2.2 ( FIG. 2 ). This annular surface 2.2b continues over the outermost radial extent of the outer annular channel housing wall 2.1a in the radial direction to the outside. Also, the outer annular channel housing wall 2.1a is adjoined by an unspecified, radially oriented, corresponding to the radial annular surface 2.2b and releasably connected annular surface, which on the outside comprises the radial annular surface 2.2b. Both radial annular surfaces have a plurality of distributed through their circumference, mutually corresponding through holes through which the front and the rear housing part 2.1, 2.2 are interconnected.

A return line 9 ( Figures 2 . 3 . 1 ) is the centrifugal pump side connected to the pressure-side interior 3 within the housing 2.1 / 2.2. A first connection point 9a is preferably provided in the annular channel 3 * or in the spiral-shaped annular channel 3 **. Here, the first connection point 9a at the radial or approximately radially oriented annular surface 2.2b, which is part of the rear housing part 2.2 and the annular channel 3 *, 3 ** in the radial direction frontally limited connected, ie the first connection point 9a opens there in the Ring channel 3 *, 3 ** off.

Best results are achieved if the first connection point 9a is positioned with respect to the pressure connection 5 such that an arrangement plane E (see also FIG FIG. 4 ), which passes through a radial direction vector which passes through the center of the first connection point 9a, is penetrated vertically by the longitudinal axis of the pressure port 5.

The return line 9 is connected via a second connection point 9b with the interior 20.3 in connection, wherein the second connection point 9b on the housing shell 20.1 or on the housing cover 20.2 or the suction nozzle 20.2a or on a suction line 24 is arranged.

An alternative embodiment with a very short return line 9 provides that the latter is arranged via a second connection point 9b on the front housing part 2.1 of the centrifugal pump 2 and consequently opens out there into the interior 20.3 of the rotating positive displacement pump 20.

In the two vorg. Basic solutions with respect to the arrangement of the second connection point 9a is further provided that the latter respectively in the plane E and laterally adjacent to the suction port 20.2a or laterally adjacent to the inlet port 2.1b, based on the axis of rotation a _{1 of} the pump aggregation 1, on the side of the first connection point 9a is arranged. In this case, according to another proposal, the second connection point 9b opens into the positive displacement pump 20 in the region of the housing jacket 20.1 close to the wall, wherein it can also be oriented with a tangential directional component and in the direction of rotation n of the pump aggregation 1.

For ease of assembly, the return line 9 is divided between the two connection points 9a, 9b and the ends are connected to one another by a screw 26. For the purpose of the fluid-tight shut-off of the return line 9, a shut-off valve 22 is arranged in this, which is remotely controllable in a preferred embodiment. The remotely controllable shut-off valve 22 is connected via a control line 27 with a signal generator 23 ( FIGS. 2 to 4 ), the one Control signal generated from a the liquid promotion in the pump aggregation 1 characterizing physical size. In this case, the signal generator 23 is a pressure sensor in the suction line 24 or in the suction port 20.2a or in the liquid ring pump 20 or in the discharge nozzle 5 or in a pressure line 25. The signal generator 23 is alternatively formed as a differential pressure transducer, which measures the pressure difference between the pressure and suction 5, 20.2a or between the pressure and suction lines 25, 24. Furthermore, the signal generator 23 is alternatively a flow meter in the suction line 24 or in the pressure line 25 or it is a liquid sensor at a point between the suction and the pressure line 24, 25th A further alternative is to use as a signal generator 23 a power sensor which detects the drive power of the motor 6 of the pump aggregation 1.

REFERENCE LIST OF ABBREVIATIONS USED

1

self-priming pump aggregation

2

(normal suction) centrifugal pump (centrifugal pump)

2.1 / 2.2

casing

2.1

front housing part

2.1a

outer ring channel housing wall

2.1b

inlet port

2.1c

suction-side interior

2.2

rear housing part

2.2a

inner ring channel housing wall

2.2b

radial or approximately radially oriented annular surface

3

pressure-side interior

3 *

annular channel

3 **

spiral annular channel

3a

Bladeless annulus

4

Wheel

5

pressure port

5a

conical extension

5b

spigot

6

engine

7

mounting flange

8th

wave

8a

hub

8b

Shaft extension

9

(liquid-carrying) return line

9a

first connection point

9b

second connection point

20

rotating positive displacement pump (liquid ring pump)

20.1

housing jacket

20.2

housing cover

20.2a

suction

20.3

inner space

21

Auger

22

shut-off valve

23

signaler

24

suction

25

pressure line

26

screw

27

control line

a ₁

Rotary axis of the pump aggregation 1

a ₂

Axial axis of symmetry of the housing shell 20.1

e

(vertical) eccentricity

n

direction of rotation

_i

local radius of curvature

e

arrangement plane

R _a

outer radius

Claims (12)

1. A naturally aspirated pump assembly (1) which constitutes a series connection of a liquid ring pump working as a rotary displacement pump (20) and a normally aspirated centrifugal pump (2), wherein the centrifugal pump (2) has, in a housing (2.1/2.2) provided with an inlet opening (2.1b) and a pressure piece (5), a rotatably mounted shaft (8) with a wheel (4), wherein the housing, seen in the flow direction, consists of a front (2.1) and a rear housing part (2.2), wherein an interior space (20.3) limited by a housing casing (20.1) of the displacement pump (20) is connected via the inlet opening (2.1b) to a suction-side interior space (2.1c) of the centrifugal pump (2) and a conveyor screw (21) is arranged in the housing casing (20.1), which is fastened on the shaft (8) engaging through the wheel (4) and into the housing casing (20.1), and wherein a recirculation line (9) is provided, which directly or indirectly connects a pressure-side region of the centrifugal pump (2) to the interior space (20.3),
   characterised in that the recirculation line (9) is connected on the centrifugal pump-side via a first connection point (9a) to a, seen in the flow direction, pressure-side interior space (3; 3*, 3**) downstream of the wheel (4) within the housing (2.1/2.2), that the first connection point (9a) opens out from a radial or approximately radially oriented annular surface (2.2b) limiting the pressure-side interior space (3; 3*, 3**) in the region of an annular channel (3*, 3**), which is part of the rear housing part (2.2) and limits the annular channel (3*, 3**) in the axial direction as the most rear-end, front-side wall region,
   and that the annular channel (3*, 3**) is an integral part of the pressure-side interior space (3; 3*, 3**).
2. The naturally aspirated pump assembly according to claim 1,
   characterised in that the annular channel (3*, 3**) is designed as a vaneless annular space (3*) with a constant passage cross-section or as a spiral-shaped annular channel (3**).
3. The naturally aspirated pump assembly according to claim 1 or 2,
   characterised in that the first connection point (9a) is positioned with respect to the pressure piece (5), such that a plane of arrangement (E), which passes through a radial direction vector which runs through the centre of the first connection point (9a), is penetrated vertically by the longitudinal axis of the pressure piece (5).
4. The naturally aspirated pump assembly according to one of claims 1 to 3,
   characterised in that the recirculation line (9) is connected via a second connection point (9b) to the interior space (20.3), wherein the second connection point (9b) is arranged

   • on the housing casing (20.1) or

   • on ahousing lid (20.2) receiving a suction piece (20.2a) or

   • on the suction piece (20.2a) or

   • on a suction line (24).
5. The naturally aspirated pump assembly according to one of claims 1 to 3,
   characterised in that the recirculation line (9) is connected via a second connection point (9b) to the interior space (20.3), wherein the second connection point (9b) is arranged on a front housing part (2.1) of the centrifugal pump (2) and opens out thereof.
6. The naturally aspirated pump assembly according to claim 4 or 5,
   characterised in that the second connection point (9b) in the plane of arrangement (E) and laterally next to the suction piece (20.2a) or laterally next to the inlet opening (2.1b), relative to the axis of rotation (a₁) of the pump assembly (1), is arranged on the side of the first connection point (9a).
7. The naturally aspirated pump assembly according to one of claims 4 to 6,
   characterised in that the second connection point (9b) in the near-wall region of the housing casing (20.1) opens into the displacement pump (20).
8. The naturally aspirated pump assembly according to one of claims 4 to 7,
   characterised in that the second connection point (9b) opens into the displacement pump (20) with a tangential directional component and in the rotational direction (n) of the pump assembly (1).
9. The naturally aspirated pump assembly according to one of claims 1 to 8,
   characterised in that a check valve (22) is arranged in the recirculation line (9).
10. The naturally aspirated pump assembly according to claim 9,
    characterised in that the check valve (22) is remotely controllable.
11. The naturally aspirated pump assembly according to claim 10,
    characterised in that the remotely controllable check valve (22) is connected via a control line (27) to a signal generator (23) which generates a control signal out of a physical size characterising the liquid delivery in the pump assembly (1).
12. The naturally aspirated pump assembly according to claim 11,
    characterised in that the signal generator (23)

    • is a pressure receiver

    in the suction line (24) or

    in the suction piece (20.2a) or

    in the liquid ring pump (20) or

    in the pressure piece (5) or

    in a pressure line (25)

    • or is a differential pressure receiver which measures the pressure difference between

    pressure and suction piece (5, 20.2a) or

    between pressure and suction line (25, 24)

    • or is a throughflow meter

    in the suction line (24) or

    in the pressure line (25)

    • or is a liquid sensor at a point between the suction and the pressure line (24, 25)

    • or is a power receiver which detects the drive power of a motor (6) of the pump assembly (1).

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