Method for releasing a blockage of a centrifugal pump and centrifugal pump

Abstract

The invention relates to a method for clearing a blockage in a centrifugal pump (1) with a bypass line (9) branching off from a pressure line (8) of the centrifugal pump (1) and / or a pump housing (2) of the centrifugal pump (1), which can be activated by a bypass valve (11), comprising the step: when an operating parameter of the centrifugal pump (1) exceeds or falls below a blockage threshold during the pumping of liquid with a possible solid content, opening the bypass valve (11).

Description

Technical area

[0001] The invention relates to a method for clearing a blockage in a centrifugal pump with a pressure line. The invention further relates to a centrifugal pump comprising a pressure line. Background of the invention

[0002] Centrifugal pumps are known from the prior art and are used to pump a liquid by means of the rotating movement of an impeller. The liquid to be pumped enters a pump chamber of the centrifugal pump via a suction port on the suction side, is captured by the rotating impeller, and is subsequently transported through a discharge line on the discharge side.

[0003] Solid particles contained in the liquid can accumulate in the area of ​​the impeller and on the inside of a pump housing and thus negatively influence the hydraulic and / or mechanical efficiency of the centrifugal pump and even cause clogging and failure of the centrifugal pump.

[0004] Although several methods for unblocking centrifugal pumps are known from the prior art, current practice shows that the known methods are not ideal for effectively unblocking a centrifugal pump and protecting the centrifugal pump from damage due to the blockage in a safe and reliable manner. Description of the invention

[0005] Based on this situation, it is an object of the present invention to provide a method for improved unblocking of a centrifugal pump and a corresponding centrifugal pump.

[0006] The object of the invention is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0007] Accordingly, the problem is solved by a method for resolving a blockage in a centrifugal pump with a bypass line branching off from a pressure line of the centrifugal pump, downstream of the pressure line and / or a pump housing of the centrifugal pump, and activatable by a bypass valve, comprising the step: if an operating parameter of the centrifugal pump exceeds or falls below a blockage threshold, particularly as an indication of blockage, during the pumping of liquid with a possible solid content, the bypass valve is opened.

[0008] A key aspect of the invention lies in the fact that, particularly in the case of a blockage, the delivery rate and / or flow rate of the centrifugal pump is increased or decreased, especially for a certain period of time, by lowering or raising a system characteristic curve of the centrifugal pump. Lowering or raising the system curve is achieved by opening the bypass line via the bypass valve, thereby reducing the overall resistance or the losses overcome by the centrifugal pump due to the activated bypass line. This shifts the intersection of the pump and system characteristic curves to a higher flow rate. The higher flow rate causes the blockage to clear. The portion of the fluid pumped through the bypass line can be discharged into a pump sump to be subsequently pumped again by the centrifugal pump. The proposed method can be applied to both wet and dry-mounted centrifugal pumps.

[0009] In other words, the proposed method allows the centrifugal pump to be brought into a safe operating state, particularly for a short time, which can be used to clear blockages in the centrifugal pump. In the event of a blockage, the bypass valve activates the bypass line. By creating a short circuit in this way between a pressure side and a suction side of the centrifugal pump, the discharge head of the centrifugal pump decreases, which leads to a shift in the operating point of the centrifugal pump towards a higher pump volume flow. As a result, the flow velocity in both an impeller and a spiral of the centrifugal pump increases and flow conditions improve, which favor the conveyance of solids contained in the liquid, such as fibers and textiles. As soon as the blockage is cleared, the bypass line can be deactivated again by closing the bypass valve.

[0010] A centrifugal pump is generally defined as a turbomachine that transfers mechanical power to the fluid being pumped through a rotary motion. Preferably, the centrifugal pump is designed as a wastewater pump, either in a dry or wet installation, for pumping wastewater. The centrifugal pump is preferably used for the hydraulic system of a building or other applications.

[0011] During normal operation of the centrifugal pump, a housing of the centrifugal pump motor can be arranged above a pump housing of the centrifugal pump, in which pump housing the impeller of the centrifugal pump, which is driven by a motor via a shaft to pump the liquid, is provided, wherein the motor housing can be fixedly connected to the pump housing and / or designed as a single piece. Likewise, the centrifugal pump and the motor can each have their own shaft, wherein the shafts can be connected to one another via a coupling. Preferably, the shaft projects from the motor housing into the pump housing on a drive side and / or is fixedly connected to the shaft on the drive side of the impeller. Accordingly, an inlet for the liquid to be pumped can preferably be arranged below or below the pump housing.

[0012] The liquid preferably comprises water or another liquid medium, such as wastewater. The liquid may contain solids such as contaminants of any kind, in particular feces, sediment, sand, or even small pieces of wood, brushwood, textiles, or rags, or the like. The motor housing and / or pump housing are preferably made of metal, in particular cast iron or stainless steel, ceramic, and / or plastic.

[0013] The phrase "during the pumping of liquid" refers specifically to the regular operation of the centrifugal pump, namely when the centrifugal pump is pumping a fluid that may contain the aforementioned solids. "Liquid with possible solids" in this context means, in particular, that during regular operation only liquid is pumped, but the liquid may contain the generally undesirable solids, for example, partially or even largely, which can cause partial or complete clogging of the centrifugal pump. The bypass line is preferably designed as a pipe, particularly as a bypass pipe. The pressure line is preferably also designed as a pipe and / or as a pressure nozzle. The term "branching" preferably means that the bypass line is connected in a fluid-tight manner to the pressure line, to a main line of the centrifugal pump, and / or to a riser line of the centrifugal pump.In the area of ​​the branch, the pressure line preferably runs linearly. 'Activatable' preferably means that the bypass valve can be opened and closed.

[0014] An operating parameter is understood to be a parameter characterizing the centrifugal pump conveying the liquid, for example the power consumed by the centrifugal pump, the torque of a centrifugal pump motor, the speed of an impeller of the centrifugal pump and / or the current consumed by the centrifugal pump, vibrations, but also liquid parameters such as the volume flow, pressure or delivery head of the centrifugal pump. An operating parameter can also be understood to be a characteristic of the centrifugal pump and / or the operation of the centrifugal pump calculated from the operating parameter. A blockage occurs in particular when the operating parameter exceeds or falls below the blockage threshold, in particular when the operating parameter deviates from a specified value, particularly during blockage-free operation.A blockage can be characterized by, for example, fibrous spinning materials as a solid component settling around a leading edge of the impeller or clogging an impeller channel, undesired changes in pump performance, particularly operating parameters, reducing pump performance, and / or leading to a failure of the centrifugal pump. In this respect, a blockage can already occur if the pump performance deviates from normal operation of the centrifugal pump by, for example, 5, 10, 20, or 50%, or if the impeller speed drops to zero, i.e., the impeller jams due to the solid component. Exceeding or falling below the blockage threshold means, in particular, that the blockage threshold deviates from blockage-free operation in terms of its value.

[0015] The clogging threshold can be a tolerance range, for example, if the power consumed by the centrifugal pump exceeds or falls short of the power measured at a respective speed in the unblocked state by 5, 10, 20, or 50% for 2, 5, 10, 30, or 60 seconds. Preferably, prior to the process, in a so-called learning phase in the unblocked state, particularly during regular operation, the speed of the centrifugal pump is varied, and a relationship between the speed and the power consumed by the centrifugal pump is stored as a speed-power reference curve (DL-Reference) as the operating characteristic of the centrifugal pump. In this respect, the clogging threshold can be 5, 10, 20, or 50% above the operating characteristic of the centrifugal pump during regular operation.

[0016] The bypass line preferably branches off from the pressure line at a right angle. More preferably, the pressure line and / or the bypass line have a circular cross-section. The bypass valve is preferably opened completely, although it is also conceivable for the bypass valve to be only partially opened, for example to 25, 50, or 75%, and / or to be partially opened depending on the degree of solids content. It is also possible for the bypass valve to be opened in discrete steps. Furthermore, it is conceivable that after each step a check is made to determine whether the blockage threshold has been undershot, i.e. whether the blockage has been cleared, so that if so, the bypass valve is closed again or, if not, the bypass valve is opened further in stages. Instead of a step-by-step opening, a continuous opening is also possible.

[0017] According to a preferred development, the method comprises the step, after opening the bypass valve: If the blockage threshold is exceeded or undershot and / or after a predefined period of time, the bypass valve is closed, or if the blockage threshold is not exceeded or undershot after a predefined alarm period, an alarm is triggered, an unblocking routine is initiated and / or the centrifugal pump is switched off.

[0018] As previously explained, opening the bypass valve increases the flow rate in the centrifugal pump, allowing the blockage to clear. The proposed design conveniently checks whether the blockage has cleared. Falling below or exceeding the blockage threshold can be interpreted as the blockage being cleared. Alternatively or simultaneously, after a predefined time period (e.g., 2, 5, 10, 20, 30, or 60 seconds), it can be checked whether the blockage threshold has again been exceeded or fallen below. If the blockage threshold has again been exceeded and / or after the predefined time period, the bypass valve is closed completely.If the blockage threshold has still not been exceeded or undershot after the predefined alarm duration, this condition of the centrifugal pump indicates that the blockage could not be cleared by previously opening the bypass valve. In this case, it is advisable to trigger an alarm, for example, via the control system, and / or shut down the centrifugal pump to protect it from damage. The predefined alarm duration can be 2, 5, 10, 20, 30, or 60 seconds and / or is preferably longer than the predefined time period. An alarm can be triggered purely electronically, for example, as a message to a higher-level control system, a web server, software, or the like.To remove the blockage, so-called unblocking routines known from the prior art can be used, which generally involve a time-limited and / or repetitive, in particular repeated at intervals and / or alternating operation of the motor in a first and / or a second direction of rotation, in particular in the forward and / or reverse direction.

[0019] According to another preferred embodiment, the method comprises the step of, when the clogging threshold value is exceeded or undershot, changing, in particular increasing, a speed of an impeller conveying the liquid with the possible solid content.

[0020] By temporarily changing the speed, particularly increasing or decreasing it, the blockage can be further improved by opening the bypass valve. This is because changing, increasing, or decreasing the speed, combined with opening the bypass valve, allows the solid particles in the pumped liquid, which may have become stuck, for example, on an edge of the impeller and / or on a tongue of the volute, in the gap of a semi-open impeller, and / or in the volute channel, and thus caused a blockage of the centrifugal pump, to be removed even more effectively. The speed is changed, increased, or decreased, in particular by 5, 10, or 20%, and can be done in a ramp-like manner and / or at intervals. Preferably, the speed is changed, increased, or decreased simultaneously with the opening of the bypass valve and / or for the same length of time as the bypass valve is open.

[0021] According to a preferred embodiment, the bypass line opens into a suction-side pump sump and / or a suction line of the centrifugal pump. The bypass line thus couples a pump pressure side with the pump sump or the suction line. Preferably, a suction-side suction opening is arranged as the inlet of the centrifugal pump in the pump sump such that the impeller extends into the pump sump.

[0022] According to another preferred embodiment, the diameter of the bypass line is at least 20, 30, 40, or 50% smaller than or equal to the diameter of the pressure line. In other words, it is preferred that the bypass line be dimensioned significantly smaller than the pressure line, in particular, it has a smaller inner diameter. Experiments have shown that, for a DN100 pressure line, a DN32 bypass line is sufficient to increase the pressure-side volume flow of the fluid by 20%. The bypass line can also have the same inner diameter as the pressure line.

[0023] According to a preferred embodiment, the bypass line is connected to the pressure line by means of a Y-piece, particularly directed opposite to the main flow direction. Such an oppositely directed Y-piece ensures that as little solid matter as possible, such as pulp, enters the bypass line and has to be pumped again by the centrifugal pump.

[0024] According to another preferred embodiment, a grid, in particular a perforated deflector, is provided between the pressure line and the bypass line. The grid is preferably provided directly at a branch from the pressure line to the bypass line. The grid or perforated deflector can limit the size and / or diameter of the solid particles, in particular at an inlet of the bypass line.

[0025] According to a preferred development, the bypass valve is designed as a slide valve and / or as a valve, in particular as a check valve. In principle, the bypass valve can be designed as any desired valve. However, the bypass valve is preferably electrically operated and / or remotely controllable, so that the bypass valve can be operated, for example, by a control system, i.e. can be opened and closed. In addition, the bypass valve can also be operated manually. A slide valve, also referred to as a gate valve or water slide valve, is generally understood to be a fitting that is used to completely open or close an entire flow cross-section of the bypass line. When designed as a check valve, the bypass valve is preferably designed such that flow is only possible away from the pressure line.The bypass valve is preferably arranged directly adjacent to the pressure line or downstream of the pressure line, for example between the pressure line and the valve.

[0026] According to another preferred embodiment, the operating parameter is selected from the power consumed by the centrifugal pump, the torque of a motor of the centrifugal pump, the speed of an impeller of the centrifugal pump, and / or the current consumed by the centrifugal pump. Other operating parameters are also conceivable, such as the delivery head, values ​​obtained from a pressure sensor, a volume flow sensor, and / or a vibration sensor. A suitable sensor can be provided to detect the operating parameter, for example, a power sensor, a torque sensor, a speed sensor, and / or a current sensor. Preferably, the operating parameter is detected continuously so that a blockage that occurs can be responded to immediately by opening the bypass valve.

[0027] The object is further achieved by a centrifugal pump having a pressure line and / or a pump housing, a bypass line branching off from the pressure line and / or the pump housing and activatable by means of a bypass valve, and a control system, wherein the control system is configured to cause the bypass valve to open if an operating parameter of the centrifugal pump exceeds or falls below a clogging threshold value during the conveyance of liquid with a possible solids content.

[0028] The control unit preferably comprises a microprocessor or the like. The control unit can be an integral part of the centrifugal pump, be provided on the centrifugal pump (e.g., on a housing of the centrifugal pump), be located remotely from the centrifugal pump, and / or be part of a "cloud" located remotely from the centrifugal pump. To detect the operating parameter, a sensor, such as a power sensor, torque sensor, speed sensor, current sensor, and / or voltage sensor, as known from the prior art, can be provided, directly or indirectly connected to the motor, shaft, impeller, and / or the centrifugal pump (especially to the housing, motor housing, and / or pump housing of the centrifugal pump) and / or monitoring the motor, shaft, impeller, and / or the centrifugal pump.

[0029] According to a preferred development, the control is further configured to cause the bypass valve to close after the bypass valve has been opened if the blockage threshold value is undershot or exceeded and / or after a predefined period of time, or to trigger an alarm, to initiate an unblocking routine and / or to switch off the centrifugal pump if the blockage threshold value is not undershot or exceeded after a predefined alarm period.

[0030] According to another preferred embodiment, the centrifugal pump has an impeller for conveying the liquid with the possible solid content and the control is further configured to increase a speed of the impeller conveying the liquid with the possible solid content when the clogging threshold value is exceeded or undershot.

[0031] According to a preferred further development, the centrifugal pump has a suction-side pump sump and / or a suction line into which the bypass line empties.

[0032] According to another preferred embodiment, the diameter of the bypass line is at least 20, 30, 40 or 50% smaller or equal to the diameter of the pressure line.

[0033] According to a preferred embodiment, the bypass line is connected to the pressure line by means of a Y-piece directed in particular against a main flow direction and / or a grid, in particular a perforated deflector, is provided between the pressure line and the bypass line.

[0034] Further features and advantages of the centrifugal pump become apparent to the expert by analogy to the previously described procedure. Short description of the drawings

[0035] The invention is explained in more detail below with reference to the attached drawings using preferred embodiments.

[0036] The drawings show Fig. 1 is a schematic view of a centrifugal pump for carrying out a method for solving a blockage of the centrifugal pump according to a preferred embodiment of the invention, and Fig. 2 is a pump characteristic diagram of the centrifugal pump according to Fig. 1 , in which the delivery head is plotted against the volume flow. Detailed description of the implementation examples

[0037] Fig. 1 shows a schematic view of a centrifugal pump 1 for carrying out a method described below for solving a blockage of the centrifugal pump 1 according to a preferred embodiment of the invention.

[0038] The centrifugal pump 1, designed as a submersible motor pump, conventionally comprises a pump housing 2 with a suction-side suction opening 3 as the inlet, located at the bottom of the pump housing 2 in the figure. A shaft (not shown) is provided in the pump housing 2, which extends vertically in the drawing. The shaft is driven by a motor 4, only indicated, which is arranged vertically opposite the suction opening 3. Facing the suction opening 3, an impeller 5 is provided in the pump housing 2, only indicated, which is driven via the shaft by the motor 4. Furthermore, the centrifugal pump 1 comprises a microprocessor-based controller 6, in which Fig. 1The control unit 6 can be integrated into the centrifugal pump 1, attached to it (e.g., on the pump housing 2), and / or located externally to the centrifugal pump 1. Furthermore, the centrifugal pump 1 has a sensor 7 for detecting an operating parameter of the centrifugal pump 1.

[0039] On the pressure side of the centrifugal pump 1, a pressure line 8 is provided, extending away from the pump housing 2. The pressure line 8 is connected to the pump housing 2 by means of a 90° pipe bend and subsequently extends vertically or linearly upwards away from the pump housing 2 in the plane of the drawing. From the linearly extending portion of the pressure line 8, a bypass line 9 branches off vertically, i.e., horizontally in the plane of the drawing. The bypass line 9 then runs vertically downwards in the plane of the drawing via another 90° pipe bend, finally emptying into a pump sump 10 of the centrifugal pump 1, which is only indicated. The suction opening 3 of the centrifugal pump 1 also extends into the pump sump 10.

[0040] On the horizontal part of the bypass line 9, a bypass valve 11 is provided, which is in the Fig. 1The valve is shown as being manually operated, but can be activated by means of the control unit 6, i.e., it can be opened and closed electrically. According to the proposed method, the control unit 6 is configured to open the bypass valve 11 when the operating parameter of the centrifugal pump 1 exceeds or falls below a blockage threshold during the pumping of liquid containing a possible solids content, as explained in more detail below.

[0041] Fig. 2 shows a pump characteristic diagram of the centrifugal pump 1 according to Fig. 1, in which the delivery head is plotted against the volume flow rate. In normal operation, the centrifugal pump 1 operates at the normal operating point 13, which lies at the intersection between a pump characteristic curve 12 and a system characteristic curve 14 of the pressure line 8, which is designed as DN 100. If the centrifugal pump 1 becomes clogged, for example, because a solid component clogs or jams the impeller 5 during the pumping of liquid, or causes additional friction, the operating parameter of the centrifugal pump 1 exceeds or falls below a clogging threshold. The operating parameter is characterized by the power consumption of the centrifugal pump 1, which, in the event of a clogging, remains below this threshold for a predefined period of time, e.g., more than 5 or 10 seconds, and / or outside a predefined tolerance, e.g., more than 5 or 10%.In addition, other operating parameters are possible, for example a current consumed by the centrifugal pump 1, a speed, a volume flow, a delivery head, pressure values ​​and / or a torque of the centrifugal pump 1.

[0042] If the operating parameter of the centrifugal pump 1 exceeds or falls below the blockage threshold during the pumping of liquid, for example due to an increasing solids content in the liquid, the control unit 6 opens the bypass valve 11. This opening shifts the regular operating point 13 on the pump characteristic curve 12 towards the common system characteristic curve 15 of the pressure line 8 (DN 100, diameter 100 mm) and the bypass line 9 (DN 65, diameter 65 mm), towards the cleaning operating point 16. As shown from Fig. 2As can be seen, the flow rate at cleaning operating point 16 is higher than at the regular operating point 13 of the centrifugal pump 1. The higher flow rate allows the solids clogging the impeller 5 to be released. While the bypass valve 11 is opening, the speed of the impeller 5 can be increased, which helps to clear the blockage.

[0043] After the bypass valve 11 has been opened in this way, the controller 6 checks, for example after 5 or 10 seconds since the bypass valve 11 was opened, whether the blockage threshold has been undershot again and / or causes the bypass valve 11 to close after a predefined period of time, for example after 5 or 10 seconds since the bypass valve 11 was opened. If the blockage threshold has not been undershot after a predefined alarm period, for example after 5 or 10 seconds since the bypass valve 11 was opened, i.e. the blockage still exists, an alarm is triggered and / or the centrifugal pump 1 is switched off.

[0044] Returning to Fig. 1 The bypass line 9 is connected to the pressure line 8 by means of a T-piece or a Y-piece 17 directed against a main flow direction. Between the pressure line 8 and the bypass line 9, a Fig. 1a grid 18, only indicated, is provided which is designed as a perforated deflector. The bypass valve 11 can also be designed as a slide valve and / or as a check valve. The sensor 7 for detecting the operating parameter of the centrifugal pump 1 can, in particular, be provided in a contacting, immediately adjacent and / or rigid manner on the motor 4, assigned to the shaft, on the pump housing 2, on a motor housing of the motor 4 and / or assigned to the impeller 5. In the case of a current sensor, the sensor 7 measures a motor current consumed by the motor 4, or in the case of the operating parameter as power consumed by the motor 4, the sensor measures the electrical power consumed by the motor 4 or the centrifugal pump 1.

[0045] The described embodiments are merely examples that can be modified and / or supplemented in a variety of ways within the scope of the claims. Each feature described for a specific embodiment can be used independently or in combination with other features in any other embodiment. Any feature described for an embodiment of a particular category can also be used in a corresponding manner in an embodiment of a different category. List of reference symbols Centrifugal pump 1 Pump housing 2 suction opening 3 Motor 4 balance bike 5 steering 6 sensor 7 pressure line 8 Bypass line 9 pump sump 10 Bypass valve 11 Pump characteristic curve 12 Regular operating point 13 System characteristic curve 14 Common system characteristic curve 15 Cleaning operating point 16 T- or Y-piece 17 Grid 18

Claims

1. Method for releasing a blockage of a centrifugal pump (1) with a bypass line (9) branching off from a pressure line (8) of the centrifugal pump (1) and / or a pump housing (2) of the centrifugal pump (1) and activatable with a bypass valve (11), comprising the step: if an operating parameter of the centrifugal pump (1) exceeds or falls below a blockage threshold value while pumping liquid with a possible solids content, opening the bypass valve (11).

2. Method according to the preceding claim, comprising the step, after opening the bypass valve (11): if the blockage threshold is undershot or exceeded and / or after a predefined period of time, closing the bypass valve (11), or if the blockage threshold is not undershot or exceeded after a predefined alarm period, triggering an alarm, initiating an unblocking routine and / or switching off the centrifugal pump (1).

3. Method according to one of the preceding claims, comprising the step, if the clogging threshold value is exceeded or undershot: changing, preferably increasing, a speed of an impeller (5) conveying the liquid with the possible solid content.

4. Method according to one of the preceding claims, wherein the bypass line (9) opens into a suction-side pump sump (10) and / or a suction line of the centrifugal pump (1).

5. Method according to one of the preceding claims, wherein a diameter of the bypass line (9) is at least 20, 30, 40 or 50% smaller than or equal to a diameter of the pressure line (8).

6. Method according to one of the preceding claims, wherein the bypass line (9) is connected to the pressure line (8) by means of a Y-piece (17) directed in particular against a main flow direction.

7. Method according to one of the preceding claims, wherein a grid (18), in particular a perforated deflector, is provided between the pressure line (8) and the bypass line (9).

8. Method according to one of the preceding claims, wherein the bypass valve (11) is designed as a slide and / or as a valve, in particular as a check valve.

9. Method according to one of the preceding claims, wherein the operating parameter is selected from power absorbed by the centrifugal pump (1), torque of a motor of the centrifugal pump (1), speed of an impeller of the centrifugal pump (1) and / or current absorbed by the centrifugal pump (1).

10. Centrifugal pump (1) comprising a pressure line (8) and / or a pump housing (2), a bypass line (9) branching off from the pressure line (8) and / or the pump housing (2) and activatable by means of a bypass valve (11), and a controller (6), wherein the controller (6) is configured to cause the bypass valve (11) to open if an operating parameter of the centrifugal pump (1) exceeds or falls below a clogging threshold value while pumping liquid with a possible solids content.

11. Centrifugal pump (1) according to the preceding centrifugal pump claim, wherein the controller (6) is further configured to cause the bypass valve (11) to close after the bypass valve (11) has been opened, if the blockage threshold value is not undershot or exceeded and / or after a predefined period of time, or to trigger an alarm, to initiate an unblocking routine and / or to switch off the centrifugal pump (1) if the blockage threshold value is not undershot or exceeded after a predefined alarm period.

12. Centrifugal pump (1) according to one of the preceding centrifugal pump claims, with an impeller for conveying the liquid with the possible solids content and wherein the control (6) is further arranged, when the blockage threshold value is exceeded or undershot: changing, preferably increasing or decreasing, a speed of the impeller (5) conveying the liquid with the possible solids content.

13. Centrifugal pump (1) according to one of the preceding centrifugal pump claims, with a suction-side pump sump (10) and / or a suction line into which the bypass line (9) opens.

14. Centrifugal pump (1) according to one of the preceding centrifugal pump claims, wherein a diameter of the bypass line (9) is at least 20, 30, 40 or 50% smaller than or equal to a diameter of the pressure line (8).

15. Centrifugal pump (1) according to one of the preceding centrifugal pump claims, wherein the bypass line (9) is connected to the pressure line (8) by means of a Y-piece directed in particular against a main flow direction and / or a grid (18), in particular a perforated deflector, is provided between the pressure line (8) and the bypass line (9).

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