EP1977112B1 - Centrifugal pump having an axial thrust balancing device - Google Patents

Description

The invention relates to a single-stage centrifugal pump with Axialschubausgleichseinrichtung, wherein in the housing of the centrifugal pump connected to a shaft impeller is rotating, at least one arranged between impeller and housing split ring seal forms a discharge space, the discharge space is connected to a pressure-transmitting connection to the pressure range of the centrifugal pump, and between shaft and housing a shaft seal is arranged.

The principle of an axial thrust relief is in KSB Centrifugal Pump Dictionary, 3rd updated edition, July 1989, pages 32-37 , described. The oldest type of Axialschubentlastung according to Figure 7 provides that an impeller is provided with suction and pressure side sealing gaps. The arranged in the pressure-side Radseitenraum sealing gap is formed as a throttle gap and separates two rooms of different pressure levels. A relief space arranged on a smaller diameter is relieved to the suction side of the impeller by relief bores which are arranged in the impeller wheel supporting the impeller blades. Thus, a desired reduction of the axial forces on the impeller and the other rotating components is achieved, depending on the respective operating conditions.

The publication FR 2 075 023 , which is considered to represent the closest prior art, discloses the features of the preamble of claim 1.

A generic Axialschubentlastungseinrichtung is through the DE 196 31 824 A1 known. In addition, a first radially flowed regulating gap between the impeller outlet and a suction-side radial bearing is arranged in the suction-side impeller region. Such a suction-side shaft bearing is designed as a sliding bearing, arranged directly on the Laufradsaugmund and consuming to produce.

Next, a second radially flowed control gap is arranged in the pressure-side impeller region with respect to the first control gap on a smaller diameter. With this control column solution, a complete compensation of the hydraulic axial thrust generated by the impeller and in the axial direction a non-contact operation of the impeller is possible. An additional thrust bearing is no longer required for the normal operating condition. At best, for briefly to be traversed operating conditions during a start-up or discharge phase of a pump, the rule column limiting surfaces are designed as thrust bearing surfaces for safety's sake.

Another device for Axialsühubausgleich for single or multi-stage centrifugal pumps with closed wheels is through the DE 34 36 979 A1 known. Here, one or more pressure compensation openings are arranged in a partition between a housing annulus and the suction-side side space of the impeller. This solution is used in applications in which can be achieved with the conventional devices for Axialschubausgleich still no satisfactory result. Above all, it serves to correct existing centrifugal pumps. Such a special case is usually given for large pumps installed in complex systems.

By the DE 20 43 550 C2 is known from a compressor, a control device for an axial thrust compensation of a hydrostatic thrust bearing assembly in which the change in the carrying capacity is achieved with a hydrostatic device. For this purpose, a shaft driving the impeller is held radially in a bearing carrier in two cylinder bearings and additionally axially positioned in two disc-shaped thrust bearings. A continuously pumping device generates in the thrust bearings a hydrostatic bearing pressure which can vary depending on the gap width of the bearing. Axial shifts of the shaft lead to such changes in the gap width and influence the hydrodynamic bearing pressures in the two thrust bearings. A pressure difference between the two bearings serves as a control variable for a control valve of an axial thrust balancing device of the impeller. It has a complex structure for special Special cases is justified. The disadvantage here is the risk of environmental hazards due to the complex lubricant lines, as they can leak or be damaged.

And the DD 231 829 A1 shows in a centrifugal pump another method to compensate for an axial thrust. Behind the impeller, a compensating piston rotating with the shaft is arranged in an additional housing part, the diameter of which corresponds approximately to half the impeller diameter. Between the balance piston and the surrounding housing a long throttle section is formed, whereby, seen in the flow direction, form different pressure regions in front of and behind the balance piston. With the aid of two pressure measuring points, which measure the pump pressure in the discharge nozzle and in the space behind the balance piston, a pressure difference that can be determined from this is transmitted to a computer. In addition, the signal of a speed measuring device is fed into the computer. The calculator determines a discharge pressure for the space behind the balance piston at a difference occurring between axial thrust and balancing force of the balance piston. And by a control signal to a control valve, the pressure in the area behind the balance piston is changed so far until a state of equilibrium and thus relief of the shaft bearing occurs. The disadvantage is the detection and processing of three parameters and the use of a special balance piston, which does not contribute directly to the function of the pump, increases the overall volume and variety of parts and increases the susceptibility to failure.

The invention is therefore based on the object to achieve a less complex and reliable reduction of the axial thrust, which ensures a high bearing life and a long life of the shaft seal for a roller bearing pump shaft.

The solution provides that the shaft is provided in a conventional manner with at least one thrust bearing receiving axial forces and that via a connection, a pressure difference between a pressure in the discharge chamber and a body other pressure in the centrifugal pump housing as a direction constant and permissible axial force presses the rotating pump parts against the rolling bearing. This ensures a continuous and defined load for the bearings and also for the shaft seal. It has been recognized that the cause of damage to bearings and shaft seals is a problem of known balancing devices at certain operating points to achieve only an insufficient reduction of the axial force or to avoid a pendulum of the axial force by the value 0 can. The conditional in the latter case sign change of such a small axial force leads to the so-called swimming of the rotating parts. This turns out to be their alternating axial movement with appreciable frequency between the stops of the axial bearing. Such minimal oscillating movements have in addition to the damage to the bearings and the shaft seals also an adverse noise result and are inventively avoided.

Since the respective operating conditions are known for the design of a centrifugal pump, the dimensions of the split-ring seals, the shaft seal chamber and the relief chamber are selected in order to achieve a defined axial thrust on the force-absorbing rolling bearing via the connection and the different pressures. In this case, according to one embodiment, the acting axial force is smaller than the permissible bearing load of the force-absorbing rolling bearing, whereby the bearing life is extended.

According to further embodiments, a throttling device arranged in the connection sets in the discharge chamber the direction-constant axial force arising from the pressure difference on the roller bearing. For a centrifugal pump operation with approximately constant operating parameters, it is a fixed or adjustable throttle device. For operating states in which the variance of the operating parameters is very low or which do not require an adaptation to changed operating parameters, the throttle device is designed as a permanently adjustable throttle device. And for applications with variable operating parameters of a centrifugal pump is by a arranged in the connection, adjustable or controllable throttle device in the discharge space, the direction constant axial force generated on the bearings. As a result, a low and constant in their direction axial force is always maintained. Their size is chosen so that it always lies well below the permissible axial bearing force in order not to adversely affect the bearing life. And their size is chosen so large that a self-adjusting axial force prevents floating of the rotating parts and thus their premature destruction reliable.

According to a further embodiment, a variable via the connection in its pressure relief space on the suction side or the pressure side of the impeller is arranged. Thus, only one relief space is changed in its pressure via the pressure-transmitting connection, in order to obtain a defined axial force on the rolling bearing. The connection can be made between the suction side or the pressure side of the pump. This depends on the dimensions inside the pump housing and those of the impeller.

According to a further embodiment, a sensor detects an axial roller bearing load, a controller generates with the sensor signal an actuating signal for an adjustable throttle device and the throttle device sets in the discharge space a rolling bearing loading axial force. This has the additional advantage of independence of the control of the wear behavior of the wetted parts. A change in size in one of the impeller throttle gaps would cause different pressure conditions in the relief space and thus other forces on the rolling bearing. However, such gradually occurring changes during a longer period of operation are detected by the sensor immediately and compensated by the controller in the form of an adapted control signal.

In this case, the sensor detects the axial bearing load according to size and direction. For this purpose, a further provision provides that one or more controller characteristic (s) stored in the controller corrects or corrects influences that alter the axial bearing load. With the aid of the sensor signal, instabilities, axial forces and / or pressures occurring in the region of the bearing are detected in a relief and / or shaft seal chamber. The controller processes these signal values and restores the permissible operating status with the help of one or several controller characteristic (s). Thus, even with incalculable operating situations, which are caused by surprising external influences, reliably prevents overloading and thus damage to the bearings and the shaft seal.

Fig. 1 - 4

verschiedene Ausbildungen eines Entlastungsraumes am Laufrad einer einstufigen Kreiselpumpe.

Embodiments of the invention are illustrated in the drawings and will be described in more detail below. It show the

Fig. 1 - 4th

various embodiments of a discharge chamber on the impeller of a single-stage centrifugal pump.

Fig. 1 shows the impeller 2 has in the region of the impeller inlet via a suction-side throttle gap in the form of a gap seal 4, which ensures a high pressure in the suction side impeller side space 5 and reduces gap losses. Depending on the operating conditions of such a centrifugal pump, the impeller 2 on a larger diameter on a second, here pressure-side gap seal 6, which ensures a high pressure in the larger side diameter impeller side space 7 in the larger diameter range. The pressure-side gap seal 6 bounded or enveloped with its diameter a arranged on a smaller diameter discharge chamber 8, which is connected via a connection 13 with an adjustable throttle device 14 disposed therein with a location other pressure, here the discharge nozzle 15 of the centrifugal pump. The connection 13 may be designed as a conventional conduit system. The in Fig. 1 selected location other pressure has a higher pressure than that of the discharge chamber 8 and the choice of location is dependent on the subsequent operating conditions of a pump. The location of other pressure may be in the area of the impeller outlet, a guide, the discharge nozzle or the location is as an external Pressure reservoir formed. As a result, acting on the opposite end faces of the impeller from the various pressures resulting forces that cause a resultant axial force F _A.

By choosing the gap diameter D of the pressure-side gap seal 6, the gap width S and with the aid of the connection 13 with throttle 14, the pressure level on the impeller back or in the impeller side impeller range is set to a value. From the area ratios in the suction-side impeller side space 5, in the pressure-side impeller side space 7 and in the relief space 8 as well as the pressures in these spaces, different forces result. Another force results from the pressure in the suction port 18 in conjunction with a shaft seal 17 in the space 16, since the latter seals against atmospheric pressure from the pressure loads on the impeller 2 results in a defined axial force F _A, the impeller 2 and the driving shaft 10 in the direction of Rolling 11 to 11.2 pushes. Of the rolling bearings arranged in the bearing support 12, the rolling bearing 11 is formed in the embodiment shown as a pure radial bearing, while two paired bearings 11.1 and 11.2 record the radial and axial forces due to their training. They consist of two angular contact ball bearings, whereby other types of rolling bearings are applicable.

And the shaft 10, which is mounted here in a bearing carrier 12, may also be formed with elimination of the bearing carrier as part of a driving electric motor. In such a case, the bearings of the motor are dimensioned accordingly to accommodate an axial thrust of the pump can. If this is not the case, the appropriately designed bearing support 12 or the pump cover 3 can be provided with a - known per se, not shown here - short stub shaft, which would be held only in a rolling bearing 11.1. Their shaft end would then be connected to a stub shaft of a block motor.

With the help of the adjustable throttle device 14, the pressure level in the discharge chamber 8 is set during operation over a wide range of values. at Use of a throttle device 14 are previously customary, shown here dashed lines relief holes 9 on the impeller 2 is no longer necessary and available. The pressure in the relief chamber 8 and a shaft seal chamber 16 is adjusted so that a resulting axial force F _{A is} formed as a fixed bearing shaft bearing in the form of rolling bearings 11.1, 11.2 always below their allowable limits. Should be set during the life of a pump by wear in the gap seal 4 of 6 other pressure conditions in space 5 and / or 8 or vibrations of the rotating parts occur, so by simply adjusting the throttle device 14 of the original load condition of the bearings can be restored.

Fig. 2 corresponds in structure to the illustration in Fig. 1 However, wherein the pressure-side discharge chamber 8 via the connection 13 with the suction side 18 of the centrifugal pump is in operative connection. Also in this case, the impeller 2 is equipped with no relief holes. Instead, the pressure level in the discharge chamber 8 and shaft seal chamber 16 is adjusted by means of the adjustable throttle device 14.1 so that the load on the shaft seal 17 and the rolling bearing 11.1, 11.2 always below the allowable bearings Limits are. For detecting the storage conditions, a sensor 19, which is connected to a controller 20 is used. Changes in the storage condition are detected by the sensor 19 and passed on to the controller 20 on. This determines a controller signal, with the aid of which the controllable throttle device 14.1 adjusted and the permissible axial force F _A is set again.

Fig. 3 shows a variant in which a suction-side relief space 21 is formed by a second, arranged on a larger diameter, suction-side throttle gap in the form of a gap seal 22 with a gap diameter D and a gap width s. The in the Fig. 1 and 2 represented pressure-side relief space is omitted in this variant. This suction-side relief chamber 21 is connected via the connection 13 with integrated throttle device 14 with the pressure range from the discharge nozzle 15 connected to the centrifugal pump. By appropriate adjustment of the throttle device 14, the generation of the continuous axial force F _{A is} ensured.

Fig. 4 shows a variant of Fig. 3 , wherein the centrifugal pump is designed for operation with a very high inlet pressure. As a result, the suction-side relief space 21 is connected to the suction region 18 via the pressure-carrying connection 13 in order to ensure the defined axial force F _A on the shaft bearing 11.1, 11.2. Again, with the aid of a bearing sensor 19, a control device 20 and a controllable throttle device 14.1 during a running operation, the axial force F _A can be influenced.

In the embodiments of the Fig. 2 and 4 is in the range of the axial forces receiving bearing, which consists of two bearings 11.1, 11.2 in the form of angular contact ball bearings, arranged a bearing load sensor, which continuously determines the axial force. He may as well in the embodiments of the Fig. 1 and 3 Find use. It provides a signal to a control device 20, which compares a respective existing axial force F _A with a stored setpoint. In the event of a deviation, the control device 20 generates a control signal for an adjustable throttle device 14.1. This regulates the pressure in the relief chamber 8 or 21 to a value which has a defined, low axial force F _A for the rolling bearings 11.1, 11.2 result.

Claims (8)

1. Single-stage centrifugal pump having an axial-thrust balancing device, an impeller connected to a shaft being arranged rotatably in the casing of the centrifugal pump, at least one split-ring seal (6) arranged between the impeller (2) and casing forming a relief space, the relief space being connected to the pressure region of the centrifugal pump by means of a pressure-transmitting connection (13), and a shaft seal being arranged between the shaft (10) and casing, characterized in that the shaft (10) is provided with at least one rolling bearing (11.1, 11.2) absorbing axial forces, and in that a pressure difference between a pressure in the relief space (8, 21) and a location of another pressure in the centrifugal-pump casing (1) presses, as a directionally constant and permissible axial force (F_A) the rotating pump parts (2, 10) against the rolling bearing (11.1, 11.2) via the connection (13).
2. Centrifugal pump according to Claim 1, characterized in that the axial force (F_A) is lower than the permissible bearing load of the force-absorbing rolling bearing (11.1, 11.2).
3. Centrifugal pump according to Claim 1 or 2, characterized in that a throttle device (14) arranged in the connection (13) sets in the relief space (8, 21) the directionally constant axial force (F_A) upon the rolling bearing (11.1, 11.2) which arises from the pressure difference.
4. Centrifugal pump according to Claim 3, characterized in that the throttle device (14) is designed to be adjustable or controllable.
5. Centrifugal pump according to Claim 1, 2, 3 or 4, characterized in that a relief space (8, 21), the pressure of which is variable via the connection (13), is arranged on the suction side or the pressure side of the impeller (2).
6. Centrifugal pump according to one of Claims 1 to 5, characterized in that a sensor (19) detects a rolling-bearing load, in that a controller (20) generates by means of the sensor signal an actuating signal for a controllable throttle device (14.1), and in that the throttle device (14.1) sets in the relief space (8, 21) a directionally constant axial force (F_A) loading the rolling bearing (11.1, 11.2).
7. Centrifugal pump according to Claim 6, characterized in that the sensor (19) detects an axial bearing load in terms of magnitude and of direction.
8. Centrifugal pump according to one of Claims 1 to 7, characterized in that one or more controller characteristic curves stored in the controller (20) corrects or correct influences which vary the axial bearing load.

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