Arrangement for receiving the axial thrust of a centrifugal pump

Abstract

An arrangement for monitoring a centrifugal pump is provided. receiving the residual axial thrust of a centrifugal pump. The arrangement includes a load-relieving device configured to receive the residual axial thrust developed during pump operation, an axial bearing, and a sensor ring is associated with the axial bearing. The ring (10) is divided into segments having sensors at the segment dividing regions.

Claims

1. An arrangement for absorbing axial thrust of a centrifugal pump having a relief device and an axial bearing, comprising: a ring configured to be arranged at the axial bearing, wherein the ring is divided into segments, the ring includes projections on one or both of surfaces of the ring facing in an axial direction which is parallel to a rotation axis of the axial bearing, adjacent segments are connected in a circumferential direction of the ring by webs having a smaller thickness in an axial direction than an axial thickness of the segments, and the projections are arranged a predetermined distance from one another on the segments in regions adjacent to the webs.

2. The arrangement as claimed in claim 1, wherein the ring has sensors in the form of strain gages.

3. The arrangement as claimed in claim 2, wherein the ring includes grooves between a radially inner side of the ring and a radially outer side of the ring.

4. The arrangement as claimed in claim 3, wherein the relief device is configured such that a residual thrust acting on the ring is in a direction of a suction side of the centrifugal pump in all operating conditions.

5. The arrangement as claimed in claim 4, wherein the ring is configured to be elastically deformed by the residual thrust.

6. The arrangement as claimed in claim 5, wherein the ring is dimensioned such that, starting from a maximum gap width in a rest state, an axial gap between a double piston and a casing part of the relief device under operating conditions is a minimum width which prevents contact between axially facing surfaces of the double piston and the casing part.

7. The arrangement as claimed in claim 6, wherein the axial bearing is a hydrodynamic bearing.

8. The arrangement as claimed in claim 7, wherein the relief device is a relief disk.

Description

(1) In the drawings:

(2) FIG. 1 shows a detail of a multistage centrifugal pump illustrated in section,

(3) FIG. 2 shows a detail of a centrifugal pump with a cardanic ring arranged on the suction side and pressure side,

(4) FIG. 3 shows a schematic illustration of a centrifugal pump with a device for processing signals,

(5) FIG. 4 shows a perspective illustration of the ring according to the invention,

(6) FIG. 5 shows a side view of the ring according to the invention.

(7) FIG. 1 shows a centrifugal pump in which a shaft 2 is mounted in a casing 1.

(8) The shaft 2 carries multiple impellers 3. The drawing as per FIG. 1 illustrates two impellers 3 by way of example.

(9) A double piston 4 of a relief device is fastened on the shaft 2. The double piston 4 is surrounded by a casing part 5. Two radial gaps 6 and 7 are formed between the double piston 4 and the casing part 5. An axial gap 8 is situated between the radial gaps 6 and 7. The axial gap 8 has a variable width s.

(10) At the pressure-side end of the centrifugal pump, the shaft 2 is received by a hydrodynamic axial bearing 9. The axial bearing 9 is assigned a ring 10. The ring 10 is in the form of a cardanic ring. The ring 10 serves for example for compensation of alignment errors which occur during the assembly of a multistage centrifugal pump. The ring 10 is preferably dimensioned in such a way that it is deformed elastically by the residual thrust occurring in the centrifugal pump, which residual thrust is directed toward the suction side. Here, the spring constant of the ring 10 is matched to the characteristics of the relief device.

(11) The relief device is designed in such a way that, in all the operating states of the centrifugal pump, a residual thrust acting in the direction of the suction side occurs. Starting from a maximum width s of the axial gap 8 in the rest state of the centrifugal pump, by way of the elastic deformation of the cardanic ring 10, the gap 8 is closed under operating conditions to a minimum width at which contact between those surfaces of the double piston 4 and of the casing part 5 which delimit the gap 8 is still avoided. The axial gap 8 has a self-regulating function for the relief device.

(12) By integration of the ring 10 into a suitable measuring apparatus, early detection of forces indicating impermissible hydraulic conditions or bearing wear becomes possible. The deformations of the ring 10 that occurred during pump operation are detected by means of sensors and are transmitted as a signal via a line 11 to a device for signal processing. The direct mechanical coupling of the ring 10, acting as an axial force transducer, to the measuring system makes it possible for signals to be measured without the damping influence of a fluid film which, in the case of contactless transducers, is at all times situated between sensor and component.

(13) FIG. 2 illustrates a variant of an axial force measuring apparatus by way of example. Such an apparatus may be attached for example to the pressure-side bearing carrier 12 of a high-pressure ring-section pump. The individual components of the measuring apparatus are accommodated by a cylindrical casing 13. In the variant illustrated in FIG. 2, two rings 14, 15 are used.

(14) In this variant of the invention allows the measurement of axial forces in both directions of action. For the purpose of stabilizing the rotodynamic behavior, the cardanic rings 14, 15 can optionally be prestressed. This occurs via a spacer ring 16 at the suction-side ring 14 and via a spacer bush 17 at the pressure-side ring 15.

(15) The introduction of force into the apparatus is realized, starting from the pump rotor, via an axial plate 18 which is connected rotationally conjointly to the shaft 2. The axial plate 18, according to the direction of action of the axial thrust, transmits the force to one of two axial grooved ball bearings 19, 20, which are coupled directly to the cardanic rings 14, 15. The cardanic rings 14, 15 are subjected to bending stress and thus constitute spring elements in a force-fit chain. Unbalanced residual forces are passed on via a spacer ring 16 or a spacer bush 17 into the casing. The cardanic rings 14, 15 are secured against rotation by in each case one cylinder pin 21. The deformation state is transmitted via lines 22 and 23 to a device for signal processing.

(16) FIG. 3 schematically illustrates the signal processing of measurement signals recorded via the cardanic rings 14, 15 at a high-pressure ring-section pump 24. The first link in the axial force measurement chain is constituted by the cardanic rings 14, 15, to which strain gages (not illustrated in FIG. 3) are applied. As already indicated, for each direction of loading, one ring 14 or 15 is provided. Installed on each ring 14, 15 are two full-bridge strain gages (not illustrated in FIG. 3), whose input and output signals are switched in parallel. Through feeding with a constant voltage via a measurement amplifier and with identical characteristic values of the strain gages used in the bridges, the circuit forms the electrical mean value of the two bridge output signals. In this way, the non-uniform stress distributions caused by possible eccentric introduction of force into the rings are compensated.

(17) The output signal is passed via a strain gage amplifier 25 on to a measurement value converter 26. This converts the signal into an output voltage of 0-10 V. The signal is subsequently passed to a data acquisition board of a computer 27, whereby the display and further processing of the recorded measurement data is possible.

(18) The apparatus illustrated in FIG. 3 is to be regarded as a test setup. For practical operation, it is mostly possible for the elements used to be integrated into the centrifugal pump 24. It is also possible for individual elements, for example the pressure-side ring 15, to be dispensed with in practical use, where appropriate. Also, a hydrodynamic axial bearing may be used instead of two axial grooved ball bearings 19, 20.

(19) FIG. 4 shows by way of example a ring as is used for example in FIG. 1 as ring 10 or in FIG. 2 as ring 14 and ring 15. The ring is divided into a total of five segments 28. The five circle segments 28 are connected to elements 29 which, in the exemplary embodiment, are in the form of webs. The height of the webs 29 is significantly less than the height of the circle segments 28. Each circle segment has projections 30 on both face sides. On one side, the individual segments 28 are delimited by the projections 30. On the opposite face side, the projections 30 are arranged slightly set back into the individual segments.

(20) FIG. 5 shows a lateral view of a ring. The projections 30 are arranged offset from one another by a distance L between one face side and the opposite face side. Moreover, in the illustration as per FIG. 5, it can be seen that the segments 28 of the ring are provided with grooves 31. Sensors 32 are arranged on the elements 29 connecting the circle segments 30 and, in the exemplary embodiment, are in the form of strain gages.