Patent ID: 12258970

FIGS.1to3illustrate an embodiment of a centrifugal pump1according to the present invention. The centrifugal pump1includes a pump casing2having a casing lower part4, a casing upper part8, and a hollow-cylindrical casing middle part6arranged there between. A fluid inlet10and a fluid outlet12of the centrifugal pump1are formed on the casing lower part4. The fluid inlet10is flow-connected to five pump stages14of the centrifugal pump1which are arranged in the region of the casing middle part6over one another in the direction of the casing upper part8. Each of the pump stages14includes a housing16which is arranged in the pump casing2in a stationary manner and in which an impeller18and a diffuser20are arranged in a manner well-known to the skilled person. The housings16are each flow-connected to adjacent housings16, wherein a housing16which is last in the direction of the casing upper part8is flow-connected via an opening22to a pressure chamber24which is formed in the region of the casing upper part8.

The impellers18of the pump stages14are connected to a pump shaft26in a rotationally fixed manner, said pump shaft extending concentrically to the casing middle part6through the pump casing2and projecting out of the pump casing2at the casing upper part8. There, an external part27of the pump shaft26has a coupling end which by means of a coupling29is connected to a motor shaft of a drive motor which is not represented and which is mounted on a motor stool28which is formed on the casing upper part8. When the pump shaft26is driven, the impellers18of the individual pump stages deliver a fluid from the fluid inlet10through the pump stages14to the pressure chamber24, from where the fluid flows via an annular gap30between the wall of the casing middle part6and the housing16of the pump stages, to the fluid outlet12of the centrifugal pump1. Alternatively, the fluid outlet12could also be situated at the opposite axial end of the centrifugal pump1.

A turbine wheel32is rotatably mounted in the pressure chamber24, downstream of the pump stage14which is last in the flow direction and which is directly adjacent the pressure chamber24. This turbine wheel32is arranged around the pump shaft26, wherein the pump shaft26engages through a hub34of the turbine wheel32, and the turbine wheel32is rotatably mounted in relation to the pump shaft26. Several blades36, departing from the hub34, extend outwards in the radial direction, where they are connected to an outer ring38of the turbine wheel32. Hereby, the blades36of the turbine wheel32in the flow direction of the centrifugal pump are arranged directly above the opening22which is formed on the last pump stage14and via which the delivery flow in the axial direction of the pump housing flows through the centrifugal pump1into the pressure chamber24. The delivery flow exerts a torque upon the turbine wheel32by way of it hitting the blades36of the turbine wheel32, by which means this is brought into a rotational movement. The torque which is exerted by the delivery flow onto the turbine wheel32is hereby directed counter to the torque which is exerted upon the impeller18via the pump shaft26for the purpose of fluid delivery. This is due to the fact that the blades36of the turbine wheel32are aligned quasi counter to blades40of the impeller18. Thus, the turbine wheel32rotates oppositely to the pump shaft26in operation.

The turbine wheel32forms a transducer of a flow measuring device3, with which the delivery flow through the centrifugal pump1may be continuously determined during the operation of the centrifugal pump, in order to e.g. subsequently be included in the activation of the not shown drive motor for the centrifugal pump1. The turbine wheel32, which is represented inFIGS.1and2, for forming a transducer is provided with three signal means in the form of permanent magnets42which are arranged in three corresponding recesses44formed on the outer peripheral side of the outer ring38of the turbine wheel32at varying angular distance in order to be able to determine the rotation direction of the turbine wheel32.

An threaded opening46is formed on the casing upper part8of the pump casing2. A sensor housing48of the flow measuring device3which extends down to the direct vicinity of the outer ring38of the turbine wheel32is in threaded connection with this opening46. The opening46may additionally serve as a vent opening for the centrifugal pump1, and a vent opening of an existing pump design may serve for the integration of a flow measuring device3according to the present invention.

This sensor housing48includes a first magnetic flux sensor50which on rotation of the turbine wheel32detects the varying magnetic field resulting from the three permanent magnets42of the turbine wheel32.

As seen inFIGS.1and2, a rotatable disc52is mounted on the pump shaft26and fixed to the pump shaft for rotation with the pump shaft. The rotatable disc52includes a number of permanent magnets53arranged at its periphery. Furthermore, the sensor housing48includes a second magnetic flux sensor51which on rotation of the rotatable disc52detects the varying magnetic field resulting from the number of permanent magnets53of the rotatable disc52.

The sensor housing48is preferably made of corrosion resistant metal, however it could also be made of plastic. However, the sensor housing48should generally not be ferromagnetic, as this could disturb the magnetic fields detected by the magnetic flux sensors50,51.

The flow measuring device3is adapted to measure, during operation of the centrifugal pump1, the delivery flow of the pump on the basis of a first measurement signal generated by the first magnetic flux sensor50as a result of the rotation of the turbine wheel32. Furthermore, according to the present invention, the flow measuring device3is adapted to include in the measurement of the delivery flow a second measurement signal generated by the second magnetic flux sensor51as a result of the rotation of the rotatable disc52.

According to an alternative embodiment of the present invention, a single magnetic flux sensor may be used for generating both the first measurement signal and the second measurement signal. Such single magnetic flux sensor may be arranged at any suitable position in the sensor housing48. However, by using a separate first magnetic flux sensor50for generating the first measurement signal and a separate second magnetic flux sensor51for generating the second measurement signal, the first and second measurement signals need not be separated in software by demodulation, as the signals are already created separately. Furthermore, the first and second magnetic flux sensors50,51may be positioned differently in the sensor housing48, so that the position of each magnetic flux sensor may be optimised in relation to the position of the magnets42of the turbine wheel32and the magnets53of the rotatable disc52, respectively. Thereby, the provided first and second measurement signals may be more reliable.

As seen inFIG.2, the pump shaft26extends through a shaft seal54arranged in the outer wall of the pump casing2. As mentioned above, the external part27of the pump shaft26has a coupling end for connection with a not shown motor shaft, and the rotatable disc52is mounted on the external part27of the pump shaft26. In the illustrated embodiment, the rotatable disc52is clamped on a ring of the shaft seal54. However, in the case of larger pumps, it may be preferred that the rotatable disc52is arranged higher on the pump shaft26, nearer to the coupling29. The rotatable disc52is easily accessible outside the casing2of the pump1and does not take up space inside the pump casing. The rotatable disc52is directly accessible and visible so that is may be controlled that it is correctly mounted and so that is may be easily serviced. It is furthermore an advantage that the magnets53of the rotatable disc52do not have to come into contact with the fluid pumped by the centrifugal pump1. Therefore, the choice of material for the magnets53is greater. For instance, neodymium-magnets may be used which are much stronger than standard permanent magnets. Neodymium-magnets should not be used in contact with drinking water.

In the embodiment illustrated inFIGS.4and5, the rotatable disc52is composed by two disc halves55,56clamped together and thereby clamping the pump shaft26in a central hole57through the rotatable disc52. The disc halves55,56are clamped together by means of screws mounted in screw holes62. As indicated inFIG.4, the permanent magnets53of the rotatable disc52may be mounted in the disc in that they are inserted in the radially outer parts of centrally open holes63. However, the rotatable disc52may be constructed in any other suitable way. The material of the rotatable disc52is preferably metal, such as aluminium, but any suitable material may be used. In the illustrated embodiment, two permanent magnets53are arranged symmetrically at the periphery of the rotatable disc52. However, any other suitable number of permanent magnets53could be used, including one, as well as three or more. Furthermore, the permanent magnets53could be arranged at varying angular distance in order to be able to determine the rotation direction of the rotatable disc52.

As seen inFIG.2, the sensor housing48is elongated and extends through the opening46formed in the outer wall of the pump casing2. The sensor housing48includes a first part58arranged inside the pump casing2and a second part59arranged outside the pump casing. The first magnetic flux sensor50is arranged in the first part58of the sensor housing48, and the second magnetic flux sensor51is arranged in the second part59of the sensor housing48. The position of the first magnetic flux sensor50may be optimised in that it may be positioned very close to the position of the magnets42of the turbine wheel32and inside the pump casing, so that the magnetic field of the turbine wheel does not have to be detected through the pump casing2. A short distance between the first magnetic flux sensor50and the magnets42of the turbine wheel32will reduce possible disturbances of the signal. On the other hand, also the position of the second magnetic flux sensor51may be optimised in that it may be positioned outside the pump casing2, so that the magnetic field of the magnets53of the rotatable disc52does not have to be detected through the pump casing. Thereby, the provided first and second measurement signals may be even more reliable.

As illustrated inFIG.2, the first magnetic flux sensor50and the second magnetic flux sensor51are arranged in the sensor housing48with a mutual first distance d1in a longitudinal direction L of the sensor housing48. The first magnetic flux sensor50is arranged at a, during rotation of the turbine wheel32, shortest second distance d2from the at least one permanent magnet42of the turbine wheel32. The second magnetic flux sensor51is arranged at a, during rotation of the rotatable disc52, shortest third distance d3from the at least one permanent magnet53of the rotatable disc52. The shortest third distance d3is at least 2 times, preferably at least 2.5 times, and most preferred at least 3 times, the shortest second distance d2. The mutual first distance d1is within ±30 percent, preferably within ±20 percent, and most preferred within ±10 percent of the shortest third distance d3.

Preferably, at least the second magnetic flux sensor51is of an omnidirectional type. Thereby, the exact position of the rotatable disc52in relation to the second magnetic flux sensor51may not be critical. This may be an advantage, for instance because the same sensor housing design may be used for centrifugal pumps of different size, whereby a preferred position of the rotatable disc52on the pump shaft26may vary due to various constructional considerations.

Preferably, the first magnetic flux sensor50has a direction of maximum sensitivity, and the first magnetic flux sensor50is arranged with its direction of maximum sensitivity extending in the longitudinal direction L of the sensor housing48and in the direction of the, during rotation of the turbine wheel32, closest position of the at least one permanent magnet42of the turbine wheel32. Thereby, the sensitivity of the first magnetic flux sensor50may be maximised. This may be advantageous in order to obtain a reliable first measurement signal without using special magnets providing a stronger magnetic field.

According to the present invention, the flow measuring device3includes a not shown processor adapted to calculate an uncorrected delivery flow on the basis of the first measurement signal generated by at least one magnetic flux sensor50,51as a result of the rotation of the turbine wheel32. The processor is adapted to calculate a corrected delivery flow by correcting the uncorrected delivery flow by means of a correction factor based on the second measurement signal generated by the at least one magnetic flux sensor50,51as a result of the rotation of the rotatable disc52.

The first and second magnetic flux sensors50,51may be Hall sensors, however, coil sensors may be preferred due to better sensitivity.

LIST OF REFERENCE NUMBERS

L longitudinal direction of sensor housing1centrifugal pump2pump casing3flow measuring device4casing lower part6casing middle part8casing upper part10fluid inlet12fluid outlet14pump stage16housing18impeller20diffuser22opening24pressure chamber26pump shaft27external part of pump shaft28motor stool29coupling30annular gap32turbine wheel34hub of turbine wheel36blade of turbine wheel38outer ring of turbine wheel40blade of impeller42permanent magnet of turbine wheel44recess of turbine wheel46vent opening of casing upper part48sensor housing50first magnetic flux sensor51second magnetic flux sensor52rotatable disc53permanent magnet of rotatable disc54shaft seal55,56disc half of rotatable disc57central hole of rotatable disc58first part of sensor housing59second part of sensor housing60ring of shaft seal61screws62screw holes63holes for magnets64electric connection for sensor housing