A shaft sealing device

Abstract

Described and claimed is a shaft sealing device for a pump housing. The shaft sealing device comprises seal housing, a shaft seal, and a pump fluid sensing device. The seal housing mounts the sealing device in an upper part of a pump housing. The shaft seal circumferentially contacts a drive shaft extending through the pump housing and prevents pump fluid from leaking out of the pump housing. The pump fluid sensing device comprises a temperature sensor mounted in a sensing space defined by the seal housing and at a position where it is only in contact with pump fluid if a level of pump fluid in the pump housing is sufficient to keep the shaft seal lubricated. Further, a pump housing comprising a shaft sealing device and a pump assembly comprising a pump housing with a shaft sealing device are described and claimed.

Description

Description

[0001] The present invention is directed to a shaft sealing device for a pump housing, a pump housing, and a pump assembly.

[0002] Centrifugal pump assemblies commonly have a pump housing with one or more impellers and an electric motor for driving the one or more impellers. A drive shaft extends between a rotor of the electric motor and the drive shaft. Many electric motors used for driving smaller pump assemblies are so-called wet-running electric motors where pump fluid is used to lubricate the bearings of the drive shaft and cool the electric motor by flowing through the rotor chamber. The pump fluid flows along the drive shaft out of the pump housing and into the rotor chamber.

[0003] For other and, in particular, larger centrifugal pump assemblies, dry-running electric motors are used. These pump assemblies are also referred to as dry runners. One challenge with dry-running electric motors is that the pump fluid needs to be contained in the pump housing and should not or at least only in controlled amounts leak out of the pump housing where the drive shaft extends through an upper part of a pump housing. Dedicated shaft seals are installed in the pump housing which allow the drive shaft to rotate while at the same time sealing the pump housing.

[0004] The surfaces of the shaft seal which are in contact with the rotating drive shaft are commonly lubricated with pump fluid, i.e., limited amounts of pump fluid are allowed to flow between the driveshaft and the pump seal as lubricant. Commonly pump fluid is available in abundance. In case air accumulates at the top of an upright standing pump housing, the shaft seal is no longer lubricate and, therefore, subject to excessive wear.

[0005] Against this background, it can be considered an object of the present invention to reduce the risk that the shaft seal of a dry-running centrifugal pump is not sufficiently lubricated with pump fluid.

[0006] The problem is solved by a shaft sealing device for a pump housing, a pump housing, and a pump assembly according to the independent claims. Preferred embodiments of the shaft sealing device and the pump assembly are the subject matter of the dependent claims.

[0007] In a first aspect, the problem underlying the present invention is solved by a shaft sealing device for a pump housing. The shaft sealing device comprises a seal housing, a shaft seal, and a pump fluid sensing device. The seal housing is configured for mounting the shaft sealing device in an upper part of a pump housing. The shaft seal is configured for circumferentially contacting a drive shaft extending along a rotational axis through the upper part of the pump housing and for preventing pump fluid from leaking out of the pump housing where the drive shaft extends through the pump housing. The pump fluid sensing device comprises a temperature sensor mounted in a sensing space partially defined. The sensing space is in fluid communication with pump fluid in the pump housing. The temperature sensor is further mounted in the seal housing at a position where it is only in contact with pump fluid if a level of pump fluid in the pump housing is sufficient to keep the shaft seal lubricated.

[0008] In other words, a sealing device to be installed in an upper part of a pump housing with a pump fluid sensing device is described. The center of the shaft sealing device is formed by a shaft seal that surrounds the drive shaft where the drive shaft protrudes through the pump housing. The drive shaft is used for transmitting torque generated by an electric motor to one or more impellers located in an impeller chamber of the pump housing.

[0009] The term drive shaft as used herein also includes drive shaft assemblies comprising multiple shaft parts. For example, a drive shaft assembly may comprise a pump drive shaft which is attached to the one or more impellers in the pump housing, a motor drive shaft that is attached to the rotor of the motor and a coupling device or coupling sleeve connecting the pump drive shaft to the motor drive shaft. In an exemplary preferred embodiment, the shaft seal is in sealing annular contact with a coupling device or coupling sleeve of a drive shaft assembly that connects the pump drive shaft to the motor drive shaft at a position where the drive shaft assembly extends through the pump housing.

[0010] Shaft seals are generally well-established. In the present embodiment, the shaft seal is surrounded by a seal housing that is shaped and configured for mounting the shaft seal in an upper part of a pump housing. The upper part of an upright standing pump housing, i.e., a pump housing with a vertically extending drive shaft may also be referred to as the pump top. In an exemplary embodiment the pump top forming the upper part of the pump housing is a separate part which is attached to the remainder of the pump housing after the impellers and at least a part of the drive shaft directly connected to the impellers has been installed in the pump housing.

[0011] The upper part of the pump housing has an opening at its center where the sealing device is installed. The shaft seal extends annularly about the drive shaft and is provided so that only a predetermined small amount of pump fluid may leak out of the pump housing along the drive shaft. The amount of pump fluid leaking along the drive shaft is used to lubricate the shaft seal. In other words, a limited amount of pump fluid is intentionally allowed to flow between the drive shaft and the adjacent sealing element of the shaft seal. The pump fluid serves as a lubricant and reduces wear of the shaft seal.

[0012] For establishing whether pump fluid is present at the shaft seal, a pump fluid sensing device is part of the shaft sealing device and a temperature sensor of the pump fluid sensing device is mounted in a sensing space defined by the seal housing. For example, the seal housing may comprise a bore allowing the insertion of the temperature sensor into the sensing space. The sensing space is in fluid communication with the inside of the pump housing that is filled with pump fluid while the pump housing is in use, i.e., during operation of a pump assembly comprising the pump housing. The temperature sensor is placed at a position where it is only in contact with pump fluid during regular operation of the pump if the level of the pump fluid in the pump housing is sufficiently high to keep the shaft seal lubricated.

[0013] For mounting the temperature sensor in the seal housing, the temperature sensor may be attached to a sensor mount. The sensor mount could, for example, be configured for sealing a bore in the seal housing through which the temperature sensor is installed into sensing space. For example, the sensor mount may comprise sealing means or may have a sealing outer surface that prevents pump fluid from leaking out of the pump housing through a bore into which the resistance temperature sensor is inserted. The temperature sensor thus protrudesout of a surface of the seal housing that is intended to be in contact with pump fluid during operation of the pump housing.

[0014] Various types of temperature sensors are known in the art. In a preferred embodiment, the temperature sensor is a resistance temperature sensor or resistance thermometer or resistance temperature detector. A resistance temperature sensor is based on an electric conductor having a temperature-dependent electrical resistance, for example, a linear relationship between resistance and temperature. Resistance temperature sensors can be made from metals such as platinum (Pt), nickel (Ni) or copper (Cu). An example of a resistance temperature sensor is a PtlOO element, a resistance temperature sensor made from Platinum which has a resistance of 100 Ohms at 0° Celsius.

[0015] In an exemplary embodiment, the pump fluid sensing device comprises a control unit which is connected to the resistance temperature sensor. The control unit may, for example, be a separate element, may be included into a motor control of a pump assembly or may be integrated into a pump mount. Also, mixed approaches are conceivable where part of the control of the pump fluid sensing device is formed by the motor control and others are formed by other elements. In other words, the control unit may be a standalone unit, integrated into another device or comprise multiple separate devices forming a distributed control unit. In a preferred embodiment, the control unit is part of or integrated into a motor control of a centrifugal pump assembly in which the sensing device is installed.

[0016] In a preferred embodiment, the shaft seal comprises a stationary part attached to the seal housing and a rotating part configured to be attached to the pump shaft. A sealing gap is formed between a sealing surface of the rotating part of the shaft seal and acorresponding seal seat of the stationary part of the shaft seal. The sealing gap is formed to be filled with pump fluid during use of the pump housing for lubricating the shaft seal, the temperature sensor is mounted along the rotational axis on a same side of the sealing gap as the stationary part of the shaft seal.

[0017] In other words, the shaft seal preferably comprises two main parts: a stationary part and a rotating part. The stationary part is attached to the seal housing and does not move relative to the seal housing when the drive shaft rotates. The stationary part of the shaft seal also comprises the seal seat. The rotating part of the shaft seal is attached in a rotationally fixed manner to the drive shaft or a drive shaft assembly. When the drive shaft rotates during operation of a pump assembly, the rotating part of the shaft assembly also rotates about the rotational axis.

[0018] The rotating part of the shaft seal comprises a sealing surface which faces the seal seat of the stationary part. The sealing surface may, for example, extend parallel to the seal seat and extend in plane which is perpendicular to the rotational axis. Preferably, the sealing surface is the only rotating part of the shaft seal that is in direct vicinity of or contact with the stationary part of the shaft seal.

[0019] Between the sealing surface and the seal seat a sealing gap is formed. The sealing gap may only be present while the pump is operating, i.e., while the pump liquid inside the pump housing is pressurized. Pump liquid fills the sealing gap and thus lubricates the interface or contact area between the rotating part of the shaft seal and the stationary part of the shaft seal.

[0020] The temperature sensor is mounted in the seal housing at a position so that it is above the sealing gap when the pump housing is inan upright operating position and the rotational axis extend vertically. In other words, in the direction of the rotational axis, the sealing gap is formed between the temperature sensor and the sealing surface. Thereby, it is ensured that when the temperature sensor is in contact with pump fluid, the sealing gap is filled with pump fluid and the shaft seal therefore lubricated.

[0021] Preferably, the entire stationary part of the shaft seal is arranged in the direction of the rotational axis between the temperature sensor and the rotating part of the shaft seal. Thereby, it is ensured that the interface of the shaft seal with the seal housing is arranged in the direction of the rotational axis below the temperature sensor. The temperature sensor can thus advantageously also be used to detect leakage of pump liquid in case the sealing between the stationary part of the shaft seal and the seal housing is damaged.

[0022] Preferably, the shaft housing comprises an annular collar extending circumferentially about the rotational axis. An inner positioning surface of the annular collar facing towards the rotational axis defines a radial position of the shaft seal with respect to the rotational axis. An outer surface of the annular collar facing away from the rotational axis delimits the sensing space.

[0023] Hence, in the preferred embodiment a ring-shaped collar or protrusion is formed on the seal housing extending generally parallel to and circumferentially about the rotational axis. The collar thus surrounds an indentation in which the stationary part of the shaft seal is placed and centers the stationary part relative to the rotational axis. An inner positioning surface of the collar may, for example, be in contact with the stationary part of the shaft sealing.

[0024] A radially outer surface of the collar delimits the sensing space towards the rotational axis. Hence, the sensing space is formed in the region of the stationary part of the shaft seal as close as possible to the rotational axis. This ensures that any leakages at the shaft seal can be detected as early as possible.

[0025] Preferably, the sensing space is formed as an elongated channel extending circumferentially about the rotational axis. For example, the sensing space may extend for more than half of a circle about the rotational axis or more than two thirds of a circle about the rotational axis. Having a circumferentially extending sensing space that extends equidistantly about the rotational axis ensures that air inside the pump housing accumulates in the sensing space and an insufficient level of pump fluid can be detected by the resistance temperature sensor even before the level of the pump fluid drops below a level where the shaft seal is insufficiently lubricated.

[0026] Preferably, a distance of the temperature sensor from the rotational axis does not exceed a distance of a radially outermost part of the shaft seal away from the rotational axis. In other words, when projected on a plane extending perpendicular to the rotational axis, the distance of the radially outermost part of the shaft is not less than the distance of the temperature sensor from the rotational axis.

[0027] In a preferred embodiment, for detecting whether the temperature sensor is in contact with pump fluid, the pump fluid sensing device is configured for heating the temperature sensor for a heating phase, determining an initial temperature value at temperature sensor after the heating phase, recording one or more cooling temperature values sensed at the temperature sensor after the heating phase and after the initial temperature value has been determined, and determining from the initial temperature value and the one or morecooling temperature values whether the resistance temperature sensor is in contact with the pump fluid.

[0028] In other words, the pump fluid sensing device can determine whether pump fluid is present at the location of the temperature sensor by measuring a cooling rate of a temperature sensor which is heated for a heating phase. For detecting the presence of pump fluid, the pump fluid sensing device is adapted to perform a sequence of steps.

[0029] In a first step, the temperature sensor is heated for a heating phase. For example, in case the temperature sensor is a resistance temperature sensor, it may advantageously be heated by supplying electric energy to it. To this end, an external power source may be instructed to supply electrical power to the resistance temperature sensor. Other sensors may require a separate heating unit. During this initial heating phase, the temperature of the resistance temperature sensor increases and thus the temperature sensed by the resistance temperature sensor increases.

[0030] Once the heating phase is completed and the temperature of the temperature sensor has risen, an initial temperature at the temperature sensor is determined. Preferably, the initial temperature value is established by recording the temperature value that is sensed by the temperature sensor immediately after the heating has been completed, preferably, at an approximate point in time where the temperature sensor has reached its peak temperature.

[0031] Subsequently, one or more further temperature values of the temperature sensor are recorded as cooling temperatures. Preferably, the first cooling temperature value is measured a predetermined time after the initial temperature value has been determined. Since no more heat is applied to the temperature sensor after the initial heatingphase, the temperature sensor cools off. After the first cooling temperature value has been recorded, one or more additional cooling temperature values sensed at the temperature sensor may be recorded.

[0032] The additional cooling temperature values are, in a preferred embodiment, recorded at the same or a different predetermined cooling time after the first cooling temperature value or a directly preceding cooling temperature value has been recorded. For example, three or five cooling temperature values may be recorded overall at intervals of two seconds, i.e., the first recorded cooling temperature value is sensed two seconds after the initial temperature value has been recorded, the second recorded cooling temperature value is sensed four seconds after the initial temperature value has been determined and so on.

[0033] In an exemplary embodiment, the temperatures sensed by the temperature sensor are continuously recorded when the presence of pump fluid shall be sensed. The first temperature value recorded after the heating phase could in this embodiment be considered an initial temperature value and one or more subsequently recorded temperature value that are considered for determining the presence of pump fluid could be deemed cooling temperature values.

[0034] Finally, in the preferred embodiment the pump fluid sensing device is configured for determining from the recorded initial temperature value and the one or more cooling temperature values whether the temperature sensor is submerged in pump fluid or whether it is surrounded by air. The inventors have observed that the rate of cooling of the temperature sensor after the initial heating phase depends on the media that surrounds the temperature sensor. If the temperature sensor is surrounded by pump fluid, the temperature dropssignificantly faster than if it the temperature sensor is surrounded by air. Therefore, by evaluating the change of temperature between the initial temperature value and the one or more cooling temperature values the control unit can establish whether pump fluid or air is present at the position in the pump housing where the temperature sensor is mounted. Provided that the temperature sensor is placed adjacent to or above the shaft seal, this result can advantageously be used to prevent excessive wear of the shaft seal, for example, by stopping the pump motor if no pump fluid is detected or no pump fluid is detected for an extended period of time.

[0035] In a preferred embodiment, the temperature sensor is a resistance temperature sensor, and the resistance temperature sensor is heated by supplying energy to the heating sensor for the heating phase. Further preferably, a predetermined amount of energy is supplied to the resistance temperature sensor by supplying a predetermined heating power for a predetermined heating time to the resistance temperature sensor. For example, a control unit may instruct an external power source to supply a predetermined heating power of 0.4 watt for a predetermined heating time of one second to the resistance temperature sensor.

[0036] In a preferred embodiment, the pump fluid sensing device is further configured for determining from the initial temperature value and the one or more cooling temperature values whether the resistance temperature sensor is in contact with a flowing pump fluid or a stagnating pump fluid. In other words, in the preferred embodiment, the pump fluid sensing device is further adapted to not only determine whether the temperature sensor is submerged in pump fluid but further establishes whether the pump fluid is in motion or rests still. If pump fluid is flowing at the position of the temperature sensor, the temperature will drop faster after the initial heating phase as compared to when thepump fluid is not flowing or stagnating. If the shaft seal is intact, the pump fluid should be stationary at the position of the sealing device. Thus, a flowing pump fluid indicates a leak at the sealing device or the shaft seal.

[0037] In an exemplary preferred embodiment, the shaft sealing device extends along the rotational axis between an impeller-facing end and a motor-facing end. The temperature sensor is mounted in the direction of the rotational axis at least at a same distance from the impellerfacing end of the shaft sealing device than the shaft seal.

[0038] Thus, in the preferred exemplary embodiment, the top and bottom of the shaft sealing device are defined as motor-facing end and the impeller-facing end, respectively. The motor-facing end of the sealing device is the part of the shaft sealing device that is closest to the motor when the shaft sealing device is a part of a pump assembly whereas the impeller-facing end of the shaft sealing device is the part of the shaft sealing device that is closest to the impeller. The impellerfacing end of the shaft sealing device may, in particular, be formed by the shaft seal.

[0039] In the preferred embodiment, the position of the temperature sensor is defined along the position of the rotational axis relative to the position of the shaft seal. In particular, it is required that the temperature sensor is mounted at least within the position over which the shaft seal extends along the rotational axis. Thereby, it is preferably ensured that in a pump assembly the temperature sensor is only submerged in pump fluid when at least the lowermost part of the shaft seal is also in contact with the pump fluid so that the latter is kept lubricated.

[0040] In a further exemplary preferred embodiment, the shaft seal is arranged in the direction of the rotational axis between the temperature sensor and the impeller-facing end of the sealing device. In other words, in the preferred embodiment, the shaft seal is arranged below the temperature sensor along the rotational axis. Thus, when the position of the temperature sensor is projected onto the rotational axis, and the same is done with the position of the shaft seal, the entire shaft seal is closer to the impeller-facing end of the sealing device than the temperature sensor. By mounting the temperature sensor above the shaft seal, it is ensured that when the temperature sensor is in contact with pump fluid, the entire shaft seal is below the upper level of the pump fluid and, thus, the shaft seal is properly lubricated over its entire extension along the rotational axis.

[0041] It is further preferred that the seal housing is configured for annular contact with the upper part of the pump housing. The temperature sensor is arranged in the direction of the rotational axis between the upper part of the pump housing and the motor-facing end of the shaft sealing device. Thus, in the preferred embodiment, the temperature sensor is mounted above that pump housing, i.e., essentially outside of the pump housing as delimited by the upper part of the pump housing. The position of the temperature sensor above the upper part of the pump housing ensures that the entire pump housing is filled with pump fluid and a sufficient lubrication of the shaft seal is ensured.

[0042] In a second aspect, the present invention is directed to pump housing comprising a shaft sealing device according to any of the preceding embodiments mounted in an upper part of the pump housing. The advantages of the pump housing correspond to the advantages of the shaft sealing device used as part of the pump top.

[0043] Finally, in a third aspect, the present invention is directed to a pump assembly comprising a pump motor and a pump housing as previously described. The pump motor is mounted to the pump housing. Furthermore, it is preferred that the pump motor comprises a motor control and the control unit of the pump fluid sensing device is part of the motor control. The advantages of the pump assembly correspond to the respective advantages of the sealing device that is integrated into the pump housing of the pump assembly.

[0044] Subsequently, the invention will be described in more detail with reference to the drawings, whereinFig. 1 shows a perspective view of an exemplary embodiment of a shaft sealing device,Fig. 2 shows a partial cut through the perspective view of Fig. 1,Fig. 3 shows a cut view of the exemplary embodiment of Fig. 1 along a vertical plane,Fig. 4 shows a cut view of the exemplary embodiment of Fig. 1 along a horizontal plane,Fig. 5 shows an exemplary embodiment of a pump assembly comprising an exemplary embodiment of a pump housing, andFig. 6 shows an exemplary embodiment of temperatures sensed with a temperature sensor of an exemplary embodiment of a shaft sealing device.

[0045] Figures 1 to 4 show on exemplary embodiment of a sealing device 1. The sealing device 1 is intended to be installed in an upper part 3 of a pump housing for a centrifugal pump assembly. The upper part 3 of the pump housing or pump top 3 of the pump housing is shown partially in figures 1 to 3. The upper part 3 forms the uppermost part of an upright standing pump housing, i.e., a pump housing where a rotational axis 5 of a drive shaft 7 of the pump housing extends vertically during regular operation of the pump. The rotational axis 5 is only shown in figures 3 and 4. The upper part 3 may be a separate part that is used to close off an upper opening of a pump housing or may be formed as a single piece with additional parts of the pump housing.

[0046] The only part of the shaft sealing device 1 visible in figure 1 is a seal housing 9. The seal housing 9 is provided for attaching the sealing device 1 to the upper part 3 of the pump housing. As can be seen best in figure 1 , for securing the seal housing 9 and, thus, the shaft sealing device 1 to the pump top 3 four threaded bolts or screws 1 1 are provided. The screws 1 1 extend through bores 13 formed in the sealing housing 9 and engage mating threads (not shown) in the upper part 3 of the pump housing.

[0047] Figure 1 further shows a part of a pump drive shaft 15 which is attached to one or more impellers of a centrifugal pump assembly when the shaft sealing device 1 has been installed in a pump housing. The pump drive shaft 15 is connected via a shaft coupling device 17 to a motor drive shaft (not shown in figures 1 to 4). The combination of the pump drive shaft 15, the motor drive shaft and the shaft coupling device 17 form the drive shaft assembly 7.

[0048] Other parts of the shaft coupling device 17 which are visible in figure 1 are a coupling sleeve 19 and a rotor clamp 21 . The rotor clamp 21 is used for securing a motor drive shaft to the coupling device 17.

[0049] As can be seen in figures 2 and 3, the coupling sleeve 19 is configured for receiving at its lower or pump-facing end 23 the pump drive shaft 15. The pump drive shaft 15 is secured in the coupling sleeve 19 via a locking element 25 and a bolt 27 attaching the locking element 25 to the pump drive shaft 15. In the vicinity of the pumpfacing end 23 of the coupling sleeve 19, an annual seal 29 in form of an O-ring prevents pump fluid from leaking along the pump drive shaft 15 into the coupling sleeve 19.

[0050] The coupling sleeve 19 of the shaft coupling device 17 is surrounded by a shaft seal 31. The shaft seal 31 comprises a rotating part 32 and a stationary part 34. The rotating part 32 comprises a bellows 33 which is made from rubber and surrounded by a helical spring 35. The bellows 33 and the helical spring 35 are attached via a bracket 37 and a spring ring 39 to the coupling sleeve 19. The bracket 37 attaches the bellows 33 in a rotationally fixed manner to the coupling sleeve 19 The helical spring 35 biases the bellows 33 towards the stationary part 34 of the shaft seal 31 .

[0051] A sealing element 36 is supported on the bellows 33 and also rotates with the coupling sleeve 19. A sealing surface 38 of the sealing element 36 faces a seal seat 40 that is part of the stationary part 34 of the shaft seal 31. The seal seat 40 does not rotate relative to the seal housing 9 during operation of the pump but remains stationary. An O- ring 42 is provided for preventing pump fluid from leaking out of the pump housing where the seal seat 40 rests against the seal housing 9. During operation of the pump, a sealing gap 44 is formed between the sealing surface 38 and the seal seat 40. The sealing gap 44 is filled with pump fluid which lubricates the shaft seal 31 as it forms a liquid film between the rotating and the non-rotating parts 32, 34 of the shaft seal 31.

[0052] In case the level of pump fluid drops below the sealing gap 44 between the sealing element 36 of the shaft seal 31 and the seal seat 40, the shaft seal 31 is no longer lubricated. This may increase wear of the sealing element 36 and the seal seat 40. To ensure that the level of pump fluid in the pump housing is sufficient, a pump fluid sensing device 41 is part of the shaft sealing device 1. The pump fluid sensing device 41 comprises a control unit (not shown in figures 1 to 4) which is connected to a temperature sensor 43. In the exemplary embodiment shown in the figures, the temperature sensor 43 is a resistance temperature sensor in form of a Pt 100 element with a resistance of 100 Ohms at 0°C.

[0053] The temperature sensor 43 is mounted via a sensor mount 45 in the seal housing 9. To this end, the seal housing 9 comprises a bore 47 through which the resistance temperature sensor 43 can be inserted into a sensing space 49 that is in fluid communication with the inside of the pump housing that is filled with pump fluid during operation. The sensor mount 45 is shaped and configured so that it seals off the bore 47 in the sensor housing 9 and prevents pump fluid from leaking out of the pump housing.

[0054] As can be seen best in figures 2 and 3, the position of the temperature sensor 43 has been chosen so that during operation of the pump assembly, the temperature sensor 43 which detects the presence of a pump fluid is mounted above the entire shaft seal 31 . In particular, the temperature sensor 43 is arranged in the vertical direction above the sealing gap 44 and the O-ring 42 sealing the seal seat 40 to the seal housing 9. Thus, when the temperature sensor 43 is in contact with pump liquid, it can be concluded that the sealing gap 44 is filled with pump liquid as it is arranged below the sensor 43. Furthermore, it can also be used to detect whether the O-ring 42 is properly sealing the seal seat 40 to the sensor housing 9 as otherwise the level of the pump liquidwould drop to the position of the O-ring 42 and thus below the temperature sensor 43.

[0055] In other words, the shaft seal 31 and, in particular, the sealing element 33 are arranged between a pump-facing end 53 of the sealing device 1 and the temperature sensor 43. Note that in the exemplary embodiment shown in the figures 1 to 4, the sealing element 33 forms the pump-facing end 53 of the sealing device 1. The temperature sensor 43 is at the same time mounted between the upper part 3 of the pump housing and a motor-facing end 55 of the sealing device 1 .

[0056] For positioning the temperature sensor 43, the sensing space 49 extends above an upper part 3 of the pump housing. The sensing space 49 further extends circumferentially about the rotational axis 5 to ensure that air is gathered in the sensing space 49 as early as possible and the risk of an insufficient level of pump fluid for lubrication of the shaft seal 31 is detected before it occurs.

[0057] Towards the rotational axis 5, the sensing space 49 is delimited by a collar 50 extending generally parallel to the rotational axis 5 away from the seal housing 9. An inner surface 51 of the collar 50 defines the radial position of the stationary part 34 of the shaft seal 31, i.e., the location of the stationary part 34 in a plane extending perpendicular to the rotational axis 5 is restricted by the collar 50. A radially outer surface 52 of the collar 50 delimits the sensing space 49 towards the rotational axis 5. By using the same collar 50 to delimit the sensing space 49 and positioning the stationary part 43 of the shaft seal 31, the temperature sensor 43 can be positioned as close as possible in the radial direction to the sealing gap 44. This ensures that any relevant drop in the level of pump fluid in the pump housing is detected as early as possible.

[0058] As can be seen best in Figures 3 and 4, the distance of the tip of the temperature sensor 43 from the rotational axis 5 corresponds to the maximum radial extension of the shaft seal away from the rotational axis 5.

[0059] As a measure for establishing whether the level of pump fluid in the pump housing is sufficient, it is determined whether the temperature sensor 43 is surrounded by air or pump fluid. To this end, in the exemplary embodiment the control unit first supplies a heating power of 0.4 W for a heating time of 1 s to the resistance temperature sensor. The time during which energy is supplied to the resistance temperature sensor 43 and the temperature sensor 43 is thus heated is referred to as a heating phase. For other implementations, different heating times, different heating powers and different ways of heating the temperature sensor 43 may be employed.

[0060] Immediately after the power is turned off, the temperature sensed by the temperature sensor 43 is recorded as an initial temperature of the temperature sensor 43 after the heating phase. The control unit then continues recording of the temperatures as the temperature sensor 43 cools off. These cooling temperatures are together with the initial temperature evaluated to determine whether the temperature sensor 43 is submerged in pump fluid or surrounded by air.

[0061] Note that in the exemplary embodiment shown in figures 1 to 4, temperatures sensed by the temperature sensor 43 are recorded continuously. Determining whether the temperature sensor 43 is submerged in pump fluid is based at least on the temperature recorded as initial temperature value and one or more additional temperature values recorded as cooling temperature values. However, this does not preclude the control unit from considering further valuessuch as the temperature of the temperature sensor 43 before heating of the temperature sensor 43 commences.

[0062] As can be seen in the exemplary curves shown in figure 6, the cooling rate of the resistance temperature sensor 43 used in the embodiments in figures 1 to 4 depends on the surrounded medium. The graphic in figure 6 shows on the vertically extending ordinate or Y-axis 57 the relative temperature of the resistance temperature sensor 43 as compared to an initial temperature before heating of the resistance temperature sensor 43 in degrees Celsius. On the horizontally extending abscissa or X-axis 59, the time in seconds is shown. The uppermost curve 61 a shows the relationship of temperature against time for an exemplary embodiment of a resistance temperature sensor 43 that is surrounded by air. The center curve 61 b shows an example of for the temperature-time curve for the resistance temperature sensor 43 that is surrounded by still standing or stagnating pump fluid. The lowermost curve 61 c shows an exemplary temperature-time dependence of the resistance temperature sensor 43 when surrounded by flowing pump fluid. As can be seen from the comparison of the three curves, by recording the drop of the temperature sensed by the resistance temperature sensor 43 after the heating phase, it can be determined by the control unit whether the sensor is surrounded by air (curve 61 a), by a stagnating pump fluid (curve 61 b) or by a flowing pump fluid (curve 61 c).

[0063] In the exemplary embodiment shown in figures 1 to 4, the resistance temperature sensor 43 is positioned vertically above the shaft seal 31. Therefore, as long as the resistance temperature sensor 43 is submerged in pump liquid, the shaft seal 31 should be lubricated and the O-ring 42 should also be sufficiently tight. The pump fluid sensing device 41 , therefore, allows with relatively simple means to detect whether the level of pump fluid in the pump housing is sufficient or not.

[0064] From figure 4 it can further be taken that the sealing device 1 comprises a venting means 62 for removing air that may have accumulated at the pump top 3.

[0065] Finally, figure 5 shows an exemplary embodiment of a pump assembly 63. The pump assembly comprises a pump housing 65 with a pump top 67 forming the upper part 3 of the pump housing 65 which comprises a sealing device 1 and a pump fluid sensing device 41 as described with references to figures 1 to 4 and 6. The control unit 69 of the pump fluid sensing device 41 is integrated into the motor electronic 71 of the pump motor 73. The electric pump motor 73 is in the exemplary embodiment a permanent magnet synchronous motor mounted on top of the pump housing 65. The pump housing 65 further comprises a pump inlet 75 and a pump outlet 77. During operation of the pump assembly 63, pump fluid is ingested into the pump housing 65 through the pump inlet 75 and expelled out of the pump housing 65 through the pump outlet 77. Figure 5 also shows a motor drive shaft 79 that is part of the shaft assembly 7.

[0066] The advantages of the pump assembly 63 shown in figure 5 correspond to the advantages of the exemplary embodiment of a pump fluid sensing device 41 and a sealing device 1 used as part of the pump assembly 63.List of reference numerals1 shaft sealing device3 upper part of a pump housing5 rotational axis7 drive shaft assembly9 seal housing1 1 bolt 13 bore15 pump drive shaft 17 shaft coupling device19 coupling sleeve 21 rotor clamp23 pump-facing end of coupling sleeve 25 locking element 27 bolt 29 seal 31 shaft seal 32 rotating part of the shaft seal33 bellows 34 stationary part of the shaft seal 35 helical spring 36 sealing element 37 bracket 38 sealing surface 39 spring ring40 seal seat 41 pump fluid sensing device 42 O-ring 43 resistance temperature sensor 44 sealing gap 45 sensor mount47 bore 49 sensing space50 collar 51 radially inner surface of the collar 52 radially outer surface of the collar 53 pump-facing end of sealing device55 motor-facing end of sealing device 57 Y-axis59 X-axis 61 a upper curve 61 b center curve 61 c lower curve 62 venting means 63 pump assembly 65 pump housing67 pump top 69 control unitmotor electronics housing pump motor pump inlet pump outlet

Claims

Claims1. A shaft sealing device (1 ) for a pump housing (65), the sealing device (1 ) comprising a seal housing (9), a shaft seal (31 ), and a pump fluid sensing device (41 ), wherein the seal housing (9) is configured for mounting the sealing device ( 1 ) in an upper part (3) of a pump housing (65), wherein the shaft seal (31 ) is configured for circumferentially contacting a drive shaft (7) extending along a rotational axis (5) through the upper part (3) of the pump housing (65) and for preventing pump fluid from leaking out of the pump housing (65) where the drive shaft (7) extends through the upper part of the pump housing (3), wherein the pump fluid sensing device (41 ) comprises a temperature sensor (43) mounted in a sensing space (49) partially defined by the seal housing (9), wherein the sensing space (49) is in fluid communication with pump fluid in the pump housing (65) and wherein the temperature sensor (43) is mounted at a position where it is only in contact with pump fluid if a level of pump fluid in the pump housing (65) is sufficient to keep the shaft seal (31 ) lubricated.

2. Shaft sealing device (1 ) according to claim 1, wherein the shaft seal (31 ) comprises a stationary part (34) attached to the seal housing (9) and a rotating part (32) configured to be attached to the drive shaft (7), wherein a sealing gap (44) is formed between a sealing surface (38) of the rotating part (32) of the shaft seal (31 ) and a corresponding seal seat (40) of the stationary part (34) of the shaft seal (34), wherein the sealing gap (44) is formed to be filled with pump fluid during use of the pump housing (65) for lubricating the shaft seal (31 ), andwherein the temperature sensor (43) is mounted along the rotational axis (5) on a same side of the sealing gap (44) as the stationary part of the shaft seal (34).

3. Shaft sealing device (1 ) according to claim 2, wherein the stationary part (34) of the shaft seal (31 ) is arranged in the direction of the rotational axis (5) between the temperature sensor (43) and the rotating part (32) of the shaft seal (31 ).

4. Shaft sealing device ( 1 ) according to claim 2 or 3, wherein the seal housing (9) comprises an annular collar (50) extending circumferentially about the rotational axis (5), wherein a radially inner surface (51 ) of the annular collar (50) facing towards the rotational axis (5) defines a radial position of the shaft seal (31 ) with respect to the rotational axis (5) and wherein an outer surface (52) of the annular collar (50) facing away from the rotational axis (5) delimits the sensing space (49).

5. Shaft sealing device (1 ) according to any of the preceding claims, wherein the sensing space (49) is formed as an elongated channel extending circumferentially about the rotational axis (5).

6. Shaft seal (31 ) according to any of the preceding claims, wherein a distance of the temperature sensor (43) from the rotational axis (5) does not exceed a distance of a radially outermost part of the shaft seal (31 ) away from the rotational axis (5).

7. Shaft sealing device (1 ) according to any of the preceding claims, wherein for detecting whether the temperature sensor (43) is in contact with pump fluid, the pump fluid sensing device (41 ) is configured for heating the temperature sensor (43) for a heatingphase, determining an initial temperature value at temperature sensor (43) after the heating phase, recording one or more cooling temperature values sensed at the temperature sensor (43) after the heating phase and after the initial temperature value has been determined, and determining from the initial temperature value and the one or more cooling temperature values whether the resistance temperature sensor (43) is in contact with the pump fluid.

8. Shaft sealing device (1 ) according to claim 7, wherein the temperature sensor (43) is a resistance temperature sensor (43) and wherein the resistance temperature sensor (43) is heated by supplying energy to the resistance temperature sensor (43) for the heating phase.

9. Shaft sealing device ( 1 ) according to any of claims 7 or 8, wherein the pump fluid sensing device (41 ) is further configured for determining from the difference of the initial temperature value and the one or more cooling temperature values whether the resistance temperature sensor (43) is in contact with a flowing pump fluid or a stagnating pump fluid.

10. Shaft sealing device (1 ) according to any of the preceding claims, wherein the pump fluid sensing device (41 ) comprises a control unit (69) which is preferably part of a motor control of a centrifugal pump assembly (63).1 1 . Shaft sealing device ( 1 ) according to any of the preceding claims, wherein the seal housing (9) is configured for annular contact with the upper part (3) of the pump housing (65), wherein the resistance temperature sensor (43) is positioned in the direction ofthe rotational axis (5) between the upper part of the pump housing (3) and the motor-facing end of the sealing device (55).

12. A pump housing (65) comprising a shaft sealing device (1 ) according to any of the preceding claims mounted in an upper part of the pump housing (3).

13. A pump assembly (63) comprising a pump motor (73) and a pump housing (65) according to claim 12, wherein the pump motor (73) is mounted to the pump housing (65).

14. Pump assembly (63) according to claim 13, wherein the pump motor (73) comprises a motor control and wherein a control unit of the pump fluid sensing device (41 ) is part of the motor control.

Images