A shaft sealing device

Abstract

Described and claimed is a shaft sealing device for a pump housing. A seal housing mounts the sealing device in an upper part of a pump housing and comprises a venting duct connecting an inside of the pump housing and an environment thereof. A shaft seal circumferentially contacts a drive shaft extending along a rotational axis through the pump housing and prevents pump fluid from leaking out of the pump housing. A pump fluid sensing device determines whether a level of pump fluid in the pump housing is sufficient to keep the shaft seal lubricated. A venting device controls a flow of fluid through the venting duct and releases air from the pump housing in case the pump fluid sensing device determines that the level of pump fluid in the pump housing is not sufficient to keep the shaft seal lubricated.

Description

A SHAFT SEALING DEVICEDescription

[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 drive shaft andthe 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 due to too much air accumulating at the top of the pump housing.

[0006] The problem underlying the present invention is solved by a shaft sealing device, a pump housing, and a pump assembly according to the respective independent claims. Preferred embodiments of the shaft sealing device 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, a pump fluid sensing device, and a venting device. The seal housing is configured for mounting the sealing device in an upper part of a pump housing and comprises a venting duct for establishing a fluid communication between an inside of the pump housing and an environment of the 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 upper part of the pump housing. The pump fluid sensing device is configured for determining whether a level of pump fluid in the pump housing is sufficient to keep the shaft seal lubricated. The venting device is configured for controlling a flow of air through the venting duct. The venting device comprises a valve element mounted in the venting duct. Further, the venting device is configured for automatically releasing air from thepump housing in case the pump fluid sensing device does not determine that the level of pump fluid is sufficient to keep the shaft seal lubricated.

[0008] In other words, a shaft sealing device to be installed in an upper part of a pump housing is disclosed. The center of the shaft sealing device is formed by a shaft seal that surrounds a 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. The pump housing is intended to be used as part of a centrifugal pump assembly.

[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 isattached 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 valve element of the shaft seal. The pump fluid serves as a lubricant and reduces wear of the shaft seal.

[0012] Without pump fluid lubricating the shaft seal, the shaft seal runs dry and will be damaged. A dry-running shaft seal may be caused by air accumulating inside the pump housing. Since air is lighter than the pressurized pump fluid, it accumulates at the top and center of the pump housing, i.e., right there were the shaft seal is installed.

[0013] The shaft sealing device comprises a pump fluid sensing device for detecting whether the shaft seal is submerged in pump fluid so that the shaft seal can be kept lubricated. A pump fluid sensing device may, for example, comprise a sensor which is mounted vertically above the shaft seal. The sensing device determines whether the sensor is surrounded by water. If the sensor is submerged in pump fluid, the sending device concludes that the shaft seal is also below the level of pump fluid and can be lubricated. Preferred embodiments of a pump fluid sensing device are the subject matter of preferred embodiments. The level of the pump fluid can, for example, be determined using a temperature sensor or optically.

[0014] For removing air trapped inside the pump housing, the present invention provides a venting device as part of the shaft sealing device. The venting device regulates or controls a flow of air from the inside of the pump housing to the environment or outside of the pump housing. Hence, the venting device can be used to release air trapped inside the pump housing in case the pump fluid sensing device determines that the level of pump fluid is not sufficient to ensure that the shaft seal remains lubricated. To this end it is not necessary to determine that the level of pump fluid has actually dropped below the shaft seal or at least those elements of the shaft seal that need to be lubricated. Rather, it would also be sufficient to determine that the level of pump fluid does, for example, not reach a sensor of the pump fluid sensing device and some air has accumulated at the top of the pump housing, i.e., there is a risk of insufficient lubrication of the shaft seal.

[0015] The venting device is installed in a venting duct which extends, for example, between a venting duct inlet and a venting duct outlet. The venting duct inlet refers to an opening in an inner surface of the seal housing where the venting duct is connected to an inside of the pump housing. The venting duct outlet is the end of the venting duct which is closer to the environment or outside of the pump housing. The venting duct thus provides a connection between the inside of a pump housing and the outside or environment of the pump housing through which air can be released from the inside of the pump housing.

[0016] A valve element of the venting device is installed in the venting duct and selectively allows or blocks a flow of fluid through the venting duct. The venting device in particular controls the flow of air from the inside of the pump housing to the environment of the pump housing. Instead of air other fluids such as pump fluid or other gases accumulating inside the pump housing can flow through the venting duct to the outside of the pump housing.

[0017] The venting device is provided for releasing air that has accumulated at the top of the pump housing when the pump fluid sensing device detects the presence of air. For operating the pump fluid sensing device and controlling the opening and closing of the venting device, a control unit may be required. The control unit may be a local processing unit that is integrated in the seal housing or in the pump housing. It could also be formed by another electronics unit that is part of a pump assembly. Also, distributed control units are conceivable where separate parts of the control unit are embodiment by different processing units. For example, the pump fluid sensing device and the venting device may comprise separate control units that communicate via a communication link. For example, a control unit of the pump fluid sensing device could notify a control unit of the venting device that air is present in the pump housing, whereupon the control unit of the venting device instructs the venting device to release air from the pump housing. Subsequently, the control unit of the pump fluid sensing device could notify the venting device that the pump housing is sufficiently filled with pump fluid, whereupon the venting device blocks the venting duct.

[0018] The venting device is configured for automatically releasing air through the venting duct when the pump fluid sensing device determines that the level of pump fluid is not sufficient to keep the shaft seal lubricated. Hence, an automatic ventilation is provided in case the level of pump fluid drops below a predetermined value and there is a risk of the shaft seal running dry.

[0019] The position of the venting device in the pump housing but also the position and shape of the venting duct have been chosen so that the pump fluid in an exemplary embodiment only reaches the valve element if the level of pump fluid is sufficient to keep the shaft seal lubricated. For example, for an upright standing pump with a verticallyextending rotational axis, the valve element is preferably positioned above the shaft seal or at least the part of the shaft seal that is lubricated using pump fluid. By positioning the venting device above the shaft seal, it can be used to release air trapped at the top of the pump housing so that it does not prevent pump fluid from reaching the top of the pump housing and, in particular, the shaft seal that needs to be lubricated.

[0020] In a preferred embodiment, the valve element is configured to move between a closed position in which a flow of fluid through the venting duct is blocked and at least one opened position in which fluid may flow through the venting duct. The venting device is configured so that the valve element maintains the closed position or moves from the opened position to the closed position if a pressure outside the pump housing exceeds a pressure inside the pump housing.

[0021] Hence, in the preferred embodiment the sealing device serves to control the flow of air from the inside of the pump housing to the outside of the pump housing but additionally functions as a check valve or non-return valve that prevents air from the environment entering the inside of the pump housing in case the pressure inside the pump housing should be lower than outside of the pump housing. In case the venting device would open when the pressure inside the pump housing is lower than the environment, air would be sucked into the pump housing and the level of pump fluid would drop. In consequence, the shaft seal would potentially not be sufficiently lubricated and could be damaged. This is prevented by ensuring that the valve element does not move to the opened position when the pressure outside the pump housing exceeds the pressure inside the pump housing.

[0022] Preferably, the venting device comprises an actuator. The actuator can be moved between a locked position and at least one un-locked position. When the actuator is in the locked position, the valve element is held by the actuator in the closed position. When the actuator is in the at least one unlocked position, the valve element may move to the at least one opened position. Hence, in the preferred embodiment the venting device comprises an actuator for holding the valve element in the closed position by moving to a locked position. Thus, when the actuator is in the locked position, flow of fluid through the venting duct is blocked by the valve element. The actuator may also be movable to one or more opened positions. When the actuator is positioned in one of the one or more unlocked positions, the valve element can move to an opened position so that fluid can flow through the venting duct.

[0023] The actuator is preferably a linear actuator which is biased by a biasing means towards the locked position. By biasing the actuator towards the closed position, the default position of the actuator is the locked position so that the venting device is by default closed which prevents pump fluid from accidentally leaking out of the pump housing. The biasing means may, for example, be a helical spring.

[0024] Further preferably, the actuator comprises a piston linearly movable between the locked position and the unlocked position. The actuator comprises an electromagnet for moving the piston from the locked position to the unlocked position and a spring for biasing the piston towards the closed position. Hence, in the preferred embodiment the valve element is solenoid valve with an electromagnetically actuated piston. The piston can be moved from the locked position to the unlocked position by powering a coil. A magnetic force created by the coil moves the piston against the biasing means towards one of the one or more unlocked positions. When the electromagnet is switch off, the biasing means moves the piston back to the locked position where the piston holds the valve element in the closed position. Using a sole-noid valve has the advantage that it can be rapidly actuated. Furthermore, in case power is lost, the electromagnet releases the piston, and the biasing means ensures that the valve element moves to the closed position.

[0025] In an exemplary preferred embodiment, the venting device including the actuator is located inside the seal housing. Thereby, the venting device is protected from damages by the seal housing.

[0026] In an exemplary preferred embodiment, the shaft sealing device comprises an electronics unit for controlling the actuator. However, the electronics may also be located elsewhere. For example, the electronics may be located in an electronics housing of a pump motor or even be part of the electronics of the pump motor.

[0027] In a preferred embodiment, the venting duct comprises an annular protrusion forming a valve seat. The valve element is arranged in the venting duct between the valve seat and an environment of the pump housing. Preferably, the valve element is ball-shaped. Hence, in the preferred embodiment the valve seat of the venting device may be formed by the walls of the venting duct. Thus, the valve seat may be formed integrally with or by the seal housing. The valve seat is essentially formed by a part of the venting duct having a narrower free internal cross section than the subsequent section of the venting duct in which the valve element is located. The valve element itself is preferably a ball-shaped valve element which tightly seals the passage of the venting duct through the annular protrusion or collar in the closed position. The diameter of the ball-shaped valve element is less than the diameter of the venting duct in the region where the valve element is positioned so that air and pump fluid can flow past the valve element when it has moved away from the closed position.

[0028] In a preferred embodiment, the venting duct comprises an inlet section extending parallel to the rotational axis and an outlet section extending perpendicular to the rotational axis. Thus, in the preferred embodiment the venting duct is split in at least two sections extending in different directions. A first or inlet section of the venting duct directly branches off an inner surface of the seal housing where the venting duct opens into the seal housing. This inlet venting section extends parallel to the rotational axis, i.e., for an upright standing pump assembly the venting section extends vertically. A second or outlet section extends perpendicular to the inlet section, for example, horizontally. In an exemplary embodiment, the outlet section extends radially away from the rotational axis.

[0029] Preferably, the annular protrusion is formed integrally with the seal housing where the outlet section branches off the inlet section and limits a free cross section of the outlet section. Hence, in the preferred embodiment the outlet section of the venting duct has a narrow internal diameter where it branches off from the inlet section and widens after a short distance for accommodating the valve element. The valve element and the linear actuator thus moves horizontally in the seal housing. This allows integrating the entire actuator in the seal housing with no parts of the actuator protruding out of the seal housing while keeping the pump housing compact. Also, part of the venting device in from of the valve seat is formed by the seal housing.

[0030] Further, the inlet section can be placed in close vicinity of the rotational axis. Since air is commonly lighter as the pump fluids, due to the rotation of the drive shaft and parts of the shaft seal, the heavier pump fluid tends to flow outward whereas the lighter air accumulates in the vicinity of the drive shaft. Therefore, air accumulating at the top of the pump housing and in the vicinity of the drive shaft can be released through the centrally located venting duct.

[0031] In an exemplary preferred embodiment, the inlet section extends in the direction of the rotational axis past the outlet section.

[0032] Preferably, the sealing device comprises means for detecting pump fluid flowing through the venting duct. These means may be used to control the venting device. If the pump fluid sensing device detects pump fluid flowing through the venting duct while the actuator is an unlocked position, the system recognizes that all air has been removed from the pump housing and the venting device can be closed by moving the actuator to the locked position. This advantageously prevents pump fluid from leaking out of the pump housing. The electronics required for operating the means for detecting the pump fluid flowing through the venting duct may be included in the seal housing. However, they could also be located externally to the seal housing, for example, in an electronics housing of a pump motor.

[0033] Further preferably, the venting duct extends between a venting duct inlet and a venting duct outlet. At the venting duct outlet, the venting duct terminates in a blower channel. The blower channel is configured so that air can be blown at a blower inlet into the blower channel and past the venting duct outlet. Pump fluid carried by air from the outer opening of the venting duct through the blower channel is optically detected at a blower outlet of the blower channel.

[0034] Hence, in the preferred embodiment a means for directing the pump fluid flowing through the venting duct is provided. For detecting pump fluid, a blower channel is provided that extends preferably along a straight line past the venting duct outlet through the seal housing. Air is blown through the venting duct from the outside. When pump fluid flows even in small amounts through the venting duct, droplets of the pump fluid are pulled away by the flow of air through the blower chan-nel. At the end of the blower channel, these droplets can be detected using optical detection methods.

[0035] In an exemplary preferred embodiment, the blower channel is also used for removing the pump fluid that lubricated the shaft seal once it has flown past the shaft seal. To this end, the blower channel is connected via a drawing duct to an outward facing indentation in the seal housing. The indentation is separated from the inside of the pump housing by the shaft seal and the seal housing and used to strip of droplets of pump fluid that flow as lubricant for the shaft seal out of the pump housing.

[0036] Preferably, the shaft seal comprises a stationary part attached to the seal housing and a rotating part configured to be attached to the drive shaft. A sealing gap is formed between a sealing surface of the rotating part of the shaft seal and a corresponding 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 venting duct extends between a venting duct inlet and a venting duct outlet. The venting duct inlet forms an opening of venting duct to an inside of the pump housing. The venting duct inlet is in the direction of the rotational axis located between the venting device and the sealing gap.

[0037] 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 apump assembly, the rotating part of the shaft assembly also rotates about the rotational axis.

[0038] 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.

[0039] 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 fluid inside the pump housing is pressurized. Pump fluid 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.

[0040] The venting duct inlet is in the preferred embodiment located above the sealing gap when the pump assembly is installed with the drive shaft extending vertically. The actual venting device including the sealing means is even placed above the venting duct inlet. Air which has accumulating above the sealing gap can already be removed from the pump housing before the sealing gap runs dry and the shaft seal is damaged. Furthermore, the position of the venting device above the sealing gap ensures that when pump fluid flows through the venting device, it is also present at the position of the sealing gap.

[0041] In another preferred embodiment, the pump fluid sensing device comprises a sensor. The sensor is mounted 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. The valve element is placedalong the direction of the rotational axis closer to or in a same distance from a motor-facing end of the shaft sealing device than the sensor.

[0042] Hence, in the preferred embodiment a pump fluid sensing device is provided in the shaft sealing device for establishing whether pump fluid is present at the shaft seal. The pump fluid sensing device comprises a sensor, for example, a temperature sensor, which is mounted in the seal housing. The 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. Hence, the sensor does not determine the actual height of the pump fluid in the pump housing but can report whether the pump fluid has reached a specific level or not.

[0043] In the preferred embodiment, the venting device is placed along the rotational axis at the same position or above the sensor of the pump fluid sensing device. Thus, when the sensing device reports that the level of the pump fluid has dropped below the sensor position, the venting device can be automatically activated for removing the air that has been accumulated at the top of the pump housing. Since the venting device is placed vertically at the same position or above the sensing device, the sensor of the pump fluid sensing device will be in contact with pump fluid if all air has been removed from the pump housing and pump fluid commences to flow through the venting duct.

[0044] The control of the pump fluid sensing device and the venting device may be performed in the shaft sealing device. However, it is also possible to use, for example, the electronics of a motor control for controlling the venting device and the pump fluid sensing device.

[0045] In a second aspect, the present invention is directed to a pump housing comprising a shaft sealing device according to any of the pre-ceding embodiment mounted in on upper port of the pump housing. The advantages of the pump housing correspond to the advantages of the shaft sealing device used as part of the upper part of the pump housing.

[0046] Finally, in a third aspect the present invention is directed to a pump assembly comprising a pump motor and a pump housing according to previous embodiment. The pump motor is mounted to the pump housing. The advantages of the pump assembly correspond to the respective advantages of the shaft sealing device that is integrated into the pump housing of the pump assembly.

[0047] 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 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 a partially exploded view of the exemplary embodiment of Fig. 1, andFig. 6 shows an exemplary embodiment of a pump assembly comprising an exemplary embodiment of a pump housing.

[0048] Figures 1 to 5 show on exemplary embodiment of a shaft sealing device 1 comprising a seal housing 3, a shaft seal 5 and a venting device 7. The shaft seal 5 is only visible in Figures 2 to 5.

[0049] The seal housing 3 is provided for mounting the shaft sealing device 1 to an upper part 9 of a pump housing 1 1 . The upper part 9 of the pump housing 1 1 is partially shown in Figures 1 to 3. For attaching the seal housing 3 to the pump housing 1 1 , four bores 13 are formed in the seal housing 3. Through the bores 13 threaded bolts 15 can be inserted for screwing the seal housing 3 to the pump housing 1 1 . In Figure 5 the shaft sealing device 1 is shown without the bolts 15. The threaded bolts 15 engage mating threads (not shown) in the pump housing 1 1 .

[0050] The upper part 9 of the pump housing 1 1 forms the uppermost part of an upright standing pump assembly, i.e., a pump housing 1 1 where a rotational axis 17 of a drive shaft 19 of the pump housing 1 1 extends vertically during regular operation of the pump. The rotational axis 17 is only shown in Figure 4. The upper part 9 may be a separate part that is used to close off an upper opening of a pump housing 1 1 or may be formed as a single piece with additional parts of the pump housing 1 1 .

[0051] In the embodiment shown in Figures 1 to 5, the drive shaft 19 is formed by a drive shaft assembly 21 comprising a pump drive shaft 23, a shaft coupling device 25 and a motor drive shaft (not shown in Figures 1 to 5). Figure 1 only shows part of the pump drive shaft 23 which is provided to be directly attached to one or more impellers of a centrifugal pump assembly when the shaft sealing device 1 has been installed in a pump housing 1 1 . The pump drive shaft 23 is connected via the shaft coupling device 25 to the motor drive shaft.

[0052] Other parts of the shaft coupling device 25 which are (partially) visible in Figures 1 to 5 are a coupling sleeve 27 and a rotor clamp 29. The rotor clamp 29 is used for securing a motor drive shaft to an upper or motor-facing end of the coupling device 17. At its lower or pumpfacing end the coupling sleeve 27 receives the pump drive shaft 23.

[0053] The coupling sleeve 27 of the shaft coupling device 25 is surrounded by the shaft seal 5. The parts of the shaft seal 31 can be seen best in Figures 2 and 3. However, it is noted that the cut shown in in Figures 2 and 3 does not extend through the rotational axis 17 but parallel thereto.

[0054] The shaft seal 5 comprises a rotating part 31 and a stationary part 33. The rotating part 31 comprises a bellows 35 which is made from rubber and surrounded by a helical spring 37. The bellows 35 and the helical spring 37 are attached via a bracket 39 to the coupling sleeve 27. The bracket 39 attaches the bellows 35 in a rotationally fixed manner to the coupling sleeve 27. The helical spring 37 biases the bellows 35 towards the stationary part 33 of the shaft seal 5.

[0055] A sealing element 41 is supported on the bellows 35 and also rotates with the coupling sleeve 27. A sealing surface 43 of the sealing element 41 faces a seal seat 45 that is part of the stationary part 33 of the shaft seal 5. The seal seat 45 does not rotate relative to the seal housing 3 during operation of the pump but remains stationary. An O- ring 47 is provided for preventing pump fluid from leaking out of the pump housing 1 1 where the seal seat 45 rests against the seal housing 3. During operation of the pump, a sealing gap 49 is formed between the sealing surface 43 and the seal seat 45. The sealing gap 49 is filled with pump fluid which lubricates the shaft seal 5 as it forms a liquid film between the rotating and the non-rotating parts 31 , 33 of the shaft seal 5.

[0056] In case the level of pump fluid drops below the sealing gap 49 between the sealing element 41 and the seal seat 45, the shaft seal 5 is no longer lubricated. This may increase wear or even damage the sealing element 41 and the seal seat 45. To ensure that the level of pump fluid in the pump housing 1 1 is sufficient, a pump fluid sensing device 51 is part of the exemplary embodiment of a shaft sealing device 1. The pump fluid sensing device 51 is only shown in Figure 4 and comprises a control unit (not shown in figures 1 to 5) which is connected to a sensor 53. In the exemplary embodiment shown in the figures, the sensor 53 is a resistance temperature sensor in form of a Pt 100 element with a resistance of 100 Ohms at 0°C.

[0057] The temperature sensor 53 is mounted in a sensing space 55 above the shaft seal 5. In particular, the temperature sensor 53 is arranged in the vertical direction above the sealing gap 49 and the O- ring 47 sealing the seal seat 45 to the seal housing 3. When the temperature sensor 53 is in contact with pump fluid, it can be concluded that the sealing gap 49 is filled with pump fluid as the sensor 53 is mounted above the sealing gap 49. Furthermore, the sensor 53 can also be used to detect whether the O-ring 47 is properly sealing the seal seat 45 to the sensor housing 5. If pump fluid leaks out of the pump housing 1 1 at the position of the O-ring 47, the level of the pump fluid would drop to the position of the O-ring 47 and thus below the sensor 53.

[0058] For detecting whether the temperature sensor 53 is surrounded by air or pump fluid, the temperature sensor 53 is first heated by supplying a heating power of 0.4 W for a heating time of 1 s to the resistance temperature sensor 53. Immediately after the power is turned off, the temperature sensed by the temperature sensor 53 is recorded as an initial temperature of the temperature sensor 53. Afterwards, a plurality of cooling temperatures is recorded as the temperature sensor 53 cools off. These cooling temperatures are together with the initial tempera-ture evaluated to determine whether the temperature sensor 53 is submerged in pump fluid or surrounded by air. If the temperature sensor 53 is submerged in pump fluid, the temperature drops faster as if it is surrounded by air.

[0059] In case the presence of air is detected using the sensor 53 of the pump fluid sensing device 51 , the air trapped at the top of the pump housing 1 1 can be released using the venting device 7. The venting device 7 is installed in a venting duct 57 which connects an inside of the pump housing 1 1 to the environment. The venting duct 57 comprises a first or inlet section 59 and a second or outlet section 61. The inlet section 59 branches of at a venting duct inlet 63 from the inside of the pump housing 1 1 and extends parallel to the rotational axis 17, i.e., in the vertical direction. The venting duct inlet 63 is located in the vertical direction above the sealing gap 49. This ensures that any air located at the position of the sealing gap 49 can be removed be means of the venting device 7 from the pump housing 1 1 .

[0060] The outlet section 61 of the venting duct 57 extends perpendicular to the inlet section 59 and, thus, also perpendicular to the vertical direction, i.e., horizontally. At the transition from the inlet section 59 to the outlet section 61 the free inner diameter of the outlet section 61 is constricted or narrowed by an annular protrusion or shoulder 65 that forms a valve head 65. Where the outlet section 61 widens, a ballshaped valve element 67 is placed. The valve element 67 can move between a closed position in which it blocks flow through the venting duct 57 by abutting or resting against the valve head 65 and an opened position in which air or pump fluid may flow through the venting duct 57.

[0061] For locking the valve element 67 in the closed position, a magnetic linear actuator 69 is provided. The linear actuator 69 comprises apiston 71 with a piston rod 73 facing the ball-shaped valve element 67. The piston 71 is surrounded by a coil 75 forming an electromagnetic magnet and housed in a cylindric actuator housing 77. On an end of the piston 71 facing away from the valve element 67, a helical spring 79 is positioned. The helical spring 79 forms a biasing means 79 biasing the piston 71 towards a locked position. The biasing means 79 is supported on a plug 81 which is used for closing a bore 83 in the seal housing 3 in which the linear actuator 69 is installed in its entirety. For preventing pump fluid from leaking along the piston rod 73 into the actuator housing 77, an O-ring 85 is provided.

[0062] A free end 87 of the piston rod 73 faces and abuts the sealing element 67. For example, when the coil 75 is not powered, the biasing means 79 pushes the piston 71 to its maximum extended or closed position as shown in the figures. In the closed position, the free end 87 of the piston rod 73 abuts the sealing element 67 and holds it in the closed position. The venting duct 57 is thus closed and no pump fluid can flow out of the inside of the pump housing 1 1. Advantageously, the closed position is assumed automatically when the coil 75 is not powered due to the biasing means.

[0063] When power is supplied to the coil 75, the piston 71 moves away from the valve head 65 to an opened position (not shown). This could, for example, be done at regular intervals or whenever air is detected using the pump fluid sensing device 51 inside the pump housing 1 1. In the opened position, the free end 87 of the piston rod 73 limits the maximum distance the valve element 67 can move away from the valve head 65 and thereby keeps the valve element 67 inside the outlet section 61 of the venting duct 57.

[0064] The valve element 67 is not actively moved by the actuator 69 to an opened position. Rather, the venting device 7 relies on a pressuredifferential between the inside of the pump housing 1 1 and the environment of the pump housing 1 1 for moving the valve element 67. Only if the pressure inside the pump housing 1 1 exceeds the pressure outside the pump housing 1 1 , the valve element 67 moves due to the pressure differential from the closed position to an opened position and air can escape from the inside of the pump housing 1 1. However, in case the pressure outside of the pump housing 1 1 exceeds the pressure inside the pump housing 1 1 , the valve element 67 stays at the valve head 65 and advantageously prevents air from entering the inside of the pump housing 1 1 . The latter could damage the shaft seal 5 if it runs dry.

[0065] The outlet section 61 of the venting duct 57 terminates at a venting duct outlet 89 into a blower channel 91. The blower channel 91 is used for removing and detecting pump fluid that flows through the venting duct 57. To this end, air is blown at a blower inlet 93 into the blower channel 91 . The air flows passed the venting duct outlet 89 and strips off drops of pump fluid that have accumulated at the venting duct outlet 89. The drops are moved by the air flowing through the blower channel 91 to the blower outlet 95, where an optical sensing device (not shown) is provided for detecting the droplets. When the droplets are detected while the linear actuator 69 is in the unlocked position, it is understood that the inside of the pump housing 1 1 has been vented and the power to the coil 75 is turned off. The biasing means 79 will then move the piston 71 to the locked position, thereby pushing the valve element 67 to the closed positioned so that the venting duct 57 is advantageously blocked.

[0066] Finally, Figure 6 shows an exemplary embodiment of a centrifugal pump assembly 97. The pump assembly comprises a pump housing 1 1 with a pump top 99 forming the upper part 9 of the pump housing 1 1 which comprises a sealing device 1 as described with references to Figures 1 to 5. A control unit for the pump fluid sensing device 51 andthe venting device 7 is integrated into the electronics housing 101 of the pump motor 103.

[0067] The electric pump motor 103 is in the exemplary embodiment a permanent magnet synchronous motor mounted on top of the pump housing 1 1. The pump housing 1 1 further comprises a pump inlet 105 and a pump outlet 107. During operation of the pump assembly 97, pump fluid is ingested into the pump housing 1 1 through the pump inlet 105 and expelled out of the pump housing 1 1 through the pump outlet 107. Figure 6 also shows a motor drive shaft 109 that is part of the drive shaft assembly 21 .

[0068] The advantages of the pump assembly 97 shown in Figure6 correspond to the advantages of the exemplary embodiment of a sealing device 1 used as part of the pump assembly 97.Reference numeralsI shaft sealing device3 seal housing5 shaft seal7 venting device9 upper partI I pump housing13 bore15 threaded bolt17 rotational axis19 drive shaft21 drive shaft assembly23 pump drive shaft25 shaft coupling device27 coupling sleeve29 rotor clamp31 rotating part of the shaft seal33 stationary part of the shaft seal35 bellows37 helical spring39 bracket41 sealing element43 sealing surface45 seal seat47 O-ring49 sealing gap51 pump fluid sensing device53 sensor55 sensing space57 venting duct59 inlet section61 outlet section63 venting duct inlet65 valve head67 valve element69 linear actuator71 piston73 piston rod75 coil77 actuator housing79 helical spring, biasing means81 plug83 bore85 O-ring87 free end of the piston rod89 venting duct outlet91 blower channel93 blower inlet5 blower outlet 7 pump assembly 9 pump top101 electronics housing 103 pump motor105 pump inlet107 pump outlet109 motor drive shaft

Claims

Claims1 . A shaft sealing device ( 1 ) for a pump housing (1 1 ), the sealing device ( 1 ) comprising a seal housing (3), a shaft seal (5), a pump fluid sensing device (51 ), and a venting device (7), wherein the seal housing (3) is configured for mounting the sealing device ( 1 ) in an upper part (9) of a pump housing (1 1 ) and comprises a venting duct (57) for establishing a fluid communication between an inside of the pump housing (1 1 ) and an environment of the pump housing (1 1 ), wherein the shaft seal (5) is configured for circumferentially contacting a drive shaft ( 1 ) extending along a rotational axis ( 17) through the upper part (9) of the pump housing (1 1 ) and for preventing pump fluid from leaking out of the pump housing (1 1 ) where the drive shaft (19) extends through the upper part (9) of the pump housing (1 1 ), wherein the pump fluid sensing device (51 ) is configured to determine whether a level of pump fluid in the pump housing (1 1 ) is sufficient to keep the shaft seal (5) lubricated, and wherein the venting device (7) is configured for controlling a flow of fluid through the venting duct (57), wherein the venting device (7) comprises a valve element (67) mounted in the venting duct (67) and is configured for automatically releasing air from the pump housing (1 1 ) in case the pump fluid sensing device (51 ) determines that the level of pump fluid in the pump housing (1 1 ) is not sufficient to keep the shaft seal (5) lubricated.

2. Shaft sealing device (1 ) according to any of the preceding claims, wherein the valve element (67) is configured to move between a closed position in which a flow of fluid through the venting duct (57) is blocked and at least one opened position in which fluid may flow through the venting duct (57),wherein the venting device (7) is configured so that the valve element (67) maintains the closed position or moves from the opened position to the closed position if a pressure outside the pump housing (1 1 ) exceeds a pressure inside the pump housing (1 1 ).

3. Shaft sealing device (l )according to claim 1 or 2, wherein the venting device (7) comprises an actuator (69), wherein the actuator (69) can be moved between a locked position and at least one unlocked position, wherein when the actuator (69) is in the locked position, the valve element (67) is held by the actuator (69) in the closed position, and wherein when the actuator (69) is in the at least one unlocked position, the valve element (67) may move to the at least one opened position.

4. Shaft sealing device (1 ) according to claim 3, wherein the actuator (69) is a linear actuator (69) which is biased by a biasing means (79) towards the locked position.

5. Shaft sealing device (1 ) according to claim 4, wherein the actuator (69) comprises a piston (71 ) linearly movable between the locked position and the unlocked position, wherein the actuator (69) comprises an electromagnet for moving the piston (71 ) from the locked position to the unlocked position and a spring (79) for biasing the piston (71 ) towards the closed position.

6. Shaft sealing device (1 ) according any of the preceding claims, wherein the venting duct (57) comprises an annular protrusion (65) forming a valve seat (65) and wherein the valve element (67) is arranged in the venting duct (57) between the valve seat (65) and an environment of the pump housing (1 1 ), wherein the valve element (67) is preferably ball shaped.

7. Shaft sealing device (1 ) according any of the preceding claims, wherein the venting duct (57) comprises an inlet section (59) extending parallel to the rotational axis (17) and an outlet section (61 ) extending perpendicular to the rotational axis (17).

8. Shaft sealing device (1 ) according to claims 6 and 7, wherein the annular protrusion (65) is formed integrally with the seal housing (3) where the outlet section (61 ) branches off the inlet section (59) and limits a free cross section of the outlet section (61 ).

9. Shaft sealing device ( 1 ) according to any of the preceding claims, wherein the sealing device (1 ) comprises means for detecting pump fluid flowing through the venting duct (57).

10. Shaft sealing device ( 1 ) according to claim 9, wherein the venting duct (57) extends between a venting duct inlet (63) and a venting duct outlet, wherein at the venting duct outlet (89) the venting duct (57) terminates in a blower channel (91 ), and wherein the blower channel (91 ) is configured so that air can be blown at a blower inlet (93) into the blower channel (91 ) and past the venting duct outlet (89), and wherein pump fluid carried by air from the venting duct outlet (89) through the blower channel (91 ) is optically detected at a blower outlet (95) of the blower channel (91 ).1 1 . Shaft sealing device ( 1 ) according to any of the preceding claims, wherein the shaft seal (5) comprises a stationary part (33) attached to the seal housing (3) and a rotating part (35) configured to be attached to the drive shaft (19), wherein a sealing gap (49) is formed between a sealing surface (43) of the rotating part (31 ) of the shaft seal (5) and a corresponding seal seat (45) of the stationary part (33) of the shaftseal (5), wherein the sealing gap (49) is formed to be filled with pump fluid during use of the pump housing (1 1 ) for lubricating the shaft seal (5), and wherein the venting duct (57) extends between a venting duct inlet (63) and a venting duct outlet (89), wherein the venting duct (57) inlet forms an opening of the venting duct (57) to the inside of the pump housing (1 1 ) and wherein the venting duct inlet (63) is in the direction of the rotational axis (17) located between the venting device (7) and the sealing gap (49).

12. Shaft sealing device ( 1 ) according to any of the preceding claims, wherein the pump fluid sensing device (51 ) comprises a sensor (53), wherein the sensor (53) is mounted at a position where it is only in contact with pump fluid if a level of pump fluid in the pump housing (1 1 ) is sufficient to keep the shaft seal (5) lubricated, and wherein the valve element (67) is placed along the direction of the rotational axis (17) closer to or in a same distance from a motor-facing end of the shaft sealing device (1 ) than the sensor (53).

13. A pump housing (1 1 ) comprising a shaft sealing device (1 ) according to any of the preceding claims mounted in an upper part (9) of the pump housing (1 1 ).

14. A pump assembly (97) comprising a pump motor (103) and a pump housing (1 1 ) according to claim 13, wherein the pump motor (103) is mounted to the pump housing (1 1 ).

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