Technical field [001] The present invention relates to a mechanical sealing arrangement in accordance with the preamble of claim 1 and a sensor ring in accordance with the preamble of claim 1 1.

Background art [002] Mechanical seals are gaining more and more acceptance in various shaft sealing applications. The mechanical seals find use in various pumps, mixers and agitators. Mechanical seals are of relatively simple construction, they endure high temperatures and their maintenance and service is relatively easy. But, just like all kinds of seals, their lifetime is hard to predict. It is also quite impossible to perform any visual monitoring of the condition of the seal. Therefore, prior art includes numerous documents that discuss the monitoring of the condition of a mechanical seal.

[003] US-A-6,065,345 discusses a method of monitoring the condition of a mechanical seal in an apparatus provided with a rotating part, in particular in a pump, which has a rotating shaft for the forwarding of a fluid. The sound emission of the seal is continually measured at discrete times in the operating state of the apparatus and at least one statistical characteristic value is won from the acoustic signals. The goal in the above discussed patent is to monitor the sliding condition of the seal. In other words, if the seal is starting to run dry, i.e. the flushing is, for some reason, not working properly, the acoustic emission from the seal changes with the condition of the lubricating film. The US- patent discusses also the effect of the speed of rotation of the pump, the tempera ture of the flushing liquid, the pressure of the fluid to be pumped, etc. on the acoustic emission of the seal, whereby the acoustic emission may change even if the sliding conditions were not changed.

[004] US-B1 -6,360,610 discusses a system and a method that are particularly suited for monitoring the interface of two liquid lubricated mechanical seal faces. The system monitors an interface by using a wave source to produce an ultrasonic shear wave, directing the wave at the interface, detecting the wave after it interacts with the interface, and comparing the detected wave to predetermined wave characteristics. Based on the comparison, an alarm may be triggered. The alarm may indicate that the mechanical seal is failing. In a preferred example, the approach involves detecting the collapse of the lubricating film between the seal faces and detecting excessive asperity contact. The collapse of the lubricating film and excessive asperity contact are precursors to seal failure. An ultrasonic transducer is placed behind one of the seal faces and used to produce ultrasonic shear waves (at a known frequency and amplitude) which propa gate toward the interface between the two seal faces. By monitoring the amplitudes of the waves transmitted through or reflected by the interface, one can detect film collapse and the degree of contact between the faces.

[005] Yet another document discussing the condition of the fluid film between the slide surfaces is GB-A-2430034. It discloses a condition monitoring system, using at least one acoustic emission sensory device to indirectly and/or remotely monitor the health status of a piece of rotating equipment, and applications thereof as for example a me chanical seal or a bearing assembly. The acoustic emission sensory device can be placed in direct or indirect contact to counter rotating surfaces. The signal emitted by the acoustic emission sensory device can be amplified, filtered for background noise, computed, compared to reference values and stored on a data storage device. [006] US-B2-8,527,214 discusses a mechanical device showing the degree of wear of the slide surfaces of the mechanical seal. The discussed mechanical device is, on the one hand, a simple device measuring the physical axial movement of a slide ring due to wear, but, on the other hand, in most applications it is, in practice, quite hard to ar range such in connection with a mechanical seal. Especially, it would also be difficult to arrange a follower to be in mechanical contact with the rotary slide ring carrier the axial movement of which is to be measured, as instructed in the patent.

[007] In other words, the above cited prior art discusses either abnormal operating con ditions in which the lubrication of the mechanical seal surfaces has failed or is about to fail resulting in dry running of the seal, or wear in normal operating conditions. However, the monitoring of dry running or wear in normal operating conditions, requires, in ac cordance with prior art such an arrangement that is, though in principle simple, hard to construct and includes a great risk of functional failure, as the follower discussed in the cited patent (US-B2-8,527,214) is apt to wear, too. [008] In addition to the above discussed prior art documents, EP-B1-2362122 needs to be mentioned. The EP- document lists a number of sensors to be arranged in or on the mechanical seal, preferably in or close to the sealing gap between the rotary and non rotary sealing surfaces. The EP- document lists the following operating parameters that may be followed: pressure of the working fluid close to the seal, temperature of the working fluid, temperature at the sealing gap, leakage flow through the sealing gap, rotational speed of the shaft and/or vibration of the seal arrangement. However, the document does not discuss the way the various sensors are arranged in connection or in communication with the mechanical seal. [009] In almost all prior art cases the condition of the seal is monitored by more or less external sensors, which is quite understandable as the access to the mechanical seal is not easy and no simple means of monitoring the seal condition has not been available on the market.

[0010] An object of the invention is to provide invention the mechanical sealing arrangement and a sensor which improve the performance of a mechanical sealing considerably compared to the prior art solutions.

Disclosure of the Invention [0011] At least one of the objects of the present invention is met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

[0012] According to an embodiment of the present invention the mechanical seal ing arrangement has a rotary part, a non-rotary part and a signal processing arrange- ment, the rotary part comprising at least a rotary slide ring and a rotary slide ring carrier, the non-rotary part comprising at least a non-rotary slide ring and a non-rotary slide ring carrier, and the signal processing arrangement comprising at least one sensor for mon itoring the operation of the mechanical sealing arrangement. The mechanical sealing arrangement comprises a sensor ring provided on the non-rotary slide ring carrier, the sensor ring being provided with the at least one sensor and means for transmitting measurement data from the at least one sensor to further processing, the sensor ring having a first wall and a second wall leaving a cavity therebetween, wherein the cavity is opening in a radially inward direction, wherein at least one opening is arranged in the second wall through which the at least one sensor is arranged to extend from the cavity to outside the sensor ring.

[0013] According to an embodiment of the invention the mechanical sealing com- prises at least one opening in the non-rotary slide ring carrier for the at least one sensor.

[0014] According to an embodiment of the invention the opening in the second wall of the sensor ring and the opening in the non-rotary slide ring carrier are coaxial with each other and are together extending from the cavity to the non-rotary slide ring to bring the at least one sensor in contact with the non-rotary slide ring. This way a direct measurement from the slide ring is obtained.

[0015] According to an embodiment of the invention the at least one sensor being a temperature or vibration sensor.

[0016] According to an embodiment of the invention the sensor ring comprises at least one opening at its first wall for at least one sensor. [0017] According to an embodiment of the invention the at least one sensor being a pressure sensor.

[0018] According to an embodiment of the invention the cavity in the sensor ring being an annular cavity in the inner circumference of the sensor ring

[0019] According to an embodiment of the invention the cavity in the sensor ring being at least one groove arranged in the inner circumference of the sensor ring. The groove extends only partially around the inner circumference of the sensor ring to at least one direction from or passing by the at least one opening arranged in the second wall of the sensor ring.

[0020] According to an embodiment of the invention the sensor ring being sealed to the non-rotary slide ring carrier by means of at least one O-ring and at least one annular plane seal.

[0021] According to an embodiment of the invention in the sensor ring being fas tened to the non-rotary slide ring carrier by means of screws. [0022] According to an embodiment of the invention in a signal processing unit (SPU) receiving the measurement data from the at least one sensor via the transmitting means.

[0023] A sensor ring according to the invention is intended for use in monitoring the operation of a mechanical seal arrangement. The sensor ring comprising a first wall and a second wall and a cavity therebetween, the cavity opening in radially inward di rection, at least one of the first wall and the second wall comprising at least one opening for at least one sensor.

[0024] According to an embodiment of the invention the sensor ring having a first wall and a second wall leaving a cavity therebetween, wherein the cavity is opening in a radially inward direction, and wherein at least one opening is arranged in the second wall through which the at least one sensor is arrangeable to extend from the cavity to outside the sensor ring when installed for use.

[0025] According to an embodiment of the invention the cavity in the sensor ring being an annular cavity in the inner circumference of the sensor ring.

[0026] According to an embodiment of the invention the cavity in the sensor ring being at least one groove arranged in the inner circumference of the sensor ring.

[0027] According to an embodiment of the invention means for transmitting data measured by the at least one sensor for further processing. [0028] According to an embodiment of the invention the transmitting means being one of a wiring, a fiber optic cable, an RF-connection and a Bluetooth connection.

[0029] By means of the present invention the reliability and or predictability of the mechanical sealing arrangement is considerably improved.

[0030] Additionally or alternatively a mechanical seal according to the invention can be provided with a reliable and simple means for monitoring the working of the mechanical seal in normal operating conditions.

[0031] Further the invention introduces a simple“sensor ring” that may be ar ranged in connection with all types of mechanical seals, including both single acting and double acting mechanical seals. [0032] The exemplary embodiments of the invention presented in this patent ap plication are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also non-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.

Brief Description of Drawings [0033] In the following, the mechanical seal arrangement and the sensor ring of the present invention are described in more detail with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a partial axial cross section of a mechanical seal arrangement in accordance with a preferred embodiment of the present invention,

Figure 2 illustrates a cross section of the sensor ring with its sealing means,

Figure 3 illustrates an isometric view of the non-rotary slide ring carrier together with the sensor ring of the mechanical seal arrangement of Figure 1 , and

Figure 4 illustrates an isometric view of the sensor ring of the present invention.

Detailed Description of Drawings

[0034] Figure 1 depicts a mechanical seal arrangement in accordance with a pre ferred embodiment of the present invention, the seal arrangement comprising a sche matically and exemplarily illustrated single-acting mechanical seal 10 and a signal pro cessing arrangement 30. The present invention is, naturally, applicable to double-acting mechanical seals, too. The mechanical seal 10 is used for sealing the shaft 8 (shown by dashed lines) of, for instance, a flow machine such that the interior of the flow ma chine, at the left hand side of the seal 10, is kept separate from the atmosphere, at the right hand side of the seal 10. The mechanical seal 10 is positioned in a seal chamber provided within a specific seal housing or within a casing cover of a flow machine. [0035] The mechanical seal 10 comprises a rotary part 12 and a non-rotary part 20. The rotary part 12 comprises a retainer ring 14, a rotary slide ring carrier 16 and a rotary slide ring 18. The rotary slide ring 18 is attached to an axial end of the rotary slide ring carrier 16. The non-rotary part 20 comprises a non-rotary slide ring carrier 22, a non-rotary slide ring 24 and a gland ring 26. The non-rotary slide ring 24 is attached to an end of the non-rotary slide ring carrier 22. The slide rings 18 and 24 are, when in use in the flow machine, in mechanical contact with one another. In addition to the shown components the mechanical seal may comprise O-rings, drive pins, set screws and bolts, but as they do not form a part of the present invention they have not been discussed in any more detail.

[0036] The signal processing arrangement 30 comprises a signal processing unit SPU, a sensor ring 32 with sensors 38 provided in connection therewith and a means 34 for transmitting data measured by the sensors 38 to the signal processing unit SPU. The sensor ring 32 is a separate ring element arranged on the non-rotatory part 20 of the mechanical seal. The sensor ring has no essential direct function in operation of the mechanical seal itself, and its function relates to holding sensors suitably for obtaining accurate measurements and for holding the transmitting means 34. The transmitting means 34 may be a traditional wiring, a fiber optic cable or wireless transmitting means like Bluetooth or radio frequency transmitting means, just to name a few optional means without any intention to limit the invention to the listed alternatives.

[0037] The rotary part 12 of the mechanical seal 10 is assembled on the shaft such that the retainer ring 14 is installed against a shoulder on the shaft 8, normally between the shoulder and, for instance, the hub of a centrifugal impeller, and the rotary slide ring carrier 16 with the rotary slide ring 18 fastened to the end thereof is pushed on O-rings provided on the retainer ring 14.

[0038] The non-rotary part 20 of the mechanical seal is assembled such that a sensor ring 32 is first pushed on the non-rotary slide ring carrier 22 against a radially outwardly extending flange-like part 28 of the non-rotary slide ring carrier 22. The sen sor ring 32 may be fastened either in an axial direction to the flange like part 28 or in radial direction to the cylindrical part of the slide ring carrier 22. The sensor ring 32 provided with a radial seal 40 and an axial sea 44, and it is assemble in sealed manner on the non-rotary slide ring carrier 22, as illustrated in Figure 2. The sensor ring 32 is sealed in radial direction to the cylindrical part of the slide ring carrier 22 by means of at least one O-ring 40 provided at the inner circumference of the first wall 42 of the sensor ring 32 and in axial direction to the flange-like part 28, preferably but not neces sarily, by means of an annular plane seal 44 provided on the outer surface of the second wall 46 of the sensor ring 32. Thereafter the non-rotary slide ring carrier 22 is coupled, preferably in a non-rotary but, preferably but not necessarily, axially movable manner (possibly with the help of drive pins to keep the slide ring carrier 22 non-rotary and springs to allow axial movement of the non-rotary slide ring) to the gland ring 26 and the gland ring 26 is pushed inside an opening in the casing of a flow machine and fas tened thereto. Thus the rotary slide ring 18 and the non-rotary slide ring 24 fastened at an end of the non-rotary slide ring carrier 22 are brought in mechanical contact with one another.

[0039] The sensor ring 32 illustrated, in addition to Figure 1 , also in Figures 2, 3 and 4 is, in this embodiment of the present invention, provided with substantially axial holes 36 for fastening the sensor ring 32 to the flange-like part 28 of the non-rotary carrier ring 22, sensors 38, 48 required for watching at least one operating parameter of the mechanical seal and for monitoring the operation of the mechanical seal and a transmitting means 34 for transmitting the data measured by the sensors 38, 48, i.e. a so called measurement data, to the signal processing unit SPU. Sensor 38 may be a temperature, acoustic or vibration sensor, just to name a few optional alternatives with out, however, limiting the present invention to the named alternatives. The sensor ring comprises an opening 50’ which is arranged through the second wall 46 of the sensor ring 32. There is also an opening 50” arranged through the flange-like part 28 of the non-rotary carrier ring 22 such that the sensor 38 may be brought through the opening 50’ in the sensor ring 32 and the flange-like part 28 in the non-rotary carrier ring 22 in direct contact with the non-rotary slide ring 24. The openings are advantageously axial in respect to the carrier ring 22 and arranged coaxially with each other.

[0040] Sensor 48 in Figures 3 and 4 is a pressure sensor configured to record the fluid pressure in front of the mechanical seal 10. Thus the sensor 48 is provided in an opening 52 in the first wall 42 of the sensor ring 32. In addition to the pressure in the seal space also the temperature therein may be followed by means of the invention, just to name two optional alternatives without, however, limiting the present invention to the named alternatives only

[0041] Preferably, the sensor ring 32 has a U-shaped cross section leaving be tween its first wall 42 and its second wall 46 such an internal cavity 54 within the sensor ring 32 that opens, when in use, radially inwardly towards the non-rotary slide ring car rier 22 so that the sensors 38 and 48, and especially the transmitting means, i.e. for instance a wiring thereof, may be arranged in the internal cavity 54 out of contact with the liquid surrounding the mechanical seal. The cavity 54 in the sensor ring 32 may be an annular cavity extending over the entire inner circumference of the sensor ring 32 or it may be formed of at least one groove machined or otherwise provided in the inner circumference of the sensor ring 32 to extend from the sensors 38, 48 to an opening 56 provided for taking the transmitting means 34 from the sensors out of the sensor ring 32. The opening 56 is arranged advantageously to extend radially through a bottom of the cavity 54. The transmitting means 34, when it is a mechanical wiring, a fibre optic cable or a set of wirings or cables, is preferably taken along a unitary channel to the signal processing unit SPU. The channel may be taken to the signal processing unit SPU through the gland ring 26 or through the bearing housing or the casing cover, i.e. through whichever machine element surrounding the mechanical seal. [0042] While the invention has been described herein by way of examples in con nection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.