JP2014219023A - Non-contact annular seal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-contact annular seal which is excellent in shaft sealing characteristics and vibration characteristics.SOLUTION: A non-contact annular seal is used for sealing a clearance between facing portions of a rotary part and a fixed part of a pump. The non-contact annular seal includes a first seal structure 45, which has excellent shaft sealing characteristics, in the rotary part and further includes a second seal structure 47, which has excellent vibration characteristics, in the fixed part.

Description

  The present invention relates to a non-contact annular seal, and in particular, in a rotary machine that handles an incompressible fluid, the amount of fluid leakage between an impeller and a casing and a casing is reduced, vibration is reduced, and stable shaft sealing characteristics are provided. The present invention relates to a non-contact annular seal that exhibits the above and a rotary machine using the same.

  Rotating machines (hereinafter referred to as “pumps”) for transferring liquids are widely used in various plants and facilities such as power generation, chemical processes, sewerage, and waterworks. In the pump, a rotary shaft having an impeller mounted inside a casing is supported rotatably by a bearing. Then, the liquid sucked from the suction port is pressurized by the rotation of the impeller and discharged from the discharge port. In the flow path inside the pump, a slight gap between the fixed portion (casing) and the rotating portion (rotating shaft) is sealed in a non-contact manner so that the pressure of the pressurized liquid is reduced to the low pressure side. This is because fluid leakage from the high pressure side to the low pressure side is a major factor that reduces pump efficiency.

  Taking the typical multi-stage centrifugal pump shown in FIG. 1 (cited from JIS handbook pump 1st edition, page 74) as an example, the non-contact annular seal is located between the impeller inlet and the next impeller, and the final impeller It is often used between the vehicle outlet and the low pressure side (pump inlet pressure) (part surrounded by a circle in the figure). In particular, the pressure difference between the high-pressure side and the low-pressure side is large between the impeller outlet and the low-pressure side, so that liquid leakage increases and the pump performance is greatly affected. For this reason, non-contact annular seals having various structures capable of reducing the leakage amount have been devised. The most basic non-contact annular seal is a smooth seal (a seal made of a double cylinder in which the flow path between the fixed part and the rotating part in the seal is parallel and smooth). Examples of the seal structure to be reduced include a parallel groove seal, a damper seal, and a thread groove seal.

  As shown in FIG. 7, the parallel groove seal has a structure in which the outer peripheral surface of the rotating part (rotating shaft 111) of the flow path in the seal is smooth, but a number of concentric grooves are provided on the surface of the fixed part. This is a parallel groove seal 136. This parallel groove seal 136 is affected by energy loss due to vortices generated when the fluid flowing in the seal passes through the groove, pressure loss due to sudden expansion and contraction of the flow path, and the like. It is a seal that can be reduced.

  On the other hand, as shown in FIGS. 8 and 9, the damper seal is a structure in which the outer peripheral surface of the rotating shaft 111 of the flow path in the seal is smooth, but a plurality of uneven portions are provided on the surface of the fixed portion of the seal flow path. It is. Examples of the uneven shape include a honeycomb pattern 137 shown in FIG. 8 and a hole pattern 138 shown in FIG. In the case of the seal structure of the honeycomb pattern 137, the surface of the fixed portion of the seal has a honeycomb structure and has a large number of hexagonal recesses. Due to the pressure loss of the fluid flowing through the uneven surface, fluid leakage is reduced. The seal of the hole pattern 138 is provided with a large number of circular concave portions on the surface of the fixed portion of the seal, and fluid leakage is reduced by pressure loss of the fluid flowing through the gap between the concave and convex portions and the rotating shaft 111.

  There is also a thread groove seal 145 as shown in FIG. The thread groove seal 145 has a structure in which a screw is formed on either the rotating part or the fixed part, or both of the sealing parts (in the figure, the rotating shaft 111). For this reason, when the rotating shaft rotates, depending on the rotation direction, the fluid can be pushed back to the high pressure side by the pumping effect, and the leakage amount can be greatly reduced. This is a great advantage of thread seals. However, since the fluid is pushed back to the high pressure side by the pumping effect, this seal exhibits its ability when used for an incompressible fluid which is a liquid such as water.

  As mentioned above, one of the important things in the non-contact annular seal technology is the shaft seal characteristic. However, in addition to the shaft seal characteristics, vibration characteristics are also important, and it is also important to achieve harmony between the shaft seal characteristics and the vibration characteristics. The pump generates vibration due to various causes. One of the causes of the vibration is an unstable fluid force. Unstable fluid force occurs when the shaft is displaced radially with the fluid flow velocity in the seal having a circumferential component, resulting in an imbalance in the circumferential distribution of fluid flow velocity in the seal. It is power.

  Generally, the shaft seal characteristics and vibration characteristics of a non-contact annular seal are in a trade-off relationship, and no single seal structure has good performance in both shaft seal performance and vibration characteristics. When comparing shaft seal characteristics and vibration characteristics between a smooth seal and another seal structure, the following can be said. That is, the parallel groove seal has excellent shaft seal characteristics, but the rigidity effect and damping effect of the liquid film in the seal cannot be expected, and the vibration characteristics deteriorate.

  On the other hand, the thread groove seal has excellent shaft sealing characteristics because the fluid is pushed back to the high pressure side depending on the direction of shaft rotation. On the other hand, however, since a circumferential force is applied to the fluid to push the fluid back to the high pressure side, it is a major cause of unstable vibration, and the seal has a great demerit in terms of vibration characteristics.

  Further, the damper seal has a large energy loss due to the unevenness of the flow path surface, and has better vibration damping efficiency than the above-described parallel groove seal and screw groove seal, and stabilizes the vibration of the rotating shaft. However, the shaft seal characteristics are not outstanding, and cannot be expected as much as parallel groove seals and thread groove seals.

  The present invention has been made in view of the above problems, and the parallel groove seal is superior in leakage prevention performance compared to a smooth seal, but the vibration characteristics are deteriorated. The thread groove seal pushes the fluid back to the high pressure side as the shaft rotates, so it has very good sealing characteristics, but it gives a circumferential component to the fluid flow velocity, creating a major cause of unstable vibrations, and has extremely high vibration characteristics. bad. Dunbar seals have excellent vibration damping effects and can reduce shaft vibration, but shaft seal characteristics cannot be expected as much as parallel groove seals and thread groove seals. Thus, there is currently no seal structure in which each seal has advantages and disadvantages, and a single shaft seal and vibration characteristics are excellent.

  The problem to be solved by the present invention is to reduce the leakage of the fluid pressurized by the impeller to the low pressure side in the rotating machine that rotates the shaft to which the impeller is attached and transfers the fluid, thereby improving the efficiency of the rotating machine. It is an object of the present invention to provide a non-contact annular seal that raises and reduces vibration of the rotating machine, and a rotating machine (pump) including the non-contact annular seal.

  The present invention has been made in view of the above problems, and the first means is a non-contact annular seal for sealing a gap at a facing portion between the rotating part and the fixed part of the pump, the rotating part This is a non-contact annular seal having a first seal structure with excellent shaft seal characteristics and a second seal structure with excellent vibration characteristics at the fixed portion.

  In the second means, the first seal structure is a thread seal structure provided in the rotating part, and the second seal structure is a damper seal structure provided in the fixed part. A non-contact annular seal according to 1 means.

  In a third means, the damper seal structure is a non-contact annular seal according to the second means, wherein the damper seal structure is a honeycomb pattern recess or a hole pattern recess.

  In the fourth means, the length of the longest diagonal line of the hexagonal holes constituting the honeycomb pattern concave portion or the diameter of the circular holes constituting the hole pattern is 3 to 7 mm, and two adjacent hexagonal holes or two circular shapes are formed. The non-contact annular seal according to the third means, wherein the distance between the holes is 4 to 9 mm.

  In the fifth means, an electric motor, a main shaft connected to the electric motor and rotating, an impeller that is fitted to the main shaft and rotates together with the main shaft, a casing that houses the impeller, and an attachment to the casing And a non-contacting annular seal according to any one of the first to fourth means.

  According to the above means, the thread groove seal as the first seal structure in the non-contact annular seal pushes the fluid back to the high pressure side by pumping as its shaft seal characteristic, and thus has an excellent shaft seal characteristic. On the other hand, there is also a damper seal as a second seal structure that has a shaft seal characteristic that is not so high but has excellent vibration characteristics (vibration damping efficiency) that can be said to be a drawback of the thread groove seal. By combining these, it is possible to offset each other's drawbacks that could not be solved by each single seal structure and take advantage of each other's advantages.

  As described above, the thread groove seal pushes the fluid back to the high pressure side by the pumping effect, so it may be less effective for compressible fluids such as air but is effective for incompressible fluids such as liquids. It is. Therefore, it is desirable to limit the fluids handled to incompressible fluids. Moreover, it is more preferable to use a honeycomb pattern seal having a higher vibration damping effect than the hole pattern seal as the damper seal. That is, it can be said that a non-contact annular seal in which a thread groove seal and a honeycomb seal are combined to face each other is more preferable. More preferably, a thread groove seal is used for the rotating part, and a honeycomb seal is installed on the fixed part concentrically with the thread groove seal facing the center line.

  According to the present invention, a screw groove seal is provided on the rotating portion, and the honeycomb seal is concentrically combined with the fixed portion so as to face the screw groove seal. For this reason, the shaft seal characteristics of the thread groove seal are utilized, and at the same time, the instability to vibration of the thread groove seal is supplemented by the honeycomb seal having good vibration damping characteristics, so that the shaft seal characteristics are excellent and the vibration of the rotating shaft is low. It became possible to provide a seal. In other words, by utilizing the excellent shaft seal characteristics of the thread groove seal that pushes the fluid back to the high pressure side by the pumping effect, and simultaneously reducing the vibration that cannot be reduced by the thread groove seal with the honeycomb seal having an excellent vibration damping effect, the shaft seal A non-contact annular seal having excellent characteristics and low vibration (excellent vibration characteristics) could be realized.

It is sectional drawing of the multistage centrifugal pump in which a non-contact annular seal is installed. It is an expanded sectional view of the impeller of the multistage centrifugal pump disclosed in FIG. It is a non-contact annular seal structure figure concerning a 1st embodiment of the present invention, and Drawing 3 (A) shows the whole outline and Drawing 3 (B) shows the surface of a honeycomb pattern seal. It is a non-contact annular seal structure figure concerning a 2nd embodiment of the present invention, and Drawing 4 (A) shows the whole outline and Drawing 4 (B) shows the surface of a hole pattern seal. It is the graph which compared the shaft sealing performance of the non-contact annular seal which concerns on a prior art and this invention. It is the graph which compared the vibration performance of the non-contact annular seal which concerns on a prior art and this invention. It is a structural diagram of a conventional parallel groove seal. It is a structural diagram of a combination of a conventional smooth seal and a honeycomb pattern seal. It is a structural diagram of a combination of a conventional smooth seal and a hole pattern seal. It is a structural diagram of a combination of a conventional thread groove seal and a smooth seal.

  Next, an embodiment of the present invention will be described with reference to the drawings. The following description is merely illustrative of the embodiment, and the technical scope of the present invention is not limited to the following embodiment. Moreover, each component demonstrated below can comprise invention by independent or arbitrary combinations.

[Overview of the pump]
FIG. 1 shows a cross-sectional view of a high-pressure pump (multistage centrifugal pump) 1 to which a non-contact annular seal according to this embodiment is applied. With reference to this cross-sectional view, the fluid flow leakage location will be described. The high-pressure pump is connected to an electric motor to rotate, a main shaft 11, an impeller 21a, 21b, 21c that is fitted to the main shaft 11 and rotates with the main shaft 11, and a casing 31 that houses the impellers 21a, 21b, 21c. And bearings 41 a and 41 b that are attached to the casing 31 and rotatably support the main shaft 11. An electric motor (not shown) for rotationally driving the high-pressure pump is connected via a coupling 13 fitted to the left end of the main shaft 11.

  The first stage impeller 21a fastened to the main shaft 11 rotates as the main shaft 11 rotates, and guides fluid from the suction port 33 into the pump. The fluid pressurized by the first stage impeller 21a passes through the first flow path 35a and is guided to the second stage impeller 21b. The fluid pressurized by the second stage impeller 21b passes through the second flow path 35b and is guided to the third stage impeller 21c. The fluid is further pressurized by the impeller 21c at the third stage, discharged from the discharge port 37, and transferred by a pipe (not shown). That is, the fluid is pressurized by the first stage impeller 21a, the second stage impeller 21b, and the third stage impeller 21c.

  The fluid always has a low pressure side and a high pressure side on the suction side and discharge side of each impeller 21a, 21b, 21c. If a high pressure side and a low pressure side occur, a part of fluid tends to leak from the high pressure side to the low pressure side through a slight gap. It is the non-contact annular seal of this embodiment that seals it. In the pump of FIG. 1, a non-contact annular seal is provided at a site surrounded by a circle. Naturally, if the amount of liquid leakage is large, the pump efficiency is lowered. The high-pressure pump has many impellers stacked to increase the fluid pressure. As a matter of course, sealing is difficult because the pressure is higher than that of a normal pump.

  FIG. 2 shows an enlarged view of the first stage impeller 21a among the impellers 21a, 21b, and 21c disclosed in FIG. Fluid leakage points in the pump are mainly the facing portion X between the outer peripheral surface of the impeller inlet 23 and the casing 31a, and the facing portion Y between the outer peripheral surface of the rear surface of the impeller 21a and the casing 31b. The non-contact annular seals 41 and 43 according to the present embodiment are installed in the gaps formed in the facing portions X and Y.

  The mechanism of fluid leakage will be described with reference to FIG. The impeller 21 a fitted to the main shaft 11 rotates simultaneously with the rotation of the main shaft 11 and sucks fluid from the impeller suction port 23. The sucked fluid is given energy by the rotating blades and is discharged at a high pressure in the flow path. If the discharged high-pressure fluid is a multistage pump, it flows through the flow path of the casing 31 and is transferred to the next second-stage impeller 21b. In the case of a single-stage pump (not shown), it is guided to the discharge pipe through the flow path of the casing. Of course, even if it is a multistage pump, if it is an impeller of the last stage, it will be guide | induced to the discharge piping from the flow path of the casing 31. FIG. However, a small part of the fluid flowing out from the discharge port 25 on the high-pressure side flows out to the low-pressure side through a slight gap between the impeller 21a and the casings 31a and 31b. The fluid that flows out is a leaking fluid, which naturally reduces the efficiency of the pump.

  In order to prevent the efficiency of the pump from being reduced, in the case of a normal pump, as shown in FIG. 2, non-contact annular seals 41 and 43 are provided in the gap between the impeller 21a as a rotating part and the casings 31a and 31b as fixed parts. It has been devised to narrow the gap and reduce the leakage flow rate.

  However, in the case of a high pressure pump such as a high pressure pump, the difference between the pressure on the high pressure side and the pressure on the low pressure side on the back of the impeller 21a is large, so that a non-contact annular seal with smooth surfaces facing each other is created. When the gap is small (several hundred μm), the amount of fluid leakage is large. For this reason, in order to reduce the amount of leakage, the gap must be further narrowed to improve the shaft seal characteristics. However, if the gap is narrowed to prevent leakage, problems such as contact between the rotating part and the fixed part occur, so there is a natural limit to narrowing the gap.

  Various devices have been devised in the past regarding the seal structure for preventing this leakage. Specifically, the parallel groove seal, the damper seal, the thread groove seal and the like described above are the examples. In these seal structures, grooves and irregularities are provided on the surface of the opposed portion of the seal to increase pressure loss, and the fluid pressure is reduced to reduce the leakage flow rate. However, each seal structure has a characteristic that if the shaft seal characteristic is good, the vibration characteristic is bad, and conversely if the vibration characteristic is good, the shaft seal characteristic is bad.

  In view of the above shaft seal characteristics, it is impossible to realize a seal structure having excellent shaft seal characteristics with only one seal structure, so it is necessary to combine a plurality of different seal structures to reduce the amount of fluid leakage. Thought.

[First Embodiment]
As the non-contact annular seal used in the first embodiment, a thread groove seal having the highest shaft sealing performance is adopted as a seal that has excellent shaft sealing characteristics but does not consider vibration characteristics. On the other hand, a damper seal was adopted as a seal with excellent vibration characteristics without considering shaft seal characteristics. Among the damper seals, a honeycomb pattern seal with particularly good shaft sealing performance and vibration characteristics was adopted.

  FIG. 3 is a view schematically showing the structure of a non-contact annular seal in which the thread groove seal 45 and the honeycomb pattern seal 47 are combined. In this figure, a thread groove seal is formed on the surface of the rotary shaft 11 in accordance with the length of the non-contact annular seal. An annular honeycomb pattern seal 47 is disposed at a position facing the thread groove seal. The honeycomb pattern seal 47 is positioned concentrically with respect to the central axis of the rotating shaft 11. The radial clearance between the outer diameter of the screw and the inner diameter of the honeycomb pattern seal 47 is approximately several hundred μm although it depends on the dimensional conditions of the rotating machine such as the shaft diameter. Moreover, although the shape of the recessed part of a honeycomb pattern is various, the diameter (equivalent to the length of the longest diagonal) of the hexagonal hole used for this embodiment is 3-7 mm, and the distance between adjacent hexagonal holes is 4-4. It is a 9 mm seal.

  When the non-contact annular seal of the present embodiment is installed and operated at the opposite part of the rotating part and the fixed part in the multistage centrifugal pump having the same structure as in FIG. 1, the shaft seal characteristics are improved and the pumping performance is several%. Improved. Further, until now, in the case of a seal with good shaft seal characteristics, there has been unstable vibration of the rotating shaft, but stable operation with less vibration has become possible.

If the fluid that is about to leak from the high pressure side to the low pressure side is water, it is an incompressible fluid. For this reason, the pumping effect of the thread groove seal 45 on the rotating part side in FIG. 3 is larger than the leakage amount of the compressive fluid, and thereby the fluid is pushed back to the high pressure side. However, at this time, there is a concern that the circumferential flow velocity of the fluid in the seal also increases, and unstable fluid force is generated, causing vibration. However, a damper seal was installed at a position facing the thread groove seal 45. For this reason, the damper seal, in particular the honeycomb pattern seal 47, works to reduce the vibration by exhibiting the vibration damping effect, and the vibration that is concerned is suppressed. The damper seal also has an effect of causing a pressure loss due to the unevenness of the seal structure and reducing the amount of fluid leakage.

  As described above, the non-contact annular seal according to the present embodiment is provided with the thread groove seal 45 on the rotating shaft 11 and the damper seal, particularly the honeycomb pattern seal 47, on the surface of the fixed portion facing it. Thus, it was possible to provide a seal with less fluid leakage and good vibration characteristics, and a pump (rotary machine) equipped with the seal.

  The material of the thread groove seal 45 and the honeycomb pattern seal 47 may be any metal material such as SUS material, SS material, NI alloy, brass, and may be a composite material, ceramic material, resin material, or the like depending on the case. Good. The optimum thread groove shape (pitch, width, groove depth) of the thread groove seal 45 varies depending on the conditions required for the seal portion, but may be any pitch as long as it can reduce fluid leakage. It is not limited to the value. In addition, the optimum values of the hexagonal hole diameter, the distance between adjacent hexagonal holes, the depth of the hexagonal hole, etc. of the honeycomb pattern seal are limited to specific dimensions because the optimum values differ depending on the shaft seal conditions. It is not something.

  In the above description, the case where the thread groove seal is provided on the rotating portion (rotating shaft side) has been described, but the present invention is not limited to this. That is, a thread groove seal may be provided on the fixed portion (casing) side, and a honeycomb pattern or hole pattern damper seal may be provided on the rotating portion side.

[Second Embodiment]
Next, a second embodiment will be described based on FIG. The second embodiment is a non-contact annular seal using a hole pattern seal 46 on the fixed part side. Since the thread groove seal on the rotating part side is the same as that disclosed in FIG. 3, only the structure on the fixed part side will be described below. An annular hole pattern seal 46 is formed on the fixed portion side so as to surround the thread groove seal of the rotating shaft 11. The hole pattern seal 46 has a structure in which a large number of circular holes (recesses of the hole pattern) are formed on the inner peripheral surface on the fixed portion side. The diameter of the circular holes used in the present invention is 3 to 7 mm, and the distance between the adjacent circular holes is 4 to 9 mm. However, these values are also examples, and are not limited to these values.

  The hole pattern seal 36 of the present embodiment also has a concentric relationship with the rotary shaft on which the thread groove seal is formed. In the hole pattern seal 36 shown in the figure, the circular holes are regularly arranged. However, even if the circular holes are irregularly arranged, it is possible to reduce the vibration of the rotating shaft. This is the same when the above-described honeycomb pattern seal is used.

[Experimental result]
In developing the non-contact annular seal according to this embodiment, the applicant compared various types of seal structures with respect to shaft seal characteristics and vibration characteristics. The comparison was made between the prior arts (1) to (5) and the present embodiments (6) and (7) with respect to shaft sealing performance (leakage flow rate) and vibration characteristics (instability). That is, as conventional technology, (1) smooth seal (rotating part side: smooth + fixed part side: smooth), (2) parallel groove seal (rotating part side: smooth + fixed part side: parallel groove), (3) Damper seal (rotating part side: smooth + fixed part side: honeycomb pattern), (4) Rotating part side thread groove seal (rotating part side: screw groove + fixed part side: smooth), (5) Double-side thread groove seal (rotating Part side: screw groove + fixed part side: screw groove) was used as a comparative example. On the other hand, (6) and (7) are non-contact annular seals according to the present embodiment, which are a combination of rotating part side: screw groove + fixed part side: damper seal. More specifically, the performance of (6) rotating part side: screw groove + fixed part side: hole pattern, and (7) rotating part side: screw groove + fixed part side: honeycomb pattern were compared.

  FIG. 5 shows the shaft seal characteristics (performance) of each seal when the working medium is water and the rotational speed of the rotary shaft 11 is 3000 rpm and the pressure difference before and after the seal is about 1.0 MPa. The smaller the value, the better the shaft seal characteristics. From this result, the most important shaft sealing performance for the seal is (5) a double-sided thread seal in the prior art, and the rotating part side of (6) and (7) according to the present invention: It can be seen that the combination of screw groove + fixed portion side: damper seal is as good as that of both-side screw groove seals of the prior art, and in particular, the rotating portion side: screw groove + fixed portion side: honeycomb pattern seal of (7) is good.

  Next, FIG. 6 shows the vibration characteristics of each seal under the same conditions as in FIG. The vibration characteristics are indexed as equivalent damping. In this figure, the larger the value, the greater the stabilizing effect of the seal alone, and the negative value indicates that the seal alone is unstable. As can be seen from the results shown in the figure, the vibration characteristics are best for (3) rotating part side: smooth + fixed part side: damper seal (honeycomb), (1) smooth seal on both sides and (2) fixed part side: parallel Groove seal + rotating part side: This means that smoothness may continue. It can be seen that the combination of the rotating part side: screw groove + fixed part side: damper seal in this embodiment is the next best combination.

  As a result of the above results, the seal structure having high shaft sealing performance and good vibration characteristics has the following conditions: (7) Rotating part side: screw groove + fixed part side: damper seal (honeycomb) of this embodiment ) Is the most excellent seal structure. Note that (6) Rotating part side: Screw groove + Fixed part side: Damper seal (hole pattern), both shaft seal and vibration characteristics are only slightly inferior to (7). This harmony is better than the combinations (1) to (5) of the prior art.

  The present invention can be used for a non-contact annular seal of a rotary machine such as a pump.

11 Pump main shaft 21a First stage impeller 21b Second stage impeller 21c Third stage impeller 33 Pump suction port 35a, 35b, 35c Channel 37 Pump discharge port 41 Non-contact seal 43 Non-contact seal 36 Low-pressure side channel 45 Thread groove seal 47 Damper seal (hole pattern)
47 Damper seal (honeycomb pattern)

Claims (5)

A non-contact annular seal for sealing a gap between opposing portions of the rotating part and the fixed part of the pump,
The rotating part has a first seal structure with excellent shaft seal characteristics,
A non-contact annular seal provided with a second seal structure having excellent vibration characteristics in the fixed portion. The first seal structure is a thread seal structure provided in the rotating part,
The non-contact annular seal according to claim 1, wherein the second seal structure is a damper seal structure provided in the fixed portion.   The non-contact annular seal according to claim 2, wherein the damper seal structure is a honeycomb pattern recess or a hole pattern recess.   The length of the longest diagonal line of the hexagonal holes constituting the honeycomb pattern recess or the diameter of the circular holes constituting the hole pattern is 3 to 7 mm, and the distance between two adjacent hexagonal holes or two circular holes is The non-contact annular seal according to claim 3, which is 4 to 9 mm. An electric motor,
A main shaft connected to the electric motor and rotating;
An impeller that is fitted to the main shaft and rotates with the main shaft;
A casing for housing the impeller,
A bearing attached to the casing and rotatably supporting the main shaft;
A rotating machine comprising: the non-contact annular seal according to any one of claims 1 to 4.

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