Shaft seal structure of axial flow pump and out-of-tank stirrer having the same

Abstract

To further surely prevent or restrain dry sliding of a shaft seal device, by further surely preventing or restraining gas from gathering on the outer periphery of a shaft in the vicinity of the shaft seal device, regardless of the transport direction of a liquid carrying object.SOLUTION: The out-casing stirrer 10 includes an impeller 40, two suction and discharge ports 13A and 13B for discharging a liquid from one to the other according to the forward and reverse rotation directions of the impeller 40, a shaft 30 having an intermediate portion to which the impeller 40 is fixed and both ends extending along a shaft support pipe portion 12j protruding from the casing 11, a shaft seal device 12j for sealing a protruding portion of the shaft 30 from the shaft support pipe portion 20A, and a connecting pipe 20A for communicating the inside of the shaft seal device 20A with a bent pipe 13B located on the opposite side of the shaft seal device across the impeller 40. 70A, in the connection pipe 70A, a suction / discharge port 73 of a connection pipe 70A end part is projected in the shaft support pipe part 12j toward an outer peripheral surface of the shaft 30.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a shaft sealing structure for an axial flow pump and an external agitator equipped with the same. [Background technology]

[0002] As an external agitator installed outside the digester tank, for example, as shown in Fig. 10, an axial flow pump 101 is used, which has an impeller shaft with an impeller 140 mounted at the axial center of a shaft 130 supported at both ends, and can suck in and discharge agitated liquid from either liquid sending direction of a casing 111 by switching between forward and reverse rotation of the shaft 130. Both ends of the shaft 130 of the axial flow pump 101 are sealed by shaft sealing devices 120A, 120B, and are rotatably supported by bearings 117 (see, for example, Patent Document 1).

[0003] In the axial flow pump 101, when the impeller 140 rotates in the forward direction, the liquid is sucked in through the suction and discharge port 113A on one side, is pressurized inside the casing 111, and is discharged from the suction and discharge port 113B on the other side. When the impeller 140 rotates in the reverse direction, the transport direction of the liquid is reversed, and the liquid is sucked in through the suction and discharge port 113B on the other side, is pressurized inside the casing 111, and is discharged from the suction and discharge port 113A on the one side.

[0004] A portion of the liquid flowing inside the casing 111 flows into the shaft support pipe 112j of the shaft sealing devices 120A and 120B. The liquid that has flowed into the shaft support pipe 112j flows in a vortex around the rotating shaft 130. During this process, in the axial flow pump 101 transporting the liquid, the upstream side of the impeller 140 experiences low pressure and the downstream side of the impeller 140 experiences high pressure. Here, in the outside-tank mixer, the liquid transported by the axial pump 101 may contain gas. In particular, when transporting a gas-containing liquid such as sludge from a sewage treatment plant or the like, the gas flows in a vortex around the shaft 130 together with the liquid in the shaft support pipe portion 112j of the shaft sealing devices 120A, 120B, and the gas tends to collect on the outer periphery of the shaft 130 in the shaft support pipe portion 112j upstream of the impeller 140, which is under low pressure. When gas accumulates on the outer periphery of the shaft 130, the sliding surfaces of the seals 120A and 120B tend to dry slide, which can damage the seals 120A and 120B. Moreover, because this type of axial flow pump 101 reverses the transport direction of the pumped liquid, the seals 120A and 120B at both ends of the shaft 130 tend to dry slide and become damaged. Damage to the seals 120A and 120B can cause the pumped liquid to leak from the shaft support pipe 112j.

[0005] In contrast, in the technology described in Patent Document 1, as shown in Figure 10, connecting pipes 170A and 170B are provided to connect the inner shaft support pipe portion 112j of each shaft sealing device 120A and 120B to the casing 111 located on the opposite side of each shaft sealing device 120A and 120B across the impeller 140. The shaft support pipe portion 112j inside the shaft sealing device and the casing 111 located on the opposite side of each shaft sealing device 120A, 120B across the impeller 140 are at low pressure on one side and high pressure on the other, and using the technology described in Patent Document 1, the liquid to be transported can be made to flow from the high-pressure side to the low-pressure side through each connecting pipe 170A, 170B. As a result, according to the technology described in Patent Document 1, the flow of the transported liquid from the high-pressure side to the low-pressure side through each connecting pipe 170A, 170B prevents or suppresses gas from collecting on the outer periphery of the shaft 130 near each sealing device 120A, 120B, and prevents or suppresses dry sliding of each sealing device 120A, 120B. In particular, in the above-mentioned external mixer, regardless of the transport direction of the transported liquid, the transported liquid passing through each connecting pipe 170A, 170B flows inside each sealing device 120A, 120B and pushes gas away from the outer periphery of the shaft 130 near each sealing device 120A, 120B, making it an excellent structure for preventing or suppressing dry sliding of the sealing devices 120A, 120B at both ends of the shaft 130. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-315121 Summary of the Invention [Problem to be solved by the invention]

[0007] Here, in the liquid transport in the above-mentioned extra-tank mixer, the present applicants have found through subsequent research that when the liquid to be transported has foaming properties, the liquid to be transported is transported along the inner wall side of the connecting pipe by centrifugal force, whereas the foaming gas clings tightly to the center side of the connecting pipe where the pressure is somewhat negative, i.e., in the vicinity of the outer periphery of the shaft. In other words, in the connecting structure of the connecting pipe described in Patent Document 1, the foaming gas that has tightly clung to the outer periphery of the shaft is difficult to smoothly introduce along with the liquid to the end of the connecting pipe that opens into the casing wall simply by connecting the end of the connecting pipe to the casing wall, and it has been found that there is still room for improvement in order to more reliably eliminate the stagnation of the clinging foaming gas.

[0008] Therefore, the present invention has been made with an eye on such problems, and its object is to provide a shaft seal structure for an axial flow pump and an external agitator equipped with the same that can more reliably prevent or suppress gas from gathering on the outer periphery of the shaft near the shaft seal device, regardless of the transport direction of the liquid being transported, and can more reliably prevent or suppress dry sliding of the shaft seal device. [Means for solving the problem]

[0009] In order to solve the above problems, one embodiment of the present invention provides an axial flow pump shaft seal structure comprising an impeller that can rotate in both forward and reverse directions within a casing to reverse the transport direction of the liquid being pumped, two suction and discharge ports, one of which sucks in and the other expels the liquid being pumped in accordance with the rotation direction of the impeller, a shaft to which the impeller is fixed at its midpoint and whose both ends protrude along a support pipe section that extends out to the sides of the casing, a seal device that seals the protruding portion of the shaft with the end face of the support pipe section, and a connecting pipe that connects a position on the support pipe section that is inside the seal device to the casing that is located on the opposite side of the seal device across the impeller, wherein the suction and discharge ports at the end of the connecting pipe that opens toward the support pipe section protrude into the support pipe section toward the outer circumferential surface of the shaft.

[0010] In addition, in order to solve the above-mentioned problems, an extra-tank agitator according to one embodiment of the present invention is provided with an axial pump that is attached outside the digestion tank and can deliver the agitated liquid in either direction from two suction and discharge ports that suck in the agitated liquid from one side of the liquid delivery direction and discharge it from the other side depending on whether the impeller is rotated forward or reverse, and the axial pump is characterized by having the shaft seal structure of the axial pump according to one embodiment of the present invention. [Effects of the Invention]

[0011] According to the present invention, the suction and discharge ports at the end of the connecting pipe that opens onto the shaft sealing device protrude into the shaft support pipe portion toward the outer circumferential surface of the shaft, so that regardless of the transport direction of the liquid being transported, gas can be more reliably prevented or suppressed from gathering on the outer periphery of the shaft near the shaft sealing device, and dry sliding of the shaft sealing device can be more reliably prevented or suppressed. [Brief explanation of the drawings]

[0012] [Figure 1] An explanatory diagram of a digestion tank equipped with one embodiment of an external agitator having a shaft sealing structure of an axial flow pump according to the present invention, in which (a) is a schematic longitudinal cross-sectional view, and (b) is a schematic transverse cross-sectional view (ZZ cross-section in (a)). [Figure 2] 1A to 1C are explanatory views of the external agitator of this embodiment, in which FIG. 1A is a plan view, FIG. 1B is a front view, and FIG. 1C is a left side view. [Figure 3] 1 is an explanatory diagram of an external agitator according to the present embodiment, showing a cross section along the axis of the shaft in a plan view. FIG. [Figure 4] FIG. 4 is a diagram showing the main part (ZZ cross section) in FIG. [Figure 5] This is an explanatory diagram of the operation of the external agitator of this embodiment when the impeller is rotating in the forward direction, where (a) shows the flow of the liquid being transported throughout the entire digestion tank, and (b) shows the flow of the liquid being transported in the external agitator. [Figure 6] This is an explanatory diagram of the operation of the extra-tank agitator of this embodiment when the impeller rotates in reverse, where (a) shows the flow of the liquid being transported throughout the entire digestion tank, and (b) shows the flow of the liquid being transported in the extra-tank agitator. [Figure 7] 1A to 1C are explanatory views of maintenance of the external agitator of this embodiment, in which FIG. 1A is a plan view, FIG. 1B is a front view, and FIG. 1C is a left side view. [Figure 8] FIG. 1 is an explanatory diagram of an external agitator of a comparative example, in which FIG. 1(a) is a diagram seen from a plan view direction, and FIG. 1(b) is a diagram showing the main part (ZZ cross section) of FIG. [Figure 9] 1A and 1B are explanatory diagrams of modified examples of the suction and discharge ports of the connecting pipe end portion that protrudes into the shaft support pipe portion in the shaft seal structure of the axial flow pump according to the present invention, in which FIG. 1A is a diagram showing the main part corresponding to FIG. 4 (Modification 1), and FIG. 1B is a schematic diagram of another modified example, taken along the line XX in FIG. 4 (Modification 2). [Figure 10] 1A and 1B are explanatory diagrams of a conventional external agitator, in which FIG. 1A is a plan view and FIG. 1B is a front view. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic. Therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. differ from the actual ones, and the drawings also include portions where the relationship and ratio of dimensions differ from each other. Furthermore, the embodiments described below are intended to exemplify devices and methods for embodying the technical ideas of the present invention, and the technical ideas of the present invention do not limit the materials, shapes, structures, arrangements, etc. of the components to the embodiments described below.

[0014] [Digestion tank] First, the digester will be described. As shown in Figure 1, the extra-tank agitator 10 of this embodiment is installed outside a digestion tank 100 in a sewage treatment plant. Sludge is stored in the digestion tank 100, and this sludge serves as the liquid to be fed by the extra-tank agitator 10. Approximately half of the lower part of the digestion tank 100 is located underground, and the position where the extra-tank agitator 10 is installed is located just above ground. In the example shown in the figure, two liquid supply pipes 110A and 110B are inserted into the digestion tank 100 from outside the tank, with one end of the liquid supply pipe 110A opening slightly below the sludge liquid level in the digestion tank 100 and the other end connected to one suction / discharge port 13A of the extra-tank agitator 10. Furthermore, one end of the liquid supply pipe 110B opening slightly above the bottom of the digestion tank 100 and the other end connected to the other suction / discharge port 13B of the extra-tank agitator 10.

[0015] [External tank mixer] Next, the external agitator 10 will be described. 2, the extra-tank mixer 10 of this embodiment is an axial flow pump having, as a casing, a hollow cylindrical main pipe 11 with its axis arranged horizontally and a pair of bent pipes 12A and 12B connected to both ends of the main pipe 11. In the extra-tank mixer 10 of this embodiment, the main pipe 11 and the pair of bent pipes 12A and 12B are made of stainless steel casting (SCS13).

[0016] In the external mixer 10 of this embodiment, a U-shaped pipeline is formed by a main pipe 11 and a pair of bent pipes 12A, 12B that are detachably connected to both ends of the main pipe 11 and arranged to form a U-shaped pipeline. The pair of bent pipes 12A, 12B have suction and discharge ports 13A, 13B, each having a circular cross section, opening at their end faces.

[0017] The pair of bent pipes 12A, 12B have their base ends detachably connected to the left and right openings of the main pipe 11, and the other ends detachably connected to the digestion tank 100 side, and are configured with a bent section 12f that bends toward the digestion tank 100 side and an axial support pipe section 12j that extends coaxially with the main pipe 11 from the side of the bent pipe section 12f, and are piped together with the main pipe 11 to form a U-shaped pipeline.

[0018] A maintenance hole 11h for work purposes is provided in the upper center of the main pipe 11. The maintenance hole 11h opens in a rectangular shape on the top surface at the upper center of the main pipe 11. A maintenance hole cover 18 can be attached and detached to the maintenance hole 11h by fastening bolts to the flange portion around the maintenance hole 11h.

[0019] 3, the outside-tank mixer 10 of this embodiment further includes a shaft set 14 that can rotate in both forward and reverse directions within the main pipe 11, and an impeller unit 15 provided at the axial center of the shaft set 14. The impeller unit 15 is provided at the center of the shaft set 14, which is supported at both ends. A driving device (not shown) is connected to one end (the right side in the examples shown in FIGS. 3 and 6) of the shaft 30 of the shaft set 14, and rotates the shaft set 14 in both forward and reverse directions. The end of the shaft 30 on the driving device side is a fixed end, so that the axial position is determined, and the opposite end is a free end that is not constrained in the axial direction, so that thermal expansion in the axial direction can be released.

[0020] The shaft assembly 14 is supported at both ends by bearings 17A and 17B via shaft seals so as to be detachable from two support housings 16A and 16B, respectively, and an impeller 15 is provided in the axial center and placed inside the main pipe 11. As a result, the outside-tank mixer 10 of this embodiment can discharge from either of the two curved pipes 13A and 13B connected to both ends of the main pipe 11 by switching the shaft assembly 14 between forward and reverse rotation.

[0021] 3, the shaft assembly 14 includes an austenitic stainless steel shaft 30, an impeller 40 that is provided as a separate component from the shaft 30 and is located in the axial center of the shaft 30 at a position visible from the maintenance hole 11h, and a fixing collar 50 that fixes the impeller 40 to the shaft 30. The fixing collar 50 has a truncated conical exterior formed coaxially with the shaft portion 31 and a hollow cylindrical interior, and has a fastening female thread 51 formed on its inner surface to be threaded onto the fastening male thread 34.

[0022] The impeller 40 has a hollow cylindrical portion 41 that can be inserted and removed coaxially with the shaft portion 31, and two stirring blades 42A and 42B that are spirally attached to the outer surface of the cylindrical portion 41 and enable suction and discharge from either side of the U-shaped pipe line by switching the shaft 30 between forward and reverse rotation.

[0023] The shaft 30 has a shaft portion 31 located within a pipeline connected to the digester tank 100 side, a truncated conical positioning flange portion 32 formed integrally with the shaft portion 31 at a position visible from the maintenance hole 11h, and whose end face forms a positioning surface 32m, an impeller holding portion 33 arranged coaxially with the shaft portion 31 on the positioning surface 32m side and holding the impeller 40, and a fastening male screw 34 formed on the outer peripheral surface of the impeller holding portion 33 opposite the positioning surface 32m.

[0024] [Shaft seal structure on both ends of the shaft] Next, the shaft seal structure at both ends of the shaft will be described in detail. Both ends of the shaft 30 penetrate the U-shaped conduit and the support pipe 12j that protrudes outside the U-shaped conduit, and the protruding portions at both ends are supported at both ends by support housings 16A and 16B attached to the U-shaped conduit. The two support housings 16A and 16B are detachably connected to the outer surfaces of the support pipes 12j of the pair of bent pipes 12A and 12B, respectively.

[0025] The shaft 30 has an outer diameter of the axial portion 31 that is the same within the curved pipe portions 12f of the pair of bent pipes 12A, 12B, and is one step smaller within each support pipe portion 12j, protruding from each support housing 16A, 16B. In this embodiment, one support housing 16A is attached to the side of one bent pipe 12A that constitutes the U-shaped pipe. Furthermore, the other support housing 16B is attached to the side of the other suction / discharge port 12B that constitutes the U-shaped pipe.

[0026] Thus, in this embodiment, both ends of the shaft 30 pass through the two bent tubes 12A, 12B and the support tube portions 12j that extend along the axial direction of the shaft set 14, and the protruding portions of the shaft 30 that protrude outside the bent tubes 12A, 12B are supported by the two support housings 16A, 16B, respectively. In this embodiment, the protruding portions at both ends of the shaft 30 are rotatably supported by the support housings 16A, 16B via bearings 17A, 17B, respectively.

[0027] Furthermore, a mechanical seal 20A is attached as a shaft sealing device to the end of the shaft support pipe portion 12j of one support housing 16A, and a mechanical seal 20B is attached as a shaft sealing device to the end of the shaft support pipe portion 12j of the other support housing 16B. Because the mechanical seals 20A, 20B are housed in the respective support housings 16A, 16B, disassembly and assembly work along the axial direction is easy.

[0028] In the example shown in the figure, bearing 17A on the right side of shaft 30 is a fixed end that restricts axial movement of shaft 30, and bearing 17B on the left side is a free end that allows axial movement of shaft 30. This makes it possible for the free end to absorb the amount of elongation of shaft assembly 14 due to thermal expansion when the relatively long shaft assembly 14 expands thermally.

[0029] Each mechanical seal 20A, 20B seals between the protruding portion of the shaft 30 and the shaft support pipe portion 12j of the bent pipe 12A, 12B, which is the communication portion with the U-shaped pipe line axially inside each bearing 17A, 17B. With this configuration, in the outside-tank mixer 10 of this embodiment, both ends of the shaft 30 of the shaft set 14 are sealed by the mechanical seals 20A, 20B as shaft sealing devices and are rotatably supported by the bearings 17A, 17B.

[0030] [Connecting pipe with shaft seal structure] Next, a connecting pipe attached to the shaft seal structure will be described. As shown in FIG. 2, the external mixer 10 of this embodiment is provided with connecting pipes 70A and 70B that connect the inside of the mechanical seals 20A and 20B of each shaft support pipe portion 12j protruding from the curved pipes 12A and 12B to the casing located on the opposite side of each mechanical seal 20A and 20B across the impeller 40.

[0031] 2, in plan view, each connecting pipe 70A, 70B of this embodiment linearly connects the inner shaft support pipe portion 12j of each mechanical seal 20A, 20B to the bent pipe 12A, 12B located on the opposite side of each mechanical seal 20A, 20B across the impeller 40. The connecting pipes 70A, 70B have a nominal diameter of 50A. Each connecting pipe 70A, 70B has a vertical pipe section 72A, 72B and a horizontal pipe section 71A, 71B. The vertical pipe sections 72A, 72B and the horizontal pipe sections 71A, 71B are connected to each other by detachable joints via ball valves 74 that can be opened and closed manually to open and close the internal flow paths. This allows each horizontal pipe section 71A, 71B to be disconnected from the vertical pipe sections 72A, 72B and removed by closing the ball valves 74 at both ends and loosening the joints (see Figure 7).

[0032] 4, each connecting pipe 70A, 70B is connected such that suction / discharge ports 73 at the end of the connecting pipe 70A, 70B that open to the mechanical seals 20A, 20B protrude into the corresponding shaft support pipe portion 12j toward the outer circumferential surface of the shaft 30. In the example shown in the figure, the open end surface 73m of the suction / discharge port 73 is formed parallel to the extension direction of the outer circumferential surface of the shaft 30 (horizontal in this example). The protrusion amount of the suction and discharge ports 73 of the connecting pipes 70A and 70B is preferably set to 50% or more and less than 99%, assuming that the radial gap between the inner wall surface of the shaft support pipe 12j and the outer circumferential surface of the shaft 30 is 100%. Note that the protrusion amount of the suction and discharge ports 73 from the inner wall surface of the shaft support pipe 12j can be changed as appropriate within the range of 50% or more and less than 99%, depending on the amount of air contained in the liquid being fed, the operating conditions, etc. Since the connecting pipes 70A, 70B have the same connection structure at the left and right shaft support pipe portions 12j, FIG. 4 shows the right connecting pipe 70A, and omits the illustration of the connecting pipe 70B on the opposite side.

[0033] [Actions and Effects] Next, the operation and effects of the external agitator 10 of this embodiment will be described. In the external mixer 10 of this embodiment, as shown in Figure 5, when the shaft 30 is rotated in the forward direction, the impeller 40 fixed on the same shaft rotates in the forward direction within the main pipe 11 of the casing. As a result, sludge located above the digester tank 100 is sucked into the liquid supply pipe 110A and flows from one suction / discharge port 13A through the bent pipe 12A into the main pipe 11. The sludge that flows into the main pipe 11 is pressurized by the impeller 40, becomes high pressure, and flows into the other curved pipe 12B, and is discharged from the curved pipe 12B through the suction and discharge port 13B into the liquid supply pipe 110B, and is discharged from the liquid supply pipe 110B below the digestion tank 100.

[0034] 6, when the shaft 30 of the external agitator 10 of this embodiment is rotated in the reverse direction, the impeller 40 rotates in the reverse direction within the main pipe 11 of the casing. As a result, sludge located at the bottom of the digester tank 100 flows from the liquid feed pipe 110B through the other suction / discharge port 13B and the bent pipe 12B into the main pipe 11. The sludge that flows into the main pipe 11 is pressurized by the impeller 40, becomes high pressure, flows into one of the curved pipes 12A, and is discharged from the curved pipe 12A through the suction and discharge port 13A into the liquid supply pipe 110A, and is discharged from the liquid supply pipe 110A above the digestion tank 100.

[0035] In this way, the external mixer 10 of this embodiment can deliver the mixed liquid in either direction from two suction and discharge ports 13A, 13B, which suck in the mixed liquid from one side of the liquid delivery direction and discharge it from the other side, depending on whether the impeller 40 is switched between forward and reverse rotation. Here, if the liquid being transported is foamable, the liquid is transported along the inner wall of the connecting pipe by centrifugal force, while the foamed gas clings tightly to the center of the connecting pipe, which is under a slight negative pressure, i.e., near the outer periphery of the shaft 30. As disclosed in Patent Document 1 above, simply connecting the end of the connecting pipe to the casing makes it difficult for the foamed gas clinging to the outer periphery of the shaft 30 to be smoothly introduced to the end of the connecting pipe that opens into the casing wall, and there is still room for improvement in more reliably eliminating the stagnation of the clinging foamed gas.

[0036] In contrast, according to the outside-tank mixer 10 of this embodiment, the suction and discharge ports 73 at the ends of the connecting pipes 70A and 70B that open to the mechanical seals 20A and 20B are protruded and connected to the inside of the support pipes 12j inside the mechanical seals 20A and 20B toward the outer circumferential surface of the shaft 30. This more reliably prevents or suppresses gas from gathering on the outer periphery of the shaft 30 near the mechanical seals 20A and 20B, regardless of the transport direction of the liquid being transported, and more reliably prevents or suppresses dry sliding of the mechanical seals 20A and 20B [Invention 1], [Invention 7].

[0037] In particular, in the extra-tank mixer 10 of this embodiment, the piping structure and diameter of the connecting pipes are set in consideration of not only the basic mixing performance as an extra-tank mixer, but also regular maintenance work and overhaul work on site. Specifically, in the external mixer 10 of this embodiment, each connecting pipe 70A, 70B linearly connects the inner shaft support pipe portion 12j of each mechanical seal 20A, 20B to the curved pipe 12A, 12B located on the opposite side of each mechanical seal 20A, 20B across the impeller 40 in a plan view [Invention 2]. This allows the piping of each connecting pipe 70A, 70B to be simply configured, while allowing easy access to the impeller 40 from the maintenance hole 11h during maintenance work, making it easy to maintain the impeller 40 from the maintenance hole 11h. In other words, in consideration of maintenance work, it is common to configure each of the connecting pipes 70A, 70B with multiple pipes 71A, 71B, 71c, and route them around the side of the maintenance hole 11h, as shown in the comparative example in Figure 8(a), relative to the opening of the maintenance hole 11h in a plan view. In contrast, in this embodiment, the connecting pipes 70A, 70B are each a single straight pipe in plan view, but are arranged so that the main parts of the impeller 40 are visible (see FIG. 3), which is preferable in terms of ensuring the maintainability (ease of disassembly and assembly) of the shaft assembly 14. In particular, during maintenance, as shown in the disassembled example in FIG. 7, the upper part of the maintenance hole 11h can be easily opened by simply closing the ball valve 74 and removing the horizontal pipe portions 71A, 71B of the connecting pipes 70A, 70B. This makes it easy to perform periodic maintenance work on the support housings 16A, 16B. This is therefore preferable in terms of providing a configuration that is excellent in maintainability of the shaft assembly 14.

[0038] Furthermore, in the external mixer 10 of this embodiment, the ball valves 74 are attached to the same axis of the linearly arranged connecting pipes 70A, 70B, so that the piping of the connecting pipes 70A, 70B can be simply configured and the maintenance of the connecting pipes 70A, 70B is easy [Invention 3]. Furthermore, in the external mixer 10 of this embodiment, the protruding amount of the suction and discharge ports 73 of the connecting pipes 70A and 70B is set to a standard of 50% or more and less than 99%, assuming that the radial opposing gap between the inner wall surface of the support pipe portion 12j and the outer circumferential surface of the shaft 30 is 100%, so that an appropriate protruding amount can be set depending on the amount of air contained in the liquid being fed, the operating conditions, etc. [Invention 4].

[0039] As described above, according to the external mixer 10 of this embodiment, regardless of the transport direction of the liquid being transported, it is possible to more reliably prevent or suppress gas from accumulating on the outer periphery of the shaft near the shaft sealing device, thereby more reliably preventing or suppressing dry sliding of the shaft sealing device. The extra-tank agitator according to the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0040] For example, in the above embodiment, the example shown in Figure 4 shows an example in which the opening end surface 73m of the suction / discharge port 73 is formed parallel to the extension direction of the outer peripheral surface of the shaft 30, but this is not limited to this. The opening end surface 73m of the suction / discharge port 73 can be formed obliquely with respect to the extension direction of the outer peripheral surface of the shaft 30 to impart directionality to the suction / discharge flow.

[0041] Specifically, as shown in Figure 9(a), the opening end face 73m of the suction and discharge port 73 may be formed at an angle toward the mechanical seal (shaft sealing device) 20A (or 20B on the opposite side) with respect to the axial direction of the shaft 30. With this configuration, the flow Fd toward the mechanical seal (shaft sealing device) 20A (or 20B on the opposite side) can be made directional, allowing the transferred liquid to be actively sprayed onto the mechanical seal (shaft sealing device) 20A (or 20B on the opposite side), which is advantageous in more reliably preventing air bubbles from remaining [Invention 5].

[0042] Also, as shown in the same figure (b), the opening end face 73m of the suction / discharge port 73 may be formed at an angle to face the rotation direction of the shaft 30 on the upstream (low pressure) side of the liquid being transported relative to the circumferential direction of the shaft 30. With this configuration, when a flow Fs is formed from the shaft support pipe portion 12j toward the suction and discharge ports 13A and 13B, the sludge B accumulated at the bottom of the shaft support pipe 12j is more effectively lifted up along with the rotation of the shaft 30 and sent to the connecting pipes 70A and 70B, which is advantageous in more actively promoting the discharge of air bubbles [Invention 6].

[0043] In addition, the configuration of the slanted opening end surface 73m shown in Figure 9(a) and the configuration of the slanted opening end surface 73m shown in Figure 9(b) may be configured to be switchable depending on the transport direction of the liquid being transported, which is forward or reverse. Specifically, when the portion of each connecting pipe 70A, 70B that protrudes toward the suction / discharge port 73 is referred to as the protruding pipe, the protruding pipe is connected to the connection between the protruding pipe of each connecting pipe 70A, 70B and the shaft support pipe 12j via a rotation mechanism 80 so that the protruding pipe can rotate about its axis. An actuator such as a hydraulic cylinder can be disposed on the outer peripheral surface of the shaft support pipe 12j, and the protruding pipe on the suction / discharge port 73 side beyond the rotation mechanism 80 can be rotated about its axis by driving this actuator. In Figure 9(a), the flexible hose is indicated by the reference numeral "81."

[0044] With this configuration, when the transport direction of the liquid being transported is switched and the mechanical seal (sealing device) 20A (20B if on the opposite side) is on the downstream (high pressure) side of the liquid being transported, the actuator is driven to rotate the protruding pipe on the suction / discharge port 73 side from the rotation mechanism 80 around its axis, and the opening end face 73m of the suction / discharge port 73 is positioned obliquely toward the mechanical seal (sealing device) 20A (20B if on the opposite side) with respect to the axial direction of the shaft 30, as shown in Figure 9(a), thereby obtaining the effect of [Invention 5] described above.

[0045] Furthermore, when the mechanical seal (shaft sealing device) 20A (or 20B on the opposite side) is on the upstream (low pressure) side of the liquid being transported, the actuator is driven to rotate the protruding pipe on the suction / discharge port 73 side from the rotation mechanism 80 around its axis (rotate 90 degrees around the axis relative to Figure 9(a)), so that the opening end face 73m of the suction / discharge port 73 is positioned obliquely so as to face the rotation direction of the shaft 30 on the upstream (low pressure) side of the liquid being transported, relative to the circumferential direction of the shaft 30, as shown in Figure 9(b), thereby achieving the effect of the above-mentioned [Invention 6] [Invention 7]. [Explanation of symbols]

[0046] 10. External agitator (axial flow pump) 11 Casing main 11am Maintenance Hall 12A, 12B bent pipe 12f bent part 12j Axial branch pipe section 13A, 13B suction and discharge ports 14 Shaft set 15 Impeller section 16A, 16B pivot housing 17A, 17B bearings 18 Maintenance hole cover 20A, 20B Mechanical seal (shaft seal device) 30 shaft 31 Shaft 32 Positioning flange 32m positioning surface 33 Impeller holder 34 Fastening male screw 40 impeller 41 Cylindrical part 42A, 42B stirring blades 50 fixed color 51 Fastening female screw 60 Fixing screw 70A, 70B connecting pipe 71A, 71B horizontal pipe section 72A, 72B Vertical pipe section 73 Suction and discharge port at end of connecting pipe 74 Ball Valve 80 Rotation mechanism 81 Flexible hose 100 Digester 110A, 110B Liquid delivery pipe

Claims

1. an impeller that can rotate in both forward and reverse directions within the casing to reverse the transport direction of the liquid; two suction and discharge ports, one of which sucks in the liquid to be pumped and the other of which discharges it in accordance with the rotation direction of the impeller; a shaft to which the impeller is fixed at a middle portion and whose both ends protrude along a shaft support pipe portion that protrudes laterally from the casing; a shaft sealing device that seals a protruding portion of the shaft with an end surface of the shaft support pipe portion; a connecting pipe that connects a position of the shaft support pipe portion that is inside the shaft sealing device to the casing that is located on the opposite side of the shaft sealing device across the impeller, A shaft seal structure for an axial flow pump, characterized in that the suction and discharge ports of the connecting pipe end that opens to the shaft support pipe portion protrude into the shaft support pipe portion toward the outer surface of the shaft.

2. 2. The shaft seal structure of an axial flow pump as described in claim 1, wherein the connecting pipe linearly connects a position inside the shaft support pipe portion relative to the shaft seal device to the casing located on the opposite side of the shaft seal device across the impeller.

3. 3. The shaft seal structure of an axial flow pump according to claim 2, wherein a ball valve is attached to the connecting pipe on the same axis as the linearly connected connecting pipe.

4. 2. The shaft seal structure of an axial flow pump according to claim 1, wherein the protrusion amount of the suction and discharge ports of the connecting pipe is 50% or more and less than 99%, when the radial opposing gap between the inner wall surface of the support pipe portion and the outer peripheral surface of the shaft is 100%.

5. 2. The shaft seal structure of an axial flow pump according to claim 1, wherein an open end face of the suction / discharge port is formed obliquely toward the shaft seal device with respect to the axial direction of the shaft.

6. 2. A shaft seal structure for an axial flow pump as described in claim 1, wherein the opening end face of the suction and discharge port is formed obliquely toward the rotation direction of the shaft on the low pressure side of the pumped liquid relative to the circumferential direction of the shaft.

7. The opening end surface of the suction / discharge port is formed obliquely, The connecting pipe has a protruding pipe line, which is a portion protruding toward the suction and discharge port, connected to the connecting portion between the connecting pipe and the shaft support pipe section via a rotation mechanism so as to be rotatable about its own axis, and is configured so as to be rotatable about its own axis in accordance with the transport direction of the liquid to be delivered by driving an actuator arranged on the outer circumferential surface side of the shaft support pipe section; When the shaft support pipe portion is located downstream of the liquid to be delivered, the actuator is driven to rotate the protruding pipe about its axis, so that the obliquely formed opening end surface is positioned obliquely toward the shaft sealing device in the axial direction of the shaft, 2. A shaft seal structure for an axial flow pump as described in claim 1, wherein when the shaft seal device is located upstream of the liquid being pumped, the actuator is driven to rotate the protruding pipe around its axis, so that the obliquely formed opening end face is positioned obliquely facing the circumferential direction of the shaft and in the direction of rotation of the shaft.

8. An external agitator equipped with an axial flow pump that is attached to the outside of a digestion tank and can send out agitated liquid in either direction from two suction and discharge ports that suck in agitated liquid in one direction and discharge it in the other direction depending on whether the impeller is rotated forward or backward, The axial flow pump has the shaft sealing structure of the axial flow pump according to any one of claims 1 to 7.

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