Mechanical seal

Abstract

To secure a force for pressing a stationary seal ring against a rotary seal ring within a desired range in a case where the pressure inside a machine becomes higher or lower than the pressure outside the machine.SOLUTION: A mechanical seal 10 comprises a rotary seal ring 11, a stationary seal ring 12, and a case 13, and separates an inside space A1 inside a rotation device 7 and an outside space A2 outside the rotation device 7. The mechanical seal 10 comprises a back pressure chamber K1 provided and sealed between the stationary seal ring 12 on the side of the outside space A2 and a part of the case 13, and a connection flow path 40 connecting the inside space A1 and the back pressure chamber K1. The connection flow path 40 has a switching unit 41 that communicates the inside space A1 and the back pressure chamber K1 when the inside space A1 has a higher pressure than the outside space A2, and isolates the inside space A1 and the back pressure chamber K1 when the inside space A1 has a lower pressure than the outside space A2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a mechanical seal. [Background technology]

[0002] Mechanical seals are known as devices for sealing internal fluids between the equipment casing and the rotating shaft in various rotating equipment (see, for example, Patent Document 1). The mechanical seal includes a rotating seal ring that rotates integrally with the rotating shaft, and a stationary seal ring that is provided on the equipment casing side to provide a seal between the rotating seal ring and the stationary seal ring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3192152 Summary of the Invention [Problem to be solved by the invention]

[0004] 5 is a cross-sectional view of a conventional mechanical seal. This mechanical seal 90 includes a rotating seal ring 91 that rotates integrally with a rotating shaft 99, a stationary seal ring 92 for sealing between the rotating seal ring 91 and the stationary seal ring 92, and a case 93 that supports the stationary seal ring 92 and is attached to a rotating device 100. The mechanical seal 90 separates an in-machine space A1 inside the rotating device 100 from an external space A2 outside the rotating device 100.

[0005] A back pressure chamber K1 is provided between the outer side (left side in FIG. 5) of the stationary seal ring 92 and a part 93a of the case 93. The back pressure chamber K1 is sealed by O-rings 94, 95 provided between the stationary seal ring 92 and the case 93. A flow path 96 connecting the in-machine space A1 and the back pressure chamber K1 is provided in the stationary seal ring 92, and the in-machine space A1 and the back pressure chamber K1 have the same pressure (internal pressure).

[0006] When the internal space A1 is at a higher pressure than the external space A2, the fluid pressure in the back pressure chamber K1 connected to the internal space A1 can press the stationary seal ring 92 against the rotary seal ring 91. This makes it possible to ensure the sealing performance between the stationary seal ring 92 and the rotary seal ring 91.

[0007] Depending on the type of the rotating device 100, the pressure in the in-machine space A1 may change from a higher pressure to a lower pressure than the external space A2, in which case the back pressure chamber K1 also becomes low pressure. Then, a force in a direction moving the stationary seal ring 92 away from the rotary seal ring 91 is generated by the fluid pressure (atmospheric pressure) in the external space A2. Although not shown, the mechanical seal 90 includes an elastic member (compression coil spring) for pressing the stationary seal ring 92 against the rotary seal ring 91. If the elastic biasing force of the elastic member is set large, it is possible to secure the force pressing the stationary seal ring 92 against the rotary seal ring 91 even if the internal space A1 becomes low pressure. However, when the internal space A1 becomes high pressure, the force pressing the stationary seal ring 92 against the rotary seal ring 91 may become excessive.

[0008] Therefore, an object of the present disclosure is to provide a mechanical seal that can ensure a force pressing a stationary seal ring against a rotating seal ring within a desired range when the pressure in the interior space of the machine is higher or lower than the pressure in the exterior space of the machine. [Means for solving the problem]

[0009] (1) The mechanical seal disclosed herein comprises a rotating seal ring that rotates integrally with a rotating shaft, a stationary seal ring for sealing between the rotating seal ring and the stationary seal ring, and a case that supports the stationary seal ring and is attached to a rotating device, and separates an in-machine space inside the rotating device from an outside space outside the rotating device. The mechanical seal comprises a back pressure chamber that is provided between the outside space side of the stationary seal ring and a part of the case and is sealed, and a connecting flow path that connects the in-machine space and the back pressure chamber, and the connecting flow path has a switching portion that connects the in-machine space and the back pressure chamber when the in-machine space is at a higher pressure than the outside space, and that blocks the in-machine space from the back pressure chamber when the in-machine space is at a lower pressure than the outside space.

[0010] According to the mechanical seal of the present disclosure, when the in-machine space is at a higher pressure than the outside space, the in-machine space and the back pressure chamber communicate with each other by the switching portion of the connecting flow passage, and the stationary seal ring can be pressed against the rotary seal ring by the fluid pressure of the back pressure chamber. On the other hand, when the in-machine space is at a lower pressure than the outside space, the fluid pressure of the in-machine space does not reach the back pressure chamber, and no force acts to separate the stationary seal ring from the rotary seal ring. As a result, even when the in-machine space is at a higher or lower pressure than the outside space, it is possible to ensure a force pressing the stationary seal ring against the rotary seal ring within a desired range.

[0011] (2) Although the switching portion may be provided on the stationary seal ring, it is preferable that the switching portion is provided on the case, because it is easier to configure the switching portion on the case than on the stationary seal ring.

[0012] (3) Also, preferably, the switching portion has a block portion in which a cavity is formed, and a piston that moves through the cavity between a first position and a second position, and when the piston is in the first position, the internal space and the back pressure chamber are connected through a part of the cavity, and when the piston is in the second position, the piston is present in the part of the cavity, thereby blocking off the internal space and the back pressure chamber. In this case, when the piston is in the first position, the interior space and the back pressure chamber are connected through a part of the cavity, and when the piston is in the second position, the interior space side and the back pressure chamber side are blocked from each other.

[0013] (4) Also, preferably, the connecting flow passage has a first flow passage connecting a first chamber, which is a part of the cavity, to the in-machine space, and a second flow passage connecting a second chamber of the cavity formed when the piston is in the second position to the back pressure chamber, and an open hole is provided in the block portion to communicate the second chamber with the out-machine space. In this case, when the pressure in the interior space becomes lower than the pressure in the exterior space, the pressure difference between the interior space and the exterior space causes fluid to flow from the exterior space into the second chamber of the cavity through the open hole, and the piston moves from the first position to the second position. When the pressure in the interior space becomes higher than the exterior space, the pressure difference between the interior space and the exterior space causes the piston to move from the second position to the first position.

[0014] (5) Also, preferably, the piston has, on a first end face on one side in the moving direction, a first partial contact surface that partially contacts a first inner surface of the cavity and a first pressure-receiving surface that is not in contact with the first inner surface, and a first internal space formed between the first inner surface and the first pressure-receiving surface is connected to the outside space through the open hole. With this configuration, even if the open hole is narrow, it is possible to ensure a pressure-receiving area on the first end face of the piston. When the pressure in the interior space becomes lower than the pressure in the exterior space, the piston obtains thrust from the fluid pressure in the first internal space connected to the exterior space, and the piston becomes movable.

[0015] (6) Also, preferably, the piston has, on a second end face on the other side in the moving direction, a second partial contact surface partially contacting a second inner surface of the cavity and a second pressure-receiving surface not in contact with the second inner surface, and a second internal space formed between the second inner surface and the second pressure-receiving surface is connected to the interior space of the aircraft through the first flow path. With this configuration, even if the first flow passage is narrow, it is possible to ensure a pressure-receiving area at the second end face of the piston. When the internal space becomes higher in pressure than the external space, the piston is provided with thrust by the fluid pressure in the second internal space connected to the internal space, and the piston is able to move. Effect of the Invention

[0016] According to the mechanical seal of the present disclosure, when the pressure in the interior space is higher or lower than the pressure in the exterior space, it is possible to ensure a force pressing the stationary seal ring against the rotating seal ring within a desired range. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a cross-sectional view of a mechanical seal with the piston in a first position. [Diagram 2] FIG. 2 is a cross-sectional view of the mechanical seal with the piston in a second position. [Diagram 3] 2 is an enlarged view showing the switching portion shown in FIG. 1 and its surroundings. [Figure 4] 3 is an enlarged view showing the switching portion shown in FIG. 2 and its surroundings. [Diagram 5] FIG. 1 is a cross-sectional view of a conventional mechanical seal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [About mechanical seals in general] 1 is a cross-sectional view of a mechanical seal 10. This mechanical seal 10 is used in a rotating device 7, such as a stirrer. The rotating device 7 includes a rotating shaft 8 and a device casing 9 surrounding the rotating shaft 8. The mechanical seal 10 seals the fluid inside the rotating device 7 between the rotating shaft 8 and the device casing 9. The rotating shaft 8 is rotatably supported by a bearing (not shown) included in the rotating device 7.

[0019] The directions in the present disclosure are defined below. The direction along the axis L of the rotating shaft 8 and the direction parallel to the axis L are defined as the "axial direction". With respect to the axial direction, the outside side of the rotating device 7 (left side in FIG. 1) is one axial side, which is referred to as the "outside side". In contrast, the inside side of the rotating device 7 (right side in FIG. 1) is the other axial side, which is referred to as the "inside side". The space inside the rotating device 7 between the device casing 9 and the rotating shaft 8 is referred to as the "inside space A1", and the space outside the rotating device 7 is referred to as the "outside space A2". The direction perpendicular to the axis L is defined as the "radial direction". The direction along the circle centered on the axis L is defined as the "circumferential direction". In other words, the rotation direction of the rotating shaft 8 is the circumferential direction.

[0020] The mechanical seal 10 separates the in-machine space A1 from the outside-machine space A2. In this embodiment, the atmosphere is present in the outside-machine space A2, and the outside-machine space A2 is at atmospheric pressure. The in-machine space A1 is at a higher or lower pressure than the outside-machine space A2 (atmospheric pressure) depending on, for example, the operating state of the rotating equipment 7. The mechanical seal 10 prevents the sealed fluid on the in-machine space A1 side from flowing out to the outside-machine space A2 side, and prevents the gas (atmosphere) on the outside-machine space A2 side from flowing into the in-machine space A1 side.

[0021] For this purpose, the mechanical seal 10 includes one rotating seal ring 11 and one stationary seal ring 12. The space between the rotating seal ring 11 and the stationary seal ring 12 forms a seal portion S that prevents the sealed fluid from flowing out and the atmosphere from flowing in. The rotating seal ring 11 has an annular seal surface 11a on the outer side of the machine. The stationary seal ring 12 has an annular seal surface 12a on the inner side of the machine that faces the seal surface 11a. The radial inner side and one axial side of the seal portion S are connected to the outside space A2. The radial outer side and the other axial side of the seal portion S are connected to the inside space A1. As will be described later, in this embodiment, a seal gas is supplied between the opposing seal surfaces 11a, 12a.

[0022] The mechanical seal 10 includes a case 13 attached to the rotating device 7. The case 13 includes a cylindrical first case 14 attached to the device casing 9 and a cylindrical second case 15 attached to the outside of the first case 14. The second case 15 has an inner diameter smaller than that of the first case 14. The second case 15 includes an outer peripheral portion 16 on the radially outer side, an inner peripheral portion 17 extending radially inward from the outer peripheral portion 16, and a cylindrical portion 18 extending from a radially inner portion of the inner peripheral portion 17 to the inside of the device. The gap between the first case 14 and the second case 15 is sealed by a seal member 33 such as an O-ring.

[0023] The mechanical seal 10 includes a rotating unit 21 including a rotating seal ring 11. In addition to the rotating seal ring 11, the rotating unit 21 includes a sleeve 22 and a cylindrical fixed member 23. The fixed member 23 is a member for integrating the sleeve 22 with the rotating shaft 8. The fixed member 23 is fitted onto a part of the rotating shaft 8, and is fixed to the rotating shaft 8 by a set screw 24.

[0024] The sleeve 22 is cylindrical and fitted onto the other part of the rotary shaft 8. The sleeve 22 has a cylindrical part 22a that is sandwiched between the fixed member 23 and the rotary shaft 8 in the radial direction, and an annular part 22b that extends radially from the end of the cylindrical part 22a on the machine interior side. The rotary seal ring 11 is fitted onto the cylindrical part 22a. The rotary seal ring 11 is prevented from rotating by a pin or the like (not shown) on the sleeve 22, and can rotate integrally with the sleeve 22. As described above, the rotary seal ring 11 rotates integrally with the rotary shaft 8. An O-ring 25 seals the gap between the rotary seal ring 11 and the sleeve 22. An O-ring 26 seals the gap between the sleeve 22 and the rotary shaft 8.

[0025] The stationary seal ring 12 is an annular member, and serves as a seal between the stationary seal ring 12 and the rotary seal ring 11. The stationary seal ring 12 is provided on the outer periphery of the cylindrical portion 18 of the second case 15, and is supported by the case 13. The space between the stationary seal ring 12 and the cylindrical portion 18 is sealed by an O-ring 27. The inner periphery 17 of the second case 15 has a pin 30 protruding toward the inside of the machine. A hole 31 is provided in the stationary seal ring 12. When the pin 30 is inserted into the hole 31, the stationary seal ring 12 cannot rotate relative to the case 13. Although not shown, an elastic member is provided between the inner periphery 17 and the stationary seal ring 12. The elastic member is a compression coil spring, and generates a force in a direction that presses the stationary seal ring 12 against the rotary seal ring 11.

[0026] A sealing flow passage 32 is formed in the stationary seal ring 12. The sealing flow passage 32 connects the outer peripheral surface 12b of the stationary seal ring 12 to the seal surface 12a. An O-ring 28 on the inside side and an O-ring 29 on the outside side are provided between the outer peripheral surface 12b of the stationary seal ring 12 and the inner peripheral surface 13a of the case 13 (first case 14). An annular sealed space K2 is formed between the outer peripheral surface 12b of the stationary seal ring 12 and the inner peripheral surface 13a of the case 13, between the two O-rings 28, 29.

[0027] Although not shown, a seal gas flow passage through which a seal gas (e.g., nitrogen gas) is supplied is provided in the case 13 (first case 14). The seal gas flow passage opens in the sealed space K2, and the seal gas is supplied to the sealed space K2. The seal gas supplied to the sealed space K2 is supplied through the sealing flow passage 32 to between the seal surface 11a of the rotary seal ring 11 and the seal surface 12a of the stationary seal ring 12, that is, to the seal portion S. The seal gas supplied to the seal portion S forms a hydrostatic fluid film between the seal surfaces 11a, 12a. In this way, the mechanical seal 10 of this embodiment is a non-contact type seal device in which the seal surfaces 11a, 12a are in a non-contact state.

[0028] An annular back pressure chamber K1 is provided between the machine exterior side (external space A2 side) of the stationary seal ring 12 and a part of the case 13. The back pressure chamber K1 is sealed by an O-ring 29 on the outer circumferential side of the stationary seal ring 12 and an O-ring 27 on the inner circumferential side of the stationary seal ring 12. The back pressure chamber K1 is connected to a connection flow passage 40 described later, but is a closed space. As described later, when the internal pressure of the back pressure chamber K1 becomes higher than the pressure of the external space A2 (atmospheric pressure), a thrust force is generated by the fluid pressure of the back pressure chamber K1 to press the stationary seal ring 12 against the rotary seal ring 11.

[0029] In the stationary seal ring 12, a pressure-receiving area that receives the internal pressure of the back pressure chamber K1 is larger than a pressure-receiving area that receives the pressure (atmospheric pressure) of the external space A2. The back pressure chamber K1 is configured so that a force pressing the stationary seal ring 12 against the rotary seal ring 11 acts when the pressure in the back pressure chamber K1 is higher than the pressure in the external space A2.

[0030] The mechanical seal 10 includes a connection flow passage 40 that connects the in-machine space A1 and the back pressure chamber K1. The connection flow passage 40 has a switching unit 41 that switches the state of the flow passage. In the embodiment shown in FIG. 1, the connection flow passage 40 and the switching unit 41 are provided in the case 13. The switching unit 41 has a block portion 42 in which a cavity 43 is formed, and a piston 44 provided in the cavity 43. The block portion 42 is formed by a part of the case 13. More specifically, a part of the outer periphery 16 of the second case 15 is the block portion 42, and the cavity 43 is formed in a part of the block portion 42.

[0031] [Regarding the switching unit 41] The piston 44 moves in the cavity 43 between a first position P1 and a second position P2. FIGS. 1 and 3 show a state where the piston 44 is in the first position P1, which is one stroke end, and FIGS. 2 and 4 show a state where the piston 44 is in the second position P2, which is the other stroke end. FIG. 3 is an enlarged view showing the switching portion 41 shown in FIG. 1 and its surroundings. FIG. 4 is an enlarged view showing the switching portion 41 shown in FIG. 2 and its surroundings. As shown in FIG. 3, when the piston 44 is in the first position P1, a first chamber Q1 is formed on one side of the cavity 43 (the right side in FIG. 3). As shown in FIG. 4, when the piston 44 is in the second position P2, a second chamber Q2 is formed on the other side of the cavity 43 (the left side in FIG. 4).

[0032] A seal member (O-ring) 45 that is in sliding contact with the inner circumferential surface of the cavity 43 is provided on the outer periphery of the piston 44. The seal member 45 divides the cavity 43 into a first chamber Q1 and a second chamber Q2.

[0033] The connection flow path 40 has a first flow path 46 and a second flow path 47. As shown in Fig. 1, the first flow path 46 connects a first chamber Q1, which is a part of the cavity 43, to the in-machine space A1. As shown in Fig. 2, the second flow path 47 connects a second chamber Q2, which is the other part of the cavity 43, to the back pressure chamber K1. An open hole 48 that constantly connects the second chamber Q2 to the out-machine space A2 is provided in a block portion 42 that is a part of the case 13.

[0034] As shown in Figures 3 and 1, when the piston 44 is in the first position P1, the in-machine space A1 and the back pressure chamber K1 communicate with each other through the first chamber Q1. As shown in Figures 4 and 2, when the piston 44 is in the second position P2, the piston 44 is present in the first chamber Q1 and blocks the first flow path 46. As a result, the flow path between the in-machine space A1 and the back pressure chamber K1 is blocked by the piston 44.

[0035] The piston 44 moves automatically due to the pressure difference between the internal space A1 and the external space A2. The mechanism behind this is described below. As described above, the external space A2 is in an atmospheric environment and is at a substantially constant atmospheric pressure. The internal space A1 becomes higher pressure (positive pressure relative to atmospheric pressure) or lower pressure (negative pressure relative to atmospheric pressure) than the external space A2 depending on the operating state of the rotating equipment 7.

[0036] When the pressure in the in-machine space A1 becomes higher than the pressure in the external space A2, the fluid pressure in the in-machine space A1 acts on the first chamber Q1 of the cavity 43 through the first flow path 46, and pushes the piston 44 toward the first position P1. Even when the piston 44 is in the second position P2, when the pressure in the in-machine space A1 becomes higher than the external space A2, the piston 44 automatically moves from the second position P2 to the first position P1 due to the pressure difference between the in-machine space A1 and the external space A2. A part of the first end surface 51 of the piston 44 comes into contact with the first inner surface 56 of the cavity 43, and the piston 44 stops at the first position P1 (see FIG. 3).

[0037] In this state, the in-machine space A1 and the back pressure chamber K1 communicate with each other through the first flow path 46, the first chamber Q1, and the second flow path 47. Then, the back pressure chamber K1 has the same pressure as the in-machine space A1 (positive pressure relative to atmospheric pressure). As a result, a force acts in a direction pressing the stationary seal ring 12 against the rotary seal ring 11 due to the fluid pressure of the back pressure chamber K1. The force in the pressing direction changes depending on the pressure of the in-machine space A1, and the higher the pressure of the in-machine space A1, the greater the force in the pressing direction.

[0038] When the pressure of the internal space A1 becomes lower than that of the external space A2, that is, when the internal space A1 becomes negative relative to the atmospheric pressure, the first chamber Q1 of the cavity 43 also becomes low pressure (negative pressure). Then, the fluid pressure (atmospheric pressure) of the external space A2 acts on the second chamber Q2 through the open hole 48 and pushes the piston 44 toward the second position P2. Even when the piston 44 is in the first position P1, when the internal space A1 becomes lower in pressure than the external space A2, the pressure difference between the internal space A1 and the external space A2 causes fluid (atmosphere) to enter the second chamber Q2 from the external space A2 through the open hole 48, and the piston 44 automatically moves from the first position P1 to the second position P2. A part of the second end surface 52 of the piston 44 comes into contact with the second inner surface 57 of the cavity 43, and the piston 44 stops at the second position P2 (see FIG. 4).

[0039] As a result, the flow path between the in-machine space A1 and the back pressure chamber K1 is blocked by the piston 44. Furthermore, the outside-machine space A2 and the back pressure chamber K1 are communicated through the open hole 48, the second chamber Q2, and the second flow path 47. Then, the back pressure chamber K1 becomes the same pressure as the outside-machine space A2 (atmospheric pressure). As a result, the pressure of the in-machine space A1 is lower than the atmospheric pressure of the outside-machine space A2 and the back pressure chamber K1, and a force acts in a direction pressing the stationary seal ring 12 against the rotary seal ring 11 due to the fluid pressure (atmospheric pressure) of the back pressure chamber K1.

[0040] As described above, the switching section 41, which includes the piston 44, connects the in-machine space A1 to the back pressure chamber K1 when the in-machine space A1 is at a higher pressure than the external space A2, and disconnects the in-machine space A1 from the back pressure chamber K1 when the in-machine space A1 is at a lower pressure than the external space A2. Furthermore, whether the pressure in the in-machine space A1 is higher or lower than the pressure in the external space A2, a force is applied to the stationary seal ring 12 by the elastic member (not shown) to press it against the rotating seal ring 11.

[0041] The open hole 48 and the first flow passage 46 connected to the cavity 43 each have a smaller flow passage cross-sectional area than the cavity 43. In order to ensure a pressure-receiving area for the piston 44 even if the open hole 48 and the first flow passage 46 are narrow, the mechanical seal 10 of the present embodiment has the following first configuration F1 and second configuration F2.

[0042] As a first configuration F1 (see FIG. 3), the piston 44 has a first partial contact surface 61 and a first pressure receiving surface 62 on a first end surface 51 on one side in the moving direction, which is the outside of the machine. The first partial contact surface 61 is formed by a tip surface of a protrusion 51a protruding from the center of the first end surface 51. The first pressure receiving surface 62 is formed by the surface of the first end surface 51 other than the protrusion 51a, and is set wider than the first partial contact surface 61. The first partial contact surface 61 can be partially in contact with the first inner surface 56 of the cavity 43. The first pressure receiving surface 62 is not in contact with the first inner surface 56. When the piston 44 is in the first position P1, a first internal space 53 is formed between the first inner surface 56 and the first pressure receiving surface 62, which is annular. The first internal space 53 communicates with the outside space A2 through the open hole 48.

[0043] With this configuration, even if the open hole 48 is narrow, it is possible to ensure a pressure-receiving area at the first end surface 51 of the piston 44. Therefore, when the pressure in the interior space A1 becomes lower than the pressure in the exterior space A2, the piston 44 obtains thrust from the fluid pressure (atmospheric pressure) in the first internal space 53 connected to the exterior space A2, and the piston 44 can move from the first position P1 to the second position P2.

[0044] The second configuration F2 will be described (see FIG. 4). A recess 65 is formed on the second inner surface 57 of the cavity 43. The recess 65 opens toward the cavity 43 and is connected to the first flow passage 46. The opening area of ​​the recess 65 with respect to the cavity 43 is smaller than the cross-sectional area of ​​the cavity 43 and the second end surface 52 of the piston 44. The opening area of ​​the first flow passage 46 with respect to the recess 65 is smaller than the cross-sectional area of ​​the recess 65.

[0045] The piston 44 has a second partial contact surface 63 and a second pressure receiving surface 64 on the second end surface 52 on the other side in the moving direction, which is the inside of the machine. The second partial contact surface 63 is a surface that partially contacts the second inner surface 57 of the cavity 43. In the embodiment shown in FIG. 4, the second partial contact surface 63 is configured by an annular outer circumferential portion that is a part of the second end surface 52. The second pressure receiving surface 64 is a surface that does not contact the second inner surface 57 and is configured by a central portion that is the remaining other portion of the second end surface 52. The second pressure receiving surface 64 is set to be wider than the second partial contact surface 63. When the piston 44 is in the second position, a second internal space 54 is formed between the recess 65 of the second inner surface 57 and the second pressure receiving surface 64. The second internal space 54 communicates with the machine interior space A1 (see FIG. 2) through the first flow path 46.

[0046] With this configuration, even if the first flow passage 46 is narrow, it is possible to ensure a pressure-receiving area at the second end face 52 of the piston 44. Therefore, when the pressure in the interior space A1 becomes higher than the exterior space A2, the thrust of the piston 44 is obtained by the fluid pressure in the second internal space 54 connected to the interior space A1, and the piston 44 can move from the second position P2 to the first position P1. When the piston 44 moves, the gas (atmosphere) in the second chamber Q2 is discharged through the open hole 48 to the exterior space A2.

[0047] The first and second components F1 and F2 may be configured in the opposite manner on the inside and outside of the machine. That is, the first component F1 may be provided on the inside of the machine, and the second component F2 may be provided on the outside of the machine. As another modification of the first and second components F1 and F2, the inside and outside of the machine may have the same configuration. As yet another modification, in order to secure the pressure receiving area of ​​the piston 44, instead of providing the recess 65 opening into the cavity 43, a recess may be provided on the end surface of the piston 44, or instead of providing the protrusion 51a on the end surface of the piston 44, a protrusion may be provided on the inner surface of the cavity 43.

[0048] [Regarding the mechanical seal 10 of this embodiment] As described above, the mechanical seal 10 of the present embodiment shown in FIG. 1 and FIG. 2 includes the rotary seal ring 11 that rotates integrally with the rotary shaft 8, the stationary seal ring 12 for sealing between the rotary seal ring 11, and the case 13 that supports the stationary seal ring 12 and is attached to the rotating device 7. The mechanical seal 10 includes a back pressure chamber K1 and a connecting flow passage 40 that connects the in-machine space A1 and the back pressure chamber K1. The back pressure chamber K1 is provided between the outer side of the stationary seal ring 12 and the inner periphery 17 of the second case 15 that is a part of the case 13, and is a space sealed by the O-rings 27 and 29. The connecting flow passage 40 has a switching portion 41. The switching portion 41 communicates the in-machine space A1 with the back pressure chamber K1 when the in-machine space A1 is at a higher pressure than the outer-machine space A2, and blocks the in-machine space A1 from the back pressure chamber K1 when the in-machine space A1 is at a lower pressure than the outer-machine space A2.

[0049] According to this mechanical seal 10, when the in-machine space A1 is at a higher pressure than the external space A2, the in-machine space A1 and the back pressure chamber K1 communicate with each other by the switching portion 41, and the stationary seal ring 12 can be pressed against the rotary seal ring 11 by the fluid pressure of the back pressure chamber K1. On the other hand, when the in-machine space A1 is at a lower pressure than the external space A2, the fluid pressure of the in-machine space A1 does not reach the back pressure chamber K1, and the force that pulls the stationary seal ring 12 away from the rotary seal ring 11, which occurs in the conventional configuration, does not act. The back pressure chamber K1 has the same pressure (atmospheric pressure) as the external space A2, and the stationary seal ring 12 can be pressed against the rotary seal ring 11. As described above, even when the in-machine space A1 is at a higher or lower pressure than the external space A2, it is possible to ensure the force that presses the stationary seal ring 12 against the rotary seal ring 11 within a desired range.

[0050] 1, the switching part 41 is provided on the case 13. This makes it relatively easy to form the switching part 41, and also makes it easy to add the switching part 41 to a mechanical seal that has already been designed.

[0051] The switching portion 41 has a block portion 42 in which a cavity 43 is formed, and a piston 44 that moves in the cavity 43 between a first position P1 and a second position P2. When the piston 44 is in the first position P1 (see FIGS. 1 and 3), the internal space A1 and the back pressure chamber K1 communicate with each other through a part (first chamber Q1) of the cavity 43. When the piston 44 is in the second position P2 (see FIGS. 2 and 4), the piston 44 is present in the part (first chamber Q1) of the cavity 43, and thus blocks the internal space A1 from the back pressure chamber K1.

[0052] The connection flow passage 40 has a first flow passage 46 that connects the first chamber Q1 of the cavity 43 and the in-machine space A1, and a second flow passage 47 that connects the second chamber Q2 of the cavity 43 and the back pressure chamber K1. An open hole 48 that connects the second chamber Q2 and the outside space A2 is provided in the block portion 42 in which the cavity 43 is provided.

[0053] With this configuration, when the in-machine space A1 becomes lower in pressure than the external space A2, the pressure difference between the in-machine space A1 and the external space A2 causes a fluid (atmosphere) to enter the second chamber Q2 of the cavity 43 from the external space A2 through the open hole 48, and the piston 44 automatically moves from the first position P1 to the second position P2. When the in-machine space A1 becomes higher in pressure than the external space A2, the pressure difference between the in-machine space A1 and the external space A2 causes the piston 44 to automatically move from the second position P2 to the first position P1.

[0054] 〔others〕 The switching unit 41 may have a configuration other than that shown in the drawing. The switching unit 41 may be configured using, for example, a manifold valve, a check valve, or the like. 1, the entirety of the connection flow path 40 is provided inside the case 13, but a part of it may be configured by piping and provided outside the case 13. In addition, the switching section 41 (the block section 42 in which the cavity 43 is formed) may also be provided separately from the case 13.

[0055] The above-described embodiment is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims rather than the above-described embodiment, and includes all modifications within the scope equivalent to the configurations described in the claims. [Explanation of symbols]

[0056] 7 Rotating Equipment 8 Rotation Axis 10 Mechanical seal 11 Rotating seal ring 12 Stationary sealing ring 13 Cases 40 Connection Channel 41 Switching section 42 Block section 43 Cavity 44 Piston 46 First Channel 47 Second flow path 48 open hole 51 First end face 52 Second end face 53 First interior space 54 Second internal space 56 First inner surface 57 Second inner surface 61 First part contact surface 62 First pressure receiving surface 63 Second partial contact surface 64 Second pressure receiving surface A1 Cabin space A2 External space K1 Back pressure chamber P1 first position P2 2nd position Q1 First room Q2 Second room

Claims

1. A mechanical seal comprising: a rotary seal ring that rotates integrally with a rotary shaft; a stationary seal ring for sealing between the rotary seal ring and the stationary seal ring; and a case that supports the stationary seal ring and is attached to a rotary device, the mechanical seal separating an in-machine space inside the rotary device from an external space outside the rotary device, a back pressure chamber that is provided between the stationary seal ring on the outside space side of the machine and a part of the case and is sealed; A connection flow path connecting the interior space and the back pressure chamber; Equipped with the connecting flow passage has a switching portion that communicates the interior space with the back pressure chamber when the interior space is at a higher pressure than the exterior space, and that blocks communication between the interior space and the back pressure chamber when the interior space is at a lower pressure than the exterior space, The switching portion includes a block portion in which a cavity is formed, and a piston that moves the cavity between a first position and a second position, When the piston is in the first position, the internal space and the back pressure chamber communicate with each other through a part of the cavity, When the piston is in the second position, the piston is present in the portion of the cavity to isolate the internal space from the back pressure chamber; the connecting passage includes a first passage that connects a first chamber, which is the part of the cavity, to the interior space, and a second passage that connects a second chamber of the cavity, which is formed when the piston is in the second position, to the back pressure chamber, The block portion is provided with an open hole that communicates the second chamber with the outside space, the piston has, on a first end surface on one side in a moving direction, a first partial contact surface that partially contacts a first inner surface of the cavity and a first pressure receiving surface that does not contact the first inner surface, A first internal space formed between the first inner surface and the first pressure-receiving surface communicates with the outside space through the open hole. Mechanical seal.

2. The mechanical seal according to claim 1 , wherein the switching portion is provided on the case.

3. the piston has, on a second end surface on the other side in the moving direction, a second partial contact surface that partially contacts a second inner surface of the cavity and a second pressure receiving surface that is not in contact with the second inner surface, The mechanical seal according to claim 1 or 2, wherein a second internal space formed between the second inner surface and the second pressure-receiving surface communicates with the aircraft interior space through the first flow path.

4. A mechanical seal as described in claim 1, wherein the first pressure surface is wider than the first partial contact surface.

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