JP7628480B2 - Mechanical seal - Google Patents

Description

The present invention relates to a mechanical seal.

Mechanical seals are known as devices for sealing the internal fluid between the equipment casing and the rotating shaft in various rotating equipment (see, for example, Patent Document 1). A 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 to provide a seal between the rotating seal ring and the stationary seal ring.

Patent No. 3192152

Figure 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 a case 93 that supports the stationary seal ring 92 and is attached to the rotating device 100. The mechanical seal 90 divides an in-machine space A1 inside the rotating device 100 from an external space A2 outside the rotating device 100.

A back pressure chamber K1 is provided between the outer side of the stationary seal ring 92 (left side in FIG. 5) 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 that connects 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).

When the pressure in the interior space A1 is higher than the exterior space A2, the fluid pressure in the back pressure chamber K1 connected to the interior space A1 can press the stationary seal ring 92 against the rotating seal ring 91. This makes it possible to ensure the sealing performance between the stationary seal ring 92 and the rotating seal ring 91.

Depending on the type of 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 is generated in the direction of moving the stationary seal ring 92 away from the rotating seal ring 91 due to the fluid pressure (atmospheric pressure) in the external space A2. Although not shown, the mechanical seal 90 is provided with an elastic member (compression coil spring) for pressing the stationary seal ring 92 against the rotating seal ring 91. If the elastic biasing force of the elastic member is set large, it is possible to ensure the force pressing the stationary seal ring 92 against the rotating 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 rotating seal ring 91 may become excessive.

Therefore, the present disclosure aims to provide a mechanical seal that can ensure a desired range of force pressing the stationary seal ring against the rotating seal ring when the pressure inside the machine space is higher or lower than the pressure outside the machine space.

(1) The mechanical seal of the present disclosure is a mechanical seal comprising a rotary seal ring that rotates integrally with a rotating shaft, a stationary seal ring for sealing between the rotary seal ring, and a case that supports the stationary seal ring and is attached to a rotating device, and that separates an internal space of the rotating device from an external space of the rotating device. The mechanical seal comprises a back pressure chamber that is provided and sealed between the external space side of the stationary seal ring and a part of the case, and a connecting flow path that connects the internal space and the back pressure chamber. The connecting flow path has a switching portion that connects the internal space and the back pressure chamber when the internal space is at a higher pressure than the external space, and that blocks the internal space from the back pressure chamber when the internal space is at a lower pressure than the external space.

According to the mechanical seal of the present disclosure, when the in-machine space is at a higher pressure than the external space, the in-machine space and the back pressure chamber are connected by the switching portion of the connecting flow passage, and the stationary seal ring can be pressed against the rotating seal ring by the fluid pressure in the back pressure chamber. In contrast, when the in-machine space is at a lower pressure than the external space, the fluid pressure in the in-machine space does not reach the back pressure chamber, and no force acts to separate the stationary seal ring from the rotating seal ring. As a result, even when the in-machine space is at a higher or lower pressure than the external space, it is possible to ensure a desired range of force pressing the stationary seal ring against the rotating seal ring.

(2) The switching portion may be provided on the stationary seal ring, but preferably, the switching portion is provided on the case. This is because it is easier to configure the switching portion on the case than on the stationary seal ring.

(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.

(4) Also, preferably, the connecting flow path has a first flow path connecting a first chamber, which is a part of the cavity, to the in-machine space, and a second flow path 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 connect the second chamber to 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.

(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.

(6) Also, preferably, the piston has, on a second end face 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, and a second internal space formed between the second inner surface and the second pressure-receiving surface is connected to the aircraft space 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 becomes movable.

The mechanical seal disclosed herein makes it possible to ensure a desired range of force pressing the stationary seal ring against the rotating seal ring when the pressure inside the machine space is higher or lower than the pressure outside the machine space.

FIG. 2 is a cross-sectional view of the mechanical seal with the piston in a first position. FIG. 2 is a cross-sectional view of the mechanical seal with the piston in a second position. 2 is an enlarged view showing the switching portion shown in FIG. 1 and its surroundings. FIG. 3 is an enlarged view showing the switching portion shown in FIG. 2 and its surroundings. FIG. FIG. 1 is a cross-sectional view of a conventional mechanical seal.

[About mechanical seals in general]
1 is a cross-sectional view of a mechanical seal 10. The 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.

The directions in the present disclosure are defined. 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.

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 can be 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.

To this end, 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 escaping and the atmosphere from entering. 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 and 12a.

The mechanical seal 10 includes a case 13 attached to the rotating equipment 7. The case 13 includes a cylindrical first case 14 attached to the equipment casing 9 and a cylindrical second case 15 attached to the outside of the first case 14. The second case 15 has a smaller inner diameter than 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 the radially inner portion of the inner peripheral portion 17 to the inside of the equipment. The gap between the first case 14 and the second case 15 is sealed by a seal member 33 such as an O-ring.

The mechanical seal 10 has a rotating unit 21 that includes a rotating seal ring 11. In addition to the rotating seal ring 11, the rotating unit 21 has 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.

The sleeve 22 is cylindrical and fitted around the other part of the rotating shaft 8. The sleeve 22 has a cylindrical portion 22a that is sandwiched between the fixed member 23 and the rotating shaft 8 in the radial direction, and an annular portion 22b that extends radially from the end of the cylindrical portion 22a on the inside of the machine. The rotating seal ring 11 is fitted around the cylindrical portion 22a. The rotating seal ring 11 is prevented from rotating by a pin or the like (not shown) on the sleeve 22, and can rotate together with the sleeve 22. As described above, the rotating seal ring 11 rotates together with the rotating shaft 8. The space between the rotating seal ring 11 and the sleeve 22 is sealed by an O-ring 25. The space between the sleeve 22 and the rotating shaft 8 is sealed by an O-ring 26.

The stationary seal ring 12 is an annular member that seals with the rotating 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 that protrudes 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 that generates a force in a direction that presses the stationary seal ring 12 against the rotating seal ring 11.

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.

Although not shown, the case 13 (first case 14) is provided with a seal gas flow passage through which a seal gas (e.g., nitrogen gas) is supplied. 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 the space between the seal surface 11a of the rotating 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 that keeps the seal surfaces 11a, 12a in a non-contact state.

An annular back pressure chamber K1 is provided between the outer 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 periphery of the stationary seal ring 12 and an O-ring 27 on the inner periphery of the stationary seal ring 12. The back pressure chamber K1 is connected to a connecting flow passage 40 described later, but is a closed space. As will be 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 rotating seal ring 11.

In the stationary seal ring 12, the pressure-receiving area that receives the internal pressure of the back pressure chamber K1 is larger than the pressure-receiving area that receives the pressure of the external space A2 (atmospheric pressure). The back pressure chamber K1 is configured so that when the back pressure chamber K1 is higher than the external space A2, a force is applied that presses the stationary seal ring 12 against the rotating seal ring 11.

The mechanical seal 10 has a connection flow path 40 that connects the internal space A1 and the back pressure chamber K1. The connection flow path 40 has a switching unit 41 that switches the state of the flow path. In the embodiment shown in FIG. 1, the connection flow path 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 from 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 that block portion.

[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).

A seal member (O-ring) 45 that slides against the inner 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.

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 the block portion 42, which is a part of the case 13.

As shown in Figures 3 and 1, when the piston 44 is in the first position P1, the internal 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 internal space A1 and the back pressure chamber K1 is blocked by the piston 44.

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

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, pushing the piston 44 toward the first position P1. Even if the piston 44 is in the second position P2, when the pressure in the in-machine space A1 becomes higher than the pressure in 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 face 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).

In this state, the in-machine space A1 and the back pressure chamber K1 are in communication 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, the fluid pressure in the back pressure chamber K1 exerts a force in a direction pressing the stationary seal ring 12 against the rotating seal ring 11. The force in the pressing direction changes depending on the pressure in the in-machine space A1, and the higher the pressure in the in-machine space A1, the greater the force in the pressing direction.

When the pressure of the in-machine space A1 becomes lower than that of the outside-machine space A2, that is, when the pressure of the in-machine space A1 changes to negative pressure relative to atmospheric pressure, the first chamber Q1 of the cavity 43 also becomes low pressure (negative pressure). Then, the fluid pressure (atmospheric pressure) of the outside-machine 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 pressure of the in-machine space A1 becomes lower than that of the outside-machine space A2, the pressure difference between the in-machine space A1 and the outside-machine space A2 causes fluid (atmosphere) to enter the second chamber Q2 from the outside-machine 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).

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 connected 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 inside-machine space A1 is at a lower pressure than the outside-machine space A2 and the back pressure chamber K1, which are at atmospheric pressure, and a force is applied in the direction of pressing the stationary seal ring 12 against the rotating seal ring 11 due to the fluid pressure (atmospheric pressure) of the back pressure chamber K1.

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 isolates 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.
In addition, 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.

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 this embodiment has the following first configuration F1 and second configuration F2.

In the first configuration F1 (see FIG. 3), the piston 44 has a first partial contact surface 61 and a first pressure receiving surface 62 on the first end surface 51 on one side in the moving direction that is the outside of the machine. The first partial contact surface 61 is formed by the tip surface of the 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 partially contact the first inner surface 56 of the cavity 43. The first pressure receiving surface 62 does not contact the first inner surface 56. When the piston 44 is in the first position P1, a first internal space 53 that is annular is formed between the first inner surface 56 and the first pressure receiving surface 62. The first internal space 53 communicates with the outside space A2 through the open hole 48.

This configuration makes it possible to ensure a pressure-receiving area at the first end face 51 of the piston 44 even if the open hole 48 is narrow. Therefore, when the pressure in the interior space A1 becomes lower than the pressure in the exterior space A2, the thrust of the piston 44 is obtained by 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.

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 path 46. The opening area of the recess 65 relative 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 path 46 relative to the recess 65 is smaller than the cross-sectional area of the recess 65.

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 of the movement 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 formed by an annular outer periphery 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 formed by the central part that is the remaining part of the second end surface 52. The second pressure receiving surface 64 is set 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 in-machine space A1 (see FIG. 2) through the first flow path 46.

This configuration makes it possible to ensure a pressure-receiving area at the second end face 52 of the piston 44 even if the first flow path 46 is narrow. 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 to the exterior space A2 through the open hole 48.

Regarding the first configuration F1 and the second configuration F2 as described above, the configurations may be reversed on the inside and outside of the machine. In other words, the first configuration F1 may be provided on the inside of the machine, and the second configuration F2 may be provided on the outside of the machine. As another modification of the first configuration F1 and the second configuration 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 a recess 65 that opens into the cavity 43, a recess may be provided on the end face of the piston 44, or instead of providing a protrusion 51a on the end face of the piston 44, a protrusion may be provided on the inner surface of the cavity 43.

[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 connection flow path 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, which is a part of the case 13, and is a space sealed by the O-rings 27 and 29. The connection flow path 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.

According to this mechanical seal 10, when the in-machine space A1 is at a higher pressure than the outside-machine 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 outside-machine 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 outside-machine space A2, and the stationary seal ring 12 can be pressed against the rotary seal ring 11. As a result, even when the in-machine space A1 is at a higher or lower pressure than the outside-machine space A2, it is possible to ensure the force pressing the stationary seal ring 12 against the rotary seal ring 11 within the desired range.

In the embodiment shown in FIG. 1, the switching portion 41 is provided on the case 13. This makes it relatively easy to form the switching portion 41, and also makes it easy to add the switching portion 41 to an already designed mechanical seal.

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

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

With this configuration, when the pressure in the in-machine space A1 becomes lower than the pressure in the external space A2, the pressure difference between the in-machine space A1 and the external space A2 causes 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 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.

〔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 portion 41 (the block portion 42 in which the cavity 43 is formed) may also be provided separately from the case 13.

The above-described embodiment is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims, not by the above-described embodiment, and includes all modifications within the scope of equivalence to the configurations described in the claims.

Reference Signs List 7 Rotating device 8 Rotating shaft 10 Mechanical seal 11 Rotating seal ring 12 Static seal ring 13 Case 40 Connecting flow passage 41 Switching portion 42 Block portion 43 Cavity 44 Piston 46 First flow passage 47 Second flow passage 48 Open hole 51 First end face 52 Second end face 53 First internal space 54 Second internal space 56 First inner surface 57 Second inner surface 61 First partial contact surface 62 First pressure receiving surface 63 Second partial contact surface 64 Second pressure receiving surface A1 In-machine space A2 Out-machine space K1 Back pressure chamber P1 First position P2 Second position Q1 First chamber Q2 Second chamber

Claims (4)

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. The mechanical seal of claim 1, wherein the switching portion is provided on the case. 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. The mechanical seal of claim 1 , wherein the first pressure surface is wider than the first partial contact surface.

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