Mechanical seal

Abstract

Provided is a mechanical seal in which the axial dimension is short and a secondary seal can be reliably sealed.　This mechanical seal 1 comprises: a mating ring 20; a seal ring 10; a case 5 having a pop-out restraining part 56 that supports the seal ring 10 such that the seal ring 10 cannot rotate but can move in the axial direction, and that comes into contact with the seal ring 10 to restrain the seal ring 10 from popping out toward the mating ring 20; an urging means 6 that is positioned between the seal ring 10 and a back surface 52 of the case 5 overlapping the seal ring 10 in the axial direction, and that urges the seal ring 10 in the axial direction toward the mating ring 20; and an annular secondary seal 7 that seals the gap between the case 5 and the seal ring 10, wherein the case 5 has a restraining wall 55 that restrains the secondary seal 7 from moving toward the side axially opposite from the mating ring 20, and when the seal ring 10 and the pop-out restraining part 56 are in contact, the axial dimension X between the seal ring 10 and the restraining wall 55 is equal to or less than half Y of the axial dimension of the secondary seal 7.

Description

[Technical field]

[0001] The present invention relates to a mechanical seal used to seal a rotating shaft of a rotary machine. [Background technology]

[0002] Mechanical seals are used by being mounted between the housing of a rotating machine in, for example, an automobile, general industrial machine, or other sealing fields, and a rotating shaft arranged to pass through the housing, and prevent leakage of fluid from the inside of the rotating machine to the outside or from the outside to the inside by bringing the sliding surface of a seal ring fixed to the housing into sliding contact with the sliding surface of a mating ring that rotates with the rotating shaft. Because the seal ring is pressed axially toward the mating ring by a spring, the sliding contact state between the sliding surfaces can be maintained even if the sliding surfaces of the seal ring and the mating ring wear.

[0003] The mechanical seal shown in Patent Document 1 has a seal ring, case, spring, spring holder, and O-ring unitized, making it easy to install in a rotating machine. The case has a cylindrical inner diameter portion into which the seal ring is inserted, an annular back surface portion extending in the outer diameter direction from the back surface side end of the inner diameter portion, and a cylindrical outer diameter portion extending in the axial direction from the outer diameter side end of the back surface portion toward the mating ring side. In addition, a spring holder and a spring are arranged between the back surface portion of the seal ring and the back surface portion of the case, which biases the seal ring toward the mating ring side.

[0004] An O-ring is disposed between the outer peripheral surface of the inner diameter part of the case and the inner peripheral surface of the seal ring, and the seal ring is attached to the case so as to be movable in the axial direction while preventing leakage of fluid. A cut-and-raised piece is formed on the outer diameter part of the case, which is bent toward the inner diameter side of the case and cut and raised so as to extend toward the back side of the case, and the cut-and-raised piece is disposed in a groove of the seal ring to restrict rotation of the seal ring. Furthermore, when the seal ring is pushed forward by the spring via the spring holder before the case is fixed to the housing, the back side end of the cut-and-raised piece abuts against the outer diameter side surface of the spring holder, restricting the seal ring from jumping out toward the mating ring. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Microfilm of Utility Model Application No. 121412 / 1982 (Unexamined Utility Model Application No. 100148 / 1984) (pages 3 and 4, Figure 2) Summary of the Invention [Problem to be solved by the invention]

[0006] As rotating machines become smaller, mechanical seals are required to have a compact structure. However, in a mechanical seal such as that in Patent Document 1, the spring and spring holder are arranged on the back side of the seal ring and the secondary seal, so there is a risk that the axial dimension of the mechanical seal will become long.

[0007] The present invention has been made in view of the above problems, and has as its object to provide a mechanical seal which has a short axial dimension and is capable of providing a reliable secondary seal. [Means for solving the problem]

[0008] In order to solve the above problems, the mechanical seal of the present invention comprises: a mating ring, a seal ring which rotates and slides relative to the mating ring, a case which supports the seal ring in a non-rotating state and in an axially movable state and has a protrusion prevention portion which abuts against the seal ring to prevent the seal ring from protruding toward the mating ring, a biasing means which is disposed between the seal ring and a back portion of the case which overlaps with the seal ring in the axial direction and biases the seal ring in the axial direction toward the mating ring, and an annular secondary seal which is pressed radially to seal a gap between the case and the seal ring, The case has a restricting wall that restricts the secondary seal from moving in the axial direction opposite to the mating ring, When the seal ring and the protrusion restriction portion are in contact with each other, the axial dimension between the seal ring and the restriction wall is equal to or less than half the axial dimension of the secondary seal. According to this, since a regulating wall is provided on the case, the axial dimension of the mechanical seal can be shortened without the need for components such as a spring holder, and since the axial dimension between the seal ring and the regulating wall is less than or equal to the axial dimension between the axial center of the secondary seal and the regulating wall, when the seal ring and case are assembled and held in a regulating position where it does not protrude from the case, the secondary seal can reliably seal between the seal ring and the case.

[0009] The seal ring may have an extension extending in the axial direction on its back surface, and the biasing means and the secondary seal may be disposed on the inner diameter side and outer diameter side of the extension, respectively. According to this, the biasing means and the secondary seal are separated by the extension portion, thereby reliably preventing interference between the biasing means and the secondary seal, and reliably sealing between the seal ring and the case by the secondary seal.

[0010] The restriction wall may be a front wall of a step portion integrally formed so as to protrude from the rear portion toward the mating ring. According to this, since the step portion protrudes toward the mating ring from the rear surface of the case, the secondary seal can be disposed closer to the mating ring than the rear surface. This allows the secondary seal to reliably seal between the case and the seal ring while ensuring the axial length of the space for disposing the biasing means. In addition, since the step portion is integrally molded with the case, the restricting wall can be easily constructed.

[0011] The biasing means may be in direct contact with the seal ring and the case. This allows the number of parts in the mechanical seal to be reduced, thereby shortening the axial dimension of the mechanical seal and reducing the integrated tolerance of the parts. [Brief description of the drawings]

[0012] [Figure 1] 1 is a vertical cross-sectional view showing a mechanical seal according to a first embodiment of the present invention. [Diagram 2] 2 is a cross-sectional view showing a seal ring unit consisting of a seal ring, a case, a spring and an O-ring. FIG. [Diagram 3] FIG. 2 is a front view showing a seal ring unit consisting of a seal ring, a case, a spring and an O-ring. [Figure 4] 1A is a cross-sectional view showing the state in which the spring and O-ring are housed in the case, FIG. 1B is a cross-sectional view showing the state in which the seal ring is pressed into the case, and FIG. 1C is a cross-sectional view showing the state in which the seal ring is rotated clockwise. [Diagram 5] 1A is a front view showing the state in which the spring and O-ring are housed in the case, FIG. 1B is a front view showing the state in which the seal ring is pressed into the case, and FIG. 1C is a front view showing the state in which the seal ring has been rotated clockwise. [Figure 6] 1 is a cross-sectional view showing a seal ring unit including a seal ring, a case, a spring, and an O-ring in a first modified example of the first embodiment. FIG. [Figure 7]11 is a cross-sectional view showing a seal ring unit including a seal ring, a case, a spring, and an O-ring in a second embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A mechanical seal according to the present invention will be described below with reference to the following examples. EXAMPLES

[0014] A mechanical seal according to a first embodiment will be described with reference to Fig. 1 to Fig. 5. In this embodiment, the outer diameter side of the seal ring will be described as the sealed fluid side (high pressure side) and the inner diameter side will be described as the atmosphere side (low pressure side). Furthermore, the sliding surface side of the seal ring will be described as the front side.

[0015] 1 is an inside type mechanical seal in which an inner space S1 is formed on the inner diameter side of the sliding surface and an outer space S2 is formed on the outer diameter side, and the inner space S1 communicates with the atmosphere A, sealing against a sealed fluid F that would otherwise leak from the outer diameter side of the sliding surface toward the inner diameter side. In this embodiment, an example is shown in which the sealed fluid F is a high-pressure liquid and the atmosphere A is a gas with a lower pressure than the sealed fluid F.

[0016] The mechanical seal 1 is mainly composed of an annular mating ring 20 and a seal ring unit U. The mating ring 20 is mounted on a rotating shaft 3 via a sleeve 2 so as to be rotatable together with the rotating shaft 3. The seal ring unit U is fixed to a housing 4 of the device to which the seal ring unit U is to be attached.

[0017] The seal ring unit U is composed of a case 5 fixed to the housing 4, a seal ring 10 provided on the case 5 in a non-rotating state but axially movable, a spring 6 as a biasing means arranged between the case 5 and the seal ring 10, and an O-ring 7 as a secondary seal that seals between the case 5 and the seal ring 10.

[0018] The seal ring 10 is biased in the axial direction by the spring 6, so that the sliding surface 11 of the seal ring 10 and the sliding surface 21 of the mating ring 20 slide closely against each other.

[0019] The seal ring 10 and the mating ring 20 are typically formed by a combination of SiC (hard material) or SiC (hard material) and carbon (soft material), but are not limited thereto and can be used as long as the sliding material is used as a sliding material for mechanical seals. Examples of SiC include sintered bodies using boron, aluminum, carbon, etc. as sintering aids, as well as materials consisting of two or more phases with different components and compositions, such as SiC with dispersed graphite particles, reaction sintered SiC consisting of SiC and Si, SiC-TiC, SiC-TiN, etc., and examples of carbon include carbonaceous and graphitic mixtures, resin molded carbon, sintered carbon, etc. In addition to the above sliding materials, metal materials, resin materials, surface modification materials (coating materials), composite materials, etc. can also be used.

[0020] 2 shows a single seal ring unit U. As will be described in detail later, the seal ring unit U can be transported as a whole because the seal ring 10, the case 5, the spring 6, and the O-ring 7 can be maintained as a unit without being separated.

[0021] 2, the seal ring 10 includes a base 12, a front extension 13 extending from the base 12 to the front side, an outer diameter extension 14 extending from the base 12 to the outer diameter side, and a cylindrical rear extension 15 as an extension extending from the base 12 to the rear side, i.e., the side opposite to the mating ring 20. A sliding surface 11 is provided on the front side of the front extension 13.

[0022] As shown in FIG. 2, the case 5 includes a cylindrical inner diameter portion 51 into which the seal ring 10 is inserted, an annular back diameter portion 52 extending radially outward from the back diameter side end of the inner diameter portion 51 and overlapping with the seal ring in the axial direction, and a cylindrical outer diameter portion 53 extending axially from the outer diameter side end of the back diameter portion 52 toward the mating ring 20.

[0023] An annular step 54 protruding toward the front side is provided at the inner diameter end portion, i.e., the inner corner portion, of the back surface portion 52, and the step 54 is integrally molded with the back surface portion 52 and the inner diameter portion 51. Also, a front wall 55 is formed on the front side of the step 54 as a restricting wall that restricts the O-ring 7 from moving in the axially opposite direction from the mating ring 20. Although the step 54 has been described as being annular, it may be divided into multiple portions in the circumferential direction and disposed therein.

[0024] A protrusion restricting portion 56 extending in the inner diameter direction is provided at the front end of the outer diameter portion 53. As shown in Fig. 3, the protrusion restricting portions 56 are provided at three locations equally spaced circumferentially on the front surface of the outer diameter portion 53 of the case 5, and each have a substantially semicircular shape slightly smaller than the notch 17 of the seal ring 10. For convenience, in the front views such as Fig. 3, the outer diameter portion 53 of the case 5 and the dynamic pressure generating groove 11a of the sliding surface 11 of the seal ring 10 are represented by dots.

[0025] 2, the spring 6 is disposed between the back surface 14a of the outer diameter extension 14 of the seal ring 10 and the inner surface 52a of the back surface 52 of the case 5, on the outer diameter side of the back surface extension 15 of the seal ring 10, in a state of being compressed in the axial direction. The type and shape of the spring 6 are not particularly limited.

[0026] As shown in FIG. 2, the O-ring 7 is made of an elastic member having a circular cross section, and is disposed between the inner circumferential surface 18 of the rear extension portion 15 of the seal ring 10 and the outer circumferential surface 51a of the inner diameter portion 51 of the case 5 in a state of abutting and being pressed radially against these surfaces.

[0027] As shown in Fig. 3, a plurality of hydrodynamic grooves 11a are formed on the inner diameter side of the sliding surface 11. Note that the hydrodynamic grooves 11a are not limited to an arc shape, and may have different forms such as, for example, a Rayleigh step or a dimple, or the hydrodynamic grooves 11a may not be formed on the sliding surface 11.

[0028] As shown in Fig. 3, on the outer edge 14b of the outer diameter extension portion 14, a circumferentially equally spaced anti-rotation groove 16 and a notch 17 are formed.

[0029] The notch 17 is formed in an arc shape so as to penetrate axially at a position adjacent to the anti-rotation groove 16 in the clockwise direction.

[0030] Specifically, the anti-rotation groove 16 includes a bottom surface 16a and an anti-rotation wall 16b. The bottom surface 16a is recessed by one step from the outer diameter side surface 14c of the outer diameter extension portion 14 and extends in the circumferential direction by a predetermined dimension. The anti-rotation wall 16b extends vertically from the counterclockwise side edge of the bottom surface 16a toward the outer diameter side surface 14c.

[0031] Further, the spring 6 is located on the outer diameter side of the O-ring 7 and is arranged so as to partially overlap the O-ring 7 in the radial direction. Further, the O-ring 7 is in contact with the front wall 55 of the stepped portion 54 of the case 5.

[0032] As shown in Fig. 2, in the single seal ring unit U, the bottom surface 16a of the anti-rotation groove 16 of the outer diameter extension portion 14 of the seal ring 10 is in contact with the back surface 56a of the overhang restriction portion 56 of the outer diameter portion 53 of the case 5 (hereinafter referred to as the natural state).

[0033] When the seal ring unit U is in the natural state, the axial separation dimension X from the back surface 15a of the back extension portion 15 to the front wall 55 of the stepped portion 54 is smaller than the radius Y which is half of the axial dimension of the O-ring 7 (X < Y). Therefore, the O-ring 7, which is a secondary seal, can surely seal between the inner peripheral surface 18 of the back extension portion 15 of the seal ring 10 and the outer peripheral surface 51a of the inner diameter portion 51 of the case 5.

[0034] In other words, the axial distance L1 from the rear surface 15a of the rear extension portion 15 of the seal ring 10 to the inner surface 52a of the rear portion 52 of the case 5 is shorter than the axial distance L2 from the axial center of the O-ring 7, i.e., the axial center position where the O-ring 7 exerts its sealing performance, to the inner surface 52a of the rear portion 52 of the case 5 (L1 <L2)。

[0035] When the seal ring unit U is in its natural state, the seal ring 10 is positioned at the frontmost position within its axial range of motion, i.e., L1 is at its maximum. In this state, the O-ring 7 is in contact with the inner peripheral surface 18 of the rear extension portion 15 of the seal ring 10, so that the seal ring unit U in its natural state is stable in its unitized state. Therefore, the seal ring unit U is easy to transport.

[0036] Furthermore, as described below, when the mechanical seal 1 is attached to the rotating shaft 3 and the housing 4, the O-ring 7 can reliably seal between the case 5 and the seal ring 10.

[0037] Next, we will explain how to assemble the seal ring unit U. As shown in Figures 4(a) and 5(a), first, the spring 6 and O-ring 7 are placed in the case 5 with a predetermined distance between them in the radial direction. The O-ring 7 is fitted onto the inner diameter portion 51 of the case 5 with the O-ring 7 abutting against the front wall 55 of the step portion 54 of the case 5.

[0038] Next, the seal ring 10 is inserted into the case 5 as shown in FIG. 4(b) and FIG. 5(b).

[0039] In detail, as shown in Figure 5 (b), the circumferential position of the seal ring 10 is adjusted so that the notch 17 of the outer diameter extension portion 14 of the seal ring 10 overlaps with the protrusion control portion 56 of the outer diameter portion 53 of the case 5, and then the seal ring 10 is moved toward the rear side.

[0040] Thereafter, with the front end of the spring 6 abutting against the back surface 14a of the outer diameter extension portion 14 of the seal ring 10, the seal ring 10 is moved further toward the back surface against the axial biasing force due to the compression of the spring 6 until the bottom surface 16a of the anti-rotation groove 16 of the outer diameter extension portion 14 of the seal ring 10 is moved toward the back surface of the back surface 56a of the pop-out prevention portion 56 of the case 5 (see Figure 4(b)).

[0041] At this time, the inner peripheral surface 18 of the back extension portion 15 of the seal ring 10 slides against the O-ring 7, and the back extension portion 15 is inserted between the spring 6 and the O-ring 7 in the radial direction.

[0042] 4(c) and 5(c), the seal ring 10 is rotated clockwise while maintaining the amount of pressure applied to the back side of the seal ring 10. This rotation causes the protrusion restricting portion 56 of the case 5 to move within the anti-rotation groove 16 of the seal ring 10, so that the back surface 56a of the protrusion restricting portion 56 faces the bottom surface 16a of the anti-rotation groove 16. Note that excessive rotation of the protrusion restricting portion 56 can be prevented by the anti-rotation wall 16b of the anti-rotation groove 16.

[0043] Thereafter, by releasing the seal ring 10 from its pressed state toward the rear side, the seal ring 10 is pushed back toward the front side by the biasing force of the spring 6, but the bottom surface 16a of the anti-rotation groove 16 of the seal ring 10 comes into contact with the rear surface 56a of the pop-out restriction portion 56 of the case 5, thereby restricting the seal ring 10 from popping out of the case 5 (see FIGS. 2 and 3). At this time, the seal ring unit U is in its natural state.

[0044] Next, the assembly of the mechanical seal 1 to the rotating shaft 3 and the housing 4 will be described. With reference to Fig. 1, first, the mating ring 20 is fixed to the rotating shaft 3 using the sleeve 2. Next, the case 5 of the seal ring unit U is fixed to a predetermined position in the housing 4.

[0045] Thereafter, the rotating shaft 3 is inserted into the inner diameter hole of the seal ring unit U, and the mating ring 20 fixed to the rotating shaft 3 is abutted against the seal ring 10. Furthermore, the axial position of the rotating shaft 3 is adjusted and fixed so that the rotating shaft 3 is pushed toward the rear side against the biasing force of the spring 6.

[0046] At this time, the bottom surface 16a of the anti-rotation groove 16 of the outer diameter extension portion 14 of the seal ring 10 moves away from the back surface 56a of the protrusion restriction portion 56 of the outer diameter portion 53 of the case 5 toward the back surface side, and the seal ring 10 is pressed axially toward the mating ring 20 by the spring 6. Therefore, even if the sliding surfaces 11, 21 of the seal ring 10 and the mating ring 20 wear, the sliding contact state between the sliding surfaces 11, 21 can be maintained. Note that the procedure for assembling the mechanical seal 1 is not limited to this.

[0047] According to this, since the mechanical seal 1 can be assembled to the rotating shaft 3 and the housing 4 without disassembling the seal ring unit U, assembly of the mechanical seal 1 can be simplified.

[0048] Also, referring to Figure 3, when the seal ring 10 rotates in the rotation direction of the mating ring 20, i.e., clockwise, when the mating ring 20 rotates, the anti-rotation wall 16b of the anti-rotation groove 16 of the seal ring 10 abuts against the pop-out prevention portion 56 of the case 5, thereby preventing the seal ring 10 from rotating together.

[0049] A first modified example of the first embodiment will be described. The same components as those shown in the above embodiment will be denoted by the same reference numerals and will not be described again. As shown in Fig. 6, the case 105 constituting the seal ring unit U' includes an inner diameter portion 151, a back surface portion 152, and an outer diameter portion 53. The case 105 is provided with an annular restricting wall 155 that extends from the inner diameter portion 151 to the outer diameter side and faces the back surface portion 152.

[0050] In this way, the case 105 is provided with the restricting wall 155 that restricts the O-ring 7 from moving toward the rear side, so that the O-ring 7 can reliably seal between the case 105 and the seal ring 10. In addition, the O-ring 7 can be easily positioned relative to the case 5.

[0051] As described above, since the front wall 55 is provided on the case 5, the axial dimension of the mechanical seal 1 can be shortened without the need for components such as a spring holder, and further, when the seal ring 10 is in contact with the protrusion prevention portion 56, the axial dimension X between the seal ring 10 and the front wall 55 is less than or equal to the radius Y of the O-ring 7. Therefore, when the seal ring 10 and the case 5 are assembled and the seal ring 10 is held in a regulated position where it does not protrude from the case 5, the O-ring 7 can reliably seal between the seal ring 10 and the case 5.

[0052] In addition, the spring 6 is disposed at a radially different position from the O-ring 7 and partially overlaps with the O-ring 7 in the radial direction, so that the spring 6 and the O-ring 7 do not interfere with each other. This allows the axial dimension of the seal ring unit U of the mechanical seal 1 to be shortened.

[0053] In addition, a back extension 15 extending in the axial direction is provided on the back side of the seal ring 10. The back extension 15 separates the O-ring 7 from the spring 6, which is disposed on the inner diameter side, and the spring 6 from the outer diameter side. This reliably prevents interference between the spring 6 and the O-ring 7, and allows the O-ring 7 to reliably seal between the seal ring 10 and the case 5.

[0054] The restricting wall is a front wall 55 of a step portion 54 that is integrally formed so as to extend from the rear portion 52 of the case 5 toward the front side. The O-ring 7 is disposed closer to the front side than the rear portion 52 while abutting against the front wall 55. This allows the O-ring 7 to reliably seal between the case 5 and the seal ring 10 while ensuring the axial length of the space in which the spring 6 is disposed. Furthermore, since the step portion 54 is integrally formed with the case 5, the restricting wall can be easily configured.

[0055] Furthermore, when the rear extension portion 15 of the seal ring 10 approaches the rear portion 52 of the case 5, the rear extension portion 15 and the rear portion 52 can be reliably prevented from biting the O-ring 7.

[0056] In addition, because the spring 6 directly contacts the seal ring 10 and the case 5, it is possible to reduce the number of parts in the seal ring unit U of the mechanical seal 1. This allows the axial dimension of the seal ring unit U to be shortened, and also allows the integrated tolerance of the parts to be reduced. EXAMPLES

[0057] Next, a mechanical seal according to a second embodiment will be described with reference to Fig. 7. Note that a description of the same configuration as in the previous embodiment will be omitted.

[0058] As shown in FIG. 7, the seal ring 210 constituting the seal ring unit U'' has a base portion 12, a front extension portion 13, an outer diameter extension portion 14, and a rear extension portion 215 as an extension portion. A rear surface 215a of the rear extension portion 215 and an inner circumferential surface 218 form a corner portion 219.

[0059] Furthermore, the case 205 constituting the seal ring unit U'' has an inner diameter portion 251, a rear surface portion 252, and an outer diameter portion 53. A step portion 254 extending slightly toward the front surface side is provided on the inner diameter side of the rear surface portion 252, and a front wall 255 is formed in front of the step portion 254 as a restricting wall. The step portion 254 is provided in the radial direction from the inner diameter end of the rear surface portion 252 to the outer diameter end of the rear surface extension portion 215 of the seal ring 210.

[0060] When the seal ring unit U'' is in a natural state, the axial separation dimension X' from the rear surface 215a of the rear extension 215 to the front wall 255 of the step portion 254 is the same as the radius Y' as half the axial dimension of the O-ring 7 (X'=Y'). Therefore, the O-ring 7, which is a secondary seal, can reliably seal between the inner peripheral surface 218 of the rear extension 215 of the seal ring 210 and the outer peripheral surface 251a of the inner diameter portion 251 of the case 205. Note that L1' and L2', which correspond to the axial separation dimensions L1 and L2 in the first embodiment, respectively match the axial separation dimension X' and the radius Y' (L1'=X', L2'=Y').

[0061] When the seal ring unit U'' is in its natural state, the seal ring 210 is positioned at the frontmost position within its axial range of motion, i.e., L1' is at its maximum. In this state, the axial center of the O-ring 7 is securely in contact with the corner 219 of the seal ring 210. For this reason, when the seal ring unit U'' is assembled into the housing 4, i.e., when the rear surface 215a is close to the front wall 255, i.e., when the axial center of the O-ring 7 is positioned closer to the front than the rear surface 215a, the O-ring 7 can securely seal between the case 205 and the seal ring 210.

[0062] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0063] For example, in the above-mentioned first and second embodiments, an inside type seal is used to seal the sealed fluid F that tends to leak from the outer diameter side to the inner diameter side of the sliding surface, but an outside type seal is also possible to seal the sealed fluid F that tends to leak from the inner diameter side to the outer diameter side of the sliding surface.

[0064] In addition, although it has been explained that the anti-rotation groove, notch, and protrusion prevention portion are formed at three equal locations on the circumference, this is not limited thereto and they may be formed at multiple locations evenly on the circumference, and the anti-rotation groove, notch, and protrusion prevention portion may be formed unequal on the circumference as long as they correspond to each other on the circumference.

[0065] Further, although the cutout and the protrusion prevention portion have been described as being arc-shaped, the shape is not limited thereto and may be, for example, rectangular.

[0066] Also, the sealed fluid has been described as a high-pressure liquid, but it is not limited thereto and may be a gas or a low-pressure liquid, or may be a mist of a mixture of liquid and gas.

[0067] Moreover, the step portion and the restricting wall may be separate from the case.

[0068] Furthermore, the rear extension portion may be separate from the seal ring. [Explanation of symbols]

[0069] 1 Mechanical seal 3 Rotation Axis 5 Cases 6 Spring (biasing means) 7 O-ring (secondary seal) 10 Seal ring 15 Rear extension part (extension part) 20 Mating Ring 52 Back section 54 Step part 55 Front wall (control wall) 105 cases 152 Back part 155 Regulatory Wall 205 cases 210 Seal ring 215 Rear extension part (extension part) 252 Back part 254 Multilayered section 255 Front wall (control wall) A. Atmosphere F Sealed fluid L1, L2 Axial spacing dimensions L1', L2' axial separation dimension S1 inner space S2 outside space U,U',U'' Seal ring unit X,X' Axial Distance Dimension Y, Y' O-ring radius (half the axial dimension of the secondary seal)

Claims

1. a mating ring, a seal ring which rotates and slides relative to the mating ring, a case which supports the seal ring in a non-rotating state and in an axially movable state and has a protrusion prevention portion which abuts against the seal ring to prevent the seal ring from protruding toward the mating ring, a biasing means which is disposed between the seal ring and a back portion of the case which overlaps with the seal ring in the axial direction and biases the seal ring in the axial direction toward the mating ring, and an annular secondary seal which is pressed radially to seal a gap between the case and the seal ring, The case has a restricting wall that restricts the secondary seal from moving in the axial direction opposite to the mating ring, A mechanical seal in which, when the seal ring and the protrusion restriction portion are in contact with each other, the axial dimension between the seal ring and the restriction wall is equal to or less than half the axial dimension of the secondary seal.

2. 2. The mechanical seal according to claim 1, wherein an extension portion extending in the axial direction is provided on the back side of the seal ring, and the biasing means and the secondary seal are respectively arranged on the inner diameter side and the outer diameter side of the extension portion.

3. 3. The mechanical seal according to claim 1, wherein the restriction wall is a front wall of a step portion integrally formed with the rear portion so as to protrude from the rear portion toward the mating ring.

4. 4. The mechanical seal according to claim 1, wherein the biasing means directly contacts the seal ring and the case.

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