JP7628482B2 - Mechanical seal and method for adjusting fluid pressure of mechanical seal - Google Patents

Description

The present invention relates to a mechanical seal and a method for adjusting fluid pressure in a mechanical seal.

For example, in high-load mechanical seals, in order to accommodate high pressure and high peripheral speed conditions, the balance ratio (the ratio between the force attempting to close the gap between the two seal faces of the stationary and rotating seal rings and the force attempting to open the gap between the two seal faces) is set to a smaller value than normal (0.6 to 0.75), allowing a certain amount of sealed fluid to leak between the two seal faces. This forms a lubricating film between the two seal faces by the sealed fluid, ensuring lubrication between the two seal faces (see Patent Document 1).

JP 2010-101361 A

When the balance ratio is reduced as described above, the pressing force that presses the seal faces together due to the fluid pressure of the sealed fluid is reduced. When the pressing force is reduced, the tracking ability of the stationary seal ring is more likely to decrease due to disturbances during operation of the mechanical seal. When the tracking ability of the stationary seal ring decreases, for example, there is a risk that a foreign object will get caught between the two seal faces, causing a large amount of the sealed fluid to leak from between the two seal faces in excess of the fixed amount.

The present invention was made in consideration of these circumstances, and aims to provide a mechanical seal that can adjust the amount of sealed fluid leaking from between the sealing surfaces of the rotating seal ring and the stationary seal ring, and a method for adjusting the fluid pressure of the mechanical seal.

(1) The present invention is a mechanical seal that includes a rotary seal ring that is provided on a rotating shaft side so as to be integrally rotatable therewith and has a seal surface formed on one axial side, and a stationary side unit that is provided on a casing that surrounds the rotating shaft and has a stationary seal ring that is provided on the other axial side and has a seal surface that faces the seal surface of the rotary seal ring, and that seals a sealed fluid in an in-machine region with the rotary seal ring and the stationary seal ring. The stationary side unit is attached to the casing side so as to be axially movable, and has a retainer that holds the stationary seal ring, a first fluid chamber that is formed in communication with the in-machine region so that the sealed fluid is introduced and the fluid pressure of the sealed fluid presses the retainer to the one axial side, a second fluid chamber that is formed independently of the in-machine region and the first fluid chamber so that a seal fluid is introduced and the fluid pressure of the seal fluid presses the retainer to the other axial side, and a pressure regulating valve that can adjust the fluid pressure of at least one of the sealed fluid and the seal fluid.

According to the present invention, the force pressing the retainer to the other axial direction can be adjusted by adjusting the fluid pressure of at least one of the sealed fluid introduced into the first fluid chamber and the sealing fluid introduced into the second fluid chamber with the pressure regulating valve. This makes it possible to adjust the pressing force with which the seal surface of the stationary seal ring held by the retainer presses against the seal surface of the rotating seal ring, thereby adjusting the amount of leakage of the sealed fluid from between the seal surfaces of the rotating seal ring and the stationary seal ring.

(2) It is preferable that the stationary unit further has an introduction passage that introduces a portion of a flushing fluid for cooling both seal surfaces of the rotary seal ring and the stationary seal ring into the second fluid chamber as the seal fluid.
In this case, a part of the flushing fluid that cools both seal surfaces can be used as the seal fluid, so that the structure of the mechanical seal can be simplified.

(3) It is preferable that the in-machine region is formed radially outward of both seal surfaces of the rotating seal ring and the stationary seal ring, the retainer has a pressing surface that presses only a radially inner portion of an end face on one axial side of the stationary seal ring toward the other axial side, and the pressure regulating valve is capable of adjusting the fluid pressure of the sealing fluid.
In this case, even if the portion of the stationary seal ring radially outward from the seal surface on the other axial side is pressed by the fluid pressure of the sealed fluid in the in-machine region, the portion of the stationary seal ring radially inward at the end face on one axial side is pressed by the pressing surface of the retainer to counteract the fluid pressure. Therefore, by adjusting the fluid pressure of the seal fluid with the pressure regulating valve and adjusting the pressing force of the stationary seal ring by the pressing surface of the retainer, the seal surface of the stationary seal ring can be uniformly pressed against the seal surface of the rotating seal ring in the radial direction. This makes it possible to suppress uneven wear of the seal surface of the stationary seal ring in the radial direction due to the fluid pressure of the sealed fluid, and therefore to suppress deterioration of the sealing performance of the mechanical seal.

(4) It is preferable that the retainer has a first pressure-receiving surface that receives the fluid pressure of the sealed fluid in the first fluid chamber from the other axial side, and a second pressure-receiving surface that receives the fluid pressure of the seal fluid in the second fluid chamber from the one axial side, and that an area of the first pressure-receiving surface is equal to or greater than an area of the second pressure-receiving surface.
In this case, by making the area of the first pressure-receiving surface of the retainer equal to or larger than the area of the second pressure-receiving surface, the balance diameter of the stationary seal ring can be made smaller than when the area of the first pressure-receiving surface is made smaller than the area of the second pressure-receiving surface. This makes it possible to reduce the pressing force of the pressing surface of the retainer on the stationary seal ring and the peripheral speed of the pressing surface. This is particularly effective in high-load mechanical seals used under high pressure and high peripheral speed conditions.

(5) The fluid pressure regulating method for a mechanical seal according to (1) above, wherein at least one of the fluid pressures is regulated by the pressure regulating valve so as to satisfy the following relationship:
P1×B1<P2×B2
Here, the variables in the above formula are defined as follows:
P1: Fluid pressure of the sealed fluid in the first fluid chamber B1: Area of a first pressure receiving surface of the retainer receiving the fluid pressure of the sealed fluid in the first fluid chamber from the other axial side P2: Fluid pressure of the seal fluid in the second fluid chamber B2: Area of a second pressure receiving surface of the retainer receiving the fluid pressure of the seal fluid in the second fluid chamber from one axial side

In this case, the force relationship of the above formula is maintained, so a force always acts on the retainer pressing it in the other axial direction. This makes it possible to adjust the force pressing the retainer in the other axial direction while preventing the retainer from moving in the one axial direction.

The mechanical seal of the present invention makes it possible to adjust the amount of leakage of the sealed fluid between the sealing surfaces of the rotating seal ring and the stationary seal ring.

1 is a cross-sectional view showing a mechanical seal according to a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a main portion of FIG. 1 . FIG. 4 is an enlarged cross-sectional view showing the periphery of a stationary seal ring. 11 is a cross-sectional view illustrating a wear state of a seal surface of a stationary seal ring in a reference example in which a pressing surface of a retainer is changed. FIG. FIG. 5 is a cross-sectional view for explaining the wear state of a seal surface of a stationary seal ring in the reference example of FIG. 4 . FIG. 4 is a cross-sectional view showing a mechanical seal according to a second embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view of a main portion of FIG. 2 .

Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[First embodiment]
Fig. 1 is a cross-sectional view showing a mechanical seal according to a first embodiment of the present invention. In Fig. 1, the mechanical seal 1 is used in rotating equipment such as pumps and mixers, and seals a sealed fluid (solvent, water, oil, etc.) inside the rotating equipment. The mechanical seal 1 is disposed between a rotating shaft 71 of the rotating equipment and a casing 72 surrounding the rotating shaft 71, along the axial direction of the rotating shaft 71 (hereinafter simply referred to as the "axial direction").

The mechanical seal 1 of this embodiment is used under high load conditions such as high pressure and high peripheral speed, and includes a rotating side unit 2 that is mounted on a rotating shaft 71 so as to be able to rotate integrally with the rotating shaft 71, and a stationary side unit 3 that is mounted on a casing 72. For convenience, the left side of FIG. 1 will be referred to as one axial side in this specification, and the right side of FIG. 1 will be referred to as the other axial side (the same applies to FIGS. 2 to 7).

<Rotation side unit>
The rotating side unit 2 includes a sleeve 11, a stopper ring 12, a rotating seal ring 13, and a retainer 14. The sleeve 11 has a cylindrical sleeve main body 11a fitted and fixed to the outer periphery of the rotating shaft 71, an annular portion 11b extending radially outward from the other axial end of the sleeve main body 11a, and a cylindrical portion 11c extending axially to one side from the radial outer end of the annular portion 11b.

A key groove 11d is formed at a predetermined location in the circumferential direction on the inner circumference of one axial end of the sleeve body 11a. A key member 15 is inserted between the key groove 11d and the outer circumferential surface of the rotating shaft 71. A stopper ring 12 is fitted on the outer periphery of the rotating shaft 71 on one axial side of the sleeve body 11a to prevent the key member 15 from slipping out to one axial side. The other axial end of the stopper ring 12 is fitted on the outer periphery of one axial end of the sleeve body 11a, and a set screw 16 is tightened radially into the fitted portion. In this way, the sleeve 11 is fixed to the rotating shaft 71. An O-ring 17 is used to seal (secondary seal) between the inner circumferential surface of the other axial end of the sleeve body 11a and the outer circumferential surface of the rotating shaft 71.

A rotary seal ring 13 is disposed between the sleeve body 11a and the cylindrical portion 11c. A seal surface 13a is formed on the end face of the rotary seal ring 13 on one side in the axial direction. The rotary seal ring 13 is concentrically attached to the cylindrical portion 11c via a cylindrical retainer 14. Specifically, the outer peripheral surface of the rotary seal ring 13 is fitted and fixed to the inner peripheral surface of the retainer 14, and the outer peripheral surface of the retainer 14 is fitted to the inner peripheral surface of the cylindrical portion 11c. A convex portion 14a (see FIG. 2) that protrudes radially outward is integrally formed on a part of the outer peripheral surface of the retainer 14 in the circumferential direction. The convex portion 14a is inserted into a concave groove 11e (see FIG. 2) formed on a part of the inner peripheral surface of the cylindrical portion 11c in the circumferential direction. This restricts the rotation of the retainer 14 and the rotary seal ring 13 relative to the sleeve 11. An O-ring 18 is disposed on the other axial side of the retainer 14. The O-ring 18 provides a seal (secondary seal) between the inner surface of the cylindrical portion 11c and the outer surface of the rotating seal ring 13.

<Stationary unit>
The stationary unit 3 includes a seal case 30, a retainer 34, and a stationary seal ring 35. The seal case 30 has a first case body 31 having an annular shape fixed to the casing 72, a second case body 32 having an annular shape fixed to the first case body 31, and a third case body 33 having a cylindrical shape fixed to the second case body 32.

The radially outer portion of the first case body 31 is fixed to the casing 72 by bolts 36 while abutting against one axial side of the casing 72. An annular groove 31a is formed on the radially inner side of the first case body 31. An O-ring 38 provides a seal (secondary seal) between the other axial side of the first case body 31 and the one axial side of the casing 72.

The second case body 32 is fixed to the first case body 31 by bolts 39 while being fitted into the annular groove 31a of the first case body 31. An O-ring 40 provides a seal (secondary seal) between the outer circumferential surface of the second case body 32 and the inner circumferential surface of the annular groove 31a.

Figure 2 is an enlarged cross-sectional view of the main part of Figure 1. As shown in Figure 2, the third case body 33 has a case main body 33a and a connecting tube portion 33b extending from the case main body 33a to one side in the axial direction. The outer peripheral surface of the case main body 33a is fitted into the inner peripheral surface of the casing 72. O-rings 41 and 42 seal between the inner peripheral surface of the casing 72 and both axial sides of the outer peripheral surface of the case main body 33a.

The connecting tube portion 33b is formed in a cylindrical shape and has a smaller diameter than the outer circumferential surface of the case body 33a. One axial side of the connecting tube portion 33b is fixed with a screw 43 with its inner circumferential surface fitted to the outer circumferential surface of the second case body 32. Also, one axial side of the connecting tube portion 33b is fitted into the annular groove 31a of the first case body 31 with the connecting tube portion 33b fixed to the second case body 32.

The retainer 34 has a retainer body 340 formed in an annular shape, a first cylindrical portion 341 extending from the inner peripheral end of the retainer body 340 to the other axial side, and a second cylindrical portion 342 extending from the inner peripheral end of the retainer body 340 to one axial side. The retainer body 340 is arranged on the inner peripheral side of the third case body 33 so as to be movable in the axial direction. An O-ring 44 seals (secondary seal) between the outer peripheral surface of the retainer body 340 and the inner peripheral surface of the third case body 33.

A pin 45 is fixed to the first side surface 340a on the other axial side of the retainer body 340, protruding in the other axial direction. A pin 46 is fixed to the second side surface 340b on one axial side of the retainer body 340, protruding in the one axial direction. The pin 46 is inserted into a pin groove 32a formed in the second case body 32. As a result, the retainer 34 is attached to the seal case 30 on the casing 72 side so as to be movable in the axial direction, and relative rotation with respect to the seal case 30 is restricted.

As shown in FIG. 1, a plurality of springs 47 (only one is shown in FIG. 1) are provided at predetermined intervals in the circumferential direction between the second case body 32 and the retainer body 340. The springs 47 bias the retainer body 340 toward the other axial side relative to the second case body 32.

As shown in FIG. 2, the outer diameter of the first cylindrical portion 341 is larger than the outer diameter of the second cylindrical portion 342. As a result, the area B1 of the first side surface 340a of the retainer body 340 is smaller than the area B2 of the second side surface 340b. The second cylindrical portion 342 is inserted into the inner periphery of the second case body 32. An O-ring 48 provides a seal (secondary seal) between the outer periphery of the second cylindrical portion 342 and the inner periphery of the second case body 32.

The stationary seal ring 35 is disposed on the other axial side of the retainer 34. A circular nose portion 35a that protrudes to the other axial side is formed on the radially inner side of the other axial end portion of the stationary seal ring 35. The end face on the other axial side of the nose portion 35a is a seal surface 35b that can face and come into contact with the seal surface 13a of the rotating seal ring 13. As a result, an in-machine area 73 in which the sealed fluid is sealed is formed radially outward of both the seal surfaces 13a, 35b of the rotating seal ring 13 and the stationary seal ring 35 in the casing 72.

Because the mechanical seal 1 of this embodiment is used under high load conditions as described above, the shape of the stationary seal ring 35 is determined so that the balance ratio (the ratio of the force that tries to close the gap between the two seal surfaces 13a, 35b of the rotating seal ring 13 and the stationary seal ring 35 to the force that tries to open the gap between the two seal surfaces 13a, 35b) is a small value (e.g., 0.6 to 0.75). Therefore, the mechanical seal 1 of this embodiment allows a certain amount of sealed fluid to leak from between the two seal surfaces 13a, 35b by reducing the balance ratio. As a result, a lubricating film is formed by the sealed fluid between the two seal surfaces 13a, 35b, ensuring lubrication between the two seal surfaces 13a, 35b.

A pin groove 35c is formed on the radially outer side of one axial end of the stationary seal ring 35. A pin 45 fixed to the retainer body 340 is inserted into the pin groove 35c. As a result, the stationary seal ring 35 is held by the retainer 34, and relative rotation with respect to the retainer 34 is restricted.

3 is an enlarged cross-sectional view showing the periphery of the stationary seal ring 35. As shown in FIG. 3, the end face 35d on one axial side of the stationary seal ring 35 is made up of a first end face 35d1, a second end face 35d2, and a third end face 35d3, which are formed in this order from the radial inside to the radial outside. The end face 341a on the other axial side of the first cylindrical portion 341 of the retainer 34 abuts against the first end face 35d1. The second end face 35d2 is formed to protrude further toward the one axial side than the first end face 35d1. A first circumferential surface 35e is formed between the first end face 35d1 and the second end face 35d2. The other axial end of the first cylindrical portion 341 is inserted into the inner circumferential side of the first circumferential surface 35e.

The third end face 35d3 is formed to protrude further toward one axial direction than the second end face 35d2. A second circumferential surface 35f is formed between the second end face 35d2 and the third end face 35d3. The inner circumferential surface of the second circumferential surface 35f and the outer circumferential surface of the first cylindrical portion 341 are sealed (secondary sealed) by an O-ring 49. The third end face 35d3 is disposed on the other axial direction side with a gap from the first side surface 340a of the retainer body 340. With the above configuration, the retainer 34 (end face 341a of the first cylindrical portion 341) abuts only against the radially inner portion (first end face 25d1) of the end face 35d on one axial side of the stationary seal ring 35.

The retainer 34 is always pressed to the other axial direction by always maintaining the force relationship of equation (1) as described below. Therefore, the end face 341a of the retainer 34 functions as a pressing surface that presses the first end face 35d1 of the stationary seal ring 35 to the other axial direction. Hereinafter, the end face 341a of the retainer 34 is also referred to as the pressing surface 341a.

<Flushing channel>
1 and 2, a flushing flow passage 74 through which a flushing fluid flows is formed in the casing 72. The flushing fluid is a fluid that is introduced into the in-machine area 73 to cool both the seal surfaces 13a, 35b of the rotating seal ring 13 and the stationary seal ring 35, and is made of the same fluid as the sealed fluid.

The flushing passage 74 is formed to extend radially at a predetermined location in the circumferential direction of the casing 72. The radial outer end of the flushing passage 74 is connected to a first pipe 75 arranged on the outside of the casing 72. The first pipe 75 is a pipe that supplies the sealed fluid in the in-machine area 73 to the flushing passage 74 as a flushing fluid.

The seal case 30 has a communication flow passage 50 that connects the flushing flow passage 74 and the in-machine area 73. The communication flow passage 50 has an annular flow passage 51, a first supply flow passage 52, and a second supply flow passage 53 formed in the third case body 33. The annular flow passage 51 is formed in a circular ring shape in the circumferential direction of the third case body 33. The annular flow passage 51 also opens at the outer periphery of the third case body 33 and communicates with the radial inner end of the flushing flow passage 74. The annular flow passage 51 in this embodiment is formed, for example, with a rectangular cross section.

The first supply passage 52 is a passage that connects the annular passage 51 with the in-machine region 73 and supplies flushing fluid to both seal surfaces 13a, 35b of the rotating seal ring 13 and the stationary seal ring 35. A plurality of first supply passages 52 are formed at predetermined intervals in the circumferential direction of the third case body 33. Each first supply passage 52 is formed in the third case body 33 so as to incline from the annular passage 51 toward the other axial side and toward the radially inward direction so that flushing fluid is supplied toward both seal surfaces 13a, 35b.

The second supply flow passage 53 is a flow passage that connects the annular flow passage 51 and the in-machine area 73 and supplies flushing fluid to the first fluid chamber 61 described below. Similar to the first supply flow passage 52, multiple second supply flow passages 53 are formed at predetermined intervals in the circumferential direction of the third case body 33. Each second supply flow passage 53 is formed radially outside the first fluid chamber 61 in the third case body 33 so that flushing fluid is supplied toward the first fluid chamber 61.

<First Fluid Chamber>
2, the stationary unit 3 includes a first fluid chamber 61 formed in communication with the in-machine region 73. The first fluid chamber 61 is formed between the retainer 34 and the stationary seal ring 35. Specifically, the first fluid chamber 61 is configured by a gap formed between the first side surface 340a of the retainer body 340 and the second end face 35d2 and the third end face 35d3 of the stationary seal ring 35. The radial inside of the first fluid chamber 61 is sealed by the O-ring 49 described above.

The first fluid chamber 61 is connected to the in-machine region 73 at its radially outer side. As a result, the flushing fluid (sealed fluid) supplied from the second supply passage 53 to the in-machine region 73 is introduced into the first fluid chamber 61. The flushing fluid introduced into the first fluid chamber 61 presses the first side surface 340a of the retainer body 340 to one axial side due to its fluid pressure. Therefore, the first side surface 340a functions as a first pressure-receiving surface that receives the fluid pressure of the flushing fluid in the first fluid chamber 61 from the other axial side. Hereinafter, the first side surface 340a of the retainer body 340 is also referred to as the first pressure-receiving surface 340a.

<Second Fluid Chamber>
The stationary unit 3 includes a second fluid chamber 62 formed independently of the in-machine area 73 and the first fluid chamber 61. The second fluid chamber 62 is defined by the second case body 32, the third case body 33, and the retainer 34. Specifically, the second fluid chamber 62 is defined by a gap formed between the other axial end face of the second case body 32 and the second side surface 340b of the retainer body 340, and a gap formed between the inner peripheral surface of the connecting tube portion 33b and the outer peripheral surface of the retainer body 340.

One axial side of the second fluid chamber 62 is sealed by the O-rings 40 and 48. The other axial side of the second fluid chamber 62 is sealed by the O-ring 44. As a result, the second fluid chamber 62 is formed independently of the in-machine area 73 and the first fluid chamber 61.

<Inlet flow path>
1 and 2, the stationary unit 3 includes an introduction flow passage 55 that introduces a seal fluid into the second fluid chamber 62. In this embodiment, a part of the flushing fluid flowing through the first piping 75 is used as the seal fluid. The introduction flow passage 55 includes a first introduction flow passage 55a formed in the first case body 31, a second introduction flow passage 55b formed between the first case body 31 and the third case body 33, and a third introduction flow passage 55c formed in the third case body 33.

The first introduction flow passage 55a is formed at a predetermined location in the circumferential direction of the first case body 31 with a cross section that is approximately L-shaped. One end of the first introduction flow passage 55a opens on the outer peripheral surface of the first case body 31 and is connected to the second pipe 76 that branches off from the first pipe 75. As a result, a portion of the flushing fluid flowing through the first pipe 75 passes through the second pipe 76 as a seal fluid and is supplied to the introduction flow passage 55, simplifying the configuration of the mechanical seal. The other end of the first introduction flow passage 55a opens on the other axial side surface of the first case body 31, radially inward from the casing 72.

The second inlet flow passage 55b is formed in an annular shape between a side surface on one axial side of the case main body 33a in the third case body 33 and a side surface on the other axial side of the first case body 31 facing the side surface, and communicates with the first inlet flow passage 55a. The other axial side of the second inlet flow passage 55b is sealed by the O-ring 41. The third inlet flow passage 55c is formed by penetrating radially at a predetermined location in the circumferential direction of the connecting tube portion 33b in the third case body 33, and communicates between the second inlet flow passage 55b and the second fluid chamber 62.

With the above configuration, the sealing fluid flowing through the second pipe 76 passes through the first introduction flow passage 55a, the second introduction flow passage 55b, and the third introduction flow passage 55c in order and is introduced into the second fluid chamber 62. The sealing fluid introduced into the second fluid chamber 62 presses the second side surface 340b of the retainer body 340 to the other axial direction due to its fluid pressure. Therefore, the second side surface 340b functions as a second pressure-receiving surface that receives the fluid pressure of the sealing fluid in the second fluid chamber 62 from one axial direction side. Hereinafter, the second side surface 340b of the retainer body 340 is also referred to as the second pressure-receiving surface 340b.

<Discharge flow path>
1, the stationary unit 3 is provided with a discharge flow passage 56 that discharges to the outside the sealing fluid introduced into the second fluid chamber 62. The discharge flow passage 56 has a first discharge flow passage 56a formed in the first case body 31, a second discharge flow passage 56b formed between the first case body 31 and the third case body 33, and a third discharge flow passage 56c formed in the third case body 33.

The first exhaust flow passage 56a is formed in a substantially L-shaped cross section at a predetermined location (a location different from the first inlet flow passage 55a) in the circumferential direction of the first case body 31. One end of the first exhaust flow passage 56a opens at the outer peripheral surface of the first case body 31 and is connected to a third pipe 77 arranged outside the casing 72. The other end of the first exhaust flow passage 56a opens at the other axial side surface of the first case body 31, radially inward from the casing 72.

The second exhaust flow passage 56b is a flow passage that communicates with the first exhaust flow passage 56a. In this embodiment, the first exhaust flow passage 56a communicates with the annular second inlet flow passage 55b, which also serves as the second exhaust flow passage 56b. The third exhaust flow passage 56c is formed by penetrating radially at a predetermined location (a location different from the third inlet flow passage 55c) in the circumferential direction of the connecting tube portion 33b in the third case body 33. As a result, the third exhaust flow passage 56c communicates with the second exhaust flow passage 56b (second inlet flow passage 55b) and the second fluid chamber 62.

With the above configuration, the sealing fluid in the second fluid chamber 62 passes through the third exhaust flow path 56c, the second exhaust flow path 56b, and the first exhaust flow path 56a in order, and is discharged to the third pipe 77. Note that the second exhaust flow path 56b may be formed independently of the second introduction flow path 55b.

<Pressure Regulating Valve>
The mechanical seal 1 further includes a pair of pressure regulating valves 4 capable of adjusting the fluid pressure of the sealing fluid, and a check valve 5. The check valve 5 is provided in the second pipe 76, and prevents the sealing fluid in the second pipe 76 from flowing back into the first pipe 75. The pair of pressure regulating valves 4 is composed of a first pressure regulating valve 4A provided in the second pipe 76 closer to the introduction flow path 55 than the check valve 5, and a second pressure regulating valve 4B provided in the third pipe 77.

The first pressure regulating valve 4A can manually adjust the fluid pressure of the sealing fluid introduced into the second fluid chamber 62 through the second pipe 76. The second pressure regulating valve 4B can manually adjust the fluid pressure of the sealing fluid discharged from the second fluid chamber 62 through the third pipe 77.

<Method of adjusting fluid pressure of seal fluid>
In Figures 1 and 2, the force exerted by the fluid pressure on the first pressure-receiving surface 340a and the second pressure-receiving surface 340b of the retainer 34 must always maintain the force relationship expressed by the following equation (1) using the areas B1 and B2 of both pressure-receiving surfaces 340a, 340b.
P1×B1<P2×B2 (1)
Here, P1 is the fluid pressure of the flushing fluid (sealed fluid) in the first fluid chamber 61 (in-machine region 73), and P2 is the fluid pressure of the sealing fluid in the second fluid chamber 62.

By constantly maintaining the force relationship of the above formula (1), a force is constantly acting on the retainer 34 pressing it toward the other axial side, preventing the retainer 34 from moving toward one axial side. This prevents the O-ring 49 from falling out from between the retainer 34 and the stationary seal ring 35 due to the retainer 34 moving toward one axial side, thereby preventing the sealed fluid in the in-machine area 73 from leaking outside the machine.

When adjusting the fluid pressure P2 of the sealing fluid by the pair of pressure regulating valves 4, the force relationship of the above formula (1) must always be maintained. In this embodiment, as described above, the area B1 of the first pressure receiving surface (first side) 340a is smaller than the area B2 of the second pressure receiving surface (second side) 340b. Therefore, the fluid pressure P2 of the sealing fluid is adjusted by the pair of pressure regulating valves 4 to a range smaller than the fluid pressure P1 of the flushing fluid so that the force relationship of the above formula (1) is always maintained based on the size relationship between the two areas B1 and B2.

As described above, the retainer 34 is biased in the other axial direction by the spring 47 (see FIG. 1). However, since the mechanical seal 1 of this embodiment is used under high load (high pressure) conditions, the fluid pressures P1 and P2 are also high. Therefore, the forces on the right and left sides of the above formula (1) are significantly greater than the biasing force of the spring 47, so there is no problem in ignoring the biasing force of the spring 47 in the above formula (1).

By adjusting the fluid pressure P2 of the sealing fluid using the pair of pressure regulating valves 4 so that the force relationship of the above formula (1) is always maintained, the force with which the pressing surface 341a of the retainer 34 (see FIG. 3) presses the stationary seal ring 35 toward the other axial direction can be adjusted. By adjusting this pressing force, the pressing force with which the seal surface 35b of the stationary seal ring 35 presses the seal surface 13a of the rotating seal ring 13 can be adjusted. This makes it possible to appropriately adjust the amount of leakage of the sealed fluid from between the seal surfaces 13a, 35b of the rotating seal ring 13 and the stationary seal ring 35.

As shown in FIG. 3, the outer periphery of the stationary seal ring 35 radially outward from the seal surface 35b is pressed toward one axial direction and toward the radial inside by the fluid pressure P1 of the sealed fluid. When the fluid pressure P1 acts in this way, the stationary seal ring 35 generates a rotational moment M1 in the clockwise direction in FIG. 3 around the center of gravity G of the cross section. For this reason, as shown in FIG. 4, for example, if the pressing surface of the retainer 34 pressing the stationary seal ring 35 is the first side surface 340a instead of the end surface 341a, and the first side surface 340a presses the third end surface 35d3 of the stationary seal ring 35, that is, if the retainer 34 presses the stationary seal ring 35 to promote the generation of the rotational moment M1, the following problems will occur.

In FIG. 4, when rotational moment M1 is generated, the radially outer portion of seal surface 35b of stationary seal ring 35 is pressed more strongly against seal surface 13a of rotary seal ring 13 than the radially inner portion, and the radially outer portion wears preferentially. As a result, as shown in FIG. 5, the radially outer portion of seal surface 35b of stationary seal ring 35 cannot be pressed against seal surface 13a of rotary seal ring 13, and there is a risk of a large amount of sealed fluid leaking from in-machine area 73.

In contrast, as shown in FIG. 3, in this embodiment, the fluid pressure P2 (see FIG. 2) of the sealing fluid causes the end face (pressing surface) 341a of the retainer 34 to press the first end face 35d1, which is located radially inward from the center of gravity G of the stationary seal ring 35, toward the other axial direction. In other words, the pressing surface 341a of the retainer 34 presses the first end face 35d1 of the stationary seal ring 35 so as to face the fluid pressure P1 of the sealed fluid. Due to this pressing force F1, a rotational moment M2 is generated in the stationary seal ring 35 in the counterclockwise direction in FIG. 3 around the center of gravity G. As a result, rotational moments M1 and M2 are generated in the stationary seal ring 35 in mutually opposite directions.

Therefore, by adjusting the fluid pressure P2 of the sealing fluid with the pair of pressure regulating valves 4 and adjusting the pressing force F1 of the stationary seal ring 35 by the pressing surface 341a of the retainer 34, the two rotational moments M1 and M2 can be made to cancel each other out. This allows the seal surface 35b of the stationary seal ring 35 to be uniformly pressed against the seal surface 13a of the rotating seal ring 13 in the radial direction. As a result, the seal surface 35b of the stationary seal ring 35 can be prevented from wearing unevenly in the radial direction, and therefore the deterioration of the sealing performance of the mechanical seal 1 can be prevented.

[Second embodiment]
6 is a cross-sectional view showing a mechanical seal according to a second embodiment of the present invention. The mechanical seal 1 of this embodiment differs from the first embodiment in the second pipe 76, the size relationship between the areas B1 and B2 of the first and second pressure receiving surfaces 340a and 340b of the retainer 34, and the method of adjusting the fluid pressure of the seal fluid.

In this embodiment, the second pipe 76 is provided independently of the first pipe 75. The same fluid as the flushing fluid (sealed fluid) flowing through the first pipe 75 flows through the second pipe 76 as a sealing fluid. Note that a fluid different from the flushing fluid may also flow through the second pipe 76 as a sealing fluid.

Figure 7 is an enlarged cross-sectional view of the main part of Figure 6. As shown in Figure 7, in the retainer 34 of this embodiment, the outer diameter of the first cylindrical portion 341 is smaller than the outer diameter of the second cylindrical portion 342. As a result, the area B1 of the first pressure receiving surface 340a of the retainer body 340 is larger than the area B2 of the second pressure receiving surface 340b. Therefore, the pair of pressure regulating valves 4 adjust the fluid pressure P2 of the sealing fluid to a range greater than the fluid pressure P1 of the flushing fluid so that the force relationship of the above formula (1) is always maintained based on the size relationship between the two areas B1 and B2.

In this embodiment, the area B1 of the first pressure receiving surface 340a of the retainer body 340 is larger than the area B2 of the second pressure receiving surface 340b. Therefore, compared to when area B1 is smaller than area B2 (see FIG. 2), the balance diameter D1 of the stationary seal ring 35 (the outer diameter of the retainer 35 (first cylindrical portion 341) that presses the stationary seal 35 in this embodiment) can be made smaller. Note that it is sufficient that the area B1 of the first pressure receiving surface 340a is equal to or larger than the area B2 of the second pressure receiving surface 340b. Other configurations of this embodiment are similar to those of the first embodiment, so the same reference numerals are used and their description is omitted.

As described above, in this embodiment as well, the force with which the pressing surface 341a of the retainer 34 presses the stationary seal ring 35 to the other axial direction can be adjusted by adjusting the fluid pressure P2 of the sealing fluid with the pair of pressure regulating valves 4. By adjusting this pressing force, the pressing force with which the seal surface 35b of the stationary seal ring 35 presses the seal surface 13a of the rotating seal ring 13 can be adjusted. This makes it possible to appropriately adjust the amount of leakage of the sealed fluid from between the seal surfaces 13a, 35b of the rotating seal ring 13 and the stationary seal ring 35.

In addition, since the area B1 of the first pressure-receiving surface 340a of the retainer 34 is larger than the area B2 of the second pressure-receiving surface 340b, the balance diameter D1 of the stationary seal ring 35 can be made smaller than when the area B1 is smaller than the area B2. This makes it possible to reduce the pressing force of the pressing surface 341a of the retainer 35 on the stationary seal ring 35 and the peripheral speed of the pressing surface 341a. This is particularly effective in a high-load mechanical seal 1 used under high pressure and high peripheral speed conditions, as in this embodiment.

[others]
Although the pressure regulating valve 4 in each of the above embodiments can manually adjust the fluid pressure P2, it may also automatically adjust the fluid pressure P2. In that case, for example, a sensor may detect the amount of leakage of the sealed fluid from between the seal surfaces 13a, 35b of the rotary seal ring 13 and the stationary seal ring 35, and if the amount of leakage is outside a predetermined range in a control unit that receives the detection information, the pressure regulating valve 4 may be controlled to automatically adjust the fluid pressure P2.

In each of the above embodiments, the pressure regulating valve 4 adjusts the fluid pressure P2 of the sealing fluid. In addition to this, or instead of this, a pressure regulating valve 4 may be provided in the first pipe 75 to manually or automatically adjust the fluid pressure P1 of the flushing fluid (sealed fluid). In this case, the pressure regulating valve 4 provided in the first pipe 75 adjusts the fluid pressure P1 in a range greater than the fluid pressure P2 in the first embodiment, and adjusts the fluid pressure P1 in a range smaller than the fluid pressure P2 in the second embodiment. Note that, when adjusting the fluid pressure P1 with the pressure regulating valve 4 in the first embodiment, it is preferable to provide a mechanism for boosting the fluid pressure P1. For example, a floating ring may be provided between the rotating shaft 71 and the casing 72 on the other axial side of the rotating side unit 2, and the gap of the flushing fluid flowing between this floating ring and the rotating shaft 71 may be reduced to boost the fluid pressure P1.

The second pipe 76 in the first embodiment branches off from the first pipe 75, but may be provided independently of the first pipe 75, as in the second embodiment. In that case, the sealing fluid flowing through the second pipe 76 may be the same fluid as the flushing fluid (sealed fluid) flowing through the first pipe 75, or may be a different fluid.

The second pipe 76 in the second embodiment is provided independently of the first pipe 75, but may be branched off from the first pipe 75 in the same manner as in the first embodiment.
The mechanical seal of the present invention can also be used under conditions other than the high load conditions. In such cases, the force relationship of the above formula (1) can be set to take into account the biasing force of the spring 47.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the meaning described above, and is intended to include all modifications within the scope of the claims and meanings equivalent thereto.

REFERENCE SIGNS LIST 1 Mechanical seal 3 Stationary side unit 4 Pressure regulating valve 13 Rotary seal ring 13a Seal surface 34 Retainer 35 Stationary seal ring 35b Seal surface 35d1 First end surface (end surface)
55: Inlet flow passage 61: First fluid chamber 62: Second fluid chamber 71: Rotating shaft 72: Casing 340a: First side surface (first pressure receiving surface)
340b Second side surface (second pressure receiving surface)
341a End surface (pressing surface)
B1: Area of the first pressure receiving surface B2: Area of the second pressure receiving surface P1: Fluid pressure of the flushing fluid (sealed fluid) P2: Fluid pressure of the seal fluid

Claims (4)

a rotary seal ring provided on the rotary shaft so as to be integrally rotatable therewith and having a seal surface formed on one axial side thereof;
a stationary side unit provided in a casing surrounding the rotary shaft, the stationary side unit having a stationary seal ring with a seal surface formed on the other axial side thereof opposed to the seal surface of the rotary seal ring,
A mechanical seal that seals a sealed fluid in an in-machine region by the rotating seal ring and the stationary seal ring,
The stationary side unit is
a retainer that is attached to the casing side so as to be movable in the axial direction and that holds the stationary seal ring;
a first fluid chamber formed in communication with the in-machine region so that the sealed fluid is introduced thereinto and the fluid pressure of the sealed fluid presses the retainer to one side in the axial direction;
a second fluid chamber formed independently of the in-machine region and the first fluid chamber so that a seal fluid is introduced thereinto and a fluid pressure of the seal fluid presses the retainer toward the other axial direction;
a pressure regulating valve capable of regulating the fluid pressure of at least one of the sealed fluid and the sealing fluid,
The in-machine region is formed radially outward of both seal surfaces of the rotary seal ring and the stationary seal ring,
the retainer has a pressing surface that presses only a radially inner portion of an end face on the one axial direction side of the stationary seal ring toward the other axial direction,
The pressure regulating valve is capable of adjusting the fluid pressure of the sealing fluid . 2. The mechanical seal according to claim 1, wherein the stationary unit further comprises an introduction passage for introducing a part of a flushing fluid for cooling both of the seal surfaces into the second fluid chamber as the seal fluid. The retainer includes:
a first pressure receiving surface that receives the fluid pressure of the sealed fluid in the first fluid chamber from the other axial direction;
a second pressure receiving surface that receives the fluid pressure of the seal fluid in the second fluid chamber from one axial side,
3. The mechanical seal according to claim 1, wherein an area of the first pressure-receiving surface is equal to or larger than an area of the second pressure-receiving surface. 2. The method for adjusting fluid pressure in a mechanical seal according to claim 1, further comprising adjusting the at least one fluid pressure by the pressure regulating valve so as to satisfy the following relationship:
P1×B1<P2×B2
Here, the variables in the above formula are defined as follows:
P1: Fluid pressure of the sealed fluid in the first fluid chamber B1: Area of a first pressure receiving surface of the retainer receiving the fluid pressure of the sealed fluid in the first fluid chamber from the other axial side P2: Fluid pressure of the seal fluid in the second fluid chamber B2: Area of a second pressure receiving surface of the retainer receiving the fluid pressure of the seal fluid in the second fluid chamber from one axial side

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