JP2024088039A - Shaft seal device - Google Patents

Abstract

To provide a shaft seal device which can maintain sufficiently high sealing performance without addition of a component irrespective of the thermal contraction of a seal material associated with low temperature.SOLUTION: A stuffing box is fit into an opening in a casing of a fluid apparatus and forms a packing chamber around a movable shaft. A seal material is packed into the packing chamber. A rib of the stuffing box separates a flow passage in the casing and the packing chamber. From the rib, a protrusion protrudes into the package chamber in an axial direction and surrounds the movable shaft. An external peripheral lip of the seal material protrudes into the packing chamber in the axial direction, and surrounds the protrusion of the stuffing box, with a tip part of the seal material making contact with the rib of the stuffing box. The seal material has a higher thermal contraction rate than that of the stuffing box, forms a seal region by pressing a tip part of the external peripheral lip against the rib with a packing pressing pressure at a normal temperature, and at a low temperature, forms the seal region by fastening an external peripheral surface of the protrusion with an internal peripheral surface of the external peripheral lip.SELECTED DRAWING: Figure 1

Description

The present invention relates to a shaft seal device, particularly one used at low temperatures.

A "shaft seal device" is a device that seals the gap between the opening of the casing of a fluid device and the movable shaft, that is, a device that prevents leakage of fluid from the gap or intrusion of foreign matter into the gap. Typical shaft seal devices include a stuffing box, a sealant, and a packing gland (see, for example, Patent Documents 1-3). A "stuffing box" is a cylindrical member that is fitted into the opening of the casing, and surrounds the movable shaft to form an annular space, i.e., a packing chamber, between its inner circumferential surface and the outer circumferential surface of the movable shaft. A "sealant" (also called "packing") is a string-like or annular flexible member, and multiple sealants are generally packed into the packing chamber. In the packing chamber, multiple sealants are arranged side by side along the movable shaft, with the sealant wound around the movable shaft if it is string-like, or with the movable shaft passing through the inner circumferential side if it is annular. A "packing gland" (also called "gland gland") is an annular member that surrounds the movable shaft at one axial end of the packing chamber, and applies axial pressure to the sealant. When the seal material is compressed axially by this pressure, it expands radially and adheres closely to the inner surface of the stuffing box and the outer surface of the movable shaft. As a result, the packing chamber is blocked by the seal material, sealing the gap between the opening of the casing and the movable shaft.

JP 2015-102132 A JP 2016-020711 A Japanese Patent No. 5153576

Resins are often chosen as sealing materials. In particular, fluororesins such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA), and polyvinylidene fluoride (PVDF) are widely used because they have high heat resistance, excellent chemical stability against fluids, and a low coefficient of friction with movable shafts. However, compared to metals, which are common materials for movable shafts and stuffing boxes, resins have a thermal contraction rate (the rate at which volume or length decreases with a drop in temperature; equal to the coefficient of thermal expansion) that is about 10 times higher. This means that the use of resin sealing materials has the following problems:

When fluid equipment handles low-temperature (in this specification, this means "several tens of degrees below zero") fluids such as liquid ammonia (boiling point -33°C), liquefied natural gas (LNG, boiling point -160°C), liquid nitrogen (boiling point -196°C), liquid hydrogen (boiling point -253°C), and liquid helium (boiling point -269°C), the fluid cools not only the movable shaft but also the shaft seal device to a low temperature. Since the seal material generally has a higher thermal contraction rate than the movable shaft and stuffing box, when the temperature drops from room temperature (in this specification, this means "several tens of degrees below zero") to a low temperature (hereinafter referred to as "low temperature"), the outer diameter of the seal material thermally contracts more than the inner diameter of the packing chamber. As a result, the seal pressure drops on the outer periphery of the seal material. If this drop is excessive, there is a risk of excessive fluid leakage. However, in situations where the fluid equipment handles low-temperature fluids, retightening is difficult, and it is difficult to increase the pressure on the packing gland to restore the sealing pressure, i.e., to prevent leakage.

A technique for preventing the deterioration of sealing performance due to low temperatures is known, for example, as described in Patent Document 1. In this technique, a resin seal (16) is sandwiched between two metal rings (18, 20) in the axial direction, and pressed against the movable shaft (10) and stuffing box (6) by radial pressure from two annular springs (22, 24) supported by one of the metal rings (18). Since the metal rings (18, 20) have less thermal contraction due to low temperatures compared to the seal (16), the metal rings (18, 20) can be configured so that the seal (16) between them is substantially maintained in its shape at room temperature regardless of low temperatures. As a result, the sealing pressure applied from the seal (16) to the movable shaft (10) and stuffing box (6) is maintained high and unchanged by the pressure of the springs (22, 24). However, this technology requires metal rings (18, 20) and springs (22, 24), which means the shaft seal device has a large number of parts, making the manufacturing process complicated and making it difficult to reduce the size in the axial direction.

The object of the present invention is to solve the above problems, and in particular to provide a shaft seal device that can maintain a sufficiently high level of sealing performance without adding any additional parts, despite the thermal contraction of the sealing material that occurs at low temperatures.

A shaft seal device according to one aspect of the present invention comprises a stuffing box, an annular sealing material, and a packing gland. The stuffing box is fitted into an opening of a casing of a fluid device to form a packing chamber around a movable shaft of the fluid device. The sealing material is packed into the packing chamber to surround the movable shaft. The packing gland applies axial pressure to the sealing material.

The stuffing box includes a rib and an annular protrusion. The rib is an annular wall that surrounds the movable shaft and separates the flow path in the casing from the packing chamber. The protrusion protrudes axially from the rib into the packing chamber and surrounds the movable shaft.

The seal material includes an annular outer lip, i.e., an outer peripheral portion that protrudes in the axial direction. The outer lip protrudes axially into the packing chamber to surround the convex portion of the stuffing box, with its tip contacting the rib of the stuffing box. The seal material has a higher thermal shrinkage rate than the stuffing box, and is configured such that the outer peripheral seal area for sealing the gap between the movable shaft and the rib is formed by (i) pressing the tip of the outer peripheral lip against the rib by the pressure of the packing gland at normal temperatures, and (ii) by tightening the outer peripheral surface of the convex portion with the inner peripheral surface of the outer peripheral lip at low temperatures.

The shaft seal device according to the present invention forms an outer seal area for sealing the gap between the movable shaft and the rib of the stuffing box by pressing the tip of the outer lip of the seal material against the rib with the pressure of the packing gland at room temperature. On the other hand, since the thermal shrinkage rate of the seal material is higher than that of the stuffing box, at low temperatures, the inner surface of the outer lip tightens the outer surface of the convex part of the stuffing box due to the difference in thermal shrinkage rates to form the outer seal area. As the temperature decreases, the force with which the tip of the outer lip presses the rib weakens, but the force with which the inner surface of the outer lip tightens the outer surface of the convex part of the stuffing box strengthens. Therefore, the decrease in sealing pressure between the tip of the outer lip and the rib is compensated for by the increase in sealing pressure between the inner surface of the outer lip and the outer surface of the convex part of the stuffing box. In this way, this shaft seal device can maintain a sufficiently high sealability without adding any parts, regardless of the thermal shrinkage of the seal material due to low temperatures.

In this shaft seal device, the seal material may further include an inner lip. The inner lip is an annular lip, i.e., a part that protrudes in the axial direction, and is configured so that the movable shaft is pressed into the inner side to bring the inner surface into close contact with the outer surface of the movable shaft, thereby forming an inner seal area for sealing the gap between the movable shaft and the rib. The inner diameter of the inner lip is already smaller than the diameter of the movable shaft at room temperature, and at low temperatures, the difference is further increased due to the difference in thermal contraction rate between the movable shaft and the seal material. Therefore, regardless of the low temperature, the inner surface of the inner lip tightly tightens the outer surface of the movable shaft, so the seal pressure is maintained sufficiently high. The inner surface of the inner lip may include a parabolic surface in the inner seal area. The parabolic surface has a larger radius of curvature at a position away from the apex, i.e., is closer to flat, so that when pressed against the outer surface of the movable shaft, it easily comes into close contact with the outer surface without any gaps. This improves the sealability of the inner seal area.

1A is a cross-sectional view of a shaft sealing device according to an embodiment of the present invention, and FIG. 1B is a partially enlarged view of the sealing material shown in FIG. 1A and its vicinity. FIG. 2 is an exploded view of the shaft seal device shown in FIG. 1A is a schematic diagram showing the sealing pressure applied by a sealing material at room temperature, and FIG. 1B is a schematic diagram showing the sealing pressure applied by a sealing material at a low temperature. 1A is a cross-sectional view of a sealing material according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of a modified example thereof.

The shaft seal device according to an embodiment of the present invention is used, for example, to seal the gap between the stem of a valve and the opening of a casing. The "stem," also called the "valve rod," is a rod-shaped member that transmits power to the valve body of a valve by rotating around a central axis or by reciprocating in the direction of the central axis. The stem is usually made of metal such as brass, bronze, cast iron, or steel. The "casing," also called the "valve box," is a housing that houses a flow path inside. Since the power transmitted by the stem is located in the flow path inside the casing, an opening is essential in the casing to allow the stem to pass through. The shaft seal device according to an embodiment of the present invention reduces the amount of fluid leaking from this opening.

Figure 1(a) is a cross-sectional view of a shaft seal device 100 according to an embodiment of the present invention. The shaft seal device 100 seals the gap between the stem 510 of the valve and the opening 551 of the casing 550. The cross section shown in Figure 1(a) includes the central axis of the stem 510. In Figure 1(a), the central axis is parallel to the left-right direction, with the flow path 540 in the casing 550 located on the right side and the external space 560 of the casing 550 extending to the left side, which is generally connected to the outside air. Hereinafter, the right side (i.e., the side closer to the flow path 540) of any part shown in Figure 1(a) will be referred to as the "fluid side", and the left side (i.e., the side closer to the external space 560) will be referred to as the "atmosphere side".

Fig. 2 is an exploded view of the shaft seal device 100. In Fig. 2, a cross section along the axial direction is shown with some of the components removed. As shown in Fig. 1(a) and Fig. 2, the shaft seal device 100 includes a stuffing box 110, a seal material 120, and a packing gland 130.
[Stuffing box]

The stuffing box 110 (also called the "gland box") is a cylindrical member made of metal such as brass, bronze, cast iron, or steel, and is fitted inside the opening 551 of the casing 550 to coaxially surround the stem 510. The fluid side end (right end in FIG. 1(a) and FIG. 2) 111 of the stuffing box 110 faces the flow path 540 in the casing 550, and the air side end (left end in FIG. 1(a) and FIG. 2) 112 protrudes to the outside of the casing 550. The inner peripheral surface 113 of the stuffing box 110 forms a cylindrical packing chamber 114 between the inner peripheral surface 511 of the stem 510 and the stuffing box 110. A ring-shaped wall portion, i.e., a rib 115, protrudes from the fluid side end 111 of the stuffing box 110 toward the outer peripheral surface 511 of the stem 510 to separate the flow path 540 from the packing chamber 114.

An annular protrusion 117 protrudes axially (to the left in FIGS. 1A and 2) from an annular surface 116 on the atmosphere side (FIG. 1A, left side in FIG. 2) of the rib 115 into the packing chamber 114 to surround the stem 510. The cross section of the protrusion 117 is, for example, a rectangular shape that is elongated in the axial direction, with an outer diameter narrower than the outer diameter of the packing chamber 114 and an inner diameter wider than the diameter of the stem 510 (= the inner diameter of the packing chamber 114).
[Sealing material]

Figure 1B is a partially enlarged view of the sealing material 120 shown in Figure 1A and its vicinity (the area surrounded by the dashed line in Figure 1A). Figure 4A is a cross-sectional view of the sealing material 120 alone. The sealing material 120 is preferably an annular lip seal made of a fluororesin such as PTFE. A "lip seal" refers to a sealing material in which a material is solidified into an annular shape in a mold, i.e., a type of molded packing, and the cross section taken along a plane including the central axis of the ring includes an axial protruding portion (called a "lip"). The sealing material 120 is packed coaxially with the stem 510 in the packing chamber 114 and surrounds the stem 510. Preferably, the sealing material 120 has an outer diameter narrower than the outer diameter of the packing chamber 114 and an inner diameter slightly narrower than the outer diameter of the stem 510 at room temperature. As a result, the stem 510 is pressed into the inner periphery of the sealing material 120, and the inner periphery is brought into close contact with the outer periphery 511 of the stem 510.

Preferably, the sealing material 120 is a U-packing. That is, the cross section including the central axis of the annular shape is U-shaped with one side in the axial direction (the right side in Fig. 1(b) and Fig. 4(b)) on the upper side. The two arms 121, 122 of this U-shape, i.e., the two concentric annular parts that protrude in the axial direction (to the right in Fig. 1(b) and Fig. 4(a)), are the lips. Due to the flexibility of their material, the lips 121, 122 can be bent to increase or decrease the opening of the U-shape, i.e., the radial distance between the tip faces 123, 124 (up and down in Fig. 1(b) and Fig. 4(a)).

The lip 121 (hereinafter referred to as the "outer lip") on the outer periphery (upper side in Fig. 1(b) and Fig. 4(a)) has an outer diameter narrower than that of the packing chamber 114 at room temperature, an inner diameter slightly wider than that of the convex portion 117 of the stuffing box 110, and is longer than the convex portion 117 in the axial direction (left-right direction in Fig. 1(b) and Fig. 4(a)). Therefore, the outer periphery lip 121 is pushed into the gap between the inner periphery 113 of the stuffing box 110 and the outer periphery 118 of the convex portion 117 until the tip surface 123 abuts against the annular surface 116 on the atmosphere side of the rib 115 (left side in Fig. 1(b) and Fig. 4(a)), and the outer periphery 125 faces the inner periphery 113 of the stuffing box 110, and the inner periphery 126 faces the outer periphery 118 of the convex portion 117.

The lip 122 (hereinafter referred to as the "inner lip") on the inner circumferential side (lower side in Fig. 1(b) and Fig. 4(a)) has an outer diameter narrower than the inner diameter of the convex portion 117 of the stuffing box 110 at room temperature, an inner diameter narrower than the diameter of the stem 510, and is shorter in the axial direction (left-right direction in Fig. 1(b) and Fig. 4(a)) than the outer circumferential lip 121. Therefore, when the tip surface 123 of the outer circumferential lip 121 abuts against the annular surface 116 on the atmospheric side (left side in Fig. 1(b) and Fig. 4(a)) of the rib 115, the inner circumferential lip 122 has its outer circumferential surface 127 facing the inner circumferential surface 119 of the convex portion 117, while its inner circumferential surface 128 closely contacts the outer circumferential surface 511 of the stem 510. The tip surface 124 of the inner lip 122 is spaced axially (to the left in FIG. 1(b) and FIG. 4(a)) from the air-side annular surface 116 of the rib 115.

Preferably, before the sealing material 120 is packed into the packing chamber 114, the tip 129 of the inner circumferential surface 128 of the inner circumferential lip 122 protrudes in the inward circumferential direction (downward in FIG. 4A). The tip 129 is preferably a paraboloid. More precisely, as shown in FIG. 4A, the contour on the lower side of the cross section including the central axis of the annular shape is a parabola with the narrowest point PK of the inner diameter (the lowest point in FIG. 4A) as the apex. As a result, the contour has a larger radius of curvature the further away from the apex PK (the further to the left and right from the apex PK in FIG. 4A), i.e., is closer to flat. At room temperature, the inner diameter of the inner circumferential lip 122 is slightly narrower than the diameter of the stem 510 at the center in the axial direction (left and right direction in FIG. 1B and FIG. 4A) of the tip 129 of the inner circumferential surface 128, while being wider than the outer diameter at other points. Therefore, when the stem 510 is press-fitted into the inner periphery of the tip portion 129, the central portion in the axial direction is flattened and comes into close contact with the outer periphery 511 of the stem 510, as shown in FIG.
[Packing gland]

A packing gland 130 is disposed on the inner periphery of the end 112 of the stuffing box 110 on the atmosphere side (the left end in FIG. 1A), and closes the opening of the packing chamber 114 on the atmosphere side (the left side in FIG. 1A) with its end 131 on the fluid side (the right end in FIG. 1A). The end 131 on the fluid side further contacts the annular surface 201 on the atmosphere side (the left side in FIG. 1A) of the seal material 120. The packing gland 130 is an annular member made of a metal such as brass, bronze, cast iron, or steel, and coaxially surrounds the stem 510. An annular flange 133 projects from the end 132 on the atmosphere side of the packing gland 130 (the left end in FIG. 1A and FIG. 2) toward the outer periphery. Although omitted in Fig. 2, a number of bolts 134 pass through the flange 133 parallel to the stem 510 (in the left-right direction in Fig. 1A) and are screwed into the atmosphere side end 112 of the stuffing box 110. Furthermore, nuts 135 are screwed into the bolts 134, and the axial force of the bolts 134 presses the flange 133. In this way, the flange 133 is fixed to the atmosphere side end 112 of the stuffing box 110. Furthermore, the axial force of the bolts 134 causes the fluid side end 131 of the packing gland 130 to press the atmosphere side annular surface 201 of the sealing material 120 in the axial direction (to the right in Fig. 1A).
[Sealing action of shaft seal device at room temperature]

3A is a schematic diagram showing the sealing pressures POR and PIR applied by the sealing material 120 at room temperature, with arrows showing the sealing pressures POR and PIR added to the cross-sectional view shown in FIG. 1B. When the nut 135 presses the flange 133 of the packing gland 130 with the axial force of the bolt 134, the fluid side end (left end in FIG. 3A) 131 of the packing gland 130 applies a pressure PP in the axial direction (rightward in FIG. 3A) to the annular surface 201 on the atmospheric side (left side in FIG. 3A) of the sealing material 120. As a result, in the gap between the inner peripheral surface 113 of the stuffing box 110 and the outer peripheral surface 118 of the convex portion 117, the tip surface 123 of the outer peripheral lip 121 of the sealing material 120 is pressed against the annular surface 116 on the atmospheric side (left side in FIG. 3A) of the rib 115 and is in close contact with it. As a result, a seal area (hereinafter referred to as the "first outer seal area") 211 is formed between the tip surface 123 of the outer lip 121 and the atmosphere-side annular surface 116 of the rib 115. The seal pressure POR that the tip surface 123 of the outer lip 121 applies to the atmosphere-side annular surface 116 of the rib 115 in the first outer seal area 211 is due to the pressure PP in the axial direction (to the right in FIG. 3A) from the packing gland 130.

Furthermore, the tip 129 of the inner surface 128 of the inner lip 122 clamps and seals the outer surface 511 of the stem 510, which is pressed into the inner side, forming a seal area (hereinafter referred to as the "inner seal area") 220 between the tip 129 and the outer surface 511 of the stem 510. As shown in FIG. 3A, the seal pressure PIR that the tip 129 applies to the outer surface 511 of the stem 510 in the inner seal area 220 is due to the restoring force of the inner lip 122 in the inner circumferential direction (downward in FIG. 3A).

When the flow passage 540 in the casing 550 is filled with fluid, the fluid also penetrates from the flow passage 540 into the gap between the rib 115 and the stem 510. However, only a very small amount of fluid can penetrate into the first outer periphery seal area 211 and the inner periphery seal area 220, so leakage of the fluid to the atmosphere side of the packing chamber 114 is suppressed. In particular, in the inner periphery seal area 220, the inner periphery lip 122 is further pressed against the outer periphery surface 511 of the stem 510 by the pressure of the fluid, so that the sealing pressure PIR is further increased, and the sealing performance is further improved. In this way, the gap between the rib 115 and the stem 510 is sealed.
[Sealing action of shaft seal device at low temperatures]

When a low-temperature fluid such as LNG, liquid nitrogen, or liquid hydrogen flows through the flow passage 540 in the casing 550, not only the stem 510 but also the shaft seal device 100 becomes cold. Compared to the stem 510, stuffing box 110, and packing gland 130, the seal material 120 has a higher thermal contraction rate, so the thermal contraction caused by the low temperature is large. Therefore, the low temperature causes the dimensional difference between the packing chamber 114 and the seal material 120 to change significantly from the value at room temperature. However, the shaft seal device 100 suppresses the deterioration of sealing performance caused by the low temperature due to the sealing action described below.

FIG. 3B is a schematic diagram showing the sealing pressures POL, POS, and PIL applied by the low-temperature sealing material 120, in which arrows indicating the sealing pressures POL, POS, and PIL are added to the cross-sectional view shown in FIG. 1B.
-Outer seal area-

Due to thermal contraction caused by low temperature, the outer lip 121 of the seal material 120 shortens in the axial direction. As a result, the sealing pressure POL applied from the tip surface 123 of the outer lip 121 to the annular surface 116 on the atmospheric side (left side in FIG. 3B) of the rib 115 is lower than the value POR at room temperature (POL<POR) at low temperature, so the sealing performance of the first outer seal area 211 is reduced. However, since the stuffing box 110 is made of metal and the seal material 120 is made of fluororesin, the thermal contraction rate is about 10 times higher. Therefore, the amount of shortening of the inner diameter of the outer lip 121 caused by low temperature is greater than the amount of shortening of the outer diameter of the protrusion 117 of the stuffing box 110. As a result, the inner circumferential surface 126 of the outer circumferential lip 121 clamps and tightly contacts the outer circumferential surface 118 of the convex portion 117, forming a second outer circumferential seal area 212 between the inner circumferential surface 126 of the outer circumferential lip 121 and the outer circumferential surface 118 of the convex portion 117. As the temperature decreases, the clamping force of the inner circumferential surface 126 of the outer circumferential lip 121 on the outer circumferential surface 118 of the convex portion 117 becomes stronger, and the sealing pressure POS of the second outer circumferential seal area 212 increases. In this way, the reduction in sealing ability of the first outer circumferential seal area 211 due to the decrease in temperature is compensated for by the formation of the second outer circumferential seal area 212.
-Inner seal area-

While the stem 510 is made of metal, the seal material 120 is made of fluororesin, and therefore has a thermal contraction rate that is about 10 times higher. Therefore, the amount of contraction of the inner diameter of the inner lip 122 of the seal material 120 due to the temperature drop is greater than the amount of contraction of the diameter of the stem 510. As a result, the inner surface 128 of the inner lip 122 further tightens the outer surface 511 of the stem 510, so that the seal pressure PIL of the inner seal area 220 exceeds the value PIR at room temperature (PIL>PIR). This further improves the sealability of the inner seal area 220.
Advantages of the embodiment

In the shaft seal device 100 according to the above embodiment of the present invention, at room temperature, the pressure PP of the packing gland 130 presses the tip surface 123 of the outer lip 121 of the seal material 120 against the atmospheric side annular surface 116 of the rib 115 of the stuffing box 110 to form the first outer seal area 211. On the other hand, at low temperatures, due to the difference in thermal contraction rate between the seal material 120 and the stuffing box 110, the inner surface 126 of the outer lip 121 tightens the outer surface 118 of the convex portion 117 of the stuffing box 110 to form the second outer seal area 212. As the temperature decreases, the force with which the tip surface 123 of the outer lip 121 presses against the atmospheric side annular surface 116 of the rib 115 weakens, i.e., the sealing pressure POL of the first outer seal area 211 decreases. However, the force with which the inner surface 126 of the outer lip 121 fastens against the outer surface 118 of the protrusion 117 increases, i.e., the sealing pressure POS in the second outer seal area 212 increases. As a result, the decrease in sealing pressure POL in the first outer seal area 211 due to the decrease in temperature is compensated for by the increase in sealing pressure POS in the second outer seal area 212. In this way, the shaft seal device 100 can maintain a sufficiently high sealing performance without adding any parts, despite the thermal contraction of the seal material 120 due to the decrease in temperature.

In the shaft seal device 100, the seal material 120 includes an inner lip 122. The stem 510 is press-fitted into the inner side of the inner lip 122, thereby bringing the inner surface 128 into close contact with the outer surface 511 of the stem 510 to form an inner seal region 220. The inner diameter of the inner lip 122 is already smaller than the diameter of the stem 510 at room temperature, and the difference becomes larger at low temperatures. Therefore, regardless of low temperatures, the inner surface 128 of the inner lip 122 tightly grips the outer surface 511 of the stem 510, so that the seal pressures PIR and PIL of the inner seal region 220 are maintained sufficiently high.
[Modification]

(1) The shaft seal device 100 is used to seal the gap between the opening 551 of the casing 550 of the valve and the stem 510. However, the shaft seal device according to the embodiment of the present invention may also be used to seal the gap between the opening of the casing of other fluid equipment and the movable shaft. In addition to equipment that mechanically controls the flow of fluid, such as valves, "fluid equipment" includes equipment that changes the pressure of the fluid with power, such as pumps, and equipment that generates power from the pressure of the fluid, such as generators. "Casing" refers to a housing that contains a flow path inside, such as the main body of a pump, and "movable shaft" refers to a rod-shaped member that transmits power by rotating around a central axis or by reciprocating in the central axis direction, such as the drive shaft of a pump. When the destination of the power transmission is located in a flow path inside the casing, such as the impeller or piston of a pump, an opening is essential in the casing to allow the movable shaft to pass through. The shaft seal device according to the embodiment of the present invention can also be used to reduce the amount of fluid leakage from this opening.

(2) The stuffing box 110 is made of metal. However, the present invention is not limited to this. The stuffing box 110 may be made of a material other than metal, such as resin, as long as its thermal shrinkage rate is sufficiently lower than that of the sealing material 120.

(3) The sealing material 120 is a single U-packing. However, the present invention is not limited to this, and the sealing material may be a lip seal with a cross-section of another shape, such as a V-packing. The outer peripheral lip 121 and the convex portion 117 of the stuffing box 110 may have any shape, so long as they are structured so that the former tightens the latter as the temperature drops, bringing their surfaces into close contact with each other and forming a sealing area.

(4) The single seal material 120 may be replaced with a combination of a seal material including only the outer peripheral lip 121 and a seal material including only the inner peripheral lip 122. These seal materials may be configured to adhere to each other by pressure from the packing gland 130.

(5) The outer diameter of the sealing material 120 is narrower than the outer diameter of the packing chamber 114. As a result, when the sealing material 120 is pressed into the packing chamber 114, the outer peripheral surface is not subjected to frictional force from the inner peripheral surface 113 of the stuffing box 110, so the tip surface 123 of the sealing material 120 is not distorted and the entire sealing material can be closely attached to the air-side annular surface 116 of the rib 115 of the stuffing box 110. However, if the distortion of the tip surface 123 due to this frictional force is sufficiently small, the outer diameter of the sealing material 120 may be slightly wider than the outer diameter of the packing chamber 114 at room temperature. As a result, a seal area may also be formed between the outer peripheral surface of the sealing material 120 and the inner peripheral surface 113 of the stuffing box 110.

(6) The inner lip 122 of the seal material 120 is shorter in the axial direction than the outer lip 121. As a result, even if the tip surface 123 of the outer lip 121 hits the air-side annular surface 116 of the rib 115 of the stuffing box 110, the tip surface 124 of the inner lip 122 is axially separated from the annular surface 116. Therefore, the tip portion 129 of the inner surface 128 of the inner lip 122 is not distorted, and the contact area with the outer surface 511 of the stem 510 is sufficiently wide. As a result, the inner seal area 220 has sufficiently high sealing properties. In addition, the inner lip 122 may be the same length as the outer lip 121 or longer in the axial direction. In this case, the air-side annular surface 116 of the rib 115 is located further back in the axial direction (to the right in FIG. 1B) on the inner side than the outer side of the convex portion 117 of the stuffing box 110. Alternatively, the inner diameter of the rib 115 is sufficiently wider than the outer diameter of the inner lip 122. As a result, even when the tip surface 123 of the outer lip 121 abuts against the annular surface 116 on the atmosphere side of the rib 115, the tip surface 124 of the inner lip 122 does not come into contact with the annular surface 116.

(7) As shown in FIG. 4A, the tip 129 of the inner surface 128 of the inner lip 122 of the seal material 120 is a parabolic surface. However, the present invention is not limited to this, and the tip 129 may have another shape that easily adheres to the outer surface 511 of the stem 510. For example, FIG. 4B is a cross-sectional view of a modified example 228 of the inner surface of the inner lip 122. This inner surface 228 has a tip 229 that protrudes inward, a rectangular cross section, and both corners in the axial direction are cut off at an angle. The center of the tip 229 in the axial direction is parallel to the outer surface 511 of the stem 510, and the inner diameter is narrower than the diameter of the stem 510. Therefore, when the stem 510 is press-fitted into the inside of the tip 229 and the tip 229 is pressed against the outer circumferential surface 511 of the stem 510, the central portion in the axial direction of the tip 229 tends to adhere closely to the outer circumferential surface 511 of the stem 510. This improves the sealing performance of the inner seal area formed by the central portion.

(8) The packing gland 130 is fixed to the atmospheric end (left end in FIG. 1A) 112 of the stuffing box 110 by bolts 134 that pass through the flange 133 and nuts 135 that are screwed into the bolts 134. However, this fixing structure is merely one example, and the number and arrangement of the bolts 134 can be changed in various ways. This structure may also be replaced with other well-known structures that can fix the packing gland 130 to the stuffing box 110. For example, a washer may be sandwiched between the flange 133 and the nut 135, and further, a spring may be sandwiched to prevent a decrease in axial force due to loosening of the nut 135.

(9) Another lip seal, adapter ring, spacer ring, or lantern ring may be inserted between the seal material 120 and the packing gland 130. If they are made of a material with a higher thermal shrinkage rate than the material of the stem 510, such as fluororesin, and are configured to form a seal area by tightening the outer peripheral surface 511 of the stem 510 with the inner peripheral surface as the temperature drops, leakage of fluid from the inner peripheral side of the packing chamber can be further suppressed. In addition, they may be connected to the seal material 120 so as to transmit the radial contraction force caused by the temperature drop to the seal material 120, thereby increasing the tightening force applied from the outer peripheral lip 121 to the protrusion 117 of the stuffing box 110.

100 Shaft seal device 110 Stuffing box 111 Fluid side end of stuffing box 112 Atmosphere side end of stuffing box 113 Inner peripheral surface of stuffing box 114 Packing chamber 115 Rib of stuffing box 116 Atmosphere side annular surface of rib 117 Convex portion of stuffing box 118 Outer peripheral surface of convex portion 119 Inner peripheral surface of convex portion 120 Sealing material 121 Outer peripheral lip of sealing material 122 Inner peripheral lip of sealing material 123 Tip surface of outer peripheral lip 124 Tip surface of inner peripheral lip 125 Outer peripheral surface of outer peripheral lip 126 Inner peripheral surface of outer peripheral lip 127 Outer peripheral surface of inner peripheral lip 128 Inner peripheral surface of inner peripheral lip 129 Tip portion of inner peripheral surface of inner peripheral lip 130 Packing gland 131 Fluid side end of packing gland 132 Atmospheric end of packing gland 133 Packing gland flange 134 Bolt 135 Nut 510 Valve stem 511 Outer circumferential surface of stem 540 Flow passage within valve 550 Valve casing 551 Casing opening 560 External space of casing

Claims (3)

a stuffing box that is fitted into an opening of a casing of a fluid device to form a packing chamber around a movable shaft of the fluid device;
an annular seal material packed in the packing chamber and surrounding the movable shaft;
A seal device comprising a packing gland that applies axial pressure to the seal material,
The stuffing box comprises:
a rib that is an annular wall surrounding the movable shaft and that separates a flow path in the casing from the packing chamber;
an annular protrusion protruding from the rib into the packing chamber in the axial direction and surrounding the movable shaft,
The sealing material is
a ring-shaped outer peripheral lip that protrudes axially into the packing chamber, surrounds the protrusion, and has a tip portion that contacts the rib;
The sealing material has a higher thermal shrinkage rate than the stuffing box, and an outer peripheral seal area for sealing a gap between the movable shaft and the rib is
At room temperature, the pressure of the packing gland causes the tip of the outer peripheral lip to be pressed against the rib,
The shaft seal device is configured such that, at low temperatures, the inner peripheral surface of the outer peripheral lip clamps against the outer peripheral surface of the protrusion. The sealing material is
2. The shaft seal device of claim 1, further comprising an inner lip which is an annular lip and is configured to press the movable shaft into its inner side to bring its inner surface into close contact with the outer surface of the movable shaft, thereby forming an inner seal area for sealing the gap between the movable shaft and the rib. The shaft seal device according to claim 2, wherein the inner surface of the inner lip includes a parabolic surface in the inner seal area.

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