Shaft seal device
The shaft sealing device addresses the challenge of thermal contraction in resin materials by using ribs and protrusions to adjust sealing pressures, maintaining effective sealing performance across temperature changes without additional parts, thus preventing fluid leakage.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-12-20
- Publication Date
- 2026-04-14
AI Technical Summary
Resin-based sealing materials used in shaft seal devices experience significant thermal contraction at low temperatures, leading to reduced sealing pressure and increased fluid leakage when handling low-temperature fluids, making it difficult to maintain effective sealing without adding additional parts.
A shaft sealing device with a stuffing box, annular sealing material, and packing retainer, featuring ribs and annular protrusions, where the sealing material's outer and inner lips form sealing regions that adjust to thermal contraction by tightening against the stuffing box and movable shaft, maintaining sealing pressure through differential thermal shrinkage rates.
The device maintains high sealing performance across temperature changes by compensating for reduced sealing pressure with increased tightening forces, ensuring minimal fluid leakage without additional parts, thus addressing the thermal contraction issue of resin materials.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a shaft seal device, and particularly to one used at low temperatures.
Background Art
[0002] A "shaft seal device" is a device that seals the gap between the opening of the casing of a fluid device and a movable shaft, that is, a device that prevents leakage of fluid from the gap or intrusion of foreign matter into the gap. A typical shaft seal device includes a stuffing box, a sealing material, and a packing retainer (see, for example, Patent Documents 1-3). The "stuffing box" is a cylindrical member fitted into the opening of the casing, and surrounds the movable shaft to form an annular space, that is, a packing chamber, between its inner peripheral surface and the outer peripheral surface of the movable shaft. The "sealing material" (also referred to as "packing") is a string-shaped or annular flexible member, and generally a plurality of them are packed into the packing chamber. In the packing chamber, a plurality of sealing materials are arranged adjacent to each other along the movable shaft, in a state where they are wound around the movable shaft if they are string-shaped, or in a state where the movable shaft passes through the inner peripheral side if they are annular. The "packing retainer" (also referred to as "gland retainer") is an annular member that surrounds the movable shaft at one end in the axial direction of the packing chamber, and applies an axial pressure to the sealing material. When the sealing material is compressed in the axial direction by this pressure, it expands in the radial direction and adheres to the inner peripheral surface of the stuffing box and the outer peripheral surface of the movable shaft. As a result, the packing chamber is blocked by the sealing material, so the gap between the opening of the casing and the movable shaft is sealed.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Patent Document 2
Patent Document 3
Summary of the Invention
[0004] Resins are frequently chosen as sealing materials. In particular, fluororesins such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkanes (PFA), and polyvinylidene fluoride (PVDF) are widely used because they have high heat resistance, excellent chemical stability with respect to 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 shrinkage rate (the rate at which volume or length decreases with temperature decrease; equal to the coefficient of thermal expansion) that is about 10 times higher. As a result, the use of resin sealing materials presents the following problems.
[0005] When fluid equipment handles low-temperature fluids (meaning "several tens of degrees below zero" in this specification), such as liquid ammonia (boiling point -33°C), liquefied natural gas (LNG, boiling point around -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 low temperatures. Generally, the sealing material has a higher thermal contraction rate than the movable shaft and stuffing box, so as the temperature drops from room temperature (meaning "several degrees below zero to several tens of degrees below zero" in this specification) to low temperatures (hereinafter referred to as "lowering temperature"), the outer diameter of the sealing material shrinks more than the inner diameter of the packing chamber. As a result, the sealing pressure decreases on the outer circumference of the sealing material. If this decrease is excessive, there is a risk of excessive fluid leakage. However, when fluid equipment handles low-temperature fluids, tightening is difficult, making it challenging to increase the packing retaining pressure to restore the seal pressure, and thus prevent leakage.
[0006] As a technique to prevent a decrease in sealing performance due to low temperatures, for example, the one described in Patent Document 1 is known. In this technique, a resin sealing material (16) is sandwiched axially between two metal rings (18, 20), and radial pressure from two annular springs (22, 24) supported by one of the metal rings (18) presses it against the movable shaft (10) and the stuffing box (6). Since the metal rings (18, 20) shrink less with temperature than the sealing material (16), the metal rings (18, 20) can be configured such that the sealing material (16) between them is maintained in substantially the same shape as at room temperature, regardless of the temperature. As a result, the sealing pressure applied from the sealing material (16) to the movable shaft (10) and the stuffing box (6) is maintained at a constant high level by the pressure of the springs (22, 24). However, since this technology requires metal rings (18, 20) and springs (22, 24), the number of parts in the shaft sealing device is large, the manufacturing process becomes complicated, and miniaturization in the axial direction is difficult.
[0007] The object of the present invention is to solve the above problems, and in particular to provide a shaft sealing device that can maintain sufficiently high sealing performance without adding any parts, regardless of the thermal shrinkage of the sealing material due to low temperatures. [Means for solving the problem]
[0008] A shaft sealing device according to one aspect of the present invention comprises a stuffing box, an annular sealing material, and a packing retainer. The stuffing box is fitted into an opening in the casing of a fluid device, forming a packing chamber around the movable shaft of the fluid device. The sealing material is packed into the packing chamber and surrounds the movable shaft. The packing retainer applies axial pressure to the sealing material.
[0009] The stuffing box includes ribs and annular protrusions. The ribs are annular walls surrounding the movable axis, separating the flow path within the casing from the packing chamber. The protrusions project axially from the ribs into the packing chamber, surrounding the movable axis.
[0010] The sealing material includes an annular outer lip, i.e., an outer portion that protrudes axially. The outer lip protrudes axially into the packing chamber, surrounding the protrusion of the stuffing box, and its tip contacts the rib of the stuffing box. The sealing material has a higher thermal shrinkage rate than the stuffing box, and the outer sealing region for sealing the gap between the movable shaft and the rib is formed (i) at room temperature by pressing the tip of the outer lip against the rib due to the pressure of the packing retainer, and (ii) at low temperatures by tightening the outer surface of the protrusion with the inner surface of the outer lip. [Effects of the Invention]
[0011] The shaft sealing device according to the present invention forms an outer peripheral sealing region for sealing the gap between the movable shaft and the rib of the stuffing box at room temperature by pressing the tip of the outer lip of the sealing material against the rib due to the pressure of the packing retainer. On the other hand, since the thermal shrinkage rate of the sealing material is higher than that of the stuffing box, at low temperatures, the difference in thermal shrinkage rates causes the inner surface of the outer lip to tighten against the outer surface of the protrusion of the stuffing box, thereby forming an outer peripheral sealing region. As the temperature decreases, the force with which the tip of the outer lip presses against the rib weakens, but the force with which the inner surface of the outer lip tightens against the outer surface of the protrusion 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 protrusion of the stuffing box. In this way, this shaft sealing device can maintain a sufficiently high sealing performance without adding any parts, regardless of the thermal shrinkage of the sealing material due to low temperatures.
[0012] In this shaft sealing device, the sealing material may further include an inner lip. The inner lip is an annular lip, i.e., a portion that protrudes in the axial direction, and is configured to form an inner sealing region for sealing the gap between the movable shaft and the rib by pressing the movable shaft into the inner side and bringing the inner surface into close contact with the outer surface of the movable shaft. At room temperature, the inner diameter of the inner lip is already smaller than the diameter of the movable shaft, and at low temperatures, this difference widens further due to the difference in thermal contraction rates between the movable shaft and the sealing material. Therefore, regardless of the temperature, the inner surface of the inner lip tightly grips the outer surface of the movable shaft, so that a sufficiently high sealing pressure is maintained. The inner surface of the inner lip may include a parabolic surface in the inner sealing region. The parabolic surface has a larger radius of curvature at positions away from the apex, i.e., it is closer to flat, so when pressed against the outer surface of the movable shaft, it easily adheres to that outer surface without gaps. Therefore, the sealing performance of the inner sealing region is improved. [Brief explanation of the drawing]
[0013] [Figure 1] (a) is a cross-sectional view of a shaft sealing device according to an embodiment of the present invention, and (b) is a partially enlarged view of the sealing material shown in (a) and its vicinity. [Figure 2] Figure 1 is an exploded view of the shaft seal device. [Figure 3] (a) is a schematic diagram showing the sealing pressure applied by a sealing material at room temperature, and (b) is a schematic diagram showing the sealing pressure applied by a sealing material at low temperature. [Figure 4] (a) is a cross-sectional view of a sealing material according to an embodiment of the present invention, and (b) is a cross-sectional view of a modified example thereof. [Modes for carrying out the invention]
[0014] The shaft sealing 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 the casing. The "stem," also called the "valve rod," is a rod-shaped member that transmits power to the valve body of the valve by rotation around a central axis or by reciprocating motion in the direction of the central axis. The stem is usually made of a metal such as brass, bronze, cast iron, or steel. The "casing," also called the "valve body," is a housing that contains a flow path inside. Since the power transmitted by the stem is located in the flow path inside the casing, an opening for the stem to pass through is essential in the casing. The shaft sealing device according to an embodiment of the present invention suppresses the amount of fluid leakage from this opening.
[0015] 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 valve stem 510 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 within the casing 550 located on the right side, and the external space 560 of the casing 550 extending to the left side, generally open to the outside air. Hereinafter, for any part shown in Figure 1(a), the right side (i.e., the side closer to the flow path 540) 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 "atmospheric side."
[0016] Figure 2 is an exploded view of the shaft sealing device 100. In Figure 2, some of the components have been removed, and a cross-section along the axial direction is shown. As shown in Figure 1(a) and Figure 2, the shaft sealing device 100 includes a stuffing box 110, a sealing material 120, and a packing retainer 130. [Stuffing box]
[0017] The stuffing box 110 (also referred to as the "grand box") is a cylindrical member made of a 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 (the right end in FIGS. 1(a) and 2) 111 of the stuffing box 110 faces the flow path 540 inside the casing 550, and the atmosphere-side end (the left end in FIGS. 1(a) and 2) 112 protrudes outside the casing 550. The inner peripheral surface 113 of the stuffing box 110 forms a cylindrical packing chamber 114 between it and the outer peripheral surface 511 of the stem 510. From the fluid-side end 111 of the stuffing box 110, an annular wall portion, that is, a rib 115 protrudes toward the outer peripheral surface 511 of the stem 510 to partition between the flow path 540 and the packing chamber 114.
[0018] From the annular surface 116 on the atmosphere side (the left side in FIGS. 1(a) and 2) of the rib 115, an annular convex portion 117 protrudes into the packing chamber 114 in the axial direction (the left direction in FIGS. 1(a) and 2) to surround the stem 510. The convex portion 117 has, for example, a rectangular cross-section that is elongated in the axial direction, 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]
[0019] FIG. 1(b) is a partial enlarged view of the sealing material 120 shown in FIG. 1(a) and the vicinity thereof (the region surrounded by the broken line shown in FIG. 1(a)). FIG. 4(a) 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 the material is formed into an annular shape by a mold, that is, a type of molded packing, and a cross-section by a plane including the central axis of the annulus includes an axially protruding portion (referred to as the "lip"). The sealing material 120 is packed coaxially with the stem 510 into the packing chamber 114 to surround the stem 510. Preferably, at normal temperature, 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. Thereby, the sealing material 120 presses the stem 510 into the inner peripheral side to make the inner peripheral surface adhere to the outer peripheral surface 511 of the stem 510.
[0020] Preferably, the sealing material 120 is a U-packing. That is, the cross-section including the central axis of the annular shape is a U-shape with one side in the axial direction (the right side in FIGS. 1(b) and 4(b)) being the upper side. The two arm portions 121 and 122 of this U-shape, that is, the two concentric annular portions projecting in the axial direction (the right direction in FIGS. 1(b) and 4(a)), are lips. Due to the flexibility of their material, the lips 121 and 122 can be bent so as to increase or decrease the opening of the U-shape, that is, the radial (vertical direction in FIGS. 1(b) and 4(a)) interval between the tip surfaces 123 and 124.
[0021] The outer peripheral lip 121 (hereinafter referred to as the "outer peripheral lip") on the outer peripheral side (the upper side in FIGS. 1(b) and 4(a)) has an outer diameter narrower than the outer diameter of the packing chamber 114 and an inner diameter slightly wider than the outer diameter of the convex portion 117 of the stuffing box 110 at normal temperature, and is longer than the convex portion 117 in the axial direction (the left-right direction in FIGS. 1(b) and 4(a)). Therefore, the outer peripheral lip 121 is pushed into the gap between the inner peripheral surface 113 of the stuffing box 110 and the outer peripheral surface 118 of the convex portion 117 until the tip surface 123 abuts against the annular surface 116 on the atmosphere side (the left side in FIGS. 1(b) and 4(a)) of the rib 115, with the outer peripheral surface 125 facing the inner peripheral surface 113 of the stuffing box 110 and the inner peripheral surface 126 facing the outer peripheral surface 118 of the convex portion 117.
[0022] The inner lip 122 (hereinafter referred to as the "inner lip") on the inner circumference side (lower side in Figure 1(b) and Figure 4(a)) has an outer diameter narrower than the inner diameter of the protrusion 117 of the stuffing box 110, an inner diameter narrower than the diameter of the stem 510, and is shorter than the outer lip 121 in the axial direction (left-right direction in Figure 1(b) and Figure 4(a)) at room temperature. Therefore, when the tip surface 123 of the outer lip 121 abuts against the annular surface 116 on the atmospheric side (left side in Figure 1(b) and Figure 4(a)) of the rib 115, the inner lip 122 faces its outer surface 127 against the inner surface 119 of the protrusion 117, while its inner surface 128 comes into close contact with the outer surface 511 of the stem 510. The tip surface 124 of the inner lip 122 is axially separated (to the left in Figure 1(b) and Figure 4(a)) from the atmospheric-side annular surface 116 of the rib 115.
[0023] Preferably, before the sealing material 120 is packed into the packing chamber 114, the tip 129 of the inner surface 128 of the inner lip 122 protrudes in the circumferential direction (downward in Figure 4(a)). The tip 129 is preferably a parabolic surface. More precisely, as shown in Figure 4(a), the lower contour of the cross section including the annular central axis is a parabola with its apex at the point PK (lowest point in Figure 4(a)) where the inner diameter is narrowest. As a result, the radius of curvature of the contour is larger the further it is from the apex PK (the further to the left and right from the apex PK in Figure 4(a)), i.e., it is closer to flat. At room temperature, the inner diameter of the inner lip 122 is slightly narrower than the diameter of the stem 510 in the central part in the axial direction of the tip 129 of the inner surface 128 (left and right direction in Figure 1(b) and Figure 4(a)), while being wider than its outer diameter elsewhere. Therefore, when the stem 510 is press-fitted into the inner circumference of the tip portion 129, the central portion in the axial direction is flattened and compressed, as shown in Figure 1(b), and it comes into close contact with the outer circumferential surface 511 of the stem 510. [Packing retainer]
[0024] At the inner circumference of the atmospheric end (left end in Figure 1(a)) 112 of the stuffing box 110, a packing retainer 130 closes the atmospheric-side opening (left side in Figure 1(a)) of the packing chamber 114 at its fluid-side end (right end in Figure 1(a)) 131. The fluid-side end 131 further contacts the atmospheric-side (left side in Figure 1(a)) annular surface 201 of the sealing material 120. The packing retainer 130 is an annular member made of metal such as brass, bronze, cast iron, or steel, and coaxially surrounds the stem 510. An annular flange 133 protrudes outward from the atmospheric-side end (left end in Figure 1(a), Figure 2) 132 of the packing retainer 130. Although not shown in Figure 2, multiple bolts 134 pass through the flange 133 parallel to the stem 510 (in the left-right direction in Figure 1(a)) and are screwed into the atmospheric end 112 of the stuffing box 110. Furthermore, nuts 135 are screwed onto the bolts 134, and the resulting axial force of the bolts 134 presses down on the flange 133. In this way, the flange 133 is fixed to the atmospheric end 112 of the stuffing box 110. In addition, the axial force of the bolts 134 causes the fluid-side end 131 of the packing retainer 130 to press down on the atmospheric-side annular surface 201 of the sealing material 120 in the axial direction (to the right in Figure 1(a)). [Sealing action of shaft seal devices at room temperature]
[0025] Figure 3(a) is a schematic diagram showing the sealing pressures POR and PIR applied by the sealing material 120 at room temperature, with arrows indicating the sealing pressures POR and PIR added to the cross-sectional view shown in Figure 1(b). When the nut 135 presses against the flange 133 of the packing retainer 130 due to the axial force of the bolt 134, the fluid-side end (left end in Figure 3(a)) 131 of the packing retainer 130 applies an axial pressure PP (to the right in Figure 3(a)) to the air-side (left side in Figure 3(a)) annular surface 201 of the sealing material 120. As a result, in the gap between the inner circumferential surface 113 of the stuffing box 110 and the outer circumferential surface 118 of the protrusion 117, the tip surface 123 of the outer lip 121 of the sealing material 120 is pressed against the air-side (left side in Figure 3(a)) annular surface 116 of the rib 115, creating a tight seal. As a result, a sealing region (hereinafter referred to as the "first outer sealing region") 211 is formed between the tip surface 123 of the outer lip 121 and the atmospheric-side annular surface 116 of the rib 115. The sealing pressure POR that the tip surface 123 of the outer lip 121 applies to the atmospheric-side annular surface 116 of the rib 115 in the first outer sealing region 211 is due to the axial pressure PP from the packing retainer 130 (to the right in Figure 3(a)).
[0026] Furthermore, the tip portion 129 of the inner surface 128 of the inner lip 122 tightens and adheres to the outer surface 511 of the stem 510 which is press-fitted to the inner side, so that a seal region (hereinafter referred to as the "inner seal region") 220 is formed between the tip portion 129 and the outer surface 511 of the stem 510. As shown in Figure 3(a), the seal pressure PIR that the tip portion 129 applies to the outer surface 511 of the stem 510 in the inner seal region 220 is due to the restoring force of the inner lip 122 in the inward direction (downward in Figure 3(a)).
[0027] When the fluid in the flow path 540 within the casing 550 fills up, fluid also seeps into the gap between the rib 115 and the stem 510 from the flow path 540. However, only a very small amount of fluid can seep into the first outer peripheral seal area 211 and the inner peripheral seal area 220, thus suppressing fluid leakage from the packing chamber 114 to the atmosphere. In particular, in the inner peripheral seal area 220, the fluid pressure further presses the inner peripheral lip 122 against the outer peripheral surface 511 of the stem 510, increasing the seal pressure PIR even more, resulting in an even higher sealing performance. In this way, the gap between the rib 115 and the stem 510 is sealed. [Sealing action of shaft seal devices at low temperatures]
[0028] When a low-temperature fluid such as LNG, liquid nitrogen, or liquid hydrogen flows through the channel 540 inside the casing 550, the temperature drops not only to the stem 510 but also to the shaft seal device 100. Since the seal material 120 has a higher thermal shrinkage rate than the stem 510, stuffing box 110, and packing retainer 130, it shrinks significantly due to the temperature drop. Therefore, the temperature drop causes a large change in the dimensional difference between the packing chamber 114 and the seal material 120 compared to the value at room temperature. However, the shaft seal device 100 suppresses the decrease in sealing performance due to the temperature drop through the sealing action described below.
[0029] Figure 3(b) is a schematic diagram showing the sealing pressures POL, POS, and PIL applied by the low-temperature sealing material 120, with arrows indicating the sealing pressures POL, POS, and PIL added to the cross-sectional view shown in Figure 1(b). -Peripheral sealing area-
[0030] Due to the thermal contraction associated with low temperature, the outer peripheral lip 121 of the sealing material 120 shortens in the axial direction. As a result, the sealing pressure POL applied from the tip surface 123 of the outer peripheral lip 121 to the annular surface 116 on the atmosphere side (left side in (b) of FIG. 3) of the rib 115 is lower than the value POR at normal temperature at low temperature (POL < POR), so the sealing performance of the first outer peripheral side sealing region 211 deteriorates. However, while the stuffing box 110 is made of metal, the sealing material 120 is made of fluororesin, so the thermal shrinkage rate is about 10 times higher. Therefore, the amount of shortening of the inner diameter of the outer peripheral lip 121 associated with low temperature is larger than the amount of shortening of the outer diameter of the convex portion 117 of the stuffing box 110. As a result, the inner peripheral surface 126 of the outer peripheral lip 121 clamps and adheres to the outer peripheral surface 118 of the convex portion 117, so a second outer peripheral side sealing region 212 is formed between the inner peripheral surface 126 of the outer peripheral lip 121 and the outer peripheral surface 118 of the convex portion 117. As the temperature decreases, the clamping force of the outer peripheral surface 118 of the convex portion 117 by the inner peripheral surface 126 of the outer peripheral lip becomes stronger, so the sealing pressure POS of the second outer peripheral side sealing region 212 increases. Thus, the deterioration of the sealing performance of the first outer peripheral side sealing region 211 associated with low temperature is compensated by the formation of the second outer peripheral side sealing region 212. -Inner peripheral side sealing region-
[0031] While the stem 510 is made of metal, the sealing material 120 is made of fluororesin, so the thermal shrinkage rate is about 10 times higher. Therefore, the amount of shortening of the inner diameter of the inner peripheral lip 122 of the sealing material 120 associated with low temperature is larger than the amount of shortening of the diameter of the stem 510. As a result, the inner peripheral surface 128 of the inner peripheral lip 122 clamps the outer peripheral surface 511 of the stem 510 more strongly, so the sealing pressure PIL of the inner peripheral side sealing region 220 exceeds the value PIR at normal temperature (PIL > PIR). Thereby, the sealing performance of the inner peripheral side sealing region 220 is further improved. [Advantages of the embodiment]
[0032] In the shaft sealing device 100 according to the above embodiment of the present invention, at room temperature, the pressure PP of the packing retainer 130 presses the tip surface 123 of the outer lip 121 of the sealing material 120 against the air-side annular surface 116 of the rib 115 of the stuffing box 110, thereby forming a first outer peripheral sealing region 211. On the other hand, at low temperatures, the difference in thermal shrinkage rates between the sealing material 120 and the stuffing box 110 causes the inner surface 126 of the outer lip 121 to tighten against the outer peripheral surface 118 of the convex portion 117 of the stuffing box 110, thereby forming a second outer peripheral sealing region 212. As the temperature decreases, the force with which the tip surface 123 of the outer lip 121 presses against the air-side annular surface 116 of the rib 115 weakens, meaning that the sealing pressure POL of the first outer peripheral sealing region 211 decreases. However, the force with which the inner surface 126 of the outer lip 121 tightens against the outer surface 118 of the protrusion 117 increases, meaning that the sealing pressure POS in the second outer seal region 212 rises. As a result, the decrease in sealing pressure POL in the first outer seal region 211 due to the decrease in temperature is compensated for by the increase in sealing pressure POS in the second outer seal region 212. In this way, the shaft seal device 100 can maintain a sufficiently high sealing performance without adding any parts, regardless of the thermal contraction of the sealing material 120 due to the decrease in temperature.
[0033] In the shaft sealing device 100, the sealing material 120 includes an inner lip 122. When the stem 510 is press-fitted to the inner side of the inner lip 122, the inner surface 128 of the inner lip 122 is brought into close contact with the outer surface 511 of the stem 510, forming an inner sealing region 220. At room temperature, the inner diameter of the inner lip 122 is already smaller than the diameter of the stem 510, and this difference widens further at low temperatures. Therefore, regardless of the temperature, the inner surface 128 of the inner lip 122 tightly grips the outer surface 511 of the stem 510, so that the sealing pressures PIR and PIL of the inner sealing region 220 are maintained at a sufficiently high level. [Differentiation]
[0034] (1) The shaft seal device 100 is used to seal the gap between the opening 551 of the valve casing 550 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. Fluid equipment includes not only devices that mechanically control the flow of fluid, such as valves, but also devices that change the pressure of fluid by power, such as pumps, and devices that generate power from the pressure of fluid, such as generators. Casing means a housing that contains a flow path inside, such as the body of a pump, and movable shaft means a rod-shaped member that transmits power by rotation around a central axis or reciprocating motion in the direction of the central axis, such as the drive shaft of a pump. When the destination of power transmission is located in a flow path inside the casing, such as the impeller or piston of a pump, an opening for the movable shaft to pass through is essential in the casing. The shaft seal device according to the embodiment of the present invention can also be used to suppress the amount of fluid leakage from this opening.
[0035] (2) The stuffing box 110 is made of metal. However, the present invention is not limited to this, and even if the stuffing box 110 is made of a material other than metal, such as resin, it is sufficient as long as its thermal shrinkage rate is sufficiently lower than that of the sealing material 120.
[0036] (3) The sealing material 120 is a single U-packing. However, the present invention is not limited thereto, and the sealing material may be a lip seal with a cross-sectional shape other than that, such as a V-packing. The outer lip 121 and the protrusion 117 of the stuffing box 110 may have any shape as long as the former tightens against the latter as the temperature decreases, causing their surfaces to come into close contact and forming a sealing area.
[0037] (4) The single seal material 120 may be replaced with a combination of a seal material including only the outer lip 121 and a seal material including only the inner lip 122. These seal materials should be configured to be tightly bound to each other by pressure from the packing retainer 130.
[0038] (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 pushed into the packing chamber 114, its outer surface does not receive frictional force from the inner surface 113 of the stuffing box 110, so that the tip surface 123 of the sealing material 120 does not distort, and the entire sealing material can be brought into close contact with 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. This may further form a sealing area between the outer surface of the sealing material 120 and the inner surface 113 of the stuffing box 110.
[0039] (6) The inner lip 122 of the sealing 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 abuts against 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 does not become distorted, and a sufficiently large contact area with the outer surface 511 of the stem 510 is secured. As a result, the inner sealing region 220 has sufficiently high sealing performance. Alternatively, the inner lip 122 may be the same length as or longer than the outer lip 121 in the axial direction. In this case, the air-side annular surface 116 of the rib 115 is located further in the axial direction (to the right in Figure 1(b)) on the inner side of the convex portion 117 of the stuffing box 110 than on the outer side. Alternatively, the inner diameter of the rib 115 is sufficiently wider than the outer diameter of the inner lip 122. This ensures that even when the tip surface 123 of the outer lip 121 abuts against the air-facing annular surface 116 of the rib 115, the tip surface 124 of the inner lip 122 does not come into contact with that annular surface 116.
[0040] (7) As shown in Figure 4(a), the tip portion 129 of the inner surface 128 of the inner lip 122 of the sealing material 120 is parabolic. However, the present invention is not limited to this, and the tip portion 129 may have other shapes that make it easier to adhere to the outer surface 511 of the stem 510. For example, Figure 4(b) is a cross-sectional view of a modified example 228 of the inner surface of the inner lip 122. In this inner surface 228, the tip portion 229 protrudes in the circumferential direction, and its cross-section is rectangular with the corners at both ends in the axial direction beveled. The central part of the tip portion 229 in the axial direction is parallel to the outer surface 511 of the stem 510, and its 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 portion 229 and the tip portion 229 is pressed against the outer circumferential surface 511 of the stem 510, the central portion of the tip portion 229 in the axial direction is more likely to come into close contact with the outer circumferential surface 511 of the stem 510. Consequently, the sealing performance of the inner circumferential sealing region formed by the central portion is improved.
[0041] (8) The packing retainer 130 is fixed to the atmospheric end (left end in Figure 1(a)) 112 of the stuffing box 110 by bolts 134 that pass through its flange 133 and nuts 135 that are screwed onto them. However, this fixing structure is merely an example, and the number and arrangement of bolts 134 can be varied in many ways. Furthermore, this structure may be replaced with other well-known structures that can fix the packing retainer 130 to the stuffing box 110. For example, a washer may be placed between the flange 133 and the nut 135, and a spring may be placed to prevent a decrease in axial force due to loosening of the nut 135.
[0042] (9) Other lip seals, adapter rings, spacer rings, or lantern rings may be inserted between the seal material 120 and the packing retainer 130. If these 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 tighten against the outer surface 511 of the stem 510 with their inner circumferential surface as the temperature decreases, thereby forming a sealing area, then leakage of fluid from the inner side of the packing chamber can be further suppressed. In addition, if these are connected to the seal material 120 so as to transmit the radial shrinkage force due to the temperature decrease to the seal material 120, the tightening force applied from the outer lip 121 to the protrusion 117 of the stuffing box 110 may be increased. [Explanation of Symbols]
[0043] 100 Shaft sealing device 110 Stuffing Box 111 Fluid-side end of stuffing box 112 Atmospheric end of stuffing box 113 Inner surface of stuffing box 114 Packing chamber 115 Ribs for Stuffing Box 116 Circular surface of the rib on the atmospheric side 117. Protruding part of the stuffing box 118 Outer circumferential surface of the protrusion 119 Inner circumferential surface of the protrusion 120 sealant 121 Outer lip of sealing material 122 Inner lip of sealing material 123 Outer lip tip surface 124 Tip surface of the inner lip 125 Outer surface of the outer lip 126 Inner surface of the outer lip 127 Outer surface of the inner lip 128 Inner surface of inner lip 129 Tip of the inner surface of the inner lip 130 Packing retainer 131 The fluid-side end of the packing retainer 132 The atmospheric end of the packing retainer 133 Packing retaining flange 134 volts 135 Nut 510 valve stem 511 Outer surface of the stem 540 Flow path inside valve 550 valve casing 551 Casing opening 560 Casing exterior space
Claims
1. A stuffing box that is fitted into the opening of the casing of a fluid device and forms a packing chamber around the movable shaft of the fluid device, An annular sealing material packed into the packing chamber and surrounding the movable shaft, A packing retainer that applies axial pressure to the sealing material A shaft sealing device equipped with, The stuffing box mentioned above, The annular wall surrounding the movable shaft, the rib that separates the flow path inside the casing from the packing chamber, An annular protrusion that protrudes axially from the rib into the packing chamber and surrounds the movable shaft Includes, The aforementioned sealing material An annular outer lip that protrudes axially into the packing chamber, surrounding the protrusion, and whose tip contacts the rib. Includes, The sealing material has a higher thermal shrinkage rate than the stuffing box, and the outer peripheral sealing region for sealing the gap between the movable shaft and the rib is At room temperature, the tip of the outer lip is pressed against the rib by the pressure of the packing retainer to form the seal. At low temperatures, the outer surface of the protrusion is formed by tightening it against the inner surface of the outer lip. A shaft seal device configured in such a way.
2. The aforementioned sealing material An annular lip, configured such that the movable shaft is press-fitted into its inner circumference, causing the inner surface to adhere closely to the outer surface of the movable shaft, thereby forming an inner sealing region for sealing the gap between the movable shaft and the rib. The shaft sealing device according to claim 1, further comprising:
3. The shaft sealing device according to claim 2, wherein the inner surface of the inner lip includes a parabolic surface in the inner sealing region.
Citation Information
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