Seal ring and reciprocating pump

Abstract

A seal ring (22) is provided with a first seal ring (31) having a first abutment gap (35), and a second seal ring (32) having a second abutment gap (36). The first seal ring (31) and the second seal ring (32) are in contact with each other, the first seal ring (31) and the second seal ring (32) have portions having different thicknesses, a thinnest portion (41) of the first seal ring (31) contacts a thickest portion (46) of the second seal ring (32), a thickest portion (42) of the first seal ring (31) contacts a thinnest portion (45) of the second seal ring (32), and the first abutment gap (35) and the second abutment gap (36) are located at different positions in the circumferential direction of the first seal ring (31) and the second seal ring (32).

Description

Seal rings and reciprocating pumps

[0001] The present invention relates to a reciprocating pump such as a plunger pump or a piston pump, and more particularly to a reciprocating pump suitable for transporting liquefied gas.

[0002] A reciprocating pump is configured to draw fluid into the cylinder by reciprocating a piston disposed in the cylinder, and then pressurize the fluid and expel it from the cylinder. Such reciprocating pumps are sometimes used to transport liquefied gases such as liquefied hydrogen, liquefied natural gas, liquefied ammonia, liquefied nitrogen, liquefied ethylene gas, and liquefied petroleum gas.

[0003] Fig. 9 is a schematic diagram showing a cross section of a conventional reciprocating pump. As shown in Fig. 9, the reciprocating pump has a cylinder 500 and a piston 501 movably disposed within the cylinder 500. The piston 501 is connected to an actuator (not shown). A seal 503 is disposed between the inner surface of the cylinder 500 and the outer surface of the piston 501. Check valves 514 and 515 are connected to a suction port 510 and a discharge port 511 of the cylinder 500, respectively.

[0004] As the actuator reciprocates the piston 501 axially, fluid flows into the cylinder 500 through the check valve 514 and the suction port 510, is pressurized by the piston 501, and is expelled from the cylinder 500 through the discharge port 511 and the check valve 515.

[0005] In order to fit the seal 503 into a seal groove formed on the outer peripheral surface of the piston 501, the seal 503 has a ring shape with a gap 520 as shown in Fig. 10. Although the gap 520 is very small, some of the fluid pressurized by the piston 501 leaks through the gap 520 of the seal 503. Therefore, in the example shown in Fig. 9, the multiple gaps 520 of the multiple seals 503 are arranged so that they are at different positions in the circumferential direction.

[0006] JP 2023-177499 A

[0007] However, as the seals 503 reciprocate, they rotate little by little about their axes, which can cause the circumferential positions of the gaps 520 to approach each other. As a result, some of the pressurized fluid is likely to leak out of the cylinder 500 through the gaps 520 of the seals 503. To prevent the seals 503 from rotating, it is possible to provide a notch in part of the seal 503 and engage a positioning member such as a pin with the notch. However, providing a notch in part of the seal 503 could cause the seal 503 to crack.

[0008] Therefore, the present invention provides a technique that can prevent rotation of a seal held by a piston and prevent leakage of fluid through a gap between the seal joints.

[0009] In one aspect, there is provided a seal ring to be disposed in a seal groove of a piston of a reciprocating pump for transporting a fluid, the seal ring comprising a first seal ring having a first gap and a second seal ring having a second gap, the first seal ring and the second seal ring being in contact with each other, the first seal ring having portions with different thicknesses, the second seal ring having portions with different thicknesses, the thinnest portion of the first seal ring being in contact with the thickest portion of the second seal ring, the thickest portion of the first seal ring being in contact with the thinnest portion of the second seal ring, and the first gap and the second gap being at different positions in the circumferential direction of the first seal ring and the second seal ring.

[0010] In one aspect, the first gap is located at the thinnest portion of the first seal ring, and the second gap is located at the thinnest portion of the second seal ring. In one aspect, the first seal ring has a first inner circumferential surface, a first outer circumferential surface, and a first end face and a first inclined end face extending from the first inner circumferential surface to the first outer circumferential surface, and the second seal ring has a second inner circumferential surface, a second outer circumferential surface, and a second end face and a second inclined end face extending from the second inner circumferential surface to the second outer circumferential surface, wherein the first inclined end face is inclined with respect to the first end face, the second inclined end face is inclined with respect to the second end face, and the first inclined end face is in contact with the second inclined end face. In one aspect, the first gap and the second gap are located symmetrically with respect to the centers of the first seal ring and the second seal ring. In one embodiment, the sum of the thickness of the thickest portion of the first seal ring and the thickness of the thickest portion of the second seal ring is greater than the width of the seal groove.

[0011] In one aspect, there is provided a reciprocating pump for transporting a fluid, comprising: a cylinder having a pressurizing chamber therein; a piston disposed in the cylinder; a suction check valve and a discharge check valve communicating with the pressurizing chamber; and the seal ring disposed in a seal groove formed on the outer peripheral surface of the piston.

[0012] The thinnest portion of the first seal ring contacts the thickest portion of the second seal ring, and the thickest portion of the first seal ring contacts the thinnest portion of the second seal ring. With this configuration, when the first seal ring and the second seal ring attempt to rotate relative to each other, the first seal ring and the second seal ring attempt to move away from each other in the axial direction. Because the first seal ring and the second seal ring are disposed in the seal groove of the piston, the seal groove prevents the first seal ring and the second seal ring from moving away from each other. As a result, the first seal ring and the second seal ring are prevented from rotating relative to each other.

[0013] FIG. 5 is a schematic diagram showing an embodiment of a fluid transfer system including a reciprocating pump. FIG. 6 is a cross-sectional view showing an embodiment of a reciprocating pump. FIG. 7 is a diagram illustrating the operation of a piston when pressurizing liquefied gas in a pressurizing chamber. FIG. 8 is a side view showing an embodiment of a part of a piston and a seal ring. FIG. 5A is a plan view of a first seal ring. FIG. 5B is a cross-sectional view taken along line A-A in FIG. 5A. FIG. 6A is a plan view of a second seal ring. FIG. 6B is a cross-sectional view taken along line B-B in FIG. 6A. FIG. 8 is a cross-sectional view of a first seal ring and a second seal ring constituting a seal ring. FIG. 9 is a diagram showing how high-pressure liquefied gas pressurized by a piston is applied to a seal ring. FIG. 10 is a schematic diagram showing a cross-section of a conventional reciprocating pump. FIG. 11 is a diagram showing an example of a seal.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. A reciprocating pump is a positive displacement pump for pressurizing and transferring a fluid. In particular, the reciprocating pump of the embodiments described below is suitable for transferring liquefied gases such as liquefied hydrogen, liquefied natural gas, liquefied ammonia, liquid nitrogen, liquefied ethylene gas, and liquefied petroleum gas. In the embodiments described below, liquefied gases are used as the fluid.

[0015] Fig. 1 is a schematic diagram showing one embodiment of a fluid transfer system equipped with a reciprocating pump. As shown in Fig. 1, the fluid transfer system includes a storage tank 1 for storing liquefied gas as a fluid, a reciprocating pump 2 disposed in the storage tank 1, and an actuator 5 for driving the reciprocating pump 2. The liquefied gas is sent into the storage tank 1 through a fluid inlet port 7 of the storage tank 1 and is stored in the storage tank 1.

[0016] Although the liquefied gas in the storage tank 1 is in a liquid state, a small amount of heat from the surrounding atmosphere is transferred to the liquefied gas through the wall of the storage tank 1. As a result, a portion of the liquefied gas is gasified to form boil-off gas (BOG). Therefore, the storage tank 1 is provided with a boil-off gas discharge port 8 for discharging the boil-off gas. The boil-off gas in the storage tank 1 is discharged from the storage tank 1 through the boil-off gas discharge port 8.

[0017] The piston rod 10 of the reciprocating pump 2 is connected to the actuator 5 via a coupling device 12. The actuator 5 is fixed to the storage tank 1 via a bracket 9. Examples of the actuator 5 include a hydraulic cylinder, a linear motor, and a combination of a crank mechanism and an electric motor. The liquefied gas suction port of the reciprocating pump 2 is located lower than the liquid level in the storage tank 1, although this is not shown in FIG. 1 . When the actuator 5 drives the reciprocating pump 2, the reciprocating pump 2 sucks in the liquefied gas in the storage tank 1, pressurizes it, and discharges it into a liquefied gas discharge line 13. The pressurized liquefied gas is transferred to the outside of the storage tank 1 through the liquefied gas discharge line 13.

[0018] FIG. 2 is a cross-sectional view showing one embodiment of a reciprocating pump 2. The reciprocating pump 2 of this embodiment is a positive displacement pump for transferring liquefied gas. As shown in FIG. 2, the reciprocating pump 2 includes a cylinder 16 having a pressure chamber 14 therein, a piston 18 disposed in the cylinder 16, and a plurality of seal rings 22 disposed in a gap between an inner surface 16a of the cylinder 16 and an outer surface of the piston 18. The piston 18 is connected to a piston rod 10, which is connected to the actuator 5 shown in FIG. 1. The piston 18 is driven by the actuator 5 to reciprocate within the cylinder 16. In one embodiment, the piston 18 may be configured integrally with the piston rod 10.

[0019] The multiple seal rings 22 are arranged along the axial direction of the piston 18. In this specification, "axial direction" refers to the direction of the central axis of the piston 18 or the direction of movement of the piston 18. The number of the multiple seal rings 22 is not limited to that in the embodiment shown in FIG. 2. The multiple seal rings 22 are held by the piston 18 and move back and forth together with the piston 18. Therefore, the multiple seal rings 22 are movable seals. The multiple seal rings 22 are made of resin that has a certain degree of elasticity at extremely low temperatures at which liquefied gas can maintain a liquid state. The piston 18 and the cylinder 16 are made of metal.

[0020] The pressurizing chamber 14 is defined by an end surface 18a of the piston 18 and an inner surface 16a of the cylinder 16. The reciprocating pump 2 has a suction check valve 26 and a discharge check valve 27 that communicate with the pressurizing chamber 14. In this embodiment, the suction check valve 26 is provided at the bottom of the cylinder 16, and the discharge check valve 27 is provided at the side wall of the cylinder 16. However, as long as the suction check valve 26 and the discharge check valve 27 communicate with the pressurizing chamber 14, the locations of the suction check valve 26 and the discharge check valve 27 are not particularly limited. For example, the suction check valve 26 may be provided at the side wall of the cylinder 16, and the discharge check valve 27 may be provided at the bottom of the cylinder 16.

[0021] The suction check valve 26 is configured to allow the liquefied gas in the storage tank 1 to flow into the pressurized chamber 14 in the cylinder 16, but not allow the liquefied gas to flow in the reverse direction. The discharge check valve 27 is configured to allow the liquefied gas to flow out of the pressurized chamber 14, but not allow the liquefied gas to flow in the reverse direction. The outlet of the discharge check valve 27 is connected to the liquefied gas discharge line 13. In Figure 2, the suction check valve 26 and the discharge check valve 27 are illustrated schematically. There are no particular limitations on the specific configurations of the suction check valve 26 and the discharge check valve 27, as long as they have the intended functions described above.

[0022] Next, the operation of the reciprocating pump 2 will be described. As shown by the white arrows in Figure 2, when the piston 18 moves away from the suction check valve 26 and the discharge check valve 27 (towards top dead center), the liquefied gas flows into the pressurization chamber 14 through the suction check valve 26. At this time, the discharge check valve 27 is closed. Next, as shown by the white arrows in Figure 3, when the piston 18 moves toward the suction check valve 26 and the discharge check valve 27 (towards bottom dead center), the liquefied gas is pressurized in the pressurization chamber 14 and is discharged from the pressurization chamber 14 through the discharge check valve 27. At this time, the suction check valve 26 is closed. Due to this reciprocating movement of the piston 18, the liquefied gas is pressurized and transported.

[0023] Next, the seal ring 22 will be described in detail. The multiple seal rings 22 have the same configuration. FIG. 4 is a side view showing a portion of the piston 18 and one embodiment of the seal ring 22. The seal ring 22 is disposed in a seal groove 30 formed in the outer peripheral surface 18a of the piston 18. The seal ring 22 has a first seal ring 31 and a second seal ring 32 that contact each other. When viewed from the side, the first seal ring 31 and the second seal ring 32 have symmetrical tapered shapes. The thickness W1 of the seal ring 22, which includes the overlapping first seal ring 31 and second seal ring 32, is smaller than the width W2 of the seal groove 30.

[0024] Fig. 5A is a plan view of the first seal ring 31, and Fig. 5B is a cross-sectional view taken along line A-A in Fig. 5A. The first seal ring 31 has a gap 35. The first seal ring 31 has an inner circumferential surface 31a, an outer circumferential surface 31b, and a first end face 31c and a first inclined end face 31d extending from the inner circumferential surface 31a to the outer circumferential surface 31b. The first end face 31c is an annular flat surface perpendicular to the central axis CL1 of the first seal ring 31. The first inclined end face 31d is an annular flat surface on the opposite side to the first end face 31c. The first inclined end face 31d is inclined with respect to the first end face 31c.

[0025] 5B , the first seal ring 31 has a tapered shape when viewed from the side (when viewed perpendicular to the central axis CL1). Therefore, the first seal ring 31 has portions with different thicknesses. The abutment gap 35 is located at the thinnest portion 41 of the first seal ring 31. The thickness of the first seal ring 31 gradually increases with the distance from the abutment gap 35. The thickest portion 42 of the first seal ring 31 is located on the opposite side of the abutment gap 35 beyond the central axis CL1 of the first seal ring 31.

[0026] Figure 6A is a plan view of the second seal ring 32, and Figure 6B is a cross-sectional view taken along line B-B in Figure 6A. The second seal ring 32 has a gap 36. The second seal ring 32 has an inner circumferential surface 32a, an outer circumferential surface 32b, and a second end surface 32c and a second inclined end surface 32d extending from the inner circumferential surface 32a to the outer circumferential surface 32b. The second end surface 32c is an annular flat surface perpendicular to the central axis CL2 of the second seal ring 32. The second inclined end surface 32d is an annular flat surface on the opposite side to the second end surface 32c. The second inclined end surface 32d is inclined with respect to the second end surface 32c.

[0027] As can be seen in Figure 6B, the second seal ring 32 has a tapered shape when viewed from the side (when viewed perpendicular to the central axis CL2). Therefore, the second seal ring 32 has portions of different thicknesses. The abutment gap 36 is located at the thinnest portion 45 of the second seal ring 32. The thickness of the second seal ring 32 gradually increases with the distance from the abutment gap 36. The thickest portion 46 of the second seal ring 32 is located on the opposite side of the abutment gap 36 beyond the central axis CL2 of the second seal ring 32.

[0028] FIG. 7 is a cross-sectional view of the first seal ring 31 and the second seal ring 32 that constitute the seal ring 22. As shown in FIG. 7, the first seal ring 31 and the second seal ring 32 overlap each other. More specifically, the first inclined end face 31d of the first seal ring 31 and the second inclined end face 32d of the second seal ring 32 are in contact with each other. The first seal ring 31 and the second seal ring 32 have the same shape and size. In one embodiment, the first seal ring 31 and the second seal ring 32 may have different thicknesses. The angle of the first inclined end face 31d relative to the first end face 31c is the same as the angle of the second inclined end face 32d relative to the second end face 32c. The second seal ring 32 is placed on top of the first seal ring 31 in an inverted state.

[0029] The abutment gap 35 and the abutment gap 36 are located at different positions in the circumferential direction of the first seal ring 31 and the second seal ring 32. In the present embodiment, the abutment gap 35 and the abutment gap 36 are located symmetrically with respect to the center CP of the seal ring 22. That is, the abutment gap 36 is located on the opposite side of the center CP of the seal ring 22 from the abutment gap 35. With this arrangement, the abutment gap 35 of the first seal ring 31 is closed by the second seal ring 32, and the abutment gap 36 of the second seal ring 32 is closed by the first seal ring 31. Therefore, leakage of liquefied gas (fluid) through the abutment gap 35 and the abutment gap 36 can be prevented.

[0030] 7, the thinnest portion 41 of the first seal ring 31 contacts the thickest portion 46 of the second seal ring 32, and the thickest portion 42 of the first seal ring 31 contacts the thinnest portion of the seal ring. The thickness W1 of the seal ring 22, which is made up of the stacked first seal ring 31 and second seal ring 32, is constant. The sum of the thickness of the thickest portion 42 of the first seal ring 31 and the thickness of the thickest portion 46 of the second seal ring 32 is greater than the width W2 of the seal groove 30 of the piston 18 (see FIG. 4).

[0031] When the first seal ring 31 and the second seal ring 32 attempt to rotate relative to each other, the first seal ring 31 and the second seal ring 32 attempt to move away from each other in the axial direction. Because the first seal ring 31 and the second seal ring 32 are disposed in the seal groove 30 of the piston 18, the first seal ring 31 and the second seal ring 32 are prevented from moving away from each other by the seal groove 30. As a result, the first seal ring 31 and the second seal ring 32 are prevented from rotating relative to each other.

[0032] 7, the gap 35 is located at the thinnest portion 41 of the first seal ring 31, and the gap 36 is located at the thinnest portion 45 of the second seal ring 32. The reason for this will be explained with reference to FIG.

[0033] FIG. 8 is a diagram showing how high-pressure liquefied gas pressurized by the piston 18 is applied to the seal ring 22. As shown in FIG. 8 , when high-pressure liquefied gas is applied to the seal ring 22 during operation of the reciprocating pump 2, the first inclined end face 31d of the first seal ring 31 is pressed firmly against the second inclined end face 32d of the second seal ring 32. As a result, the first seal ring 31 and the second seal ring 32 are displaced radially in opposite directions. Even in this case, the gap 35 of the first seal ring 31 is closed by the thickest portion 46 of the second seal ring 32, and the gap 36 of the second seal ring 32 is closed by the thickest portion 42 of the first seal ring 31. Therefore, leakage of the liquefied gas (fluid) through the gap 35 and the gap 36 is prevented.

[0034] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims.

[0035] The present invention is applicable to reciprocating pumps such as plunger pumps and piston pumps, and is particularly applicable to reciprocating pumps suitable for transporting liquefied gases.

[0036] REFERENCE SIGNS LIST 1 storage tank 2 reciprocating pump 5 actuator 7 fluid inlet port 8 boil-off gas discharge port 10 piston rod 12 coupling device 13 liquefied gas discharge line 14 pressurizing chamber 16 cylinder 18 piston 22 seal ring 26 suction check valve 27 discharge check valve 30 seal groove 31 first seal ring 31a inner circumferential surface 31b outer circumferential surface 31c first end face 31d first inclined end face 32 second seal ring 32a inner circumferential surface 32b outer circumferential surface 32c second end face 32d second inclined end face 35 joint gap 36 joint gap 41 thinnest part of first seal ring 42 thickest part of first seal ring 45 thinnest part of second seal ring 46 thickest part of second seal ring

Claims

1. A seal ring to be placed in a seal groove of a piston of a reciprocating pump for transporting a fluid, comprising: a first seal ring having a first gap; and a second seal ring having a second gap, the first seal ring and the second seal ring being in contact with each other, the first seal ring having portions of different thicknesses, the second seal ring having portions of different thicknesses, the thinnest portion of the first seal ring being in contact with the thickest portion of the second seal ring, the thickest portion of the first seal ring being in contact with the thinnest portion of the second seal ring, and the first gap and the second gap being at different positions circumferentially of the first seal ring and the second seal ring.

2. The seal ring according to claim 1, wherein the first gap is located at the thinnest part of the first seal ring, and the second gap is located at the thinnest part of the second seal ring.

3. The seal ring according to claim 1, wherein the first seal ring has a first inner peripheral surface, a first outer peripheral surface, a first end face and a first inclined end face extending from the first inner peripheral surface to the first outer peripheral surface, and the second seal ring has a second inner peripheral surface, a second outer peripheral surface, a second end face and a second inclined end face extending from the second inner peripheral surface to the second outer peripheral surface, the first inclined end face is inclined relative to the first end face, the second inclined end face is inclined relative to the second end face, and the first inclined end face is in contact with the second inclined end face.

4. The seal ring according to claim 1, wherein the first gap and the second gap are positioned symmetrically with respect to the centers of the first seal ring and the second seal ring.

5. The seal ring according to claim 1, wherein the sum of the thickness of the thickest portion of said first seal ring and the thickness of the thickest portion of said second seal ring is greater than the width of said seal groove.

6. A reciprocating pump for transporting a fluid, comprising: a cylinder having a pressurizing chamber therein; a piston disposed in said cylinder; a suction check valve and a discharge check valve communicating with said pressurizing chamber; and a seal ring according to any one of claims 1 to 5 disposed in a seal groove formed on the outer peripheral surface of said piston.

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