Reciprocating pump

Abstract

This reciprocating pump comprises: a pump body with a piston that compresses liquid and a cylinder covering the piston from the outside; a drive unit that causes the piston to reciprocate in a reciprocating direction; and a piston ring provided in a gap between the piston and the cylinder, wherein an annular groove is formed in the outer circumferential surface of the piston, the space inside the cylinder is partitioned by the piston ring into a high-pressure region where compressed liquid circulates and a low-pressure region where the internal pressure is lower than in the high-pressure region, the piston ring has a high-pressure–side ring located on the high-pressure region side of the annular groove and a low-pressure–side ring provided on the low-pressure region side of the annular groove relative to the high-pressure–side ring, and on the outer circumferential edge of the surface of the low-pressure–side ring facing the low-pressure region side, there is formed a notched surface retreating toward the high-pressure region side.

Description

Reciprocating Pump

[0001] This application claims priority to Japanese Patent Application No. 2023-201753, filed on November 29, 2023, the contents of which are incorporated herein by reference.

[0002] Reciprocating pumps have been used as devices for compressing liquid hydrogen. This type of pump is capable of pressurizing liquid hydrogen up to approximately 90 MPa, for example. Specifically, a reciprocating pump mainly comprises a piston that reciprocates in the axial direction and a cylinder that surrounds the piston. As the piston reciprocates within the cylinder, the liquid hydrogen is gradually compressed and discharged to the outside. The piston is driven by a drive unit.

[0003] An annular groove extending in the circumferential direction is formed on the outer peripheral surface of the piston, and piston rings are inserted into the annular groove. The piston rings are composed of a high-pressure ring and a low-pressure ring, as described in Patent Document 1 below, for example. In both rings, the surface facing the reciprocating direction is generally flat.

[0004] Patent No. 6424369

[0005] If the end face of the low-pressure ring is flat, the pressure in the high-pressure region (for example, about 90 MPa) can deform the outer edge of the low-pressure ring, forcing it toward the inside of the gap (i.e., toward the low-pressure region). This deformation reduces the contact area between the outer surface of the low-pressure ring and the inner surface of the cylinder. This can result in problems such as a decrease in sealing performance and uneven wear on the outer surface of the ring.

[0006] The present disclosure provides a reciprocating pump having piston rings that provide improved sealing performance.

[0007] The reciprocating pump according to the present disclosure comprises a pump body having a piston that compresses a liquid and a cylinder that covers the piston from the outside, a drive unit that reciprocates the piston in a reciprocating direction relative to the cylinder, and a piston ring provided in a gap between the piston and the cylinder, wherein an annular groove is formed on the outer peripheral surface of the piston that is recessed toward the inner peripheral side and extends circumferentially around the outer peripheral surface, and the space within the cylinder is partitioned by the piston ring into a high-pressure region through which the compressed liquid flows and a low-pressure region where the internal pressure is lower than that of the high-pressure region, and the piston ring comprises a high-pressure side ring arranged on the high-pressure region side of the annular groove, and a low-pressure side ring provided on the low-pressure region side of the annular groove relative to the high-pressure side ring, and a notched surface that recedes toward the high-pressure region side is formed on the outer peripheral edge of the surface of the low-pressure side ring that faces the low-pressure region side.

[0008] According to the present disclosure, it is possible to provide a reciprocating pump having a piston ring that exhibits higher sealing performance.

[0009] FIG. 1 is a longitudinal sectional view showing the configuration of a reciprocating pump according to a first embodiment of the present disclosure; FIG. 2 is an enlarged sectional view of a main portion of the reciprocating pump according to the first embodiment of the present disclosure; FIG. 3 is a perspective view showing the configuration of a low-pressure side ring according to the first embodiment of the present disclosure; FIG. 4 is a plan view showing the configuration of a piston ring according to the first embodiment of the present disclosure; FIG. 5 is an explanatory view showing dimensions of a main portion of a reciprocating pump according to the first embodiment of the present disclosure; FIG. 6 is an enlarged sectional view of a main portion of a reciprocating pump according to a second embodiment of the present disclosure; FIG. 7 is an enlarged sectional view of a main portion of a reciprocating pump according to a third embodiment of the present disclosure; FIG. 8 is an enlarged sectional view of a main portion of a first modified example of a reciprocating pump according to each embodiment of the present disclosure; FIG. 9 is an enlarged sectional view of a main portion of a reciprocating pump according to a third embodiment of the present disclosure;

[0010] First Embodiment A reciprocating pump 100 according to a first embodiment of the present disclosure will be described below with reference to FIGS. 1 to 5 .

[0011] (Configuration of Reciprocating Pump 100) The reciprocating pump 100 is a device for pressurizing a cryogenic liquid, such as liquid hydrogen, to a high pressure (approximately 90 MPa). As shown in Fig. 1, the reciprocating pump 100 includes a piston 1, a cylinder 2, a drive unit 3, a casing 4, a check valve 5, a discharge pipe 6, and a discharge valve 7. The piston 1 and the cylinder 2 form a pump body 9.

[0012] (Configuration of piston 1) The piston 1 has a cylindrical piston body 10 that extends in the vertical direction and is centered on the axis O, and a wear ring 11 and a piston ring 12 that are attached to the piston body 10. The radial dimension of the piston body 10 is constant throughout the entire area in the direction of the axis O. The wear ring 11 is provided at the tip of the piston body 10. The wear ring 11 has an annular shape centered on the axis O and is made of a resin material.

[0013] One wear ring 11 is provided at the lower end of the piston body 10, and another wear ring 11 is provided at a distance from the wear ring 11 in the axial direction O. A plurality of (for example, six) piston rings 12 are provided between the pair of wear rings 11 and arranged at intervals in the axial direction O. The wear ring 11 is provided to guide the piston body 10 along the inner circumferential surface of the cylinder 2, which will be described later. On the other hand, the piston ring 12 is provided to maintain liquid-tightness and air-tightness between the piston body 10 and the inner circumferential surface of the cylinder 2. The configuration of the piston ring 12 will be described later.

[0014] (Configuration of Cylinder 2) The cylinder 2 is a cylindrical cylinder with a bottom that covers the piston 1 from the outer periphery. The piston 1 is inserted into the cylinder 2 from an opening h at the top of the cylinder 2. The space inside the cylinder 2 below the tip of the piston 1 forms a compression chamber 21. A check valve 5 is provided at the bottom of the cylinder 2 for guiding liquid hydrogen to this compression chamber 21. This check valve 5 is capable of allowing liquid hydrogen to flow only in a direction from outside the cylinder 2 toward the inside of the compression chamber 21. In other words, even if the pressure in the compression chamber 21 increases, liquid hydrogen will not flow out of the cylinder 2 through the check valve 5.

[0015] A discharge pipe 6 is connected to the side of the cylinder 2 facing the compression chamber 21. The discharge pipe 6 is provided to extract the liquid hydrogen compressed in the compression chamber 21 to the outside of the cylinder 2. A discharge valve 7 is provided on this discharge pipe 6. The discharge valve 7 is capable of circulating liquid hydrogen only in the direction from the compression chamber 21 to the outside when the pressure inside the compression chamber 21 reaches or exceeds a predetermined value.

[0016] (Configuration of Drive Unit 3) The piston 1 described above reciprocates in the direction of the axis O by being given a driving force by the drive unit 3 within the cylinder 2. The drive unit 3 reciprocates the piston 1 within the cylinder 2 by means of an electric motor and a link mechanism (not shown).

[0017] (Configuration of Casing 4) The casing 4 is a container that covers the cylinder 2 from the outside. The casing 4 has a cylindrical casing body 41 with a bottom, a supply pipe 42, and a gas discharge pipe 43. The supply pipe 42 is a pipe for guiding liquid hydrogen from an external supply source into the casing body 41 (liquid storage chamber 44). The supply pipe 42 is provided near the bottom of the casing body 41. The gas discharge pipe 43 is provided for discharging vaporized components (gas components) in the liquid storage chamber 44 to the outside. The gas discharge pipe 43 is provided at a position spaced above the supply pipe 42. The liquid level of the liquid hydrogen in the liquid storage chamber 44 is adjusted so that it is located below the gas discharge pipe 43. The discharge pipe 6 described above extends to the outside of the casing 4.

[0018] (Configuration of Piston Ring 12) Next, the configuration of the piston ring 12 will be described in detail with reference to Figures 2 to 5. The piston ring 12 divides the space within the cylinder 2 into a high-pressure region V1 and a low-pressure region V2 that are continuous in the direction of the axis O. The high-pressure region V1 is a region on the compression chamber 21 side within the cylinder 2, and the low-pressure region V2 is a region located opposite the compression chamber 21 across the piston ring 12. In the following description, the high-pressure region V1 side may be simply referred to as the "high-pressure side," and the low-pressure region V2 side may be simply referred to as the "low-pressure side."

[0019] As shown in FIG. 2 , the piston ring 12 is accommodated in an annular groove 30 formed on the outer peripheral surface of the piston body 10. The annular groove 30 extends circumferentially about the axis O and has a rectangular cross section that is recessed inward. The annular groove 30 is formed by a bottom wall surface 31, a low-pressure side wall surface 32, and a high-pressure side wall surface 33. The bottom wall surface 31 faces the outer periphery and is cylindrical with the axis O as its center. The low-pressure side wall surface 32 has an annular shape that expands from the low-pressure side (i.e., upper) edge of the bottom wall surface 31 toward the outer periphery. In a cross-sectional view including the axis O, the low-pressure side wall surface 32 extends radially. The high-pressure side wall surface 33 has an annular shape that expands from the high-pressure side (i.e., lower) edge of the bottom wall surface 31 toward the outer periphery. In a cross-sectional view including the axis O, the low-pressure side wall surface 32 extends radially.

[0020] The piston ring 12 has a high-pressure side ring 50, a low-pressure side ring 60, a backup ring 70, and a spring member 80. The high-pressure side ring 50 is disposed on the high-pressure side of the annular groove 30, i.e., on the lower side in the up-down direction. The low-pressure side ring 60 is disposed on the low-pressure side of the annular groove 30, i.e., above the high-pressure side ring 50. The high-pressure side ring 50 and the low-pressure side ring 60 abut against each other in the direction of the axis O.

[0021] As shown in FIG. 3 , the low-pressure side ring 60 has an annular shape centered on the axis O. An opening called a gap P is formed in a portion of the low-pressure side ring 60 in the circumferential direction. This gap P is provided so that the low-pressure side ring 60 can be deformed by expanding it and fitted into the annular groove 30 of the piston body 10 from the outer periphery. The high-pressure side ring 50 also has an annular shape with a gap P similar to that of the low-pressure side ring 60. On the other hand, as shown in FIG. 4 , the gap P of the high-pressure side ring 50 and the gap P of the low-pressure side ring 60 are positioned 180° apart in the circumferential direction. In other words, if the gaps P overlap each other, liquid leakage will occur through the gaps P. To prevent leakage, the gaps P are out of phase with each other, as described above.

[0022] As shown in FIG. 2 , the high-pressure side ring 50 has a first outer peripheral surface 51, a first abutment surface 52, a first inner peripheral surface 53, and a first bottom surface 54. The first outer peripheral surface 51 faces the outer periphery and is cylindrical, centered in the circumferential direction of the axis O. The first outer peripheral surface 51 is in surface contact with the inner periphery of the cylinder 2 and slides in the direction of the axis O in accordance with the reciprocating motion of the piston 1. The first abutment surface 52 faces the low-pressure side (i.e., the upper side) and is annular, centered on the axis O. The first abutment surface 52 extends radially relative to the axis O in a cross-sectional view including the axis O. The first abutment surface 52 is in surface contact with the low-pressure side ring 60. The first inner peripheral surface 53 faces the inner periphery and is cylindrical, centered in the circumferential direction of the axis O. The first bottom surface 54 faces the high-pressure side and faces the high-pressure side wall surface 33 of the annular groove 30 .

[0023] The low-pressure side ring 60 has a second outer peripheral surface 61, a second abutment surface 62, a second inner peripheral surface 63, a second bottom surface 64, and a notched surface 65. The second outer peripheral surface 61 is a surface facing the outer peripheral side and has a cylindrical surface shape centered in the circumferential direction of the axis O. The second outer peripheral surface 61 is in surface contact with the inner peripheral surface of the cylinder 2 and slides in the direction of the axis O as the piston 1 reciprocates. The second abutment surface 62 is a surface facing the low-pressure side (i.e., the upper side) and has an annular shape centered on the axis O. The second abutment surface 62 expands in the radial direction relative to the axis O in a cross-sectional view including the axis O. The second abutment surface 62 is in surface contact with the low-pressure side wall surface 32 of the annular groove 30. The second inner peripheral surface 63 is a surface facing the inner peripheral side and has a cylindrical surface shape centered in the circumferential direction of the axis O. The second bottom surface 64 is a surface facing the high-pressure side, and is in surface contact with the first abutment surface 52 of the high-pressure side ring 50 .

[0024] The cutout surface 65 extends between the second abutment surface 62 and the second outer peripheral surface 61. In a cross-sectional view including the axis O, the cutout surface 65 recedes toward the high-pressure side. More specifically, the cutout surface 65 extends from the low-pressure side toward the high-pressure side as it moves from the inner peripheral side toward the outer peripheral side. In this embodiment, the angle that the cutout surface 65 forms with respect to the axis O is constant throughout the radial direction. Furthermore, as shown in FIG. 5 , when the radial gap dimension between the outer peripheral surface of the piston body 10 and the inner peripheral surface of the cylinder 2 is G, the radial dimension A of the cutout surface 65 is set to satisfy G≦A≦2G. In other words, the inner peripheral edge of the cutout surface 65 is located at the same radial position as the outer peripheral edge of the low-pressure side wall surface 32 of the annular groove 30 or is located radially inward relative to the outer peripheral edge. More preferably, G≦A≦1.8G. Most desirably, G≦A≦1.5G. In this embodiment, the dimension of the low-pressure side ring 60 in the direction of the axis O is equal to the dimension of the high-pressure side ring 50 in the direction of the axis O. Note that "same" or "equivalent" here refers to substantial identity, and slight errors are permitted.

[0025] Resin materials are preferably used as materials for forming the high-pressure side ring 50 and the low-pressure side ring 60. Specifically, materials containing at least one selected from the group including PTFE (polytetrafluoroethylene), PI (polyimide), PAI (polyamideimide), PPA (polyphthalamide), PPS (polyphenylene sulfide), PSU (polysulfone), and PES (polyethersulfone) as a main component are preferably used. These resin materials are relatively soft, and therefore can prevent seizure during sliding contact with the cylinder 2 and ensure flame retardancy when the liquid is flammable.

[0026] As shown in FIG. 2 , the backup ring 70 is provided on the inner circumferential side of the high-pressure side ring 50 and the low-pressure side ring 60. The backup ring 70 has an annular shape centered on the axis O. The dimension of the backup ring 70 in the direction of the axis O is equal to the sum of the dimensions of the high-pressure side ring 50 and the low-pressure side ring 60 in the direction of the axis O. The backup ring 70 is biased from the inner circumferential side by a spring member 80. The spring member 80 is an annular elastic body that biases the backup ring 70 so as to expand its diameter toward the outer circumferential side. By being pressed from the inner circumferential side by the backup ring 70 and the spring member 80, the high-pressure side ring 50 and the low-pressure side ring 60 are configured to constantly slide against the inner circumferential surface of the cylinder 2. Therefore, a certain space is formed between the inner circumferential surface of the backup ring 70 and the bottom wall surface 31 of the annular groove 30.

[0027] (Operation and Effect) When operating the reciprocating pump 100, first, liquid hydrogen is supplied into the cylinder 2 through the supply pipe 42, and then the piston 1 is reciprocated within the cylinder 2 by the drive unit 3. As a result, the liquid hydrogen within the cylinder 2 is gradually compressed to a high-pressure state. The high-pressure liquid hydrogen is then discharged to the outside through the discharge pipe 6.

[0028] Here, unlike the above-described configuration, if the notched surface 65 is not formed and the end face of the low-pressure side ring 160 is flat, the pressure on the high-pressure region V1 side (e.g., approximately 90 MPa) may cause the outer edge of the low-pressure side ring 160 to be deformed so as to be pushed toward the inside of the gap (i.e., toward the low-pressure region V2) (see the reference example shown in FIG. 11 ). This deformation reduces the contact area between the outer surface of the low-pressure side ring 160 and the inner surface of the cylinder 2. This results in problems such as a reduction in the sealing performance of the low-pressure side ring 160 and uneven wear on the outer surface of the low-pressure side ring 160. To solve these problems, the present embodiment employs the above-described configurations.

[0029] According to the above configuration, the notched surface 65 is pre-formed in the outer peripheral region, which is prone to deformation due to pressure. This allows a certain degree of deformation toward the low-pressure region V2, even when high pressure is applied to the outer peripheral edge, due to the cutout. This reduces the possibility of a portion of the low-pressure side ring 60 being pushed into the gap between the piston 1 and the cylinder 2. As a result, a reduction in the contact area between the low-pressure side ring 60 and the cylinder 2 is avoided. Furthermore, detachment of the deformed portion is also avoided. This avoids a deterioration in sealing performance, enabling the reciprocating pump 100 to operate stably for a long period of time. The notched surface 65 extends from the low-pressure region V2 toward the high-pressure region V1 as it moves from the inner peripheral side to the outer peripheral side.

[0030] According to the above configuration, the cutout surface 65 extends from the low-pressure side toward the high-pressure side as it moves from the inner periphery toward the outer periphery. This allows the cutout surface 65 to be formed simply by chamfering, simplifying the processing. This reduces the costs required for maintenance and manufacturing of the reciprocating pump 100.

[0031] According to the above configuration, the radial dimension of the cutout surface 65 is equal to or greater than the radial dimension of the gap between the piston 1 and the cylinder 2, but is within a range of two times the radial dimension of the gap. This provides a margin of error, making it possible to avoid deformation of the low-pressure side ring 60 and the resulting deterioration of sealing performance. This allows the reciprocating pump 100 to continue operating stably for an even longer period of time.

[0032] The first embodiment of the present disclosure has been described above. Note that various changes and modifications can be made to the above configuration without departing from the gist of the present disclosure.

[0033] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to Fig. 6. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0034] 6 , in this embodiment, the cross-sectional shape of the low-pressure side ring 60 is different from that of the first embodiment. Specifically, the low-pressure side ring 60 further has a second cutout surface 66 in addition to the second outer peripheral surface 61, second abutment surface 62, second inner peripheral surface 63, second bottom surface 64, and cutout surface 65 described above.

[0035] The second cutout surface 66 is provided between the second bottom surface 64 and the second outer peripheral surface 61. The second cutout surface 66 is recessed toward the low-pressure side. More specifically, in a cross-sectional view including the axis O, the second cutout surface 66 extends from the high-pressure side toward the low-pressure side as it moves from the inner peripheral side toward the outer peripheral side. The angle that the second cutout surface 66 forms with respect to the axis O is constant throughout the radial direction. Furthermore, it is desirable that the radial dimension of the second cutout surface 66 be set to fall within the same numerical range as the radial dimension of the cutout surface 65 described in the first embodiment.

[0036] (Effects) According to the above configuration, in addition to the notched surface 65 formed on the surface facing the low-pressure region V2, a second notched surface 66 is also formed on the surface facing the low-pressure region V2. This not only prevents a decrease in sealing performance caused by a portion of the ring being pressed into the gap between the piston 1 and the cylinder 2, but also eliminates the need to specify the assembly direction of the low-pressure side ring 60 during assembly. This makes it possible to achieve more efficient and faster assembly work. It also reduces the possibility of malfunctions in the final product due to assembly errors.

[0037] The second embodiment of the present disclosure has been described above. Note that various changes and modifications can be made to the above configuration without departing from the gist of the present disclosure.

[0038] Third Embodiment Next, a third embodiment of the present disclosure will be described with reference to Fig. 7. Note that the same components as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0039] In this embodiment, the shapes of the high-pressure side ring 50 and the low-pressure side ring 60 (i.e., the configuration of the surfaces of these rings) are the same as those in the first embodiment described above. On the other hand, the dimensions of the high-pressure side ring 50 and the low-pressure side ring 60 in the direction of the axis O are different from those in the first embodiment. Specifically, when the dimension of the high-pressure side ring 50 in the direction of the axis O is X and the dimension of the low-pressure side ring 60 in the direction of the axis O is Y, X≧1.5Y is satisfied. More preferably, X≧1.7Y. Most preferably, X≧2.0Y.

[0040] (Effects) Here, the high-pressure side ring 50 and the low-pressure side ring 60 have openings (gap P) formed in parts of the circumferential direction to allow these components to be fitted onto the piston 1. The high-pressure side ring 50 is generally assembled so that the gap P is 180° different in the circumferential direction from the gap P of the low-pressure side ring 60. Over time, the low-pressure side ring 60 may wear radially inward. This causes deformation of the gap P of the low-pressure side ring 60, widening it to both sides in the circumferential direction. As a result, a portion of the high-pressure side ring 50 may deform through the gap P toward the low-pressure region V2, ultimately resulting in breakage of the high-pressure side ring 50. However, with the above-described configuration, the dimension of the high-pressure side ring 50 in the reciprocating direction is set larger than that of the low-pressure side ring 60, thereby improving the rigidity of the high-pressure side ring 50. This makes it possible to reduce the likelihood of deformation at the gap P as described above. Therefore, deterioration and deformation of the piston rings 12 due to aging are suppressed, and the reciprocating pump 100 can be operated stably for an even longer period of time.

[0041] Other Embodiments The embodiments of the present disclosure have been described above. Note that various changes and modifications can be made to the above configurations without departing from the spirit and scope of the present disclosure.

[0042] <First Modification> As a first modification of the low-pressure side ring 60, the configuration shown in Fig. 8 can be adopted. In the example shown in Fig. 8, the cutout surface 65 has a convex curved shape that is convex toward the low-pressure side. The cutout surface 65 may be arc-shaped, or may be a curved surface whose curvature gradually changes. This modification can also be applied in combination with any of the first to third embodiments described above.

[0043] With the above configuration, the cutout surface 65 has a convex curved shape that is convex toward the low-pressure region V2, thereby preventing stress concentration at the cutout surface 65. Conversely, if corners were formed on the outer or inner edges of the cutout surface 65, stress could be concentrated at the corners, potentially resulting in defects such as cracks. However, with the above configuration, no such corners are formed, significantly reducing the likelihood of stress concentration. As a result, the reciprocating pump 100 can be operated stably for an even longer period of time.

[0044] <Second Modification> As a second modification of the low-pressure side ring 60, the configuration shown in Fig. 9 can be adopted. In the example shown in Fig. 9, the cutout surface 65 is a concave curved surface that is recessed toward the high-pressure side. The cutout surface 65 may be an arc or a curved surface whose curvature gradually changes. This modification can also be applied in combination with any of the first to third embodiments described above.

[0045] With the above configuration, the cutout surface 65 has a concave curved shape that is recessed toward the high-pressure region V1, thereby preventing stress concentration at the cutout surface 65. Conversely, if corners were formed on the outer or inner edges of the cutout surface 65, stress could be concentrated at the corners, potentially resulting in defects such as cracks. However, with the above configuration, no such corners are formed, significantly reducing the possibility of stress concentration. As a result, the reciprocating pump 100 can be operated stably for an even longer period of time.

[0046] <Third Modification> As a third modification of the low-pressure side ring 60, the configuration shown in FIG. 10 can be adopted. In the example shown in the figure, the cutout surface 65 has a first surface 67 and a second surface 68. The first surface 67 faces the outer periphery. The second surface 68 widens from the high-pressure side edge of the first surface 67 toward the outer periphery. As an example, the first surface 67 and the second surface 68 are perpendicular to each other in a cross section including the axis O. Note that this modification can be applied in combination with any of the first to third embodiments described above.

[0047] According to the above configuration, the cutout surface 65 has a rectangular cross-sectional shape due to the first surface 67 and the second surface 68. This improves the visibility of the cutout surface 65 itself. In other words, it becomes possible to easily see on which surface the cutout surface 65 is formed. This makes it possible to achieve more efficient and faster assembly work. It also makes it possible to reduce the possibility of malfunctions in the final product due to assembly errors.

[0048] <Other Modifications> Furthermore, in each of the above embodiments, an example has been described in which the reciprocating pump 100 is used to compress liquid hydrogen. However, the reciprocating pump 100 can also be suitably used to compress low-temperature liquefied gases such as liquefied carbon dioxide, liquefied natural gas, and liquefied petroleum gas.

[0049] <Additional Notes> The reciprocating pump 100 described in each embodiment can be understood, for example, as follows.

[0050] (1) A reciprocating pump 100 according to a first aspect includes a pump body 9 having a piston 1 for compressing a liquid and a cylinder 2 that covers the piston 1 from the outside, a drive unit 3 that reciprocates the piston 1 in a reciprocating direction relative to the cylinder 2, and a piston ring 12 provided in a gap between the piston 1 and the cylinder 2. The piston 1 has an outer peripheral surface formed with an annular groove 30 that is recessed toward the inner peripheral side and extends in the circumferential direction of the outer peripheral surface, and the space within the cylinder 2 is filled with the piston ring 12. Thus, the piston ring 12 is divided into a high-pressure region V1 through which the compressed liquid flows, and a low-pressure region V2 in which the internal pressure is lower than that of the high-pressure region V1. The piston ring 12 has a high-pressure side ring 50 arranged on the high-pressure region V1 side of the annular groove 30, and a low-pressure side ring 60 provided on the low-pressure region V2 side of the annular groove 30 with respect to the high-pressure side ring 50. A notched surface 65 receding toward the high-pressure region V1 side is formed on the outer peripheral edge of the surface of the low-pressure side ring 60 facing the low-pressure region V2 side.

[0051] According to the above configuration, the notched surface 65 is formed in advance in the outer peripheral region that is prone to deformation due to pressure. As a result, even when high pressure is applied to the outer peripheral edge, a certain degree of deformation toward the low-pressure region V2 can be tolerated due to the notched portion. This reduces the possibility that part of the low-pressure side ring 60 will be pushed into the gap between the piston 1 and the cylinder 2.

[0052] (2) The reciprocating pump 100 according to the second aspect is the reciprocating pump 100 of (1), in which the cutout surface 65 extends from the low pressure region V2 side to the high pressure region V1 side as it moves from the inner circumferential side to the outer circumferential side.

[0053] According to the above configuration, the notched surface 65 is formed in advance in the outer peripheral region that is prone to deformation due to pressure. As a result, even when high pressure is applied to the outer peripheral edge, a certain degree of deformation toward the low-pressure region V2 can be tolerated due to the notched portion. This reduces the possibility that part of the low-pressure side ring 60 will be pushed into the gap between the piston 1 and the cylinder 2.

[0054] (3) A reciprocating pump 100 according to a third aspect is the reciprocating pump 100 of (1), wherein the cutout surface 65 has a convex curved surface that is convex toward the low-pressure region V2.

[0055] According to the above configuration, the cutout surface 65 has a convex curved shape that is convex toward the low pressure region V2 side, so that stress concentration on the cutout surface 65 can be avoided.

[0056] (4) The reciprocating pump 100 according to a fourth aspect is the reciprocating pump 100 of (1), wherein the cutout surface 65 is a concave curved surface that is recessed toward the high pressure region V1.

[0057] According to the above configuration, the notched surface 65 is a concave curved surface recessed toward the high pressure region V1, so that stress concentration on the notched surface 65 can be avoided.

[0058] (5) The reciprocating pump 100 according to the fifth aspect is the reciprocating pump 100 of (1), wherein the cutout surface 65 has a first surface 67 facing the outer periphery and a second surface 68 extending from the edge of the first surface 67 on the high-pressure region V1 side toward the outer periphery.

[0059] According to the above configuration, the cutout surface 65 has a rectangular cross-sectional shape due to the first surface 67 and the second surface 68. This improves the visibility of the cutout surface 65 itself. Therefore, it is possible to achieve efficient and rapid assembly work.

[0060] (6) The reciprocating pump 100 according to the sixth aspect is a reciprocating pump 100 according to any one of the aspects (1) to (5), in which the radial dimension of the cutout surface 65 is set within a range of greater than or equal to the radial dimension of the gap and less than or equal to twice the radial dimension of the gap.

[0061] According to the above-described configuration, a margin can be provided to avoid deformation of the low-pressure side ring 60 and the resulting deterioration of sealing performance.

[0062] (7) The reciprocating pump 100 according to the seventh aspect is a reciprocating pump 100 according to any one of the aspects (1) to (6), in which the dimension of the high-pressure side ring 50 in the reciprocating direction is set to be 1.5 times or more the dimension of the low-pressure side ring 60 in the reciprocating direction.

[0063] According to the above configuration, the rigidity of the high-pressure side ring 50 is improved because the dimension in the reciprocating direction of the high-pressure side ring 50 is set to be larger than that of the low-pressure side ring 60. This makes it possible to make deformation at the abutment P less likely to occur.

[0064] (8) The reciprocating pump 100 according to the eighth aspect is a reciprocating pump 100 according to any one of the aspects (1) to (7), in which a second cutout surface 66 receding toward the low-pressure region V2 is formed on the outer edge of the surface of the low-pressure side ring 60 facing the high-pressure region V1.

[0065] According to the above configuration, in addition to the notched surface 65 formed on the surface facing the low-pressure region V2, the second notched surface 66 is also formed on the surface facing the low-pressure region V2. This not only makes it possible to avoid a decrease in sealing performance, but also eliminates the need to specify the assembly direction of the low-pressure side ring 60 during assembly.

[0066] According to the present disclosure, it is possible to provide a reciprocating pump having a piston ring that exhibits higher sealing performance.

[0067] DESCRIPTION OF SYMBOLS 1...Piston 2...Cylinder 3...Drive unit 4...Casing 5...Check valve 6...Discharge pipe 7...Discharge valve 9...Pump body 10...Piston body 11...Wear ring 12...Piston ring 21...Compression chamber 30...Annular groove 31...Bottom wall surface 32...Low-pressure side wall surface 33...High-pressure side wall surface 41...Casing body 42...Supply pipe 43...Gas discharge pipe 44...Liquid storage chamber 50...High-pressure side ring 51...First outer peripheral surface 52...First abutment surface 53...First inner peripheral surface 54...First bottom surface 60...Low-pressure side ring 61...Second outer peripheral surface 62...Second abutment surface 63...Second inner peripheral surface 64...Second bottom surface 65...Notched surface 66...Second notched surface 67...First surface 68...Second surface 70...Backup ring 80...Spring member 100...Reciprocating pump h...Opening O...Axis P...Gap V1...High pressure area V2...Low pressure area

Claims

1. A reciprocating pump comprising: a pump body having a piston that compresses liquid and a cylinder that covers the piston from the outside; a drive unit that reciprocates the piston in a reciprocating direction relative to the cylinder; and a piston ring provided in a gap between the piston and the cylinder, wherein an annular groove is formed on the outer peripheral surface of the piston that is recessed toward the inner peripheral side and extends circumferentially of the outer peripheral surface, and the space within the cylinder is divided by the piston ring into a high-pressure region through which the compressed liquid flows and a low-pressure region where the internal pressure is lower than that of the high-pressure region, and the piston ring comprises: a high-pressure side ring arranged on the high-pressure region side of the annular groove; and a low-pressure side ring provided on the low-pressure region side of the annular groove relative to the high-pressure side ring, and wherein a notched surface is formed on the outer peripheral edge of the surface of the low-pressure side ring that faces the low-pressure region, receding toward the high-pressure region.

2. A reciprocating pump as set forth in claim 1, wherein said cutout surface extends from said low pressure region side to said high pressure region side as it moves from the inner periphery side to the outer periphery side.

3. A reciprocating pump according to claim 1, wherein said cutout surface is a convex curved surface that is convex towards said low pressure region.

4. A reciprocating pump as set forth in claim 1, wherein said cutout surface is a concave curved surface recessed toward said high pressure region.

5. A reciprocating pump according to claim 1, wherein said cutout surface has a first surface facing the outer periphery, and a second surface extending from an edge of said first surface on the side of said high pressure region toward the outer periphery.

6. A reciprocating pump as claimed in any one of claims 1 to 5, wherein the radial dimension of the cutout surface is set within a range of greater than or equal to the radial dimension of the gap and less than twice the radial dimension of the gap.

7. A reciprocating pump as claimed in any one of claims 1 to 5, wherein the dimension of the high pressure side ring in the reciprocating direction is set to be at least 1.5 times the dimension of the low pressure side ring in the reciprocating direction.

8. A reciprocating pump as described in any one of claims 1 to 5, wherein a second cutout surface receding toward the low pressure region is formed on the outer edge of the surface of the low pressure side ring facing the high pressure region.

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