Reciprocating pump

Abstract

A reciprocating pump (2) comprises: a cylinder (16) having a pressurizing chamber (14) inside; a piston (18) disposed in the cylinder (16); and a suction check valve (26) communicating with the pressurizing chamber (14). The suction check valve (26) comprises: a valving element (31); a first seal surface (35) that contacts the back side of the valving element (31); a second seal surface (36) surrounded by the first seal surface (35); a suction channel (37) surrounded by the second seal surface (36); and a fluid relief channel (50) having a fluid inlet (51) that surrounds the second seal surface (36). The fluid inlet (51) is positioned between the first seal surface (35) and the second seal surface (36), and the fluid relief channel (50) has a fluid outlet (52) communicating with the outside of the reciprocating pump (2).

Description

Reciprocating Pump

[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. 22 is a schematic diagram showing a cross section of a conventional reciprocating pump. As shown in Fig. 22, 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] JP 2023-177499 A

[0006] When piston 501 pressurizes the fluid in cylinder 500, the high-enthalpy fluid may leak to the suction side (primary side) of check valve 514 through a small gap in check valve 514. If the fluid is liquefied gas, the high-enthalpy liquefied gas that leaks to the suction side of check valve 514 gasifies as the pressure drops. The gas present on the suction side of check valve 514 inhibits the suction of the liquefied gas into cylinder 500 and the compression of the liquefied gas within cylinder 500, reducing the performance of the reciprocating pump.

[0007] Therefore, the present invention provides a reciprocating pump that can prevent high-enthalpy fluid pressurized by a piston from leaking to the suction side.

[0008] In one aspect, there is provided a reciprocating pump for transporting a fluid, the reciprocating pump comprising: a cylinder having a pressurizing chamber therein; a piston disposed within the cylinder; and a suction check valve communicating with the pressurizing chamber, the suction check valve comprising a valve body, a first sealing surface in contact with the back side of the valve body, a second sealing surface surrounded by the first sealing surface, a suction flow path surrounded by the second sealing surface, and a fluid relief flow path having a fluid inlet surrounding the second sealing surface, the fluid inlet being located between the first sealing surface and the second sealing surface, and the fluid relief flow path having a fluid outlet communicating with the outside of the reciprocating pump.

[0009] In one aspect, the fluid relief passage includes a descending passage extending downward from the fluid inlet. In one aspect, the fluid relief passage further includes an ascending passage extending obliquely upward from the descending passage to the fluid outlet. In one aspect, the fluid inlet has an annular shape. In one aspect, the fluid relief passage includes a descending passage located radially inward from the fluid inlet and a communicating passage communicating the fluid inlet and the descending passage, and the descending passage extends to the fluid outlet. In one aspect, the fluid relief passage further includes a fluid chamber connected to an upper end of the descending passage, and the communicating passage extends from the fluid inlet to the fluid chamber. In one aspect, the communicating passage is connected to a side wall of the fluid chamber in a direction oblique to the radial direction of the fluid chamber when viewed from above. In one aspect, a spiral groove is formed in the side wall of the fluid chamber. In one aspect, the suction check valve further includes a spiral stationary vane provided on the side wall of the fluid chamber. In one aspect, the suction check valve further comprises a rotor disposed within the fluid chamber.

[0010] When the suction check valve is closed, high-enthalpy fluid that enters between the valve body and the first seal surface flows into the fluid inlet and is discharged to the outside of the reciprocating pump through the fluid relief passage before reaching the second seal surface, thereby preventing the high-enthalpy fluid from entering the suction passage.

[0011] 1 is a schematic diagram showing an embodiment of a fluid transfer system including a reciprocating pump; FIG. 1 is a cross-sectional view showing an embodiment of a reciprocating pump; FIG. 2 is a view illustrating the operation of a piston when pressurizing liquefied gas in a pressurizing chamber; FIG. 3 is an enlarged cross-sectional view showing an embodiment of a suction check valve; FIG. 4 is an enlarged cross-sectional view of a portion of the suction check valve; FIG. 5 is a top view of a first seal surface, a second seal surface, and a fluid inlet of a fluid relief channel, as viewed from the axial direction; FIG. 6 is a view of another embodiment of a fluid relief channel; FIG. 7 is a view of yet another embodiment of a fluid relief channel; FIG. 8 is a view of yet another embodiment of a fluid relief channel; FIG. 9 is a view of yet another embodiment of a fluid relief channel; FIG. 10 is an enlarged cross-sectional view of another embodiment of a suction check valve; FIG. 11 is a plan view of a valve body, as viewed from above; FIG. 12 is an enlarged cross-sectional view showing the suction check valve in an open state; FIG. 13 is a top view of a first seal surface, a second seal surface, and a fluid inlet of a fluid relief channel, as viewed from the axial direction; FIG. 14 is a top view of another embodiment of a plurality of communicating channels; FIG. 15 is a view of an embodiment in which a spiral groove is formed on a side wall of a fluid chamber; FIG. 16 is a view of an embodiment in which a stationary vane is provided on a side wall of a fluid chamber. Fig. 20 is a schematic diagram showing a cross section of a conventional reciprocating pump. Fig. 21 is a top view of the stationary impeller shown in Fig. 18. Fig. 22 is a diagram showing an embodiment of the rotary impeller disposed in the fluid chamber. Fig. 23 is a top view of the rotary impeller shown in Fig. 20. Fig. 24 is a schematic diagram showing a cross section of a conventional reciprocating pump.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] Next, the suction check valve 26 will be described in detail. Fig. 4 is an enlarged cross-sectional view showing one embodiment of the suction check valve 26, and Fig. 5 is an enlarged cross-sectional view of a portion of the suction check valve 26. In Fig. 4, the discharge check valve 27 is depicted schematically. The suction check valve 26 has a valve element 31 and a valve seat 32 that supports the back side (suction side) of the valve element 31. The valve seat 32 has a first seal surface 35 that contacts the back side of the valve element 31, a second seal surface 36 surrounded by the first seal surface 35, and a suction flow path 37 surrounded by the second seal surface 36.

[0022] The valve element 31 is connected to a valve rod 40, which is supported by a valve guide 41 fixed to the valve seat 32 so as to be able to move up and down. The valve element 31 may be configured integrally with the valve rod 40. A spring stopper 43 is fixed to the valve rod 40. A spring 44 is disposed between the valve guide 41 and the spring stopper 43. The spring 44 presses the valve element 31 toward the first seal surface 35 and the second seal surface 36. The valve guide 41, spring stopper 43, and spring 44 are disposed in the suction flow path 37.

[0023] The valve disc 31 is pressed against the first seal surface 35 by the spring 44 and comes into contact with the first seal surface 35. Meanwhile, a small gap is formed between the valve disc 31 and the second seal surface 36. That is, when the back side of the valve disc 31 is in contact with the first seal surface 35, a small gap exists between the back side of the valve disc 31 and the second seal surface 36. The gap between the back side of the valve disc 31 and the second seal surface 36 is provided to prevent the valve disc 31 from contacting the second seal surface 36 before the first seal surface 35 when the valve disc 31 is deformed by high-pressure liquefied gas, and to ensure that the valve disc 31 comes into contact with the first seal surface 35.

[0024] However, the high-pressure liquefied gas (high-enthalpy fluid) pressurized by the piston 18 in the pressurizing chamber 14 may enter between the valve body 31 and the first seal surface 35. When the high-pressure liquefied gas reaches the suction passage 37, the liquefied gas vaporizes in the suction passage 37, causing a decrease in the pumping performance of the reciprocating pump 2.

[0025] Therefore, in this embodiment, the suction check valve 26 is provided with a fluid relief passage 50 that releases liquefied gas that has entered between the valve body 31 and the first seal surface 35 to the outside of the reciprocating pump 2. The fluid relief passage 50 has a fluid inlet 51 located between the first seal surface 35 and the second seal surface 36. The fluid relief passage 50 communicates with the outside of the reciprocating pump 2. In the embodiment shown in FIG. 4 , the fluid relief passage 50 has a fluid outlet 52 located on a side surface of the valve seat 32 of the suction check valve 26.

[0026] 6 is a top view of the first seal surface 35, the second seal surface 36, and the fluid inlet 51 of the fluid relief passage 50 as viewed from the axial direction. The fluid inlet 51 surrounds the second seal surface 36. In this embodiment, the first seal surface 35, the second seal surface 36, and the fluid inlet 51 are each annular. The fluid inlet 51 of the fluid relief passage 50 is located radially inward of the first seal surface 35, the second seal surface 36 is located radially inward of the fluid inlet 51, and the suction passage 37 is located radially inward of the second seal surface 36.

[0027] When the suction check valve 26 is closed, high-pressure liquefied gas (high-enthalpy fluid) that enters between the valve body 31 and the first seal surface 35 flows into the fluid inlet 51 before reaching the second seal surface 36, and is discharged to the outside of the reciprocating pump 2 through the fluid relief flow path 50. Therefore, the high-pressure liquefied gas is prevented from flowing into the suction flow path 37, and the pumping performance of the reciprocating pump 2 can be maintained.

[0028] As shown in FIG. 4 , the fluid relief channel 50 includes a descending channel 54 extending downward from the fluid inlet 51. The descending channel 54 has a cylindrical shape. The descending channel 54 encourages the high-pressure liquefied gas to flow downward by gravity, preventing the liquefied gas from flowing back. In addition, the piston 18 pushes the liquefied gas into the descending channel 54, forcing it to move downward. The fluid relief channel 50 further includes a plurality of discharge channels 55 extending horizontally from the cylindrical descending channel 54. These discharge channels 55 extend to the fluid outlet 52. In one embodiment, as shown in FIG. 7 , the descending channel 54 may have a frusto-conical shape.

[0029] In one embodiment, as shown in Fig. 8 , the entire fluid relief passage 50 may be composed of a frusto-conical descending passage 54. In this embodiment, the descending passage 54 extends diagonally downward from the fluid inlet 51 to the fluid outlet 52. In one embodiment, as shown in Fig. 9 , the entire fluid relief passage 50 may be composed of a cylindrical descending passage 54. In this embodiment, the descending passage 54 extends vertically downward from the fluid inlet 51 to the fluid outlet 52. The fluid outlet 52 is provided on the bottom surface of the valve seat 32.

[0030] 10 , the fluid escape channel 50 includes a cylindrical downward channel 54 extending downward from the fluid inlet 51 and multiple discharge channels 55 extending diagonally upward from the downward channel 54. At least a portion of the high-pressure liquefied gas may evaporate and become gas as it flows through the low-pressure discharge channel 55. The buoyancy of this gas assists the liquefied gas in the multiple discharge channels 55 to move toward the fluid outlet 52.

[0031] In one embodiment, as shown in FIG. 11, the downward flow passage 54 having a truncated cone shape shown in FIG. 7 may be combined with a plurality of discharge flow passages 55 extending obliquely upward as shown in FIG.

[0032] Figure 12 is a cross-sectional view showing another embodiment of the suction check valve 26. The configuration and operation of this embodiment, which will not be specifically described, are the same as those of the embodiment described with reference to Figures 1 to 6, and therefore, redundant description will be omitted.

[0033] As shown in Figure 12, the valve disc 31 is not connected to the valve rod 40. The valve disc 31 is supported on the inner surface 16a of the cylinder 16 so as to be able to move up and down. A spring 60 is disposed radially outward of the valve disc 31. The spring 60 is disposed between the upper wall 31a of the valve disc 31 and the valve seat 32. The spring 60 pushes the valve disc 31 in a direction away from the first seal surface 35 and the second seal surface 36. When the piston 18 pressurizes the liquefied gas in the pressurizing chamber 14, the pressure of the liquefied gas closes the valve disc 31 (i.e., the back side of the valve disc 31 contacts the first seal surface 35). A plurality of suction flow paths 37 are provided below the valve disc 31.

[0034] The fluid relief passage 50 includes a descending passage 54 located radially inward of the fluid inlet 51, and a plurality of communicating passages 63 that communicate between the fluid inlet 51 and the descending passage 54. The descending passage 54 extends downward in the vertical direction to the fluid outlet 52. The fluid relief passage 50 further includes a fluid chamber 64 connected to the upper end of the descending passage 54. The fluid chamber 64 is located below the center of the valve body 31. The fluid chamber 64 is located radially inward of the second seal surface 36 and the fluid inlet 51. The fluid chamber 64 has a frusto-conical or cylindrical shape.

[0035] Figure 13 is a plan view of the valve body 31 as viewed from above. The upper wall 31a of the valve body 31 has a plurality of openings 65. When the suction check valve 26 is open (i.e., when the valve body 31 is separated from the first seal surface 35), liquefied gas flows from the suction flow path 37 into the pressurizing chamber 14 through the openings 65 of the valve body 31. The number and shape of the openings 65 of the valve body 31 are not limited to the embodiment shown in Figure 13. Figure 14 is a diagram showing the state when the suction check valve 26 is open.

[0036] 15 is a top view of the first seal surface 35, the second seal surface 36, and the fluid inlet 51 of the fluid escape channel 50 as viewed from the axial direction. In this embodiment, the first seal surface 35, the second seal surface 36, and the fluid inlet 51 are each annular. The fluid inlet 51 is located radially inward of the first seal surface 35, the second seal surface 36 is located radially inward of the fluid inlet 51, and the multiple suction channels 37 are surrounded by the second seal surface 36.

[0037] The descending passage 54 is adjacent to the plurality of suction passages 37. More specifically, the plurality of suction passages 37 are arranged around the descending passage 54. The plurality of communicating passages 63 are grooves formed in the second sealing surface 36. The plurality of communicating passages 63 extend from the fluid inlet 51 to the fluid chamber 64. The fluid inlet 51 is connected to the descending passage 54 through the plurality of communicating passages 63 and the fluid chamber 64. In this embodiment, three suction passages 37 and three communicating passages 63 are provided, but the number of suction passages 37 and the number of communicating passages 63 are not limited to this embodiment. In one embodiment, a single suction passage 37 and a single communicating passage 63 may be provided.

[0038] High-pressure liquefied gas (high-enthalpy fluid) that flows into the fluid inlet 51 flows through the multiple communication channels 63 into the fluid chamber 64. The liquefied gas in the fluid chamber 64 is forced into the descending channel 54 by the piston 18 and is discharged from the fluid outlet 52 to the outside of the reciprocating pump 2.

[0039] 16 is a top view showing another embodiment of the multiple communicating channels 63. In this embodiment, each communicating channel 63 is connected to the side wall of the fluid chamber 64 in a direction inclined relative to the radial direction of the fluid chamber 64 when viewed from above. In other words, the multiple communicating channels 63 extend in a tangential direction to the side wall of the fluid chamber 64, which has a truncated cone or cylindrical shape. The liquefied gas that passes through these multiple communicating channels 63 forms a swirling flow within the fluid chamber 64, and the liquefied gas easily flows into the descending channel 54 connected to the center of the bottom of the fluid chamber 64.

[0040] In one embodiment, as shown in Fig. 17, a spiral groove 67 may be formed on the side wall of the fluid chamber 64 so as to maintain a swirling flow of the liquefied gas in the fluid chamber 64. In another embodiment, as shown in Figs. 18 and 19, a spiral stationary vane 68 may be provided on the side wall of the fluid chamber 64 so as to maintain a swirling flow of the liquefied gas in the fluid chamber 64.

[0041] Furthermore, in another embodiment, as shown in Figures 20 and 21 , a rotor 69 may be disposed in the fluid chamber 64 so as to maintain a swirling flow of the liquefied gas in the fluid chamber 64. The rotor 69 is configured to be rotatable within the fluid chamber 64. In one embodiment, the rotor 69 is rotatably supported by a support shaft 70, which is fixed to the bottom of the valve body 31. The rotor 69 and the support shaft 70 move integrally with the valve body 31. When the valve body 31 is closed, as shown in Figure 20 , the rotor 69 is located within the fluid chamber 64 and rotates within the fluid chamber 64.

[0042] 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.

[0043] 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.

[0044] 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 31 valve body 32 valve seat 35 first seal surface 36 second seal surface 37 suction flow path 40 valve rod 41 valve guide 43 spring stopper 44 spring 50 fluid relief flow path 51 fluid inlet 52 fluid outlet 54 downflow path 55 discharge flow path 60 spring 63 communicating flow path 64 fluid chamber 65 opening 67 spiral groove 68 stationary vane 69 rotating vane

Claims

1. A reciprocating pump for transporting a fluid, comprising: a cylinder having a pressurizing chamber therein; a piston disposed within the cylinder; and a suction check valve communicating with the pressurizing chamber, the suction check valve comprising: a valve body; a first sealing surface in contact with the back side of the valve body; a second sealing surface surrounded by the first sealing surface; a suction flow path surrounded by the second sealing surface; and a fluid relief flow path having a fluid inlet surrounding the second sealing surface, the fluid inlet being located between the first sealing surface and the second sealing surface, and the fluid relief flow path having a fluid outlet communicating with the outside of the reciprocating pump.

2. The reciprocating pump of claim 1, wherein said fluid relief passage includes a downflow passage extending downward from said fluid inlet.

3. The reciprocating pump according to claim 2, wherein said fluid relief passage further includes an ascending passage extending obliquely upward from said descending passage to said fluid outlet.

4. The reciprocating pump of claim 1, wherein said fluid inlet has an annular shape.

5. A reciprocating pump as described in claim 1, wherein the fluid relief flow path includes a downward flow path located radially inward from the fluid inlet and a connecting flow path that connects the fluid inlet and the downward flow path, and the downward flow path extends to the fluid outlet.

6. A reciprocating pump according to claim 5, wherein the fluid relief passage further comprises a fluid chamber connected to an upper end of the descending passage, and the communicating passage extends from the fluid inlet to the fluid chamber.

7. A reciprocating pump according to claim 6, wherein the communication passage is connected to the side wall of the fluid chamber in a direction inclined relative to the radial direction of the fluid chamber when viewed from above.

8. A reciprocating pump according to claim 7, wherein a spiral groove is formed on the side wall of said fluid chamber.

9. The reciprocating pump according to claim 7, wherein said suction check valve further comprises a spiral stationary vane provided on a side wall of said fluid chamber.

10. The reciprocating pump of claim 7, wherein the suction check valve further comprises a rotor disposed within the fluid chamber.

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