Screw compressor and gas compression facility

Abstract

This screw compressor comprises: a pair of rotor shafts; a balance piston mounted on at least one of the rotor shafts; a balance piston chamber positioned on a suction side in an axial direction with respect to the balance piston; and a stationary member having an inner peripheral surface facing an outer peripheral surface of the balance piston. The balance piston has therein a communication path communicating with the balance piston chamber and an oil reservoir between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member. The communication path includes a radial flow path extending along a radial direction in the balance piston.

Description

Screw compressors and gas compression equipment

[0001] The present disclosure relates to screw compressors and gas compression equipment.

[0002] To reduce the load on the thrust bearing in a screw compressor, a balance piston is sometimes provided on the rotor shaft of the screw compressor. Oil having a pressure equal to or greater than the discharge pressure of the screw compressor is introduced into the balance piston chamber facing the end face of the balance piston, and a force in the opposite direction to the thrust gas load acting on the rotor shaft (thrust load acting on the rotor shaft due to the difference between the suction pressure and discharge pressure of the screw compressor) is applied to the rotor shaft via the end face of the balance piston, thereby reducing the load on the thrust bearing.

[0003] Patent Document 1 describes a screw compressor in which a balance piston is provided on a rotor shaft. In this screw compressor, a labyrinth (unevenness) is provided on the outer peripheral surface of the balance piston, and this labyrinth seal is designed to prevent oil from leaking from the balance piston chamber through a gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the casing facing the outer peripheral surface.

[0004] Japanese Unexamined Patent Publication No. 62-19658

[0005] In order to reduce oil leakage through the gap between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member (such as a casing or a sleeve) that faces the outer circumferential surface, it is conceivable to narrow the gap as much as possible. However, narrowing the gap may cause problems such as damage due to contact between the balance piston and the stationary member, or may reduce the ease of assembly of the screw compressor.

[0006] In view of the above circumstances, at least one embodiment of the present invention aims to provide a screw compressor and gas compression equipment that can effectively suppress oil leakage from the balance piston while preventing damage due to contact between components or ensuring good assembly of the screw compressor.

[0007] A screw compressor according to at least one embodiment of the present invention comprises: a pair of rotor shafts; a balance piston provided on at least one of the rotor shafts; a balance piston chamber located on the suction side of the balance piston in the axial direction; and a stationary member having an inner peripheral surface facing an outer peripheral surface of the balance piston, wherein the balance piston has a communication passage therein that communicates with the balance piston chamber and with an oil reservoir between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member, and the communication passage includes a radial flow path extending radially within the balance piston.

[0008] Furthermore, a gas compression facility according to at least one embodiment of the present invention includes the above-described screw compressor configured to compress gas, and an oil separator for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor.

[0009] According to at least one embodiment of the present invention, a screw compressor and gas compression equipment are provided that can effectively suppress oil leakage from the balance piston while preventing damage due to contact between components or ensuring good assembly of the screw compressor.

[0010] Fig. 4 is a schematic diagram of a gas compression facility according to one embodiment. Fig. 5 is a schematic cross-sectional view of a screw compressor according to one embodiment in a plan view. Fig. 6 is a schematic cross-sectional view of a screw compressor according to one embodiment in a plan view. Fig. 7 is an enlarged view showing a part of the schematic view of the screw compressor 2 shown in Fig. 2. Fig. 8 is a view of the balance piston shown in Fig. 4 from the radial outside. Fig. 9 is a view showing the AA cross section of the balance piston shown in Fig. 4.

[0011] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0012] 1 is a schematic diagram of a gas compression facility including a screw compressor according to some embodiments. As shown in the figure, the gas compression facility 1 includes a screw compressor 2, an oil separator 4, a cooler 6, and a pump 8.

[0013] The screw compressor 2 is configured to compress and discharge the gas that it has drawn in. In the drawing, the symbol Ps indicates the suction pressure of the screw compressor 2, and the symbol Pd indicates the discharge pressure of the screw compressor 2. Oil is supplied to the screw compressor 2 via an oil supply line 10 for cooling, lubrication, etc. The oil supplied to the screw compressor 2 is discharged together with the compressed gas.

[0014] The oil separator 4 is configured to separate oil from a mixture of compressed gas and oil discharged from the screw compressor 2. The oil separated in the oil separator 4 is supplied again to the screw compressor 2 via an oil supply line 10. Typically, the oil separated in the oil separator 4 is pressurized by a pump 8 and then supplied to the screw compressor 2 via the oil supply line 10. In this case, the pressure Poil of the oil supplied to the screw compressor 2 is higher than the discharge pressure Pd (Poil = Pd + α). The oil separated in the oil separator 4 may be cooled in a cooler 6 and then pressurized by the pump 8. Alternatively, the oil separated in the oil separator 4 may be cooled in the cooler 6 and then differentially supplied to the screw compressor via an oil supply line 10′ without passing through the pump 8.

[0015] 2 and 3 are schematic cross-sectional views in plan view of a screw compressor according to one embodiment. As shown in Fig. 2 and Fig. 3, the screw compressor 2 includes a pair of screw rotors (a male rotor 15 and a female rotor 17) including a pair of rotor shafts 14, 16, and a casing 12 that houses the pair of screw rotors.

[0016] The pair of rotor shafts 14, 16 are rotatably supported by radial bearings 18, 19, 20, 21 and thrust bearings 22, 23. Oil at a pressure Poil is supplied to each bearing via an oil supply line 10.

[0017] The male rotor 15 and the female rotor 17 have helical teeth that mesh with each other. The meshing of the teeth of the male rotor 15 and the female rotor 17 and the casing 12 form a plurality of tooth gap spaces (chambers) along the axial direction of the rotor shafts 14, 16.

[0018] The rotor shaft 14 that constitutes the male rotor 15 is connected to the output shaft of a motor (not shown) and is configured to be rotationally driven by the motor. The female rotor 17 that meshes with the male rotor 15 is rotationally driven by the rotation of the male rotor 15. The female rotor 17 rotates in the opposite direction to the rotation of the male rotor 15. When the male rotor 15 and female rotor 17 rotate in their meshed state, the tooth groove space moves axially from the suction side to the discharge side.

[0019] In the exemplary embodiment shown in Fig. 2, the rotor shaft 14 is configured so that the connection portion 11 located at the suction side end of the rotor shaft 14 is connected to the output shaft of the motor. That is, the screw compressor 2 shown in Fig. 2 is a suction side driven screw compressor 2.

[0020] In the exemplary embodiment shown in Fig. 3, the rotor shaft 14 is configured so that the connection portion 11 located at the discharge side end of both ends of the rotor shaft 14 is connected to the output shaft of the motor. In other words, the screw compressor 2 shown in Fig. 3 is a discharge-side driven screw compressor 2.

[0021] A shaft seal 24 for suppressing gas leakage through the penetration portion of the casing 12, which is formed by the rotor shaft 14, is provided at the penetration portion. Oil at a pressure Poil may be supplied to the shaft seal 24 through the oil supply line 10.

[0022] The oil supplied to the bearings and shaft seal portion 24 is discharged from the casing 12 and returned via a return line 28 to a relatively low-pressure space in the screw rotor accommodating portion of the casing 12 .

[0023] Gas is drawn into the tooth groove spaces from the suction spaces 50 formed in the casing 12 via the suction ports 52. When the male rotor 15 and the female rotor 17 rotate, the tooth groove spaces move axially from the suction side to the discharge side in accordance with the rotation of these screw rotors. During this process, the volume of the tooth groove spaces decreases after the suction ports 52 are closed, compressing the gas in the tooth groove spaces. When the tooth groove spaces reach the discharge ports 54 and communicate with a discharge space (not shown) formed in the casing 12, the compressed gas in the tooth groove spaces is discharged into the discharge space.

[0024] In some embodiments, the screw compressor 2 includes a disk-shaped balance piston 30 provided on at least one of the pair of rotor shafts 14, 16. In the exemplary embodiment shown in Fig. 2, the balance piston 30 is provided at the discharge side end of the rotor shaft 14 that constitutes the male rotor 15. In the exemplary embodiment shown in Fig. 3, the balance piston 30 is provided at the suction side end of the rotor shaft 14 that constitutes the male rotor 15. As shown in Figs. 2 and 3, the balance piston 30 is accommodated in an accommodation space 45 formed inside the casing 12. The balance piston 30 is fixed to the rotor shaft 14 and is adapted to rotate together with the rotor shaft 14.

[0025] Fig. 4 is an enlarged view showing a part of the schematic diagram of the screw compressor 2 shown in Fig. 2. The balance piston 30 shown in Fig. 3 basically has the same configuration as the balance piston 30 shown in Fig. 2 (Fig. 4). Fig. 5 is a view of the balance piston 30 shown in Fig. 4 as seen from the radial outside. Fig. 6 is a view showing a cross section A-A of the balance piston 30 shown in Fig. 4.

[0026] 4, the balance piston 30 has an outer peripheral surface 31 and two axial end surfaces, that is, a first end surface 32 and a second end surface 34. The first end surface 32 is located on the suction side in the axial direction, and the second end surface 34 is located on the discharge side in the axial direction.

[0027] An outer peripheral surface 31 of the balance piston 30 faces an inner peripheral surface 13 of a stationary member (the casing 12 in this embodiment), and a gap G is formed between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member). Note that in some embodiments, a sleeve (stationary member) fixed to the casing 12 may be provided on the outer periphery of the balance piston 30, so that the outer peripheral surface 31 of the balance piston 30 faces the inner peripheral surface of the sleeve (stationary member).

[0028] The accommodation space 45 that accommodates the balance piston 30 has a first chamber (balance piston chamber) 42 facing the first end face 32 of the balance piston 30, and a second chamber (low-pressure chamber) 44 facing the second end face 34 of the balance piston 30. The first chamber (balance piston chamber) 42 is located on the suction side of the balance piston 30 in the axial direction. The second chamber (low-pressure chamber) 44 is located on the discharge side of the balance piston 30 in the axial direction.

[0029] The first chamber (balance piston chamber) 42 is supplied with oil (relatively high-pressure oil discharged from the screw compressor 2) separated in the oil separator 4 (see FIG. 1). Oil pressurized by the pump 8 (Poil = Pd + α) may be supplied to the first chamber 42 via the oil supply line 10, or the oil separated in the oil separator 4 (Poil = Pd) may be supplied directly (without being pressurized by the pump) via the oil supply line 10' (see FIG. 1). The oil from the oil supply line 10 (or 10') is supplied to the first chamber 42 via an oil supply passage 46 provided in the casing 12.

[0030] A portion of the oil supplied to the first chamber 42 leaks into the second chamber 44 through a gap G between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12. As shown in Figures 2 and 3, the oil in the second chamber 44 is recovered into the return line 28 through an oil drain passage 48 provided in the casing 12 and is returned to the relatively low-pressure space of the screw rotor accommodating portion of the casing 12.

[0031] A seal portion 26 may be provided to prevent oil from leaking from the first chamber 42 through the gap between the casing 12 and the rotor shaft 14 .

[0032] When relatively high-pressure oil is introduced from the oil supply line 10 (or 10′) into the first chamber (balance piston chamber) 42 facing the first end face 32 on the suction side of the balance piston 30, a force (a force in the axial direction from the suction side to the discharge side) in the opposite direction to the thrust gas load acting on the rotor shaft 14 (a thrust load acting on the rotor shaft 14 in the axial direction from the discharge side to the suction side due to the difference between the suction pressure Ps and the discharge pressure Pd of the screw compressor 2) acts on the rotor shaft 14 via the first end face 32 of the balance piston 30. This reduces the load on the thrust bearing 22.

[0033] 2 to 5, in some embodiments, the balance piston 30 has a communication passage 36 formed inside the balance piston 30. The communication passage 36 communicates with a first chamber (balance piston chamber) 42 and also communicates with an oil reservoir 40 formed between the outer circumferential surface 31 of the balance piston 30 and the inner circumferential surface 13 of the casing 12 (stationary member). As shown in FIG. 4, the communication passage 36 includes a radial flow passage 38 extending radially inside the balance piston 30.

[0034] The oil reservoir 40 is a space formed between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member), and is larger in radial size than the gap G. As shown in FIGS. 4 to 6 , the oil reservoir 40 may include a groove 41 provided in the outer peripheral surface 31 of the balance piston 30. A plurality of grooves 41 (a plurality of oil reservoirs 40) spaced apart in the circumferential direction may be formed between the balance piston 30 and the casing 12. Note that FIGS. 2 and 3 show two oil reservoirs 40 spaced 180 degrees apart in the circumferential direction. Alternatively, although not specifically shown, the oil reservoir 40 may include a circumferential groove that is continuous in the circumferential direction.

[0035] The balance piston 30 may also be provided with a plurality of communication passages 36, each having a radial flow passage 38. In the embodiment shown in Figures 2 and 3, two communication passages 36 are provided corresponding to the two oil reservoirs 40, respectively.

[0036] The communication passage 36 includes a first open end 36a that opens to the first end face 32 of the balance piston 30, and a second open end 36b that opens to a portion of the outer circumferential surface 31 of the balance piston 30 that forms the oil reservoir 40. In the embodiment shown in FIG. 4 , the second open end 36b is one end of a radial flow passage 38. As shown in FIG. 4 , the communication passage 36 may include an axial flow passage 37 that is connected to the radial flow passage 38 and extends along the axial direction. In the exemplary embodiment shown in FIG. 4 , the first open end 36a is one end of the axial flow passage 37.

[0037] In the configuration according to the above-described embodiment, oil from the first chamber (balance piston chamber) 42 is introduced into the communicating passage 36 formed inside the balance piston 30, pressurized in the radial flow passage 38 by centrifugal force caused by rotation of the rotor shaft 14, and supplied to the oil reservoir 40 between the outer circumferential surface 31 of the balance piston 30 and the inner circumferential surface 13 of the casing 12 (stationary member). That is, oil at a pressure slightly higher than that of the first chamber (balance piston chamber) 42 is supplied to the oil reservoir 40, which effectively prevents oil from moving from the first chamber (balance piston chamber) 42 to the opposite second chamber (low-pressure chamber) 44 via the gap G between the outer circumferential surface 31 of the balance piston 30 and the inner circumferential surface 13 of the casing 12 (stationary member). Therefore, even if the gap G between the outer circumferential surface 31 of the balance piston 30 and the inner circumferential surface 13 of the casing 12 (stationary member) is widened to some extent, oil leakage via the gap G can be appropriately prevented. Therefore, according to the above-described embodiment, it is possible to prevent damage caused by contact between the balance piston 30 and the casing 12 (stationary member), or to effectively suppress oil leakage from the balance piston 30 while realizing good assembly ease of the screw compressor 2.

[0038] In some embodiments, the width W2 of the oil reservoir 40 in the axial direction (see FIG. 5 ) may be greater than or equal to ¼ and less than or equal to ½ of the width W1 of the balance piston 30 in the axial direction (see FIG. 5 ). If the width W2 of the oil reservoir 40 is greater than or equal to ¼ of the width W1 of the balance piston 30, oil pressurized in the radial flow passages 38 is supplied to a relatively wide area of ​​the outer circumferential surface 31 of the balance piston 30, making it easier to suppress oil leakage from the first chamber (balance piston chamber) 42 through the gap G. Furthermore, if the width W2 of the oil reservoir 40 is less than or equal to ½ of the width W1 of the balance piston 30, the axial distance L2 (see FIG. 5 ) between the oil reservoir 40 and the second end face 34 is not too short, ensuring a certain degree of pressure loss between the oil reservoir 40 and the second end face 34 and making it easier to suppress oil movement from the oil reservoir toward the second chamber (low-pressure chamber) 44 (the second end face 34 side). This makes it possible to more effectively suppress oil leakage through the gap G between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member).

[0039] In some embodiments, the distance L1 (see FIG. 5 ) between the oil reservoir 40 and the first end face 32 in the axial direction is shorter than the distance L2 (see FIG. 5 ) between the oil reservoir 40 and the second end face 34 in the axial direction. For example, the distance L1 between the oil reservoir 40 and the first end face 32 in the axial direction may be equal to or less than half the distance L2 between the oil reservoir 40 and the second end face 34 in the axial direction.

[0040] In the above-described embodiment, the axial distance L2 between the oil reservoir 40 and the second end face 34 (the end face on the second chamber (low pressure chamber) 44 side) of the balance piston 30 is relatively long, which ensures a certain degree of pressure loss between the oil reservoir 40 and the second end face 34 and makes it easier to suppress the movement of oil from the oil reservoir 40 toward the second chamber (low pressure chamber) 44 side (the second end face 34 side). This makes it possible to more effectively suppress oil leakage through the gap G between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member).

[0041] In some embodiments, the radial length L3 (see FIG. 4) of the radial flow passage 38 is equal to or greater than one-third of the difference L4 (=r1-r2) (see FIG. 4) between the outer radius r1 and the inner radius r2 of the first end face 32. Alternatively, the radial length L3 of the radial flow passage 38 may be equal to or greater than one-half or two-thirds of the difference L4 (=r1-r2) between the outer radius r1 and the inner radius r2 of the first end face 32.

[0042] According to the above-described embodiment, the radial length L3 of the radial flow passage 38 is relatively long, so that the oil guided from the first chamber (balance piston chamber) 42 to the radial flow passage 38 is easily pressurized by the centrifugal force caused by the rotation of the rotor shaft 14. This makes it easier for relatively high-pressure oil to be supplied to the oil reservoir 40, making it possible to more effectively suppress oil leakage through the gap G between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member).

[0043] In some embodiments, the outer peripheral surface 31 of the balance piston 30 is formed as a smooth surface. That is, in some embodiments, the outer peripheral surface 31 of the balance piston 30 does not have any irregularities that would form a labyrinth seal.

[0044] In the above-described embodiment, the outer peripheral surface 31 of the balance piston 30 is a smooth surface, so that rotation of the rotor shaft 14 (i.e., rotation of the balance piston 30) forms a boundary layer on the surface of the outer peripheral surface 31. This boundary layer inhibits axial movement of oil in the gap G between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member). Therefore, oil leakage through the gap G can be more effectively suppressed.

[0045] In the above description, an oil-injected screw compressor including an oil separator in which oil is supplied from the oil separator to the screw rotors and the like has been described as a screw compressor according to some embodiments. However, the balance piston described above can also be applied to an oil-free screw compressor that does not include an oil separator. That is, the screw compressor according to some embodiments may be an oil-free screw compressor. In the case of an oil-free screw compressor, oil may be pressurized by a pump and supplied to the balance piston from an oil reservoir such as an oil tank.

[0046] The contents described in each of the above embodiments can be understood, for example, as follows.

[0047] [1] A screw compressor (2) according to at least one embodiment of the present invention comprises: a pair of rotor shafts (14, 16); a balance piston (30) provided on at least one of the rotor shafts (14); a balance piston chamber (e.g., a first chamber 42) located on the suction side of the balance piston in the axial direction; and a stationary member (e.g., a casing 12) having an inner peripheral surface (13) facing an outer peripheral surface (31) of the balance piston, wherein the balance piston has therein a communication passage (36) communicating with the balance piston chamber and an oil reservoir (40) between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member, and the communication passage includes a radial flow path (38) extending radially within the balance piston.

[0048] In the configuration [1] above, oil from the balance piston chamber is introduced into a communicating passage formed inside the balance piston, pressurized in the radial flow passage by centrifugal force caused by rotation of the rotor shaft, and supplied to an oil reservoir between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member. That is, oil at a pressure slightly higher than that of the balance piston chamber is supplied to the oil reservoir, effectively preventing oil from moving from the balance piston chamber to the opposite low-pressure chamber through the gap between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member. Therefore, even if the gap between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member is widened to a certain extent, oil leakage through the gap can be appropriately prevented. Therefore, the configuration [1] above can prevent damage due to contact between the balance piston and the stationary member, or effectively prevent oil leakage from the balance piston while achieving good assembly ease of the screw compressor.

[0049] [2] In some embodiments, in the configuration of [1] above, the balance piston has a first end face (32) facing the balance piston chamber and a second end face (34) opposite the first end face in the axial direction, and the distance (L1) between the oil reservoir and the first end face in the axial direction is shorter than the distance (L2) between the oil reservoir and the second end face in the axial direction.

[0050] According to the configuration [2] above, the axial distance between the oil reservoir and the first end face of the balance piston (the end face facing the balance piston chamber) is shorter than the axial distance between the oil reservoir and the second end face of the balance piston (the end face facing the low-pressure chamber). This ensures a certain degree of pressure loss between the oil reservoir and the second end face, thereby suppressing oil movement from the oil reservoir toward the low-pressure chamber (the second end face). This more effectively suppresses oil leakage through the gap between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member.

[0051] [3] In some embodiments, in the configuration of [1] or [2] above, the balance piston has a first end face (32) facing the balance piston chamber, and the radial length (L3) of the radial flow path is equal to or greater than 1 / 3 of the difference (L4) between the outer radius and the inner radius of the first end face.

[0052] According to the configuration [3], the radial length of the radial flow passage is relatively long, being 1 / 3 of the difference between the outer radius and the inner radius of the first end face, so that the oil guided to the radial flow passage is easily pressurized by the centrifugal force caused by the rotation of the rotor shaft. Therefore, relatively high-pressure oil is easily supplied to the oil reservoir, and oil leakage through the gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member can be more effectively suppressed.

[0053] [4] In some embodiments, in the configuration of any one of the above [1] to [3], the oil reservoir includes a groove (41) formed in the outer circumferential surface of the balance piston.

[0054] According to the above configuration [4], the oil reservoir includes a groove formed on the outer peripheral surface of the balance piston, so that the oil reservoir can be formed relatively easily by machining the balance piston.

[0055] [5] In some embodiments, in the configuration of any one of the above [1] to [4], the outer circumferential surface of the balance piston is a smooth surface.

[0056] According to the configuration [5] above, since the outer peripheral surface of the balance piston is smooth, a boundary layer is formed on the outer peripheral surface due to the rotation of the rotor shaft (i.e., due to the rotation of the balance piston). This boundary layer inhibits the axial movement of oil in the gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member. Therefore, oil leakage through the gap can be more effectively suppressed.

[0057] [6] A gas compression facility (1) according to at least one embodiment of the present invention comprises: a screw compressor (2) configured to compress gas according to any one of claims [1] to [5]; and an oil separator (4) for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor.

[0058] In the configuration [6] above, oil from the balance piston chamber is introduced into a communicating passage formed inside the balance piston, pressurized by centrifugal force in the radial flow passage, and supplied to an oil reservoir between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member. That is, oil at a pressure slightly higher than that of the balance piston chamber is supplied to the oil reservoir, effectively preventing oil from moving from the balance piston chamber to the opposite low-pressure chamber through the gap between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member. Therefore, even if the gap between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member is widened to some extent, oil leakage through the gap can be appropriately prevented. Therefore, the configuration [6] above can prevent damage due to contact between the balance piston and the stationary member, or effectively prevent oil leakage from the balance piston while achieving good assembly ease of the screw compressor.

[0059] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0060] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0061] REFERENCE SIGNS LIST 1 gas compression equipment 2 screw compressor 4 oil separator 6 cooler 8 pump 10 oil supply line 10' oil supply line 11 connection portion 12 casing 13 inner peripheral surface 14 rotor shaft 15 male rotor 16 rotor shaft 17 female rotor 18 radial bearing 19 radial bearing 20 radial bearing 21 radial bearing 22 thrust bearing 23 thrust bearing 24 shaft seal portion 26 seal portion 28 return line 30 balance piston 31 outer peripheral surface 32 first end face 34 second end face 36 communicating passage 36a first opening end 36b second opening end 37 axial flow passage 38 radial flow passage 40 oil reservoir 41 groove 42 first chamber (balance piston chamber) 44 second chamber (low pressure chamber) 45 accommodation space 46 Oil supply passage 48 Oil drain passage 50 Intake space 52 Intake port 54 Discharge port G Gap L1 Distance L2 Distance Pd Discharge pressure Ps Intake pressure r1 Outer radius r2 Inner radius

Claims

1. A screw compressor comprising: a pair of rotor shafts; a balance piston provided on at least one of the rotor shafts; a balance piston chamber located on the suction side of the balance piston in the axial direction; and a stationary member having an inner circumferential surface facing an outer circumferential surface of the balance piston, wherein the balance piston has an internal communication passage communicating with the balance piston chamber and with an oil reservoir between the outer circumferential surface of the balance piston and the inner circumferential surface of the stationary member, and the communication passage includes a radial flow path extending radially within the balance piston.

2. The screw compressor according to claim 1, wherein the balance piston has a first end face facing the balance piston chamber and a second end face opposite the first end face in the axial direction, and the distance between the oil reservoir and the first end face in the axial direction is shorter than the distance between the oil reservoir and the second end face in the axial direction.

3. The screw compressor according to claim 1 or 2, wherein the balance piston has a first end face facing the balance piston chamber, and the radial length of the radial flow passage is equal to or greater than 1 / 3 of the difference between the outer radius and the inner radius of the first end face.

4. A screw compressor according to claim 1 or 2, wherein the oil reservoir includes a groove formed on the outer circumferential surface of the balance piston.

5. The screw compressor according to claim 1 or 2, wherein the outer peripheral surface of the balance piston is a smooth surface.

6. A gas compression installation comprising: a screw compressor according to claim 1 or 2 configured to compress a gas; and an oil separator for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor.

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