Screw compressor and gas compression facility

Abstract

A screw compressor includes: a pair of rotor shafts; a balance piston disposed on at least one of the rotor shafts; a balance piston chamber disposed 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 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 along a radial direction inside the balance piston.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a screw compressor and a gas compression facility.BACKGROUND

[0002] In order to reduce the load on a thrust bearing in a screw compressor, a balance piston may be provided on a rotor shaft of the screw compressor. Oil having a pressure equal to or higher than the discharge pressure of the screw compressor is introduced into a balance piston chamber facing an end surface of the balance piston, and a force in a direction opposite to a thrust gas load acting on the rotor shaft (a thrust load acting on the rotor shaft due to a difference between the suction pressure and the discharge pressure of the screw compressor) is applied to the rotor shaft via the end surface 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 (irregularities) is provided on an outer peripheral surface of the balance piston, and this labyrinth seal suppresses leakage of oil from the balance piston chamber through a gap between the outer peripheral surface of the balance piston and an inner peripheral surface of a casing facing the outer peripheral surface.Citation ListPatent Literature

[0004] Patent Document 1: JPS62-19658ASUMMARYProblems to be Solved

[0005] Here, in order to reduce leakage of oil through a gap between the outer peripheral surface of the balance piston and an inner peripheral surface of a stationary member (such as a casing or a sleeve) facing the outer peripheral surface, it is conceivable to narrow the gap as much as possible. On the other hand, narrowing the gap may cause a problem that damage occurs due to contact between the balance piston and the stationary member, or assemblability of the screw compressor deteriorates.

[0006] In view of the above circumstances, an object of at least one embodiment of the present invention is to provide a screw compressor and a gas compression facility capable of achieving both effective suppression of oil leakage in the balance piston and prevention of damage due to contact between members or good assemblability of the screw compressor.Solution to the Problems

[0007] A screw compressor according to at least one embodiment of the present invention includes: a pair of rotor shafts; a balance piston disposed on at least one of the rotor shafts; a balance piston chamber disposed 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.

[0008] 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.

[0009] The communication passage includes a radial flow path extending along a radial direction inside the balance piston.

[0010] Further, a gas compression facility according to at least one embodiment of the present invention includes: the above-described screw compressor 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. Advantageous Effects

[0011] At least one embodiment of the present invention provides a screw compressor and a gas compression facility capable of achieving both effective suppression of oil leakage in the balance piston and prevention of damage due to contact between members or good assemblability of the screw compressor.BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 is a schematic diagram of a gas compression facility according to an embodiment. FIG. 2 is a schematic cross-sectional view of a screw compressor according to an embodiment in plan view. FIG. 3 is a schematic cross-sectional view of a screw compressor according to an embodiment in plan view. FIG. 4 is an enlarged view showing a part of the schematic diagram of the screw compressor 2 shown in FIG. 2. FIG. 5 is a diagram of the balance piston shown in FIG. 4 as viewed from the radially outer side. FIG. 6 is a cross-sectional view of the balance piston shown in FIG. 4 taken along line A-A. DETAILED DESCRIPTION

[0013] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions, and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.(Configuration of Gas Compression Facility)

[0014] FIG. 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.

[0015] The screw compressor 2 is configured to compress and discharge sucked gas. The reference character Ps shown in the figure indicates the suction pressure of the screw compressor 2, and the reference character Pd indicates the discharge pressure of the screw compressor 2. Oil is supplied to the screw compressor 2 through an oil supply line 10 for cooling, lubrication, and the like. The oil supplied to the screw compressor 2 is discharged together with compressed gas.

[0016] The oil separator 4 is configured to separate the oil from a mixture of compressed gas and oil discharged from the screw compressor 2. The oil separated by the oil separator 4 is supplied again to the screw compressor 2 through the oil supply line 10. Typically, the oil separated by the oil separator 4 is pressurized by the pump 8 and then supplied to the screw compressor 2 through 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 by the oil separator 4 may be cooled by the cooler 6 and then pressurized by the pump 8. Also, the oil separated by the oil separator 4 may be cooled by the cooler 6 and then supplied to the screw compressor by differential pressure through an oil supply line 10' without passing through the pump 8.(Configuration of Screw Compressor)

[0017] FIGs. 2 and 3 are each a schematic cross-sectional view of a screw compressor according to an embodiment in plan view. As shown in FIGs. 2 and 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 accommodating the pair of screw rotors.

[0018] The pair of rotor shafts 14, 16 are rotatably supported by radial bearings 18, 19, 20, 21 and thrust bearings 22, 23, respectively. Oil at pressure Poil is supplied to each bearing through the oil supply line 10.

[0019] The male rotor 15 and the female rotor 17 have helical teeth that mesh with each other. A plurality of tooth groove spaces (chambers) are formed along the axial direction of the rotor shafts 14, 16 by meshing of the teeth of the male rotor 15 and the female rotor 17 together with the casing 12.

[0020] The rotor shaft 14 constituting the male rotor 15 is connected to an output shaft of a motor (not shown) and is configured to be rotationally driven by the motor. The female rotor 17 meshing with the male rotor 15 is rotationally driven by rotation of the male rotor 15. The female rotor 17 rotates in a direction opposite to the rotation direction of the male rotor 15. When the male rotor 15 and the female rotor 17 rotate in a meshed state, the tooth groove spaces move from the suction side to the discharge side in the axial direction.

[0021] In the exemplary embodiment shown in FIG. 2, the rotor shaft 14 is configured such that a connection part 11 located at a suction-side end portion among both end portions 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 drive screw compressor 2.

[0022] In the exemplary embodiment shown in FIG. 3, the rotor shaft 14 is configured such that a connection part 11 located at a discharge-side end portion among both end portions of the rotor shaft 14 is connected to the output shaft of the motor. That is, the screw compressor 2 shown in FIG. 3 is a discharge-side drive screw compressor 2.

[0023] A shaft seal part 24 is provided at a portion of the casing 12 through which the rotor shaft 14 passes to suppress leakage of gas through this portion. Oil at pressure Poil may be supplied to the shaft seal part 24 through the oil supply line 10.

[0024] The oil supplied to the bearings and the shaft seal part 24 is discharged from the casing 12 and returned to a relatively low-pressure space of a screw rotor accommodating portion of the casing 12 via a return line 28.

[0025] Gas is sucked into the above-described tooth groove space from a suction space 50 formed in the casing 12 via a suction port 52. When the male rotor 15 and the female rotor 17 rotate, the tooth groove space moves from the suction side to the discharge side in the axial direction with the rotation of these screw rotors. In this process, since the volume of the tooth groove space is reduced after the suction port 52 is closed, the gas in the tooth groove space is compressed. When the tooth groove space reaches a discharge port 54 and the tooth groove space communicates with a discharge space (not shown) formed in the casing 12, the compressed gas in the tooth groove space is discharged to the discharge space.

[0026] In some embodiments, the screw compressor 2 includes a disk-shaped balance piston 30 disposed 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 disposed at a discharge-side end portion of the rotor shaft 14 constituting the male rotor 15. In the exemplary embodiment shown in FIG. 3, the balance piston 30 is disposed at a suction-side end portion of the rotor shaft 14 constituting 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 rotates together with the rotor shaft 14.

[0027] 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 diagram of the balance piston 30 shown in FIG. 4 as viewed from the radially outer side. FIG. 6 is a cross-sectional view of the balance piston 30 shown in FIG. 4 taken along line A-A.

[0028] As shown in FIG. 4, the balance piston 30 has an outer peripheral surface 31, and has a first end surface 32 and a second end surface 34 which are both end surfaces in the axial direction. 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.

[0029] The outer peripheral surface 31 of the balance piston 30 faces an inner peripheral surface 13 of a stationary member (the casing 12 in the present 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). In some embodiments, a sleeve (stationary member) fixed to the casing 12 may be provided on the outer peripheral side of the balance piston 30, and the outer peripheral surface 31 of the balance piston 30 and an inner peripheral surface of the sleeve (stationary member) may face each other.

[0030] The accommodation space 45, in which the balance piston 30 is accommodated, has a first chamber (balance piston chamber) 42 facing the first end surface 32 of the balance piston 30, and a second chamber (low-pressure chamber) 44 facing the second end surface 34 of the balance piston 30. The first chamber (balance piston chamber) 42 is located on the suction side in the axial direction with respect to the balance piston 30. The second chamber (low-pressure chamber) 44 is located on the discharge side in the axial direction with respect to the balance piston 30.

[0031] The oil separated by the oil separator 4 (see FIG. 1) (relatively high-pressure oil discharged from the screw compressor 2) is supplied to the first chamber (balance piston chamber) 42. The oil pressurized by the pump 8 (Poil = Pd + α) may be supplied to the first chamber 42 through the oil supply line 10, or the oil separated by the oil separator 4 (Poil = Pd) may be supplied as it is (without being pressurized by the pump) through 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 disposed in the casing 12.

[0032] A part of the oil supplied to the first chamber 42 leaks to the second chamber 44 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. As shown in FIGs. 2 and 3, the oil in the second chamber 44 is recovered to the return line 28 through an oil discharge passage 48 disposed in the casing 12, and returned to the relatively low-pressure space of the screw rotor accommodating portion of the casing 12.

[0033] A seal part 26 may be provided to suppress leakage of oil from the first chamber 42 through a gap between the casing 12 and the rotor shaft 14.

[0034] 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 surface 32 on the suction side of the balance piston 30, a force (a force in a direction from the suction side to the discharge side in the axial direction) opposite to a thrust gas load acting on the rotor shaft 14 (a thrust load acting on the rotor shaft 14 due to a difference between the suction pressure Ps and the discharge pressure Pd of the screw compressor 2, in a direction from the discharge side to the suction side in the axial direction) acts on the rotor shaft 14 via the first end surface 32 of the balance piston 30. Thus, the load on the thrust bearing 22 can be reduced.

[0035] As shown in FIGs. 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 the first chamber (balance piston chamber) 42 and communicates with an oil reservoir 40 formed between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member). As shown in FIG. 4, the communication passage 36 includes a radial flow path 38 extending along the radial direction inside the balance piston 30.

[0036] 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 having a size in the radial direction larger than the gap G. As shown in FIGs. 4 to 6, the oil reservoir 40 may include a groove 41 provided on the outer peripheral surface 31 of the balance piston 30. A plurality of grooves 41 (a plurality of oil reservoirs 40) apart from each other in the circumferential direction may be formed between the balance piston 30 and the casing 12. FIGs. 2 and 3 show two oil reservoirs 40 at 180 degrees apart in the circumferential direction. Alternatively, although not particularly shown, the oil reservoir 40 may include a circumferential groove continuous in the circumferential direction.

[0037] Further, the balance piston 30 may be provided with a plurality of communication passages 36 each having a radial flow path 38. In the embodiment shown in FIGs. 2 and 3, two communication passages 36 respectively corresponding to the two oil reservoirs 40 are provided.

[0038] The communication passage 36 includes a first open end 36a opening to the first end surface 32 of the balance piston 30, and a second open end 36b opening to a portion forming the oil reservoir 40 in the outer peripheral surface 31 of the balance piston 30. In the embodiment shown in FIG. 4, the second open end 36b is one end of the radial flow path 38. As shown in FIG. 4, the communication passage 36 may include an axial flow path 37 connected to the radial flow path 38 and extending along the axial direction. In the exemplary embodiment shown in FIG. 4, the first open end 36a is one end of the axial flow path 37.

[0039] In the configuration according to the above-described embodiment, the oil from the first chamber (balance piston chamber) 42 is introduced into the communication passage 36 formed inside the balance piston 30, pressurized by centrifugal force due to rotation of the rotor shaft 14 in the radial flow path 38, and supplied to the oil reservoir 40 between the outer peripheral surface 31 of the balance piston 30 and the inner peripheral surface 13 of the casing 12 (stationary member). That is, since oil having a pressure slightly higher than the pressure of the first chamber (balance piston chamber) 42 is supplied to the oil reservoir 40, movement of oil from the first chamber (balance piston chamber) 42 to the opposite second chamber (low-pressure chamber) 44 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) can be effectively suppressed. Therefore, even if 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) is widened to some extent, oil leakage through the gap G can be appropriately suppressed. Thus, according to the above-described embodiment, it is possible to effectively suppress oil leakage in the balance piston 30 while preventing damage due to contact between the balance piston 30 and the casing 12 (stationary member) or realizing good assemblability of the screw compressor 2.

[0040] In some embodiments, the width W2 (see FIG. 5) of the oil reservoir 40 in the axial direction may be not less than 1 / 4 and not more than 1 / 2 of the width W1 (see FIG. 5) of the balance piston 30 in the axial direction. If the width W2 of the oil reservoir 40 is not less than 1 / 4 of the width W1 of the balance piston 30, the oil pressurized in the radial flow path 38 is supplied to a relatively wide region of the outer peripheral surface 31 of the balance piston 30, so that oil leakage from the first chamber (balance piston chamber) 42 through the gap G is easily suppressed. Further, if the width W2 of the oil reservoir 40 is not more than 1 / 2 of the width W1 of the balance piston 30, the distance L2 (see FIG. 5) between the oil reservoir 40 and the second end surface 34 in the axial direction is not too short, so that pressure loss between the oil reservoir 40 and the second end surface 34 is secured to some extent, and movement of oil from the oil reservoir toward the second chamber (low-pressure chamber) 44 (toward the second end surface 34) is easily suppressed. Thus, 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) can be more effectively suppressed.

[0041] In some embodiments, the distance L1 (see FIG. 5) between the oil reservoir 40 and the first end surface 32 in the axial direction is shorter than the distance L2 (see FIG. 5) between the oil reservoir 40 and the second end surface 34 in the axial direction. For example, the distance L1 between the oil reservoir 40 and the first end surface 32 in the axial direction may be not more than 1 / 2 of the distance L2 between the oil reservoir 40 and the second end surface 34 in the axial direction.

[0042] In the above-described embodiment, since the distance L2 between the oil reservoir 40 and the second end surface 34 (end surface on the second chamber (low-pressure chamber) 44 side) of the balance piston 30 in the axial direction is relatively long, pressure loss between the oil reservoir 40 and the second end surface 34 is secured to some extent, making it easier to suppress movement of oil from the oil reservoir 40 toward the second chamber (low-pressure chamber) 44 (toward the second end surface 34). Thus, 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) can be more effectively suppressed.

[0043] In some embodiments, the length L3 (see FIG. 4) of the radial flow path 38 in the radial direction is not less than 1 / 3 of a difference L4 (= r1 - r2) (see FIG. 4) between the outer radius r1 and the inner radius r2 of the first end surface 32. Alternatively, the length L3 of the radial flow path 38 in the radial direction may be not less than 1 / 2 or not less than 2 / 3 of the difference L4 (= r1 - r2) between the outer radius r1 and the inner radius r2 of the first end surface 32.

[0044] According to the above-described embodiment, since the length L3 of the radial flow path 38 in the radial direction is relatively long, the oil introduced from the first chamber (balance piston chamber) 42 to the radial flow path 38 is easily pressurized by centrifugal force due to rotation of the rotor shaft 14. Therefore, relatively high-pressure oil is easily supplied to the oil reservoir 40, so that leakage of oil 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) can be more effectively suppressed.

[0045] In some embodiments, the outer peripheral surface 31 of the balance piston 30 is formed of a smooth surface. In other words, in some embodiments, irregularities that form a labyrinth seal are not formed on the outer peripheral surface 31 of the balance piston 30.

[0046] In the above-described embodiment, since the outer peripheral surface 31 of the balance piston 30 is a smooth surface, a boundary layer is formed on the surface of the outer peripheral surface 31 by rotation of the rotor shaft 14 (that is, rotation of the balance piston 30). This boundary layer inhibits movement of oil in the axial direction 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, leakage of oil through the gap G can be more effectively suppressed.

[0047] In the above description, the oil-supply type screw compressor including the oil separator and supplying oil from the oil separator to the screw rotor and the like has been described as the screw compressor according to some embodiments, but the above-described balance piston can also be applied to an oil-free type screw compressor not including an oil separator. That is, the screw compressor according to some embodiments may be an oil-free type screw compressor. In the case of the oil-free type screw compressor, oil from an oil storage part such as an oil tank may be pressurized by a pump and supplied to the balance piston.

[0048] The contents described in the above embodiments would be understood as follows, for instance. [1] A screw compressor (2) according to at least one embodiment of the present invention includes: a pair of rotor shafts (14, 16); a balance piston (30) disposed on at least one of the rotor shafts (14); a balance piston chamber (e.g., the first chamber 42) disposed on a suction side in an axial direction with respect to the balance piston; and a stationary member (e.g., the casing 12) having an inner peripheral surface (13) facing an outer peripheral surface (31) of the balance piston.

[0049] The balance piston has a communication passage (36) therein that communicates with the balance piston chamber and with an oil reservoir (40) between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member.

[0050] The communication passage includes a radial flow path (38) extending along a radial direction inside the balance piston.

[0051] In the above configuration [1], the oil from the balance piston chamber is introduced into the communication passage formed inside the balance piston, pressurized by centrifugal force due to rotation of the rotor shaft in the radial flow path, and supplied to the oil reservoir between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member. That is, since oil having a pressure slightly higher than the pressure of the balance piston chamber is supplied to the oil reservoir, movement of oil from the balance piston chamber to the opposite low-pressure chamber through the gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member can be effectively suppressed. Therefore, even if the gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member is widened to some extent, oil leakage through the gap can be appropriately suppressed. Therefore, with the above configuration [1], it is possible to effectively suppress oil leakage in the balance piston while preventing damage due to contact between the balance piston and the stationary member or realizing good assemblability of the screw compressor.

[0052] [2] In some embodiments, in the above configuration [1], the balance piston has a first end surface (32) facing the balance piston chamber, and a second end surface (34) opposite to the first end surface in the axial direction.

[0053] A distance (L1) between the oil reservoir and the first end surface in the axial direction is shorter than a distance (L2) between the oil reservoir and the second end surface in the axial direction.

[0054] With the above configuration [2], the distance between the oil reservoir and the first end surface (end surface on the balance piston chamber side) of the balance piston in the axial direction is shorter than the distance between the oil reservoir and the second end surface (end surface on the low-pressure chamber side) of the balance piston in the axial direction. Therefore, pressure loss between the oil reservoir and the second end surface is secured to some extent, and movement of oil from the oil reservoir toward the low-pressure chamber (toward the second end surface) can be suppressed. Thus, 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.

[0055] [3] In some embodiments, in the above configuration [1] or [2], the balance piston has a first end surface (32) facing the balance piston chamber.

[0056] A length (L3) of the radial flow path in the radial direction is not less than 1 / 3 of a difference (L4) between an outer radius and an inner radius of the first end surface.

[0057] With the above configuration [3], since the length of the radial flow path in the radial direction is 1 / 3 of the difference between the outer radius and the inner radius of the first end surface and is relatively long, the oil introduced to the radial flow path is easily pressurized by centrifugal force due to rotation of the rotor shaft. Therefore, relatively high-pressure oil is easily supplied to the oil reservoir, so that leakage of oil 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.

[0058] [4] In some embodiments, in any one of the above configurations [1] to [3], the oil reservoir includes a groove (41) formed on the outer peripheral surface of the balance piston.

[0059] With the above configuration [4], since the oil reservoir includes the groove formed on the outer peripheral surface of the balance piston, the oil reservoir can be relatively easily formed by processing the balance piston.

[0060] [5] In some embodiments, in any one of the above configurations [1] to [4], the outer peripheral surface of the balance piston is a smooth surface.

[0061] With the above configuration [5], since the outer peripheral surface of the balance piston is a smooth surface, a boundary layer is formed on the surface of the outer peripheral surface by rotation of the rotor shaft (that is, rotation of the balance piston). This boundary layer inhibits movement of oil in the axial direction in the gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member. Therefore, leakage of oil through the gap can be more effectively suppressed.

[0062] [6] A gas compression facility (1) according to at least one embodiment of the present invention includes: the screw compressor (2) according to any one of [1] to [5] configured to compress a gas; and an oil separator (4) for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor.

[0063] In the above configuration [6], oil from the balance piston chamber is introduced into the communication passage formed inside the balance piston, pressurized by centrifugal force in the radial flow path, and supplied to the oil reservoir between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member. That is, since oil having a pressure slightly higher than the pressure of the balance piston chamber is supplied to the oil reservoir, movement of oil from the balance piston chamber to the opposite low-pressure chamber through the gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member can be effectively suppressed. Therefore, even if the gap between the outer peripheral surface of the balance piston and the inner peripheral surface of the stationary member is widened to some extent, oil leakage through the gap can be appropriately suppressed. Therefore, with the above configuration [6], it is possible to effectively suppress oil leakage in the balance piston while preventing damage due to contact between the balance piston and the stationary member or realizing good assemblability of the screw compressor.

[0064] Embodiments of the present invention were described in detail above, but the present invention is not limited thereto, and various amendments and modifications may be implemented.

[0065] In the present specification, an expression of relative or absolute arrangement such as "in a direction", "along a direction", "parallel", "orthogonal", "centered", "concentric" and "coaxial" shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.

[0066] For instance, an expression of an equal state such as "same", "equal", and "uniform" shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function.

[0067] Further, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.

[0068] On the other hand, an expression such as "comprise", "include", and "have" are not intended to be exclusive of other components.Reference Signs List

[0069] 1Gas compression facility 2Screw compressor 4Oil separator 6Cooler 8Pump 10Oil supply line 10'Oil supply line 11Connection part 12Casing 13Inner peripheral surface 14Rotor shaft 15Male rotor 16Rotor shaft 17Female rotor 18Radial bearing 19Radial bearing 20Radial bearing 21Radial bearing 22Thrust bearing 23Thrust bearing 24Shaft seal part 26Seal part 28Return line 30Balance piston 31Outer peripheral surface 32First end surface 34Second end surface 36Communication passage 36aFirst open end 36bSecond open end 37Axial flow path 38Radial flow path 40Oil reservoir 41Groove 42First chamber (Balance piston chamber) 44Second chamber (Low-pressure chamber) 45Accommodation space 46Oil supply passage 48Oil discharge passage 50Suction space 52Suction port 54Discharge port GGap L1Distance L2Distance PdDischarge pressure PsSuction pressure r1Outer radius r2Inner radius

Claims

1. A screw compressor, comprising: a pair of rotor shafts; a balance piston disposed on at least one of the rotor shafts; a balance piston chamber disposed 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, 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 wherein the communication passage includes a radial flow path extending along a radial direction inside the balance piston.

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

3. The screw compressor according to claim 1 or 2, wherein the balance piston has a first end surface facing the balance piston chamber, and wherein a length of the radial flow path in the radial direction is not less than 1 / 3 of a difference between an outer radius and an inner radius of the first end surface.

4. The screw compressor according to claim 1 or 2, wherein the oil reservoir includes a groove formed on the outer peripheral 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 facility, comprising: the 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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