JPS6053199B2 - screw compressor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a casing in which an outer wall of a working space is formed by at least two intersecting cylindrical walls, and at least two cylindrical walls having outer diameters substantially inscribed in the cylindrical walls. A rotor having male and female helical lands is rotatably disposed, and by meshing rotation of these rotors, fluid to be compressed is sucked from an end wall at one end in the axial direction of the rotor, compressed and discharged from an end wall at the other end. , relates to a type of screw compressor in which a sealing liquid is jetted or supplied to the working space or shaft sealing portion between the outer wall and the helical outer circumferential surface of the rotor to perform sealing, cooling, lubrication, etc. This is a screw compressor that improves the efficiency of liquid recovery and reduces energy loss.

In conventional compressors of this type, a sealing liquid is jetted into the working space to seal between the rotor and the outer wall of the working space and the mating surface between the rotors, and at the same time cool the compressed liquid. The liquid ejected into the working space is discharged from the working space through the discharge port together with the compressed fluid, and is then separated from the fluid, collected, and used again for sealing. On the other hand, a shaft sealing device is disposed in the bearing portion of each rotor in the casing, and the sealing liquid is supplied to the shaft sealing device under pressure to seal and lubricate the bearing portion. The sealing liquid supplied to the shaft sealing device is normally collected in a passage on the low pressure side and sucked into the working space from the suction port together with the compressed fluid. However, the shaft sealing device formed on the low pressure side leaks the supplied sealing liquid into the working space and also outside the working space, compared to the shaft sealing device formed on the high pressure side.

Although the sealing liquid leaking into the working space is useful for cooling and sealing, recovering the sealing liquid leaking outside the working space from the low-pressure side passage is a loss of energy. In addition to the above-mentioned effects, the sealing liquid under pressure is also used to adjust the thrust in the direction of the central axis of the rotor.

For example, in some types of compressors, the shaft of the male rotor is extended outward from the bearing of the rotor to form an extended shaft, and the extended shaft on the low pressure side is connected to a drive source. A piston, usually called a balance piston, is fixed to the shaft, and the sealing liquid is supplied to the working chamber formed between the piston and the casing, and the male rotor is moved to the low pressure side by the pressure inside the compression chamber of the working space. A force is applied that opposes the thrust that is pushed in the axial direction. The sealing liquid introduced into the working chamber leaks into the space between the low-pressure side bearing and the piston, and at the same time, the sealing liquid that lubricates the bearing also leaks from the shaft sealing device formed on the low-pressure side bearing. leaks into the space. The pressure of this leaked sealing liquid is low. Japanese Patent Publication No. 50-17686 discloses that a compressor is manufactured by collecting the oil that lubricates the high-pressure side bearing part and the low-pressure side bearing part into the working space through an opening located at a special position in the working space. It is proposed that the special position of this opening is such that the land of the female rotor facing this opening cooperates with the edge of the inlet to reduce the volumetric efficiency of said land and the land following it. When the rotor groove between the land and the land is connected to the suction port and the rotor groove is in a position such that it is sealed from the suction port at the next moment, that is, substantially sealed, the land is located close to the land, in other words, The opening is described as being at a distance from the edge of the bore communicating with the suction side that is less than the distance between two successive lands of the female rotor. However, the pressure of the oil recovered into the working space by the opening is the average pressure of the high pressure oil directly recovered from the high pressure side bearing and the low pressure oil leaked from the low pressure side bearing. In particular, in compressors that handle compressed fluids that easily dissolve in sealing liquids, the fluid re-expands and the volumetric efficiency is not significantly improved.In compressors equipped with a balance piston, this average pressure may act on the balance piston and cause it to malfunction.

In view of these known facts, the present invention communicates a sealing liquid recovery passage with at least the shaft sealing apparatus formed on the end wall on the suction port side of the shaft sealing apparatus, and collects the sealing liquid from the recovery passageway. By collecting the sealing liquid leaking from the balance piston into the working space on the compression side according to the pressure to be maintained, and collecting the sealing liquid leaking from the balance piston into the low pressure side of the working space, the compression efficiency is not reduced and the sealing liquid is kept in good condition. The purpose is to recover the waste.

The present invention will be described based on an embodiment of the present invention shown in the drawings.

FIG. 1 of the attached drawings is a plan sectional view thereof, and I of FIG.
Fig. 2 is a cross-sectional view taken along line -1 in Fig. 1, Fig. 3 is a developed sectional view taken along line - H in Fig. 2, and Fig. 4 is a cross-sectional view taken along line - H in Fig. 2. FIG. 5 is an enlarged plan sectional view of the main part, and FIG. 6 is a diagram showing the inner periphery of the casing and the outer periphery of the rotor of the above-mentioned embodiment in relation to the circumferential direction.
The casing 1 includes a wall 2 in which two cylindrical holes for accommodating two rotors, which will be described later, are bored with their central axes parallel to each other and partially intersecting with each other, and a wall 2 with a diameter smaller than that of the holes. a part 6 having two cylindrical holes 3, 4 and a low pressure passage 5 drilled concentrically with each conical hole;
The cylindrical holes 7, 8 of substantially the same shape drilled concentrically with the section 4 and the section 10 having the high pressure passage 9 are made to face each other, and the cylindrical holes 3, 4 of the section 6 are separated into independent chambers. It is formed by connecting an end plate 11 that extends the portion 10 and an end plate 12 that covers the end of the portion 10.

The male rotor 21 has four helical protruding lands 22 that are approximately arc-shaped in a cross section perpendicular to the axial direction, and grooves 23 are formed between the lands 22. 24 has a groove 25 carved from the circumferential surface to receive the land 22 of the male rotor, and has a land 26 formed by the groove 25 in a spiral shape, and has a land 26 formed by the groove 25 in a hole formed by the wall 2 of the portion 6. Land 22, 2 on wall 2 respectively
The male and female rotors 24 and 21 are inserted so that the outer circumferences of the rotors 6 and 6 are inscribed with a very small gap therebetween, and the male and female rotors 24 and 21 are in a mutually meshing relationship.

The shaft 27 of the male rotor 21 extends into the holes 4 and 8 and is supported by shaft sealing devices 41 and 42 fitted in the holes 4 and 8, and is also supported in the hole 8 by a thrust bearing 43. Ru.

A balance piston 44 whose outer periphery fits into the hole 4 is fixed to the end of the extended shaft portion 28 at one end of the shaft 27, and the space of the hole 4 between the balance piston 44 and the end plate 11 is used as an operating chamber. It is set at 45. Further, the extension shaft portion 2 at the other end of the shaft 27
9 extends outside through the end plate 12 and is connected to a driving shaft (not shown). A shaft sealing device 46 such as a mechanical seal is provided between them. The shaft 31 of the female rotor 24 extends into the holes 3, 7 and
It is supported by shaft sealing devices 47 and 48 fitted into the shaft, and is also supported by a thrust bearing 49 within the hole 7.

The slide valve 50 is slidable in a gutter-like groove 13 formed in a portion 6 of the casing 1 parallel to the central axis of the wall 2 and at the intersection of two cylindrical holes constituting the wall 2. It has a sliding surface 51 and a wall surface 52 which is connected to the wall 2 and is the same as the surface of the intersection of the two cylindrical holes, and its low pressure side edge 53 is connected to the wall 2 of the part 6 of the casing 1. It is adapted to abut against the constituting edge 14.

Wall 2 of part 6 of housing 1 and slide valve 50
A working space 15 surrounded by two mutually intersecting cylindrical surfaces (hereinafter referred to as the outer walls of the working space) constituted by a wall surface 52 of and lands 26, 22 and grooves 25, 23 of the male and female rotors 24, 21, 16 communicates with the low pressure passage 5 through an inlet 17 and communicates with the high pressure passage 9 through an outlet 18.

A rod 54 is fixed to the slide valve 50 and passes through the portion 6 of the housing 1 in the axial direction, and a piston 56 disposed in a cylinder chamber 55 formed in the end plate 11 is connected to the rod 54. By supplying pressure oil to either one of the chambers partitioned by the piston 56 in the cylinder chamber 55, the slide valve 50 is slid along the groove 13, and the end edge 53 of the valve 50 is caused to slide along the groove 13.
The amount of compressed fluid discharged into the high pressure passage 9 is maximum when the slide valve 50 is in contact with the side edge 14, and the distance between the edge 53 of the slide valve 50 and the casing side edge 14 is the greatest. Therefore, the amount of compressed fluid b sucked into the working spaces 15, 16 from the suction port 17 and returned to the low pressure passage increases, and the amount of compressed fluid discharged into the high pressure passage 9 decreases.

At this time, the high-pressure side edge 57 of the slide valve 50 is made to protrude into the high-pressure passage 9 through the discharge port 18. The sealing liquid is supplied through a supply port 61 provided in part 6 of casing 1.
a passage 62 that opens to the sliding surface of the groove 13 with respect to the slide valve 50; a long groove 63 that communicates with the passage 62 on the sliding surface 51 of the slide valve and is formed parallel to the axial direction; The liquid is ejected into the working spaces 15 and 16 from a nozzle 65 that opens in the wall surface 52 of the slide valve 50 through a passage 64. The present invention provides such a screw compressor, as shown in FIG. 1, through passages 102, 103, 104 and 105 to the shaft sealing devices 41, 42, 47, 48 of the shafts 27, 31 of the male and female rotors, and the shaft sealing devices prevent leakage of the compressed fluid and lubricate and cool the sliding parts with the shafts. . A shaft sealing device 46 provided on the extended shaft portion 29 of the shaft 27 includes a housing 3
A sealing liquid is supplied through the oil supply hole 106 formed at 0.

Further, a sealing liquid is supplied to the working chamber 45 for the balance piston 44 attached to the other extended shaft portion 28 of the shaft 27 through a passage 107 extending from the passage 104.

On the other hand, as shown in FIG. 3 and partially enlarged in FIG.
A passage 111 is opened on the low pressure side of the balance piston 44 attached to the extended shaft portion 28 of 7, and the passage 111 is communicated with a recovery passage 112, and this recovery passage 112 is connected to the first opening 113 of the wall 2 of the casing 1. I will contact you. This first opening 113 is such that the end edge 53 of the slide valve 50 abuts against the end edge 14 of the casing 1 to close the return passage on the suction side. When the lands 22 and 26 are in a position to close the working space in cooperation with the edges of the lands 22 and 26, the lands 22 and 26 open near the position closed by another land adjacent to the high pressure side, that is, into the working space at the end of suction or at the beginning of compression. It will be done. Furthermore, if there is a position where the slide valve is frequently located depending on the purpose of use of the compressor, the opening may be bored near the suction end position when the slide valve is in that position.
Depending on the purpose of use of the compressor, the opening may be made at the center of the stroke of the slide valve. Further, as shown in FIGS. 3 and 5, shaft sealing devices 41 and 47 provided on the shaft 27 of the male rotor 21 and the shaft 31 of the female rotor 24 are provided with sealing devices 41 and 47 for maintaining pressure facing the shafts 27 and 31. A bearing pocket 114 is formed, and a recovery pocket 115 is formed on the lower pressure side of the pocket 114, and the bearing pocket 114 is communicated with the passages 104 and 105, and the recovery pocket 115 is communicated with the passages 116 and 117.
The recovery passage 11 is connected to the recovery passage 118 via the
8 communicates with a second opening 119 drilled in the wall 2 of the casing 1.

The position of this second opening 119 is on the higher pressure side than the position of the opening 113, and is preferably located closer to the high pressure side end wall 19 of the portion 10 of the casing 1. FIG. 6 is a diagram showing the wall 2 of the casing 1 and the outer periphery of the rotors 21, 24 in the circumferential direction, and showing the seal line between the wall 2 and the lands 22, 26 of the rotors 21, 24. In the figure, a line 35 indicates the meshing position of the male and female rotors 24 and 21. The right side of the figure is the male rotor 21 side, and the left side is the female rotor 2.
4 side shown. The line 36 is the low pressure passage 5 formed in the wall 2.
, a connecting portion between the inner hole 37 communicating with the suction port 17 and the wall,
221, 222, 223 are seal lines of the land 22 of the male rotor 21, and 261, 262, 263 are seal lines of the land 26 of the female rotor 24, respectively.

When the lands 22 and 26 of the male and female rotors seal the suction port at the connecting portion 36 to confine the suction, the seal line gradually moves upward in the figure, gradually reducing the volume of the trapped working space and confining it. The fluid to be compressed is compressed and discharged from the discharge port 18. When a particular land 22, 26 of the rotors 21, 24 advances toward the discharge side, this land 22, 26
, 25, the compressed fluid is sucked from 17 into the grooves 23, 25 behind the lands 22, 26 and the lines 221, 26.
1 and the land following this land reaches the connection part 36, the working space 15 surrounded by the grooves 23, 25
, 16 are confined.

The first opening 113 is located at the closing end line 221,
Drill an opening in wall 2 near 261. Preferably, it is provided at a position immediately after the closing end line 221, 261 (on the high pressure side) and as close as possible to the engagement line 35 of the rotors 21, 24. The second opening 119 is the first opening 113
It may be provided on the higher pressure side. In FIG. 6, the slide valve 50 is illustrated by dotted lines, and when the first opening and the second opening are bored in the slide valve 50, the first opening 513 is located at the position of the reference numeral 113, and the line 22
1 and 261, and the second opening 519 is opened at a position parallel to lines 223 and 263 from the reference numeral 119 onto the slide valve 50.

When the first opening 513 and the second opening 519 are bored into the slide valve 50, as shown in FIG.
The sliding surface 51 of the slide valve 50 with respect to the groove 13 is provided with a long groove 502 that communicates with the opening 501 along the sliding direction of the slide valve 50. The long groove 50
2 is communicated with the first opening 513.

Similarly, the passage 118 is connected to the opening 50 of the sliding surface on the groove 13.
The sliding surface 51 of the slide valve is provided with a long groove 504 that communicates with the opening 203 along the sliding direction, and the long groove 504 communicates with the second opening 519. Note that there is an opening 501 on the groove 13 side of the casing 1.
, 503, a long groove along the sliding direction of the slide valve 50, and a long groove 502 on the sliding surface 51 of the slide valve.
, 504, and the two are communicated with each other, the same effect can be achieved, so there is no problem in adopting either method.

In the screw compressor configured as described above, the sealing liquid is supplied to the passages 102, 103, 104 and 10 through the oil supply hole 101 from a pressure liquid source (not shown).
5 to the shaft sealing devices 41, 42, 47 and 48 of the shafts 31, 27 of the male and female rotors 24, 21.

The pressure of the compressed fluid compressed to the high compression ratio of the working space in the casing 1 acts on the shaft sealing devices 42 and 48 formed on the high-pressure side edges of both the shafts 27 and 31, and the shaft sealing devices 42
, 48 , the sealing liquid leaks into the holes 7 , 8 in the part 10 of the casing 1 and the thrust bearings 43 , 4 .
9 is stored in a chamber between part 10 and end plate 12 and collected. Passages 103, 104, 1 are provided in shaft sealing devices 41, 47 formed on the low pressure side edges of both shafts 27, 31.
The sealing liquid is supplied through 05, and the sealing liquid fills the bearing pocket 114 and performs a shaft sealing action, and the sealing liquid does not directly leak into the working space of the compressor, and is connected to the shaft sealing device on the lower pressure side of the pocket 114. 41, 47, and overflows from the pocket 115 into the collection passage 118 via the passages 116, 117,
A second opening 119 drilled in the wall 2 of the casing 1
and is collected into the working space of the screw compressor.

The collection pocket 115 of the shaft sealing devices 41 and 47 is located in the passage 1.
16, 117, and 118 to the working space on the high pressure side, and from the bearing pocket 114 to the collection pocket 115
The sealing liquid leaking to the casing also retains pressure and is passed directly through the first opening 119 to the high pressure side, preferably to the high pressure side end wall of the section 10 of the casing, without collecting it in the low pressure side recovery passage. Since the energy is recovered to the working space at a position close to 19, energy loss is extremely small. In addition, the balance piston 44 provided on the extended shaft portion 28 of one of the male and female rotors, in this embodiment the female rotor 21, is heated by the pressure of the sealing liquid supplied to the working chamber 45 through the passage 107. A force is applied to the shaft 27 that opposes the axial thrust that acts from the high pressure side toward the low pressure side due to the compression action of both rotors.

The balance piston 44 is fixed to the extended shaft portion 28 of the shaft 27 of the male rotor 21 and rotates together with the male rotor 21, and as described above, the balance piston 44 is attached to the shaft 27 by the pressure of the sealing liquid supplied to the working chamber 45. Since it applies a force that counteracts the directional thrust, it is fitted with the inner circumferential surface of the cylindrical hole 4 formed in the portion 6 of the housing 1 with a slight gap therebetween, as is well known. A labyrinth groove is carved in the working chamber 45 so that the inner peripheral surface of the hole 4 is concentrically supported and rotates relative to the inner peripheral surface without slidingly contacting the inner peripheral surface.
The pressure of the sealing liquid supplied to the sealing liquid is not significantly reduced. The sealing liquid supplied to the working chamber 45 leaks to the low pressure side from the sliding surface of the balance piston 44, but it is structurally difficult to recover this leaked liquid without reducing the retained pressure. Therefore, the recovery passageway communicated with the low pressure side space of the balance piston 44 is communicated with the first opening 113 of the outer wall 2 of the working space where the compression ratio is low and corresponds to the end of the suction stroke and the beginning of the compression stroke of the compressor. It is designed to collect leaked liquid. Note that in a type of screw compressor equipped with a slide valve 50, there is a groove 1 formed in a portion 6 of the casing 1 for sliding the slide valve 50.
An opening 501 that communicates with the first recovery passage 112 and a second opening 503 that communicates with the recovery passage 118 are bored in the sliding surface for the slide valve 50 on No. 3, and communicate with these openings 501 and 503, respectively. long groove 502
, 504, the first opening 513 communicates with the first recovery passage 112 through a wall surface of the slide valve 50 forming the wall of the working space at a portion corresponding to the end of the suction stroke and the beginning of the compression stroke of the compressor. Open at 52,
a second opening 519 that communicates with the second collection passage 118;
is opened in the wall surface 52 on the higher pressure side than the first opening 513, so that the balance piston 44 is opened as described above.
The sealing liquid recovered from the low pressure side of the shaft sealing device is recovered into the low compression ratio working space, and the sealing liquid recovered from the low pressure side shaft sealing device is collected into the high compression ratio working space. Moreover, in this embodiment, when the slide valve 50 is slid to the high pressure side to adjust the discharge amount, the first The opening 513 is located at a predetermined position at the end of the suction stroke and at the beginning of the compression stroke at the position of the slide valve 50.
The sealing liquid recovered from the recovery passage 118 can be recovered into the working space under the same conditions from beginning to end, regardless of the position of the slide valve 50.

As described in detail above, in the present invention, in a screw compressor including a casing and at least a pair of male and female rotors that rotate while meshing with each other within the cylindrical wall of the casing, the casing of each rotor is A shaft sealing device is formed on the shaft portion bearing against the end wall, and the shaft sealing device is supplied with a sealing liquid under pressure, and at least one of the rotors is provided with a sealing device from the shaft sealing device. A balance piston is provided on the extended shaft of the balance piston, and a sealing liquid under pressure is supplied to a working chamber formed on one side of the balance piston to counteract the axial thrust of the screw compressor. The other end of the first recovery passage communicated with the space is communicated with a first opening opening into the working space at the end of the suction stroke and at the beginning of the compression stroke of the working space of the compressor, thereby leaking into the low pressure side space. The other end of the second recovery passage is connected to the shaft sealing device formed in the end wall on the low pressure side, and the other end is in the working space on the high pressure side from the first opening. Since the high-pressure recovered liquid from the shaft seal device is communicated with the second opening opened in the compressor and is recovered into the high-pressure working space without leaking into the low-pressure working space of the compressor, energy loss is reduced. This makes it possible to achieve less efficient operation.

That is, the sealing liquid from the sealing liquid supply source is supplied to the shaft sealing device formed in the shaft portion bearing in contact with the end wall of the casing of the rotor, and is also supplied to the shaft sealing device on one axial side of the balance piston. A working chamber formed in the casing is also supplied.

The balance piston rotates together with the extended shaft of the rotor shaft, and uses the pressure of the sealing liquid supplied to the working chamber to apply force against the thrust force generated in the rotor as the rotor rotates to the shaft of the rotor shaft. Since the purpose is to provide liquid in the working chamber, the peripheral surface of the balance piston is in frictional contact with the part of the casing that houses it, and the sealing liquid in the working chamber is in contact with the peripheral surface of the balance piston. A gap is formed that is large enough to maintain the pressure of , and the sealing liquid in the working chamber leaks into the space on the low pressure side of the balance piston through this gap.

The pressure of the sealing liquid leaked into this low pressure side space is low. Therefore, a first recovery passage that communicates this low-pressure side space with an opening in the outer wall of the working space at a portion corresponding to the end of the suction stroke and the beginning of the compression stroke of the working space of the compressor,
When the sealing liquid leaked into the low pressure side space is supplied to the working space, the opening position of the first recovery passage to the working space is such that one land of the rotor cooperates with the suction edge on the suction port side to open the working space. When confinement is attempted, the low-pressure sealing liquid in the first recovery passage is located just before or after the land is closed by the land adjacent to the high-pressure side of the land. It is supplied to the working space just before or after the working space is about to be enclosed in cooperation with the suction edge on the suction port side, and there is no communication leakage to the suction port side, so the sealing liquid is not exposed to the sealing liquid. When the compressed fluid is dissolved or when the fluid to be compressed is mixed in the form of foam, the low pressure side space of the balance piston or the first
Even if the compressed fluid expands in the recovery passage of the first
Since the difference between the pressure in the recovery passage and the pressure in the working space immediately before or after the confinement is small, there is little risk of re-expansion within the working space. On the other hand, the sealing liquid supplied to the shaft seal device cools, lubricates, and seals the shaft seal device.

The sealing liquid supplied to the shaft seal device provided on the discharge side end wall of the casing is intended to prevent leakage against the pressure of the compressed fluid leaking from the working space through the shaft seal device. However, since the suction pressure acts on the shaft sealing device installed on the suction side end wall, which is supplied with sealing liquid at the same pressure, the sealing liquid leaks to the suction side of the working space and is sucked from the suction port. The compressed fluid is mixed with the fluid to be compressed. Therefore, the pressure of the sealing liquid recovered from the shaft seal device provided on the suction side end wall of the casing into the second recovery passage is the same as that of the sealing liquid recovered from the shaft seal device provided on the discharge side end wall. Although the pressure is lower than that of the casing, it still maintains a considerable pressure.Therefore, by communicating the second recovery passage with an opening in the outer wall of the working space at a portion corresponding to the initial stage of the compression stroke of the working space, the pressure of the casing is reduced. The sealing liquid, which is supplied to the shaft sealing device provided on the suction side end wall and recovered from the second recovery passage, is supplied to the working space that is already confined and is in the compression stroke, so that The sealing liquid is collected in the working space where the pressure difference between the sealing liquid and the pressure it holds is not large, and even if the fluid to be compressed is dissolved or mixed in the form of a foam with the sealing liquid, there is little risk of re-expansion within the working space. In this way, in the present invention, the low pressure that is supplied to the working chamber of the balance piston and leaked into the low compression space of the balance piston is sealed in order to provide the rotor with a force that counteracts the thrust force generated during operation of the screw compressor. The sealing liquid is supplied to the working space just before or after confinement, and is used to cool and lubricate the shaft sealing device installed on the low-pressure side end wall of the casing. Since the working space during the compression stroke after the initial stage is recovered separately via the first and second recovery passages, the volumetric efficiency of the compressed fluid of the compressor is improved and energy loss is reduced. This is what I did.

Further, in the screw compressor having a slide valve according to the present invention, the first and second openings are opened in a wall surface of the slide valve forming an outer wall of the working space, and the first and second recovery passages are connected to each other. The first and second openings are opened to face the groove for supporting the slide valve in the casing and the sliding surface of the slide valve relative to the groove, and one opening is opened to face the sliding surface of the slide valve with respect to the groove. By forming a long groove parallel to the moving direction and an opening communicating with the long groove on the other side, the first recovery passage and the first opening are always connected while the slide valve is sliding.
Further, the second recovery passage and the second opening are connected to each other, and the first and second openings are formed in the slide valve, so that the respective recovered liquids are transferred to the slide valve. Regardless of the location, it can always be collected in a working space under the same conditions.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a plan sectional view of one embodiment, FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1, and FIG. -, Figure 4 is a longitudinal cross-sectional view taken along line ■-■ in Figure 2, Figure 5 is an enlarged plane cross-sectional view of the main part, Figure 6 is the inner periphery of the casing and the rotor. FIG. 7, which is a diagram showing the outer periphery in the circumferential direction, shows a cross-sectional view of another embodiment. In the figure, 1 is the casing, 2 is the outer wall of the working space, 13 is the concave groove, 21 is the male rotor, 22 is the land, 23 is the groove, 24 is the female rotor, 25 is the groove, 26 is the land, 27 , 31 is the shaft of the rotor, 28, 29 are its extended shaft parts, 41, 42, 47, 48 are shaft sealing devices, 44 is a balance piston, 45 is a working chamber, 50 is a slide valve, 51
is its sliding surface, 52 is its wall surface, 101 is the oil supply hole, 10
2, 103, 104, 105, 107 are refueling passages,
112 is a first collection passage, 118 is a second collection passage, 1
11, 116, 117, 113, 513 are first openings,
119, 519 are second openings, 502, 504 are long grooves,
Reference numeral 114 indicates a bearing pocket, and reference numeral 115 indicates a collection pocket.

Claims (1)

[Claims] 1. An effect of being surrounded by at least two cylindrical walls having central axes parallel to each other and intersecting each other, and wall surfaces of end walls perpendicular to the central axis and facing each other. a casing forming an outer wall of the space; and a casing having an outer diameter substantially inscribed in the wall surface of the cylindrical wall of the casing, and rotatably disposed inside the outer wall of the working space so as to mesh with each other; at least two rotors having female and male helical lands whose outer surfaces form the inner wall of the working space, and the fluid to be compressed is supplied to the wall surface of the casing and the male and female from an inlet formed near the one end wall. In a screw compressor that draws fluid into a working space surrounded by the outer surface of the land of the rotor and compresses and discharges the suction fluid from a discharge port formed in the other end wall, shaft portions bearing the bearings are formed with shaft seals to communicate these shaft seals with a supply passage from a source of sealing liquid under pressure, and at least one of said rotors is provided with said shaft seals. A balance piston is installed on the extended shaft of the
A working chamber is formed on one axial side of the balance piston, and the working chamber is communicated with a supply passage from the sealing liquid supply source to act on the rotor in the axial direction from the discharge side to the suction side. A first recovery passage faces the thrust and communicates with a space on the low pressure side of the balance piston, and the other end of the recovery passage is connected to a working space at a portion corresponding to the end of the suction stroke and the beginning of the compression stroke of the working space. A second recovery passage for the sealing liquid is communicated with a shaft sealing device formed in a wall surface forming an outer wall of the suction side and in contact with the suction side end wall, and the other end of the recovery passage is connected to a shaft sealing device formed in a wall surface forming an outer wall of the suction side. A screw compressor characterized in that an opening is formed in a wall surface forming an outer wall of a working space in a portion corresponding to the initial stage and subsequent stages of the stroke. 2. The balance piston is provided on an extended shaft extending from a shaft sealing device formed in contact with the suction side end wall of one of the rotors, and the working chamber is formed on the shaft end side of the extended shaft. A patent characterized in that the sealing liquid supplied to the rotor opposes the axial thrust acting on the rotor, and the first recovery passage communicates with a space between the balance piston and the shaft sealing device. A screw compressor according to claim 1. 3. The other end of the first recovery passage that communicates with the chamber on the low pressure side of the balance piston is configured to close the working space when one land of the rotor cooperates with the suction edge on the suction port side. Claim 1 or 2, characterized in that the opening is opened in the wall surface forming the outer wall of the working space at a position immediately before or after the position closed by one land adjacent to the high pressure side of the land. The screw compressor according to item 2. 4. Forming an outer wall of a working space surrounded by two cylindrical walls having central axes parallel to each other and intersecting with each other, and wall surfaces of end walls facing each other and having planes perpendicular to the central axis. a casing having an outer diameter substantially inscribed in the wall surface of the cylindrical wall of the casing, the casing being rotatably disposed within the outer wall of the working space in a mutually meshing relationship; two rotors having male and female helical lands that form a slide valve formed as part of the outer wall of the working space of the rotor, and the fluid to be compressed from the suction port formed near the one end wall is surrounded by the casing, the wall surface of the slide valve, and the outer surface of the lands of the male and female rotors. In the screw compressor, the suction fluid is sucked into a working space, compressed and discharged from a discharge port formed in the other end wall, and a shaft portion of each rotor that is bearing in contact with the end wall of the casing is provided with a shaft seal. forming an apparatus for communicating the shaft seals with a supply passageway from a source of sealing liquid under pressure, at least one of the rotors having a balance piston in an extension of the shaft from the shaft seal; A working chamber is formed on one axial side of the balance piston, and the working chamber is communicated with a supply passage from the sealing liquid source to prevent an axial thrust acting on the rotor from the discharge side toward the suction side. A first recovery passage is opened to communicate with a space on the low pressure side of the balance piston, and the other end of the passage is opened to a sliding surface of the casing with respect to the slide valve, A long groove parallel to the central axis that communicates with the opening of the first recovery passage communicating with the space on the low pressure side of the piston is formed on the sliding surface thereof, and the long groove is connected to the outer wall of the working space of the slide valve. A shaft sealing device formed in contact with the suction side end wall is connected to a first opening bored in a partial wall surface, and a second recovery passage for the sealing liquid is communicated with the shaft sealing device formed in contact with the suction side end wall. The other end communicates with a second opening formed in a wall surface forming an outer wall of the working space, and the first opening is connected to the slide valve which closes the return passage on the suction side and which is connected to one of the rotors. When the land is in a position to close the working space in cooperation with the edge of the suction port, a perforated opening is formed at a position immediately before or after the position closed by one land adjacent to the high pressure side of the land, A screw compressor, wherein the second opening is opened at a position closer to the discharge side than the first opening. 5. The balance piston is provided on an extended shaft extending from a shaft sealing device formed in contact with the suction side end wall of one of the rotors, and the working chamber is formed on the shaft end side of the extended shaft. A patent characterized in that the sealing liquid supplied to the rotor opposes the axial thrust acting on the rotor, and the first recovery passage communicates with a space between the balance piston and the shaft sealing device. A screw compressor according to claim 4. 6. The second opening is formed in a surface forming a part of the outer wall of the working space of the slide valve, and the other end of the second recovery passage slides with the slide valve of the casing. A long groove parallel to the central axis that communicates with the opening of the casing is bored in the surface of the slide valve that slides on the casing of the slide valve, and the long groove communicates with the second opening. A screw compressor according to claim 4 or 5, characterized in that: