JP4050657B2 - Screw compressor with balance piston device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is applied to a compressor or the like of a refrigeration cycle, and is a screw compressor that compresses fluid sucked from a suction port by a male rotor and a female rotor that are rotated in reverse to each other and sends the fluid to the outside from a discharge port. The present invention relates to a screw compressor provided with a balance piston device for reducing a thrust load on one or both of a male rotor and a female rotor.
[0002]
[Prior art]
A screw compressor used in a compressor of a refrigeration cycle compresses a fluid such as a refrigerant gas sucked from a suction port by a male rotor and a female rotor that are rotated in reverse to each other, and sends the fluid from the discharge port to the outside. In such a screw compressor, a thrust load due to a differential pressure (pressure difference) between a discharge pressure and a suction pressure of the compression fluid such as the refrigerant gas acts on the male rotor and the female rotor.
Such a thrust load is larger in the drive-side male rotor. However, a screw compressor provided with a balance piston device that reduces the thrust load and protects the thrust bearing is disclosed in Patent Documents 1 and 2. Etc. are disclosed.
[0003]
In a screw compressor for a fuel cell disclosed in Patent Document 1, a balance piston device is provided at both axial ends of a male rotor and a female rotor, and the balance piston device discharges to the male rotor and the female rotor. The working fluid pressure is applied in the direction opposite to the pressure difference between the pressure and the suction pressure to cancel the thrust load.
Further, in the screw compressor for the compressor of the refrigeration cycle disclosed in FIG. 5 of Patent Document 2, a balance piston device is provided at the shaft end of the drive-side male rotor where the thrust load increases, The thrust load is canceled out by applying a working fluid pressure to the male rotor in a direction opposite to a differential pressure between the discharge pressure and the suction pressure by the balance piston device.
[0004]
[Patent Document 1]
JP 2002-310081 A [Patent Document 2]
Japanese Patent Laid-Open No. 2002-168185
[Problems to be solved by the invention]
The balance piston device of the screw compressor disclosed in Patent Document 1, Patent Document 2 and the like is such that the discharge pressure and the suction pressure are always applied only to the male rotor and the female rotor, or only the male rotor during the operation of the screw compressor. The working fluid pressure is applied in the direction opposite to the thrust load acting on the thrust bearing due to the differential pressure of the pressure and the differential pressure between the internal maximum pressure and the suction pressure.
[0006]
For this reason, in such a conventional screw compressor, the fluid suction pressure increases during low-load unload operation, the differential pressure between the fluid discharge pressure and the suction pressure decreases, and the internal maximum pressure decreases. Due to the effect that the differential pressure between the internal pressure and the suction pressure becomes small, the thrust load acting on the thrust bearing is reduced by the differential pressure, and the working fluid force acting on the balance piston device greatly exceeds the thrust load. .
In such a state, a large reverse thrust load is applied to the bearing, which causes a reduction in the life of the thrust bearing.
There are problems to be solved.
[0007]
In view of the problems of the conventional technology, the present invention reduces the thrust load applied to the thrust bearing by generating a large thrust force of the thrust load when the balance piston device is at a high load, and reduces the thrust load at a low load. An object of the present invention is to provide a screw compressor equipped with a balance piston device that can reduce the load acting on the thrust bearing in an appropriate range at all times and prevent the life of the thrust bearing from being reduced due to the canceling force. And
[0008]
[Means for Solving the Problems]
The present invention achieves such an object, and is a screw compressor that compresses fluid sucked from a suction port by a male rotor and a female rotor that are rotated in reverse to each other and sends the fluid to the outside from a discharge port, In either or both of the male rotor and the female rotor, a screw compressor provided with a balance piston device that reduces a thrust load acting on the male rotor or the female rotor. In the screw compressor, a pressure device such as a pump is attached to the balance piston device. A discharge pressure sensor that detects a discharge pressure (Pd) of the fluid in the screw compressor, and a suction pressure of the fluid are provided in the working fluid passage for supplying the working fluid with a pressure adjusting valve that opens and closes the working fluid passage. A suction pressure sensor for detecting (Ps), a discharge pressure detection value inputted from the discharge pressure sensor, and the suction pressure sensor; When one or both of the differential pressure (Pd-Ps) and the pressure ratio (Pd / Ps) with respect to the suction pressure detection value inputted from the pressure exceeds the reference pressure ratio or the reference differential pressure, the pressure regulating valve is opened. The working fluid is supplied to the balance piston device to cancel the thrust load, and either one or both of the differential pressure (Pd−Ps) and the pressure ratio (Pd / Ps) is the reference difference. And a controller for shutting off the pressurized supply of the working fluid to the balance piston device when the pressure is below the reference pressure ratio or below the reference pressure ratio .
[0009]
In this invention, preferably, a bypass passage is provided that bypasses the pressure regulating valve and is connected to a discharge site of the pressure regulating valve, and when the pressurized fluid supply to the balance piston device is shut off, the bypass passage It is characterized in that a working fluid depressurized by a certain amount from the discharge pressure (Pd) can be supplied to the balance piston device .
[0010]
(Delete)
[0011]
In the screw compressor, the difference between the discharge pressure (Pd) and the suction pressure (Ps) of the compression fluid such as refrigerant gas acting on the male rotor or the female rotor (pressure difference 1), the internal pressure and the suction pressure. A thrust load due to a differential pressure (pressure difference 2) is generated, and the thrust load is supported by a thrust bearing. In order to reduce the thrust load acting on the thrust bearing, the balance piston device reduces the male rotor or female. The thrust load is canceled out by applying a working fluid pressure to the rotor in a direction opposite to the differential pressure.
[0012]
On the other hand, in such a screw compressor, as described above, the suction pressure (Ps) becomes high during unload operation at a low load, and the differential pressure between the fluid discharge pressure (Pd) and the suction pressure (Ps) of the screw compressor. (Pressure difference) is reduced, and the internal maximum pressure is reduced and the differential pressure between the internal pressure and the suction pressure is reduced, so that the thrust load acting on the thrust bearing is reduced by the differential pressure, and the balance piston The canceling force generated in the apparatus becomes larger than the thrust load, and the difference in the force is applied to the thrust bearing in the opposite direction, causing a reduction in the life of the thrust bearing.
[0013]
Accordingly, in the invention according to the present invention, the pressure adjustment valve installed in the working fluid passage to the balance piston device is configured such that the differential pressure (Pd−Ps) between the discharge pressure (Pd) and the suction pressure (Ps) is the thrust load. A pressure ratio (Pd) between the discharge pressure (Pd) and the suction pressure (Ps) corresponding to the reference value of the differential pressure (Pd−Ps) corresponding to the allowable value, that is, exceeding the reference differential pressure, or corresponding to the allowable value of the thrust load. / Ps) is configured to open at a high load that exceeds the reference value of the pressure ratio, that is, the reference pressure ratio, so that the working fluid is pressurized and supplied to the balance piston device by opening the pressure regulating valve. Thus, the thrust load canceling force can be generated, whereby the thrust load applied to the thrust bearing can be reduced.
[0014]
On the other hand, the pressure regulating valve has a low differential pressure (Pd−Ps) corresponding to the allowable value of the thrust load or less than the reference differential pressure, or the pressure ratio (Pd / Ps) is less than or equal to the reference pressure ratio. When the load is applied, the valve is closed to shut off the pressurized supply of working fluid to the balance piston device, and the balance piston device has a discharge pressure (Pd) that is reduced by an appropriate amount by the check valve having a throttling function and an orifice function. Since the thrust load canceling force is reduced by supplying (pressure reduction supply) through the bypass passage , the thrust load canceling force by the balance piston device is small at the low load. Thus, a moderately reduced load is applied to the thrust bearing, and this cancels out the canceling force generated in the balance piston device at low load. It is prevented from entering, thereby preventing the reduction of the service life of the thrust bearing.
[0015]
Therefore, according to this invention, the pressure adjusting valve installed in the working fluid passage to the balance piston device is opened at high load, and the working fluid is pressurized and supplied to the balance piston device, so that the thrust load is increased. It is possible to reduce the thrust load applied to the thrust bearing and close the valve at low load to shut off the supply of working fluid to the balance piston device and supply the pressure reduced from the bypass passage. This makes it possible to reduce the thrust load canceling force by the balance piston device, and prevents the life of the thrust bearing from being reduced due to the excessive thrust load canceling force by the balance piston device at low load. it can.
[0016]
(Delete)
[0017]
(Delete)
[0018]
Further, the discharge pressure (Pd), the suction pressure (Ps), and the working fluid pressure of the fluid in the screw compressor are detected and input to the controller. In the controller, the differential pressure (Pd−Ps), the pressure ratio (Pd / Ps), and feedback control of the pressure regulating valve is performed so that the working fluid pressure becomes a target value (reference value), so that the thrust load applied to the thrust bearing is always minimized by controlling the opening and closing of the pressure regulating valve. Can be performed with high accuracy.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, unless otherwise specified, the dimensions, shapes, relative arrangements, and the like of the components described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention.
[0020]
FIG. 1 is a block diagram of a screw compressor having a balance piston device according to an embodiment of the present invention and its control system, and FIG. 2 is a control block diagram. FIG. 3 is a cross-sectional view of the screw compressor. FIG. 4 is a switching load diagram of the balance piston device, and FIG. 5 is a life diagram of the thrust bearing.
[0021]
In FIG. 3 showing a screw compressor to which the present invention is applied, 1 is a casing, 11 is a discharge case, 12 is a suction case, 13 is a discharge case cover, and 14 is a suction case cover.
In the casing 1, a male rotor 2 and a female rotor 3 formed with helical gears having different numbers of teeth are engaged with each other and accommodated so as to be capable of rotating in the reverse direction. Reference numeral 4 denotes a male rotor shaft to which the male rotor 2 is fixed, and is rotated by a motor (not shown). Reference numeral 5 denotes a female rotor shaft to which the female rotor 3 is fixed.
[0022]
7 and 9 are bearings on the male rotor side, and the male rotor shaft 4 is rotatably supported by the discharge case 11 and the suction case 12 by the bearings 7 and 9, respectively. 8 and 10 are female rotor side bearings.
6a is a thrust bearing on the male rotor side, 17a and 17b are thrust collars, and the thrust load of the male rotor 2 is supported by the discharge case 11 via the male rotor shaft 4, the thrust collars 17a and 17b and the thrust bearing 6a. It is like that.
6b is a thrust bearing on the female rotor side, 18a and 18b are thrust collars, and the thrust load of the female rotor 3 is applied to the discharge case 11 via the female rotor shaft 5, the thrust collars 18a and 18b, and the thrust bearing 6b. It comes to support.
[0023]
Reference numeral 19 denotes a mechanical seal that seals the male rotor shaft 4. Reference numeral 15 denotes a refrigerant gas inlet formed in the suction case 12, and reference numeral 16 denotes a refrigerant gas outlet formed in the discharge case 11.
Reference numeral 30 denotes a balance piston device, which is attached to the opposite end of the driving-side male rotor shaft 4 where the thrust load increases. 31 is a piston of the balance piston device 30, which is fixed to the opposite end of the male rotor shaft 4 and is slidably fitted in a cylinder 34 formed in the suction case 12. . The hydraulic oil chambers 32 and 33 are defined in the cylinder 34 by the piston 31, and the hydraulic oil chamber 35 is connected to the hydraulic oil chamber 35 from the hydraulic oil inlet 35 depending on the direction of the thrust load determined by the torsional direction of the male rotor 2 and the female rotor 3. Hydraulic oil is introduced into either one of 32 and 33.
[0024]
During the operation of the screw compressor 100, the gas refrigerant introduced from the suction port 15 of the suction case 12 through the suction pipe 55 (see FIG. 1) is rotated between the male rotor 2 and the female rotor 3. Compressed by the gap volume change between the two, is sent from the discharge port 16 of the discharge case 11 to the condenser (not shown) through the discharge pipe 56 (see FIG. 1).
The thrust load generated by the gap volume change accompanying the rotation of the male rotor 2 and the female rotor 3 is, on the male rotor 2 side, the discharge case 11 via the male rotor shaft 4, the thrust collars 17a and 17b, and the thrust bearing 6a. On the female rotor 3 side, it is supported by the discharge case 11 via the female rotor shaft 5, the thrust collars 18a and 18b, and the thrust bearing 6b.
The structure and operation of the screw compressor 100 shown above are the same as those of a conventional screw compressor with a balance piston device.
[0025]
The present invention relates to hydraulic oil control of the balance piston device 30 in the screw compressor.
In FIG. 1 showing an embodiment, 51 is a hydraulic oil tank, 52 is a hydraulic oil filter, 50 is a hydraulic oil pump, 53 is a hydraulic oil pipe that connects the hydraulic oil outlet of the hydraulic oil pump 50 and the balance piston device 30, 41 is an electromagnetic valve installed in the pipeline of the hydraulic oil pipe 53, and the hydraulic oil in the hydraulic oil tank 51 is moved through the hydraulic oil pipe 53 by the hydraulic oil pump 50 into the hydraulic oil filter 52 and the electromagnetic valve. 41 is fed into the oil chamber 32 of the balance piston device 30 (inside the oil chamber 33 depending on the twisting direction of the male rotor 2 and the female rotor 3).
[0026]
Reference numeral 57 denotes a bypass passage branched from the inlet pipe 059 of the hydraulic oil pump 50 and connected to the outlet side of the solenoid valve 41 of the hydraulic oil pipe 53. The bypass passage 57 includes the inlet pipe 059 side, the hydraulic oil pipe 53 side, and the like. And a check valve (check valve) 58 that has a non-return function of hydraulic oil from the hydraulic oil pipe 53 side to the inlet pipe 059 side and opens at a certain pressure difference or more. .
In addition, as shown in FIG. 1B, a pressure reducing valve 59 having a pressure adjusting function can be provided in the bypass passage 57 in series with the check valve 58.
[0027]
40 is a controller, 46 is a solenoid valve control device, and the solenoid valve 41 receives a control signal as will be described later from the controller 40 and is controlled to open and close by the solenoid valve control device 46 to the balance piston device 30. The hydraulic oil is supplied and discharged.
A suction pressure sensor 43 is attached to the suction pipe 55 and detects the suction pressure Ps of the screw compressor 100. A discharge pressure 44 is attached to the discharge pipe 56 and detects the discharge pressure Pd of the screw compressor 100. A sensor 45 is a hydraulic oil pressure sensor that is attached to the hydraulic oil pipe 53 and detects the hydraulic oil pressure at the inlet of the balance piston device 30. The suction pressure detection value from the suction pressure sensor 43 and the discharge pressure sensor 44 The discharge pressure detection value and the hydraulic oil pressure detection value from the hydraulic oil pressure sensor 45 are input to the controller 40.
In addition, the component of the screw compressor 100 in FIG. 1 respond | corresponds to FIG.
[0028]
Next, the operation of this embodiment will be described with reference to FIGS.
The suction pressure detection value Ps from the suction pressure sensor 43, the discharge pressure detection value Pd from the discharge pressure sensor 44, and the hydraulic oil pressure detection value from the hydraulic oil pressure sensor 45 are the differential pressure calculation unit 401 of the controller 40, or Input to the pressure ratio calculation unit 404.
The differential pressure calculation unit 401 calculates a differential pressure (pressure difference) ΔP (ΔP = Pd−Ps) between the discharge pressure Pd and the suction pressure Ps. Further, the pressure ratio calculation unit 404 calculates a pressure ratio N (N = Pd−Ps) between the discharge pressure Pd and the suction pressure Ps. The calculated value of the differential pressure ΔP and the calculated value of the pressure ratio N are input to the solenoid valve switching determination unit 403. Further, the hydraulic oil pressure detection value from the hydraulic oil pressure sensor 45 is also input to the solenoid valve switching determination unit 403.
[0029]
Reference numeral 402 denotes a switching pressure setting unit, in which a switching reference differential pressure ΔPa or a switching reference pressure ratio Na serving as a reference for switching the opening and closing of the solenoid valve 41 is set.
Here, as described above, in the screw compressor 100, the thrust acting on the thrust bearings 6 a and 6 b from the differential pressure ΔP (ΔP = Pd−Ps) of the refrigerant gas acting on the male rotor 2 or the female rotor 3. In order to reduce the load, the balance piston device 30 applies a hydraulic oil pressure to the male rotor 2 or the female rotor 3 in the direction opposite to the differential pressure ΔP to cancel the thrust load.
On the other hand, at the time of low load unloading operation in the screw compressor 100, the suction pressure Ps is increased and the differential pressure ΔP is decreased, and the internal maximum pressure is decreased and the differential pressure between the internal pressure and the suction pressure is increased. Due to the small effect, the thrust load acting on the thrust bearings 6a and 6b is reduced by the differential pressure, and the working fluid force acting on the balance piston device 30 greatly exceeds the thrust load.
In such a state, a large reverse thrust load is applied to the thrust bearings 6a and 6b, which may cause a reduction in the life of the thrust bearings 6a and 6b.
[0030]
Accordingly, the switching pressure setting unit 402 has a point below the point at which the thrust load canceling force due to the hydraulic oil pressure is larger than the differential pressure ΔP and the thrust load due to the differential pressure between the internal pressure and the suction pressure at a low load. At this pressure level, the switching pressure level for shutting off the supply of hydraulic oil to the balance piston device 30 is set as the reference differential pressure ΔPa or the switching reference pressure ratio Na.
For example, in the case of a pressure ratio, the reference pressure ratio Na is set to a point of the pressure ratio 5, and the switching pressure level is a balance piston at a low load of the reference pressure ratio Na = 5 or less. The supply of hydraulic oil to the device 30 is shut off.
[0031]
The switching reference differential pressure ΔPa or the switching reference pressure ratio Na from the switching pressure setting unit 402 is input to the solenoid valve switching determination unit 403.
The solenoid valve switching determination unit 403 compares the calculated value of the differential pressure ΔP with the reference differential pressure ΔPa, compares the calculated value of the pressure ratio N with the reference pressure ratio Na, and compares the differential pressure ΔP. When the calculated value of the pressure ratio exceeds the reference differential pressure ΔPa or the calculated value of the pressure ratio N exceeds the reference pressure ratio Na, the solenoid valve 41 is opened, and the calculated value of the differential pressure ΔP is the reference value. A determination is made to close the solenoid valve 41 either when the pressure difference is equal to or less than ΔPa or when the calculated value of the pressure ratio N is equal to or less than the reference pressure ratio Na.
In addition, in the electromagnetic valve switching determination unit 403, in addition to the above conditions, when the hydraulic oil pressure detection value input from the hydraulic oil pressure sensor 45 is equal to or higher than a preset reference hydraulic oil pressure, The electromagnetic valve 41 is opened so that the hydraulic oil can be supplied to the balance piston device 30.
The solenoid valve 41 opening / closing judgment result in the solenoid valve switching judgment unit 403 is input to the solenoid valve control device 46. The electromagnetic valve control device 46 opens and closes the electromagnetic valve 41 according to the determination result in the electromagnetic valve switching determination unit 403.
[0032]
Accordingly, when the calculated value of the differential pressure ΔP exceeds the reference differential pressure ΔPa, or when the calculated value of the pressure ratio N exceeds the reference pressure ratio Na, the solenoid valve 41 is opened by the solenoid valve controller 46. , Hydraulic oil is supplied to the balance piston device 30. Thereby, a canceling force of the thrust load is generated, and the thrust load applied to the thrust bearings 6a and 6b by the canceling force can be reduced.
[0033]
In addition, when the load is low when the calculated value of the differential pressure ΔP and the differential pressure between the internal pressure and the suction pressure is a reference differential pressure ΔPa or less, or the calculated value of the pressure ratio N is less than the reference pressure ratio Na, the solenoid valve The electromagnetic valve 41 is closed by the control device 46.
On the other hand, at the time of such a low load, the solenoid valve 41 is closed as described above, but the check valve 58 having a throttling function and an orifice function in the bypass passage 57 is connected to the suction side of the hydraulic oil pump 50 and the solenoid valve 41. The valve is opened by a pressure difference from the downstream side, and a pressure equal to or lower than the discharge pressure (Pd) reduced in pressure by an appropriate amount is supplied to the balance piston device 30 (reduced pressure supply).
Thereby, the thrust load canceling force can be reduced, and at the time of the low load, the thrust load canceling force by the balance piston device 30 is reduced, and the thrust bearings 6a and 6b are moderately reduced. As a result, a load is applied, which prevents an excessive cancellation force generated in the balance piston device 30 when the load is low, and prevents a reduction in the life of the thrust bearing.
[0034]
FIG. 5 shows the case where the balance piston device 30 is operated by opening the electromagnetic valve 41 (shown in B), and the case where the electromagnetic valve 41 is closed and only the thrust load due to the differential pressure ΔP is shown (shown in A). An example of the life of the thrust bearings 6a and 6b is shown.
As is apparent from the figure, the life when the balance piston device 30 is operated becomes longer in a high load range exceeding 70% load, but the operation of the balance piston device 30 is stopped in a low load range of 70% load or less. Thus, the life is longer when only the thrust load due to the differential pressure ΔP is used.
In the above embodiment, the opening / closing judgment of the electromagnetic valve 41 is made by both the differential pressure ΔP and the pressure ratio N. However, the opening / closing judgment of the electromagnetic valve 41 is made by either the differential pressure ΔP or the pressure ratio N. May be.
[0035]
【The invention's effect】
As described above, according to the present invention, the pressure adjustment valve installed in the working fluid passage to the balance piston device is opened at high load and the working fluid is supplied to the balance piston device, so that the thrust load is reduced. It is possible to generate a counteracting force, reduce the thrust load applied to the thrust bearing, and close the valve when the load is low, reducing the thrust load canceling force by the balance piston device. It is possible to prevent the life of the thrust bearing from being reduced due to the canceling force of the thrust load by the balance piston device.
[0036]
Further, the discharge pressure (Pd), the suction pressure (Ps), and the working fluid pressure of the fluid in the screw compressor are detected and input to the controller, and the differential pressure (Pd−Ps), the pressure ratio (Pd / Ps) and feedback control of the pressure regulating valve is performed so that the working fluid pressure becomes a target value (reference value). Therefore, the opening / closing control of the pressure regulating valve is performed so that the thrust load applied to the thrust bearing is always minimized. It becomes possible to carry out with high precision.
[Brief description of the drawings]
FIG. 1A is a configuration diagram of a screw compressor including a balance piston device according to an embodiment of the present invention and a control system thereof, and FIG.
FIG. 2 is a control block diagram in the embodiment.
FIG. 3 is a cross-sectional view of a screw compressor.
FIG. 4 is a switching load diagram of the balance piston device.
FIG. 5 is a life diagram of a thrust bearing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Casing 2 Male rotor 3 Female rotor 4 Male rotor shaft 5 Female rotor shaft 6a, 6b Thrust bearing 15 Suction port 16 Discharge port 30 Balance piston device 31 Piston 32, 33 Hydraulic oil chamber 40 Controller 41 Electromagnetic valve 43 Suction pressure sensor 44 Discharge Pressure sensor 45 Hydraulic oil pressure sensor 46 Solenoid valve control device 50 Hydraulic oil pump 53 Hydraulic oil pipe 57 Bypass passage 58 Check valve (check valve)
100 screw compressor

Claims (2)

A screw compressor that compresses fluid sucked from a suction port by a male rotor and a female rotor that are rotated in reverse to each other and sends the fluid to the outside from a discharge port, and either or both of the male rotor and the female rotor In addition, in the screw compressor provided with a balance piston device that reduces the thrust load acting on the male rotor or the female rotor,
A pressure adjusting valve for opening and closing the working fluid passage is provided in the working fluid passage for supplying the working fluid to the balance piston device by a pressurizing device such as a pump, and the fluid discharge pressure (Pd) in the screw compressor is set. A discharge pressure sensor for detecting, a suction pressure sensor for detecting a suction pressure (Ps) of the fluid, a discharge pressure detection value input from the discharge pressure sensor, and a suction pressure detection value input from the suction pressure sensor; When either one or both of the differential pressure (Pd−Ps) and the pressure ratio (Pd / Ps) exceed the reference pressure ratio or the reference differential pressure, the pressure adjusting valve is opened to allow the working fluid to be supplied to the balance piston device. The thrust pressure is canceled to cancel the thrust load, and either one or both of the differential pressure (Pd−Ps) and the pressure ratio (Pd / Ps) is less than the reference differential pressure. Alternatively a screw compressor provided with balancing piston device which is characterized by comprising a controller that allowed to shut off the pressurized supply of hydraulic fluid to the balance piston device when the following reference pressure ratio. A bypass passage that bypasses the pressure regulating valve and is connected to a discharge portion of the pressure regulating valve is provided, and when the pressurized fluid supply to the balance piston device is cut off, the discharge pressure (Pd) is reduced by the bypass passage. 2. A screw compressor provided with a balance piston device according to claim 1 , wherein a working fluid whose pressure is reduced by a certain amount can be supplied to the balance piston device.

Images