Variable capacity bypass valve for screw compressors.

Abstract

A screw compressor and a variable capacity bypass valve for a screw compressor are provided that include a bore formed in a rotor bore discharge face of a compressor housing upstream of a compression chamber outlet end of the compression chamber, a sliding valve member inserted into the bore to block the bore cavity, the valve member having a sealing surface configured to interact with threads of the compressor screw during operation of the screw compressor, and an actuator structure coupled to the valve member and oriented to move the valve member radially along the bore to open a fluid path communicatively connecting the compression chamber with a bypass chamber configured to return compressed fluid to a fluid inlet of the compression chamber.

Description

[Technical field]

[0001] The present disclosure relates to screw compressors, and more particularly to screw compressors having a variable capacity bypass valve. [Background technology]

[0002] Screw gas compressors are known in the related art. In the related art, a screw compressor may include a compressor housing, and a motor (e.g., a permanent magnet rotor / stator motor) is used to drive one of two compression screws (e.g., a first compression screw). The second of the two compression screws may be mechanically coupled to the compression screw driven by the motor. Thus, the second compression screw may be driven by the first compression screw. In the related art, gas may be drawn into the compressor through an inlet, compressed between the two compression screws as they rotate, and pushed out through a gas inlet and an outlet downstream of the compression screws.

[0003] In some related art, a gas compressor may include a mechanical capacity control mechanism that provides one or more bypass ports or valve openings formed in the compressor housing or rotor cowling to allow gas to exit the compressor housing to control or prevent over-pressurization or over-compression along the length of the compression screw. In related art, the one or more bypass ports or valve openings may be located adjacent to a helical valve that controls the opening and closing of the bypass ports or valve openings by a shutter that is rotated to a point where the bypass ports are exposed and one or more of the bypass ports communicate with the bypass chamber, allowing the compression length of the compressor to be changed.

[0004] However, in some related art, the efficiency of compressors equipped with helical valves can decrease significantly at turndown levels higher than 50% because the higher pressures that arise where the valves need to operate overcome the seal formed by the oil in the gap between the helical valve shutter and the rotor housing window.

[0005] Additionally, in some related art, other variable displacement control (VCC) devices may be used, such as poppet or lift valves or axial slide valves, but these devices also leak more at higher pressures, even though they may have better seals than helical valves. Additionally, both lift and axial slide valves are more expensive to manufacture, more difficult to assemble, and more difficult to maintain. Summary of the Invention [Problem to be solved by the invention]

[0006] These difficulties may result from the complex geometry of the moving seal surface and the way in which it meets its complex mating surface. Additionally, lift valve designs may work against rotor designs because rotor apex seals are inherently narrow and lift valves are inherently wide. Additionally, the valves may span adjacent rotor threads that have large pressure differentials, making it difficult for the lift valve to precisely control turndown. The exemplary implementations described herein can address these challenges. [Means for solving the problem]

[0007] Aspects of the disclosure may include a variable capacity bypass valve for a screw compressor having a compressor housing defining a compression chamber, the variable capacity bypass valve may include a bore formed in a rotor bore discharge face of the compressor housing upstream of a compression chamber outlet end of the compression chamber, a sliding valve member inserted in the bore to block a cavity formed in the rotor bore discharge face of the compressor housing, the sliding valve member having a sealing surface configured to interact with threads of the compressor screw during operation of the screw compressor, and an actuator structure coupled to the valve member and oriented to move the valve member radially along the bore to open a fluid path communicatively connecting the compression chamber with a bypass chamber configured to return compressed fluid to a fluid inlet of the compression chamber.

[0008] Additionally, aspects of the present disclosure also include a screw compressor having a compressor housing defining a compression chamber having a compression chamber outlet end and a plurality of bypass ports in communication with the compression chamber, a helical valve disposed adjacent the plurality of bypass ports in communication with the compression chamber, the helical valve including a shutter configured to selectively open and close one or more of the plurality of bypass ports based on a rotational position, and a variable capacity bypass valve. The variable displacement bypass valve may include a bore formed in a rotor bore discharge face of the compressor housing upstream of a compression chamber outlet end of the compression chamber, a sliding valve member inserted into the bore to block a cavity formed in the rotor bore discharge face of the compressor housing, the sliding valve member having a sealing surface configured to interact with threads of the compressor screw during operation of the screw compressor, and an actuator structure coupled to the valve member, the actuator structure oriented to move the valve member radially along the bore to open a fluid path communicatively connecting the bypass chamber containing a helical valve configured to return compressed fluid to a fluid inlet of the compression chamber.

[0009] Aspects of the present disclosure may also include that the sealing surface is a flat sealing surface that extends parallel to a rotor bore discharge surface of the compressor housing.

[0010] Aspects of the present disclosure may also include that the valve member is aligned within the bore such that the sealing surface projects outwardly from the rotor bore discharge face into the compression chamber.

[0011] Aspects of the present disclosure may also include the valve member having a partial cylindrical shape with the open area opposite the sealing surface.

[0012] Aspects of the present disclosure may also include that the sealing surface is a flat sealing surface that extends parallel to a rotor bore discharge surface of the compressor housing.

[0013] Aspects of the present disclosure may also include that the valve member is aligned within the bore such that the sealing surface projects outwardly from the rotor bore discharge face into the compression chamber. [Brief description of the drawings]

[0014] A general architecture for implementing various features of the present disclosure will now be described with reference to the drawings. The drawings and the associated description are provided to illustrate example implementations of the present disclosure and are not intended to limit the scope of the disclosure. Reference numbers are repeated throughout the drawings to indicate correspondence between referenced elements.

[0015] [Figure 1] FIG. 1 illustrates a perspective view of a screw compressor having a helical valve design and a variable capacity bypass valve according to an exemplary implementation of the present application. [Diagram 2] FIG. 1 illustrates a side view of a screw compressor according to an exemplary implementation of the present application. [Diagram 3] FIG. 1 illustrates a top view of a screw compressor according to an exemplary implementation of the present application. [Figure 4] 4 shows a cross-sectional view of the screw compressor taken along line IV-IV' in FIG. [Diagram 5] 4 shows a cross-sectional view of the screw compressor taken along line VV' in FIG. [Figure 6] 6 shows a cross-sectional view of the screw compressor taken along line VI-VI' in FIG. 5. [Figure 7] 7 shows a cross-sectional view of the screw compressor taken along line VII-VII' in FIG. 5. [Figure 8] 8 shows a cross-sectional view of the screw compressor taken along line VIII-VIII' in FIG. 5. [Figure 9A] 9 is a cross-sectional view taken along line IX-IX' in FIG. [Figure 9B] 9 is a cross-sectional view taken along line IX-IX' in FIG. [Figure 9C] 9 is a cross-sectional view taken along line IX-IX' in FIG. [Figure 9D] 9 is a cross-sectional view taken along line IX-IX' in FIG. [Figure 10A] FIG. 5 is a cross-sectional view taken along line XX' in FIG. [Figure 10B] FIG. 5 is a cross-sectional view taken along line XX' in FIG. [Figure 11] 1 shows the top of a variable displacement bypass valve with the valve member in a fully retracted position. [Figure 12] 1 shows the top of a variable displacement bypass valve with the valve member in a partially extended position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The following detailed description provides further details of the figures and exemplary implementations of the present disclosure. Reference numbers and descriptions of overlapping elements between figures are omitted for clarity. Terms used throughout the description are provided as examples and are not intended to be limiting. For example, the use of the term "automatic" may include fully automatic implementations or semi-automatic implementations with user or operator control over certain aspects of the implementation, depending on the desired implementation of the skilled artisan implementing the present disclosure. Furthermore, order terms such as "first", "second", "third", etc. may be used in the description and claims merely for labeling purposes and should not be limited to indicating that the operations or items described are performed in the order described. Operations or items may be ordered in different orders or performed in parallel or dynamically without departing from the scope of the present disclosure.

[0017] As explained above, in some related art, a gas compressor may include a mechanical capacity control mechanism that provides one or more bypass ports or valve openings formed in the compressor housing or rotor cowling to allow gas to exit the compression housing to control or prevent over-pressurization or over-compression along the length of the compression screw. These one or more bypass ports or valve openings may be located adjacent to a helical valve that controls the opening and closing of the bypass port or valve openings by a shutter that is rotated to a point where the bypass port is exposed and allows one or more of the bypass ports to communicate with the bypass chamber, thereby changing the compression length of the compressor. However, the efficiency of a compressor equipped with a helical valve may be significantly reduced at a capacity reduction (turndown) level higher than 50% due to the higher pressures that arise where the valve needs to operate overpowering the seal formed by oil in the gap between the helical valve shutter and the rotor housing window.

[0018] To address these challenges, example implementations may provide a variable capacity bypass valve (VCBV) in conjunction with a helical valve or other VCC device as a turn down extender. Alternatively, the VCBV device shown in the example implementations of the present application may also be used as a stand-alone capacity control system.

[0019] In some exemplary implementations, the VCBV may be a cylindrical valve peripherally positioned on the rotor housing discharge face so that when moved outward, it opens a passageway back to the inlet. As described below, the VCBV may be applied to the male, female, or both rotor bore faces and may be actuated by a pneumatic cylinder, hydraulic cylinder, electronic solenoid, or other similar actuator. In exemplary implementations, using a single valve may provide cost advantages, while using multiple valves may provide greater turndown and / or better performance. Because the valves are peripherally positioned on the rotor housing, they utilize space not normally used for bearings or other compressor components and do not occupy the normal path required for exhaust gases.

[0020] FIG. 1 shows a perspective view of a screw compressor 100 having a helical valve structure and a variable capacity bypass valve according to an exemplary implementation of the present application. Additionally, FIG. 2 and FIG. 3 show side and top views, respectively, of the screw compressor 100 according to an exemplary implementation of the present application. As shown, the screw compressor 100 has a compressor housing 10 that encloses the compressor internals and forms a compression chamber 3 (not shown in FIGS. 1-3, but shown in FIGS. 4-8). The housing 10 may include one or more mounting brackets or feet 2 that support the screw compressor 100 and allow the screw compressor 100 to be secured to a floor or other support platform. For example, the feet 2 may allow the screw compressor 100 to be mounted to a transportable support platform or trailer.

[0021] The housing 10 also defines a main gas flow inlet 26 and a main gas flow outlet 28. Arrows are provided to indicate gas flow through the screw compressor 100. Additionally, the compressor housing 10 may allow a drive shaft 15 to pass from the compressor internals (shown in FIGS. 4-8) through the area surrounding the compressor 100.

[0022] The drive shaft 15 can be used to mechanically couple the screw compressor 100 to a motor or engine to drive the screw compressor 100. The screw compressor 100 can be driven by an IC engine, such as a gasoline engine, a diesel engine, or any other type of engine that would be apparent to one of ordinary skill in the art. The screw compressor 100 can also be driven by an electric motor or any type of machine that provides rotational power that would be apparent to one of ordinary skill in the art.

[0023] Further, an actuator module 5 can be attached to the compressor housing 10 and control a helical valve structure (shown in FIGS. 4-8) disposed within the compressor housing 10. The actuator module 5 can include an electric motor coupled to a gearbox that is coupled to the helical valve. In addition, the actuator module 5 can also include an integrated processor component that can have on-board control logic to control the actuator module 5 automatically, semi-automatically based in part on user input, or manually based in full on user input. One or more separate actuator modules can also be used to control a variable capacity bypass valve (VCBV), as shown in FIGS. 5-8, 9A-9D, and 10A-10B.

[0024] Figures 4 to 8 show cross-sectional views of the screw compressor. Specifically, Figures 4 and 5 show cross-sectional views of the screw compressor taken along lines IV-IV' and V-V', respectively, in Figure 2. Furthermore, Figures 6 to 8 show cross-sectional views of the screw compressor taken along lines VI-VI', VII-VII', and VIII-VIII', respectively, in Figure 5.

[0025] The compressor housing 10, when the unit is assembled and functional, forms a compression chamber 3 that defines two adjacent bores 6 and 8, each of which contains a screw 7, 9 of the twin screw gas compressor 100. Each screw 7, 9 is composed of a number of lobes 305 / 310 / 315 / 320. As shown, one of the screws, screw 9 (also known as the drive screw), is attached to a driven gear 210 and is mechanically coupled to a shaft 15 by a driven gear 205. A motor or engine that drives the screw gas compressor is coupled to the shaft 15. The other screw 7 (also known as the driven screw) is driven by the drive screw 9. Both screws 7, 9 may each be supported by a bearing group 225, such as a roller bearing or any other type of bearing or bushing that would be apparent to one skilled in the art.

[0026] Further, in some exemplary implementations, one of the screws may have a female lobe configuration and the other of the screws may have a male lobe configuration. In other words, one of the screws may be a female compressor screw and the other screw may be a male compressor screw that interacts with a female compressor screw. For example, the driving screw 9 may be a male compression screw and the driven screw 7 may be a female compression screw. As would be apparent to one skilled in the art, exemplary implementations of the present application are not limited to this configuration and some exemplary implementations may have alternative configurations (e.g., the driving screw 9 may be a female compression screw and the driven screw 7 may be a male compression screw).

[0027] An end of the compressor housing 10 includes an outlet 28 in fluid communication with the inlet 26 (shown in FIGS. 1-3). A gas flow channel 215, 220 may connect each bore 6, 8 with the inlet 26 to allow gas to flow into each bore 6, 8. Each bore 6 and 8 also includes one or more bypass ports, collectively represented by the numerals 12a-12j. The illustrated bypass ports 12a-12f are formed in the bore 6 associated with the driven screw 7. Additionally, similar bypass ports 12g-12j are formed in the bore 8 associated with the driving screw 9. As shown, each bypass port 12a-12j is in fluid communication with a bypass chamber 22 that houses a helical valve 20 that is rotatable along an axis 24. The length of each bore 6, 8 associated with the bypass ports 12a-12j may be referred to as a bypass window 245.

[0028] As mentioned above, the compressor housing 10 has a gas inlet 26 and a gas outlet 28. Within the compressor housing, gas flow channels 215, 220 provide fluid communication between the inlet 26 and the compression chamber 3. As the screws 7 and 9 rotate within their respective bores 6, 8 of the compression chamber 3, gas is compressed within the compression chamber 3. The compression chamber 3 has a length that spans between the compression chamber inlet 230, 235 and the compression chamber outlet end 240. The compressed gas is then forced out through the gas outlet 28. Arrows indicate the gas flow through the compression chamber 3.

[0029] 5-8, the helical valve 20 includes a shutter 335 that selectively closes or opens the bypass ports 12a-12j depending on the rotational position of the helical valve 20. As the helical valve 20 is rotated to a point that allows one or more of the bypass ports 12a-12j to be in fluid communication with the helical valve chamber 22, the amount of effective compression of the compression chamber 3 can be reduced due to the shorter compression chamber length.

[0030] For example, bypass ports 12c-12e can be open to indicate flow, and bypass ports 12a and 12b can be closed to indicate no flow. When at least one bypass port 12c-12e is open, the effective compression length of compression chamber 3 is defined by the distance between the open bypass port closest to compression chamber outlet end 240 and compression chamber outlet end 240 itself.

[0031] When the amount of effective compression is reduced in this manner, torque is reduced, which saves power, increases efficiency, and extends the life of the gas compressor components. However, as explained above, a reduction in capacity of more than 50% can significantly reduce the efficiency of the helical valve, as the higher operating pressures can overcome the seal formed by the oil in the gap between the helical valve shutter 305 and the rotor housing window 245. The variable capacity bypass valve 600 discussed below can address this deficiency.

[0032] The helical valve 20 is coupled to an actuator module 5 that controls the rotation and position of a shutter 335 of the helical valve 20. As shown, the actuator module 5 includes a motor 325 that is mechanically coupled to a gearbox 330. The gearbox 330 mechanically couples the motor 325 to the helical valve 20. Thus, the gearbox 330 allows torque from the motor to be transferred to the shutter 335 of the helical valve 20 to rotate the shutter 335. The motor 325 can be an electric actuator motor that provides precise control of the rotational speed and rotational position of the helical valve.

[0033] The actuator module 5 may be mounted to the compressor housing 10 to control a helical valve structure disposed within the compressor housing 10. In addition, the actuator module 5 may also include an integrated processor component that may have on-board control logic to control the motor 325 module automatically, semi-automatically based in part on user input, or manually based in full on user input.

[0034] The helical valve 20 can be rotated (or actuated) along its axis 24 from a fully open position (all of the bypass ports are open), to a fully closed position (all of the bypass ports are closed), and all points in between. In Figures 5-8, the flow is shown as the helical valve 20 is rotated to a point that allows partial bypass of gas from the compression chamber 3 to the bypass chamber 22. Specifically, the bypass ports 12i-12j allow gas to flow from the compression chamber 3 to the bypass chamber 22.

[0035] In addition, the screw compressor 100 may also include a variable capacity bypass valve (VCBV) 600 positioned near the compression chamber outlet end 240 of the compression chamber 3. The VCBV may include one or more bores 605 formed in the discharge face 610 of the housing 10 upstream of the compression chamber outlet end 240. The one or more bores 605 may be cylindrical in shape and receive a semi-cylindrical sliding valve member 615 inserted therein. Furthermore, an actuator 620 may be disposed below the compression chamber 3 to radially articulate the valve member 615 within the bore 605 to seal and unseal the bore 605 during operation of the screw compressor 100 to open a fluid path connecting with the bypass chamber. The actuator 620 may be a linear actuator, a rotary actuator, a stepper motor, or any other actuator that would be apparent to one skilled in the art. Furthermore, the actuator 620 may be hydraulically actuated, electronically actuated, pneumatically actuated, or actuated in any manner that would be apparent to one skilled in the art.

[0036] As shown by Figures 6-8, when the VCBV 600 is opened, air can flow back into the bypass chamber 22 and circulate therein back to the gas flow channels 215, 220 of the compression chamber 3. The operation and implementation of the VCBV 600 is discussed in more detail below with respect to Figures 9A-9D and 10A-10B.

[0037] 9A-9D and 10A-10B show cross-sectional views of a screw compressor showing various states of the variable capacity bypass valve 600 and the twin screws 7, 9. Specifically, FIGS. 9A-9B are cross-sectional views taken along line IX-IX' in FIG. 4, in which the variable capacity bypass valve 600 is in a closed state when the twin screws 7, 9 rotate. Furthermore, FIGS. 9C-9D are cross-sectional views taken along line IX-IX' in FIG. 4, in which the variable capacity bypass valve 600 is in an open state when the twin screws 7, 9 rotate. Furthermore, FIG. 10A is a cross-sectional view taken along line X-X' in FIG. 4, in which the variable capacity bypass valve 600 is in a closed state. As shown by FIGS. 6-8, when the VCBV 600 is opened, air can flow back into the bypass chamber 22 and circulate in the bypass chamber back to the gas flow channels 215, 220 of the compression chamber 3. Furthermore, FIG. 10B is a cross-sectional view taken along line X-X' in FIG. 4, in which the variable capacity bypass valve 600 is in an open state.

[0038] The VCBV 600 may be implemented with one or more bores 605 in the rotor bore discharge face 610 of the male, female, or both. As shown, the VCBV 600 may be implemented with multiple bores 605 arranged circumferentially around the rotor bore discharge face 610 of the compressor housing 10 in the direction of rotation of the screws 7, 9. However, if the valve member 615 is large enough for the desired flow and turndown, only one bore 605 may be required in the discharge face. A single VCBV 600 configuration is possible because the lobes 320 of the male screw 9 and female screw 7 interlock and connect to the same pressure cavity. Placing the VCBV 600 only on the male side may provide the advantage that the bore 605 may be sized to coordinate its design with the rotor design, and the larger male lobes completely cover the VCBV 600, thus eliminating any leakage to the lower pressure threads.

[0039] Thus, as shown, the bore 605 is formed in the discharge face 610 rather than on the side of the compression chamber 3, so that the lobes 320 of the screw 9 cover the bore 605 as the screw rotates in the compression chamber. Furthermore, the bore 605 has a width that is smaller than the width of the lobes 320 of the screw 9, so that the lobes 320 completely cover the bore 605 as the screw 9 rotates. This prevents fluid from flowing back through the bore 605 and around the lobes.

[0040] Thus, as shown in Figures 9A, 9B, and 10A, when the VCBV 600 is closed (valve member 615 fully extended to block cavity 635 formed in rotor bore discharge face 610), the compressed fluid can remain on the high pressure side of screw 9 lobe 320 until it reaches compression chamber outlet 240 and then exit compressor outlet 28. Conversely, as shown in Figures 9C, 9D, and 10B, when the VCBV 600 is opened (valve member 615 retracted), a portion of the compressed fluid can exit compression chamber 3 and be discharged into bypass chamber 22 and circulate in the bypass chamber back to gas inlet 215, 220 of compression chamber 3 instead of exiting compression chamber outlet 240 of the compression chamber. As described in Figures 11 and 12, the valve member 615 can have certain shape features to improve sealing efficiency.

[0041] FIG. 11 shows the top of the VCBV 600 with the valve member 615 in a fully retracted position. FIG. 12 shows the top of the VCBV 600 with the valve member 615 in a partially extended position. As shown, to better seal against the screw 9, the valve member 615 may be positioned against a seal 625 built into the valve seat that closes the flow path back to the inlet. Additionally, the valve member 615 has a semi-cylindrical shape that provides a flat surface 630 for interacting with the lobe 320 of the screw 9. The flat surface 630 may be positioned to extend parallel to the rotor bore discharge surface. Additionally, the valve member 615 may be positioned or aligned off-center within the bore 605 to have the flat surface 630 protrude outwardly from the rotor bore discharge surface into the compression chamber 3. This allows the valve member 615 to be positioned within the rotor bore discharge surface 610 without creating a gap that reduces compressor efficiency. This flat face 630 moving sealing surface of the valve disc may be easier to manufacture, assemble, and maintain than the complex moving sealing surfaces of lift or axial slide valves.

[0042] Additionally, valve member 615 may be positioned within bore 605 such that it extends slightly off-center into the rotor bore. With valve member 615 partially within the rotor bore, a valve plug 625 may be provided to plug any voids in the surface of the rotor bore that would cause gas leakage past the rotor apex seal to the low pressure side of lobe 320. Valve plug 625 is also used to maintain the valve orientation so as not to interfere with rotor motion.

[0043] Additionally, in some exemplary implementations, the valve member 615 may have an open area 640 opposite the flat surface 630, which forms a sealing surface to increase the flow of compressed fluid through the VCBV 600 when the VCBV 600 is opened. In these implementations, as described above, when the valve member 615 is lowered, compressed fluid may flow over the top of the flat surface 630 into the open area 640 and down the length of the valve member 615 into the bypass chamber 220. This allows compressed fluid to flow through the VCBV 600 while it is open in these exemplary implementations. In other exemplary implementations, the valve member 615 may be solid on the rear side of the flat surface 630.

[0044] While the invention is susceptible to modifications and alternative forms, various specific embodiments thereof have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that the description of the specific embodiments herein is not intended to limit the invention to the specific forms disclosed. Moreover, the exemplary implementation is not limited to an industrial or fixed location, and a portable configuration can be achieved by mounting the screw compressor 100 on a vehicle, trailer, or other portable structure.

[0045] In the above detailed description, various exemplary implementations of devices and / or processes have been described by using figures, diagrams, and examples. To the extent that such figures, diagrams, and examples include one or more functions and / or operations, each function and / or operation in such figures or examples can be individually and / or collectively implemented by various structures. Although certain exemplary implementations have been described, these implementations are presented merely as examples and are not intended to limit the scope of protection. In fact, the novel methods and apparatuses described herein may be embodied in various other forms. Furthermore, various omissions, substitutions, and changes in the form of the devices and systems described herein may be made without departing from the spirit of protection. The appended claims and their equivalents are intended to cover such forms or modifications that fall within the scope and spirit of protection.

Claims

1. 1. A variable displacement bypass valve for a screw compressor having a compressor housing defining a compression chamber, comprising: a bore formed in a rotor bore discharge face of the compressor housing upstream of a compression chamber outlet end of the compression chamber; a slide valve member inserted into the rotor bore discharge face of the compressor housing to block a cavity formed in the bore, the slide valve member having a sealing surface configured to interact with threads of a compressor screw during operation of the screw compressor; an actuator structure coupled to the valve member, the actuator structure oriented to move the valve member radially along the bore to open a fluid path communicatively connecting the compression chamber with a bypass chamber configured to return compressed fluid to a fluid inlet of the compression chamber; A variable capacity bypass valve comprising:

2. 2. The variable capacity bypass valve of claim 1, wherein the sealing surface is a planar sealing surface extending parallel to the rotor bore discharge face of the compressor housing.

3. 3. The variable capacity bypass valve of claim 2, wherein said valve member is aligned within said bore such that said sealing surface projects outwardly from said rotor bore discharge face into said compression chamber.

4. 2. The variable capacity bypass valve of claim 1, wherein the valve member has a partial cylindrical shape with an open area opposite the sealing surface.

5. 5. The variable capacity bypass valve of claim 4, wherein the sealing surface is a planar sealing surface extending parallel to the rotor bore discharge surface of the compressor housing.

6. 6. The variable capacity bypass valve of claim 5, wherein said valve member is aligned within said bore such that said sealing surface projects outwardly from said rotor bore discharge face into said compression chamber.

7. 1. A screw compressor comprising: a compressor housing defining a compression chamber having a compression chamber outlet end and a plurality of bypass ports in communication with the compression chamber; a helical valve disposed adjacent the plurality of bypass ports communicating with the compression chamber, the helical valve including a shutter configured to selectively open and close one or more of the plurality of bypass ports based on a rotational position; Variable capacity bypass valve The variable capacity bypass valve comprises: a bore formed in a rotor bore discharge face of the compressor housing upstream of a compression chamber outlet end of the compression chamber; a slide valve member inserted into the rotor bore discharge face of the compressor housing to block a cavity formed in the bore, the slide valve member having a sealing surface configured to interact with threads of a compressor screw during operation of the screw compressor; an actuator structure coupled to the valve member, the actuator structure oriented to move the valve member radially along the bore to open a fluid path communicatively connecting the compression chamber with a bypass chamber containing the helical valve, the bypass chamber being configured to return compressed fluid to a fluid inlet of the compression chamber; Including, a screw compressor.

8. 8. The screw compressor of claim 7, wherein the sealing surface of the variable capacity bypass valve is a flat sealing surface extending parallel to the rotor bore discharge face of the compressor housing.

9. 9. The screw compressor of claim 8, wherein the valve member of the variable capacity bypass valve is aligned within the bore such that the sealing surface projects outwardly from the rotor bore discharge face into the compression chamber.

10. 8. The screw compressor of claim 7, wherein the valve member of the variable capacity bypass valve has a part-cylindrical shape with an open area opposite the sealing surface.

11. 11. The screw compressor of claim 10, wherein the sealing surface of the variable capacity bypass valve is a flat sealing surface extending parallel to the rotor bore discharge face of the compressor housing.

12. 12. The screw compressor of claim 11, wherein the valve member of the variable capacity bypass valve is aligned within the bore such that the sealing surface projects outwardly from the rotor bore discharge face into the compression chamber.

13. The system further includes a plurality of variable displacement bypass valves, each of which comprises: a bore formed in a rotor bore discharge face of the compressor housing upstream of a compression chamber outlet end of the compression chamber; a slide valve member inserted into the rotor bore discharge face of the compressor housing to block a cavity formed in the bore, the slide valve member having a sealing surface configured to interact with threads of a compressor screw during operation of the screw compressor; an actuator structure coupled to the valve member, the actuator structure oriented to move the valve member radially along the bore to open a fluid path communicatively connecting the compression chamber with a bypass chamber containing the helical valve, the bypass chamber being configured to return compressed fluid to a fluid inlet of the compression chamber; Including, 8. The screw compressor of claim 7, wherein the bores of the plurality of variable capacity bypass valves are arranged circumferentially around the rotor bore discharge surface of the compressor housing in a rotational direction of at least one screw disposed within the compression chamber.

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