Spiral valve for screw capacity control

Abstract

A spiral valve and a screw compressor having a compressor housing and a spiral valve are provided, the spiral valve including an actuator module having an electric motor and a gearbox mechanically coupled to the electric motor and transmitting torque from the electric motor, and a spiral valve body coupled to the gearbox and rotating in response to the torque transmitted from the electric motor. The spiral valve body has a first shutter arranged to open and close one or more of a plurality of bypass ports formed in the compressor housing based on a rotational position, a second shutter arranged to progressively open and close a compressor inlet conveying duct formed in the compressor housing based on a rotational position, and a gap formed between the first and second shutters.

Description

[Technical Field]

[0001] The present disclosure relates to spiral valves, and more particularly to spiral valves configured for electronic control. [Background technology]

[0002] It is believed that screw gas compressors are known in the prior art. In the prior art, a screw compressor includes a compressor housing and may use a motor (e.g., a permanent magnet rotor / stator motor) to drive one of two compression screws (e.g., a first compression screw). The second compression screw 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 prior art, gas is drawn into the compressor through an inlet, compressed between the two compression screws as they rotate, and output through a gas inlet and an outlet downstream of the compression screws.

[0003] In some prior art, one or more bypass ports or valve openings may be formed in the compressor housing or rotor cowling to allow gas to exit the housing and control or prevent over-pressurization or over-compression along the length of the compression screw. In prior art, one or more bypass ports or valve openings may be located adjacent to a spiral valve that controls the opening and closing of the bypass port or valve opening with a shutter that rotates to a point where it disengages from the bypass port and allows one or more of the bypass ports to communicate with the bypass chamber.

[0004] However, in some prior art screw air compressors equipped with spiral valve capacity control mechanisms, the adiabatic efficiency may be reduced by the amount of gas leaking around the rotor housing and spiral valve shutter. This efficiency reduction is due to the compressed gas losing work that does not contribute to the system capacity, and the hot gas and oil leaking around the spiral valve shutter enter the inlet and contribute to preheating the inlet gas.

[0005] In the prior art, many design tradeoffs can be made to reduce shutter leakage. Some of these include increased shutter overlap, larger valve size, smaller rotor housing window area, smaller gap between the spiral valve and rotor housing, and designs that cause the shutter to open more abruptly. These either increase cost or reduce functionality. Summary of the Invention

[0006] Aspects of the present disclosure may include a spiral valve for a screw compressor having a compressor housing. The spiral valve may include an actuator module disposed adjacent to the exterior of the compressor housing. The actuator module may include an electric motor, a gearbox mechanically coupled to the electric motor and configured to transmit torque from the electric motor, and a spiral valve body coupled to the gearbox and configured to rotate in response to the torque transmitted from the electric motor. The spiral valve body may include a first shell area defining a first shutter configured to open and close one or more of a plurality of bypass ports formed in the compressor housing based on a rotational position thereof, a second shell area defining a second shutter configured to progressively open and close a compressor inlet conveying duct formed in the compressor housing based on a rotational position thereof, and a gap formed between the first shell area and the second shell area. The compression length of the screw compressor may be controlled by controlling the opening and closing of the plurality of bypass ports.

[0007] Another aspect of the present disclosure may include a screw compressor having a compressor housing defining a compression chamber, a female compression screw disposed in the compression chamber, a male compression screw disposed in the compression chamber and mating with the female compression screw, a plurality of bypass ports formed in the compressor housing to provide fluid communication through the compressor housing, a compressor inlet transfer duct formed in the compressor housing to allow fluid communication with the compressor inlet, and a spiral valve. The spiral valve may include an actuator module disposed adjacent to the exterior of the compressor housing, and a spiral valve body coupled to a gearbox and rotating in response to torque transmitted from an electric motor. The actuator module may include an electric motor and a gearbox mechanically coupled to the electric motor and transmitting torque from the electric motor. The spiral valve body may include a first shell area defining a first shutter arranged to open and close a plurality of bypass ports formed in the compressor housing based on a rotational position thereof, a second shell area defining a second shutter arranged to gradually open and close a compressor inlet conveying duct formed in the compressor housing based on a rotational position thereof, and a gap formed between the first shell area and the second shell area, and the compression length of the screw compressor can be controlled by controlling the opening and closing of the plurality of bypass ports.

[0008] In an additional aspect of the present disclosure, an edge of the first shell area adjacent the gap may be angled relative to the axis of the spiral valve body to impart a tapered shape to the first shutter.

[0009] In an additional aspect of the present disclosure, an edge of the second shell area adjacent the gap may be perpendicular to the axis of the spiral valve body, giving the second shutter a rectangular shape.

[0010] In an additional aspect of the present disclosure, the spiral valve body may have a hollow, partial cylindrical shell that allows fluid communication through the interior of the spiral valve body.

[0011] In an additional aspect of the present disclosure, the first shell area defining the first shutter may be configured to rotate independently of the second shell area defining the second shutter. [Brief explanation of the drawings]

[0012] A general configuration for implementing various features of the present disclosure will now be described with reference to the drawings. The drawings and associated description are provided to illustrate exemplary embodiments of the present disclosure and are not intended to limit the scope of the disclosure. Reference numbers are reused throughout the drawings to indicate correspondence between referenced elements. [Figure 1] FIG. 1 is a perspective view of a screw compressor having a spiral valve configuration according to an exemplary embodiment of the present disclosure. [Figure 2] Fig. 2A is a partial end view of a screw compressor having the spiral valve structure of Fig. 1. Fig. 2B is a cross-sectional view taken along line IIb-IIb' of Fig. 2A. [Figure 3] 1A-1C are cross-sectional views of a spiral valve structure with the shutter valve rotated through a series of rotational positions. [Figure 4] 1A-1C are cross-sectional views of a spiral valve structure with the shutter valve rotated through a series of rotational positions. [Figure 5] 1A-1C are cross-sectional views of a spiral valve structure with the shutter valve rotated through a series of rotational positions. [Figure 6] 1A-1C are cross-sectional views of a spiral valve structure with the shutter valve rotated through a series of rotational positions. [Figure 7] 1A-1C are cross-sectional views of a spiral valve structure with the shutter valve rotated through a series of rotational positions. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following detailed description provides further details of the figures and exemplary embodiments of the present disclosure. For clarity, reference numbers and descriptions of elements that are duplicated between figures have been omitted. Terms used throughout this specification are provided by way of example and are not intended to be limiting in any way. For example, the use of the term "automatic" can 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 one skilled in the art practicing embodiments of the present disclosure. Furthermore, sequence terms such as "first," "second," "third," etc. may be used in the specification and claims for descriptive purposes only and are not intended to be limited to referring to described acts or items occurring in the described order. Acts or items may be arranged in different orders, or performed in parallel or dynamically, without departing from the scope of the present disclosure.

[0014] As mentioned above, prior art screw compressors may include one or more bypass ports or valve openings located adjacent to a spiral valve that controls the opening and closing of the bypass ports or valve openings by using a shutter that rotates to a point where it disengages from the bypass port and allows one or more of the bypass ports to communicate with the bypass chamber. However, in these prior art systems, adiabatic efficiency may be reduced by the amount of gas that leaks around the rotor housing and spiral valve shutter due to work-losing compressed gas that does not contribute to the system capacity and hot gas and oil that leaks around the spiral valve shutter and enters the inlet and contributes to preheating the inlet gas.

[0015] To address these issues, exemplary embodiments of the present disclosure may add a second shutter to the spiral valve. The second shutter traps gas that would normally go straight to the inlet in a bypass chamber. The second shutter may be located in an area that allows for more effective sealing. In exemplary embodiments of the present disclosure, the second shutter may be located in an area that is not restricted by the angled shape of the rotor.

[0016] In exemplary embodiments, this trapping feature may minimize design tradeoffs associated with the prior art. Additionally, in exemplary embodiments, while the spiral valve may need to be increased in length to accommodate the second shutter, the valve diameter, shutter overlap, and shutter aperture ratio may not need to be increased. This may reduce the need for a smaller clearance between the spiral valve outer diameter and the spiral valve bore in the rotor housing. In exemplary embodiments, this configuration may also reduce the need for additional window area reduction.

[0017] FIG. 1 is a perspective view of a screw compressor 100 having a spiral valve design according to an exemplary embodiment of the present disclosure. As shown, the screw compressor 100 includes a compressor housing 10 that encloses compressor internals and defines a compression chamber 3 (not shown in FIG. 1 but shown in FIG. 2B). The housing 10 may include one or more mounting brackets or feet 2 that support the screw compressor 100 and allow it to be secured to a support platform, such as a floor. For example, the feet 2 may allow the screw compressor 100 to be mounted to a portable support platform or trailer. The housing 10 also defines a main gas flow inlet or compressor inlet 26 and a main gas flow outlet 28. Arrows are intended to indicate gas flow through the screw compressor 100. The compressor housing 10 may also allow passage of a drive shaft 15 from the compressor internals (shown in FIG. 2B) to the area surrounding the compressor 100.

[0018] The drive shaft 15 may be used to drive the screw compressor 100 by a motor or mechanical coupling to an engine. The screw compressor 100 may 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 skilled in the art. The screw compressor 100 may also be driven by an electric motor or any other type of machine that provides rotational power that would be apparent to one skilled in the art.

[0019] Additionally, an actuator module 5 may be disposed and mounted externally to the compressor housing 10 to control a spiral valve 300 (shown in FIGS. 2B and 3-7) located within the compressor housing 10. As described below, the actuator module 5 may include an electric motor coupled to a gearbox coupled to the spiral valve, which rotates in response to torque generated by the electric motor and transmitted by the gearbox. The actuator module 5 may also include an integrated processor component that may include on-board control logic to control the actuator module 5 automatically, semi-automatically based in part on user input, or manually based entirely on user input.

[0020] FIG. 2A is a partial end view of the screw compressor 100 having the spiral valve structure of FIG. 1. FIG. 2B is a cross-sectional view taken along line IIb-IIb' in FIG. 2A. The compressor housing 10 defines a compression chamber 3 that defines two adjacent bores 6 and 8 in which the screws 7 and 9 of the twin-screw gas compressor 100 are disposed, respectively, when the unit is assembled and functional. One screw 9 (also known as the drive screw) is mechanically coupled to a shaft 15, which is also coupled to a motor or engine that drives the screw gas compressor. The other screw 7 (also known as the driven screw) is driven by the drive screw 9. Each of the screws 7 and 9 may be supported by a bearing group (not shown herein), such as a roller bearing, or any other type of bearing or bushing that would be apparent to one skilled in the art.

[0021] Furthermore, in some exemplary embodiments, 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 compression screw and the other screw may be a male compression screw that mates with the female compression 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 of ordinary skill in the art, exemplary embodiments of the present disclosure are not limited to this configuration, and some exemplary embodiments 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).

[0022] Each bore 6 and 8 also includes one or more bypass ports 12 in fluid communication with a bypass chamber 22 that includes a spiral valve body 20 rotatable along an axis 24. The length of each bore 6, 8 associated with a bypass port 12 may be referred to as a bypass window 245. The bypass chamber 22 may be in communication with a compressor inlet return chamber 205 via a compressor inlet transfer duct 200. Air entering the bypass chamber 22 may be selectively returned to the compressor inlet 26 through the compressor inlet return chamber 205.

[0023] As shown in Figures 3-7 below, the spiral valve body 20 includes a first shutter 335 that selectively blocks (closes) or opens the bypass ports 12 depending on the rotational position of the spiral valve body 20. When the spiral valve body 20 rotates to a point where one or more of the bypass ports 12 can be in fluid communication with the bypass chamber 22, the length of the compression chamber 3 may be reduced, thereby reducing the effective compression volume of the compression chamber. The spiral valve body 20 also includes a second shutter 340 that allows air to escape from the bypass chamber 22 by gradually blocking (closing) or opening the compressor inlet delivery duct 200.

[0024] The spiral valve body 20 is coupled to an actuator module 5 that controls the rotation and position of a first shutter 335 of the spiral valve body 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 spiral valve body 20. Thus, torque from the motor can be transmitted by the gearbox 330 to the first shutter 335 of the spiral valve body 20, thereby rotating the first shutter 335. The motor 325 can be an electric actuator motor or a stepper motor that provides precise control of the rotational speed and rotational position of the spiral valve.

[0025] The actuator module 5 may be mounted to the compressor housing 10 and adapted to control a spiral valve structure disposed within the compressor housing 10. The actuator module 5 may also include an integrated processor component that may include on-board control logic to control the motor 325 module automatically, semi-automatically based in part on user input, or manually based entirely on user input.

[0026] The spiral valve body 20 can rotate (or actuate) along its axis 24 from a fully open position (where all bypass ports 12 are open) to a fully closed position (where all bypass ports are closed) and all points in between.

[0027] In some exemplary embodiments, the spacing or distance between adjacent bypass ports 12 (e.g., the spacing between a first bypass port and a second bypass port adjacent to the first bypass port) may be within 20% of the minimum spacing allowed based on manufacturing tolerances associated with the manufacture of the compressor housing 10 (e.g., less than 120% of the manufacturing tolerance and greater than or equal to 100% of the manufacturing tolerance). For example, if the compressor housing 10 is formed by a casting process, the casting tolerance may require a minimum spacing of at least 5 mm between bypass ports to ensure proper flow of molten metal in the mold. If the casting tolerance is 5 mm, the spacing between adjacent bypass ports may be less than 6 mm (5 mm casting tolerance + 20%) and greater than or equal to 5 mm (the casting tolerance). Different manufacturing tolerances may also dictate different bypass port spacing parameters.

[0028] In some exemplary embodiments, the leading edge of the first bypass port 12 of the bypass window 245 associated with the compression screws 7, 9 of the screw compressor 100 may be located at or forward (toward the inlet) of the apex (maximum diameter) of the first lobe of the compression screws 7, 9. Furthermore, in some exemplary embodiments, the trailing edge of the last bypass port 12 of the bypass window 245 may be located at the apex (maximum diameter) of the lobe of the compression screws 7, 9, which is located at the position where the lowest desired compression volume is generated. In other words, the volume between the lobe and the chamber outlet end 240 may be associated with the lowest desired compression volume of the bore 6 of the screw compressor 100. Thus, in some exemplary embodiments, the last bypass port 12 may be located adjacent to the apex of the lobe.

[0029] 3-7 are cross-sectional views of a spiral valve 300 with the spiral valve body 20 rotated through a series of rotational positions. As shown, the bypass chamber 22 has a generally cylindrical shell and extends from adjacent the compression chamber 3 to adjacent the compressor inlet return chamber 205. The spiral valve body 20 may be inserted into the generally cylindrical bypass chamber 22 and may have a hollow, partially cylindrical shell that fits against the inner surface 345 of the cylindrical bypass chamber 22 to allow fluid communication through the interior of the spiral valve body.

[0030] In some exemplary embodiments, the partial cylindrical shell of the spiral valve body 20 may define at least two shell areas 350a, 350b or tabs, each serving as one of the first shutter 335 and second shutter 340 of the spiral valve body 5. A gap 355 may be formed between the shell area 350b (second shutter 340) and the shell area 350a (first shutter 335), separating the first shutter 335 and the second shutter 340. In some exemplary embodiments, an edge 360 ​​of the shell area 350b (second shutter 340) adjacent to the gap 355 may be substantially perpendicular to the axis 24 of the spiral valve body 20, such that the second shutter 340 has a substantially rectangular shape. Additionally, an edge 365 of the shell area 350a (first shutter 335) adjacent the gap 355 may be angled relative to the axis 24 of the spiral valve body 20, giving the first shutter a tapered shape.

[0031] Because the spiral valve body 20 is mechanically coupled to the actuator module 5 by the gearbox 330, the motor 325 of the actuator module 5 can selectively rotate the spiral valve body 20 to gradually open the first shutter 335 to sequentially expose the bypass ports 12, thereby gradually increasing the size of the bypass window 245, and gradually open the second shutter 335 to gradually open the compressor inlet delivery duct 200. In some exemplary embodiments, the first shutter 335 and the second shutter 340 may rotate together, thereby preventing relative rotation between the first shutter 335 and the second shutter 340.

[0032] In other exemplary embodiments, the actuator module 5 may rotate the first shutter 335 and the second shutter 340 independently of each other. For example, in the spiral valve body 20, the first shell area 350a may be configured to be rotatable relative to the second shell area 350b, and the gearbox 330 may be configured to rotate the first shell area 350a and the second shell area 350b in different increments based on input rotation from the motor 325. Alternatively, the actuator module may use two motors 325 to independently rotate the first shell area 350a and the second shell area 350b.

[0033] 3 shows the spiral valve body 20 in a fully closed position, with the first shutter 335 closing all of the bypass ports 12 and the second shutter 340 completely covering the compressor inlet transfer duct 200. In this configuration, the bypass chamber 22 does not communicate with either the compression chamber 3 or the compressor inlet return chamber 205. With all of the bypass ports closed, the effective compression length of the compression chamber 3 is defined by the overall length of the compression chamber 3.

[0034] 4 shows the spiral valve body 20 in a first stage partially open position, where the first shutter 335 exposes only one or two bypass ports 12 to form a small bypass window 245. Additionally, the second shutter 340 partially exposes the compressor inlet transfer duct 200. In this configuration, the bypass chamber 22 can communicate with only the compression chamber 3 through the first one or two bypass ports 12. Additionally, the bypass chamber 22 can communicate with the compressor inlet return chamber 205 through the outermost portion of the compressor inlet transfer duct 200.

[0035] With at least one bypass port open, the effective compression length of the compression chamber 3 is defined by the distance between the open bypass port closest to the compression chamber outlet end 240 and the compression chamber outlet end 240 itself. Therefore, in the configuration of Figure 4, the effective compression length of the compression chamber 3 is reduced compared to the configuration of Figure 3.

[0036] 5 shows the spiral valve body 20 in a second stage partially open position in which the first shutter 335 exposes three or more bypass ports 12 to form a larger bypass window 245. Additionally, the second shutter 340 exposes more of the compressor inlet transfer duct 200. In this configuration, the bypass chamber 22 can communicate with the compression chamber 3 through at least the first three bypass ports 12. Additionally, the bypass chamber 22 can communicate with the compressor inlet return chamber 205 through approximately half of the compressor inlet transfer duct 200.

[0037] With multiple bypass ports open, the effective compression length of the compression chamber 3 is defined by the distance between the last open bypass port closest to the compression chamber outlet end 240 and the compression chamber outlet end 240 itself. Therefore, in the configuration of Figure 5, the effective compression length of the compression chamber 3 is smaller than in the configuration of Figure 4.

[0038] 6 shows the spiral valve body 20 in a third stage or substantially fully open position, in which the first shutter 335 exposes at least four bypass ports 12 to form an even larger bypass window 245. Additionally, the second shutter 340 further exposes most of the compressor inlet transfer duct 200 while still blocking a portion of the compressor inlet transfer duct 200. In this configuration, the bypass chamber 22 can communicate with the compression chamber 3 through substantially all of the bypass ports 12. Furthermore, the bypass chamber 22 can communicate with the compressor inlet return chamber 205 through most of the compressor inlet transfer duct 200, while only a portion of the compressor inlet transfer duct 200 is slightly blocked.

[0039] With substantially all of the bypass ports open, the effective compression length of the compression chamber 3 is defined by the distance between the last open bypass port closest to the compression chamber outlet end 240 and the compression chamber outlet end 240 itself. Therefore, in the configuration of Figure 6, the effective compression length of the compression chamber 3 is smaller than in the configuration of Figure 5.

[0040] 7 shows the spiral valve body 20 in a fourth stage or fully open position in which the first shutter 335 exposes all of the bypass ports 12, forming the largest possible bypass window 245. Additionally, the second shutter 340 exposes the entire compressor inlet transfer duct 200. In this configuration, the bypass chamber 22 can communicate with the compression chamber 3 through all of the bypass ports 12. Additionally, the bypass chamber 22 can communicate with the compressor inlet return chamber 205 through the entire compressor inlet transfer duct 200.

[0041] With all bypass ports open, the effective compression length of the compression chamber 3 is defined by the distance between the last open bypass port in the compression chamber 3 and the compression chamber outlet end 240 itself. Thus, in the configuration of FIG. 7, the effective compression length of the compression chamber 3 is reduced to the minimum compression length of the compression chamber 3.

[0042] This reduced effective compression volume reduces torque, saves power, increases efficiency, and extends the life of screw compressor 100 components.

[0043] While the present invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are described in detail herein. It will be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed. Moreover, the exemplary implementations are not limited to industrial or fixed locations. A portable configuration may be achieved by mounting the screw compressor 100 on a portable structure such as a vehicle, trailer, or the like.

[0044] The foregoing detailed description has used diagrams, schematic diagrams, and examples to illustrate various exemplary embodiments of devices and / or processes. To the extent that such diagrams, schematic diagrams, and examples include one or more functions and / or operations, each function and / or operation in such diagrams or examples may be individually and / or collectively realized by a variety of structures. While specific exemplary embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of protection. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions, and changes can be made in the form of the devices and systems described herein without departing from the spirit of protection. The appended claims and their respective equivalents are intended to cover such forms or modifications as fall within the scope and spirit of protection.

Claims

1. 1. A spiral valve for a screw compressor having a compressor housing, comprising: an actuator module disposed adjacent to the exterior of the compressor housing; an electric motor; a gearbox mechanically coupled to the electric motor to transfer torque from the electric motor; an actuator module comprising: a spiral valve body coupled to the gearbox and configured to rotate in response to the torque transmitted from the electric motor; a first shell area defining a first shutter arranged to open and close one or more of a plurality of bypass ports formed in the compressor housing based on a rotational position; a second shell area defining a second shutter arranged to progressively open and close a compressor inlet transfer duct formed in the compressor housing based on rotational position; a gap formed between the first shell area and the second shell area; a spiral valve body comprising: Equipped with a compression length of the screw compressor can be controlled by controlling the opening and closing of the plurality of bypass ports; A spiral valve, wherein the first shell area defining the first shutter is configured to rotate independently of the second shell area defining the second shutter.

2. 2. The spiral valve of claim 1, wherein an edge of the first shell area adjacent the gap is angled relative to an axis of the spiral valve body, imparting a tapered shape to the first shutter.

3. 2. The spiral valve of claim 1, wherein an edge of the second shell area adjacent the gap is perpendicular to an axis of the spiral valve body, giving the second shutter a rectangular shape.

4. 10. The spiral valve of claim 1, wherein the spiral valve body has a hollow, partial cylindrical shell that allows fluid communication through an interior of the spiral valve body.

5. A screw compressor, a compressor housing defining a compression chamber; a female compression screw disposed within the compression chamber; a male compression screw disposed within the compression chamber and mating with the female compression screw; a plurality of bypass ports formed in the compressor housing to provide fluid communication through the compressor housing; a compressor inlet transfer duct formed in the compressor housing and providing fluid communication with the compressor inlet; an actuator module disposed adjacent to the exterior of the compressor housing; an electric motor; a gearbox mechanically coupled to the electric motor to transfer torque from the electric motor; an actuator module comprising: a spiral valve body coupled to the gearbox and configured to rotate in response to the torque transmitted from the electric motor; a first shell area defining a first shutter arranged to open and close the plurality of bypass ports formed in the compressor housing based on a rotational position of the first shutter; a second shell area defining a second shutter arranged to progressively open and close the compressor inlet transfer duct formed in the compressor housing based on rotational position; and a gap formed between the first shell area and the second shell area; a spiral valve body comprising: A spiral valve comprising: Equipped with a compression length of the screw compressor can be controlled by controlling opening and closing of the plurality of bypass ports, A screw compressor, wherein the first shell area defining the first shutter is configured to rotate independently of the second shell area defining the second shutter.

6. 6. The screw compressor of claim 5, wherein an edge of the first shell area adjacent the gap is angled relative to an axis of the spiral valve body to impart a tapered shape to the first shutter.

7. 6. The screw compressor of claim 5, wherein an edge of the second shell area adjacent the gap is perpendicular to the axis of the spiral valve body, giving the second shutter a rectangular shape.

8. 6. The screw compressor of claim 5, wherein the spiral valve body has a hollow, partial cylindrical shell that allows fluid communication through the interior of the spiral valve body.

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