Capacity control valve and method for screw compressors

Abstract

An example implementation relates to a sealed liquid delivery system for a mechanical capacity control device for a screw compressor, comprising: a mechanical capacity control device including a mechanical capacity control valve movable to change the amount of gas compressed by the screw compressor; a mechanical capacity control device housing including a cavity configured to receive the mechanical capacity control device, a gap being formed between the mechanical capacity control device housing and the mechanical capacity control valve; and a pressurized sealed liquid delivery member carried by the mechanical capacity control device housing and configured to supply sealed liquid under pressure to the cavity of the mechanical capacity control device housing to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

Description

[0001] background Technical Field

[0002] This disclosure relates in general to mechanical capacity control valves for screw compressors, and more specifically to rotary slide valves for screw compressors. Background Technology

[0003] Continued pressure on energy supplies has led the compressor industry to focus on efficiency improvements. Supply shortages have created demand for products that are less complex to use and more readily available. Rotary slide valve technology helps achieve both goals. Mechanical capacity control valves have existed in the past, but none of them included a method for supplying the sealing fluid to the valve, except in cases such as when the mechanical capacity control valve is located above the rotor housing and the sealing fluid unintentionally moves into the valve.

[0004] The efficiency of screw compressors equipped with mechanical capacity control valves is reduced by the amount of gas leaking from the rotor housing and surrounding the capacity control valve. This is especially true when the valve is not located in a position where the gap between the valve and the rotor housing can be substantially filled by a sealing fluid (e.g., oil) moved by unintentional forces, such as gravity (e.g., when the valve is below the rotor housing) or centrifugal force, which move the sealing fluid into the gap. This efficiency reduction is due to wasted work in compressing gases that do not contribute to system capacity, or to preheating of the inlet gas caused by hot gas and oil leaking around the valve and entering the inlet. Many design trade-offs can be made to reduce leakage. Some of these include increasing overlap, increasing valve size, reducing rotor housing window area, reducing the gap between the valve and the rotor housing, and designing the valve to open more abruptly. All of these either increase cost or reduce functionality. Summary of the Invention

[0005] One aspect of this disclosure relates to a sealing fluid delivery system for a mechanical capacity control device in a screw compressor, which improves the efficiency of the screw compressor without the aforementioned design trade-offs or the need to move the valve to a location such as below the rotor housing (where unintentional forces act on the sealing fluid to move it and fill the gap). This sealing fluid delivery system allows the gap between the valve and its housing to be filled with sealing fluid at any location. A supply line for the sealing fluid is installed to the valve chamber, and a circulation method is provided to move the sealing fluid through the supply line to the valve chamber. This sealing fluid delivery system is advantageous for all screw compressors equipped with mechanical capacity control devices that cannot be positioned where the sealing fluid can be supplied by unintentional methods of delivery, such as gravity (e.g., when the mechanical capacity control device is below the rotor housing) or centrifugal force. This mechanical capacity control device can be used in place of a variable speed drive (VSD), or in combination with a VSD to increase the adjustment range.

[0006] Another aspect of this disclosure relates to a sealed liquid delivery system for a mechanical capacity control device for a screw compressor, comprising: a mechanical capacity control device including a mechanical capacity control valve movable to change the amount of gas compressed by the screw compressor; a mechanical capacity control device housing including a cavity configured to receive the mechanical capacity control device, a gap being formed between the mechanical capacity control device housing and the mechanical capacity control valve; and a pressurized sealed liquid delivery member carried by the mechanical capacity control device housing and configured to supply sealed liquid under pressure to the cavity of the mechanical capacity control device housing to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

[0007] One or more embodiments of the present disclosure described above include one or more of the following: the mechanical capacity control valve is a rotary spool valve, which rotates to open or close a passage to change the amount of gas compressed by the screw compressor; the mechanical capacity control valve is one of a sliding valve, a lift valve, and a gate valve, wherein a clearance is designed between the valve mechanism and its seat to open or close a passage to change the amount of gas compressed by the screw compressor; the sealing liquid delivery system includes the sealing liquid, and the sealing liquid may be the same as or different from the sealing liquid used in the compressor; the pressurized sealing liquid delivery component includes a sealing liquid control orifice communicating with the cavity of the mechanical capacity control device housing to supply the sealing liquid to the cavity of the mechanical capacity control device housing under pressure; the pressurized sealing liquid delivery system includes a sealing liquid control orifice communicating with the cavity of the mechanical capacity control device housing to supply the sealing liquid to the cavity of the mechanical capacity control device housing under pressure; the pressurized sealing liquid delivery system includes a sealing liquid control orifice communicating with the cavity of the mechanical capacity control device housing to supply the sealing liquid to the cavity of the mechanical capacity control device housing under pressure; the pressurized sealing liquid delivery system includes a sealing liquid control orifice communicating with the cavity of the mechanical capacity control device housing to change the amount of gas compressed by the screw compressor; the pressurized sealing liquid control orifice communicates with the cavity of the screw compressor ... The sealing liquid delivery device includes an internally or externally arranged sealing liquid supply line, which is carried by the housing of the mechanical capacity control device and communicates with the sealing liquid control orifice to supply sealing liquid to the cavity of the mechanical capacity control device housing under pressure; the mechanical capacity control device housing includes an intake end and an exhaust end, the intake end being closer to the gas outlet of the screw compressor than the exhaust end, and the exhaust end being closer to the gas inlet of the screw compressor than the intake end, the intake end carrying the pressurized sealing liquid delivery device; the mechanical capacity control device is a top-mounted mechanical capacity control device; the mechanical capacity control device is a side-mounted mechanical capacity control device; and / or the mechanical capacity control device is a bottom-mounted mechanical capacity control device.

[0008] Another aspect of this disclosure relates to a sealed liquid delivery system for a mechanical capacity control device for a screw compressor, comprising: a mechanical capacity control device including means for changing the amount of gas compressed by the screw compressor; means for receiving the changing means, with a gap formed between the receiving means and the changing means; and means for supplying a sealing liquid to the receiving means under pressure to suppress leakage through the gap between the receiving means and the changing means.

[0009] One or more embodiments of the present disclosure described above include one or more of the following: the changing device is a rotary slide valve, which rotates to open or close a passage to change the amount of gas compressed by the screw compressor; the changing device is one of a slide valve, a lift valve, and a gate valve, wherein a clearance is designed between the valve mechanism and its seat to open or close a passage to change the amount of gas compressed by the screw compressor; the supply device includes the sealing liquid, and the sealing liquid may be the same as or different from the sealing liquid used in the compressor; the supply device includes a sealing liquid control orifice communicating with the receiving device to supply the receiving device under pressure. A sealing liquid; the supply device includes an internally or externally arranged sealing liquid supply line, the sealing liquid supply line being carried by the receiving device and communicating with the sealing liquid control orifice to supply sealing liquid to the receiving device under pressure; the receiving device includes an intake end and an exhaust end, the intake end being closer to the gas outlet of the screw compressor than the exhaust end, the exhaust end being closer to the gas inlet of the screw compressor than the intake end, the intake end carrying the supply device; the mechanical capacity control device is a top-mounted mechanical capacity control device; the mechanical capacity control device is a side-mounted mechanical capacity control device; and / or the mechanical capacity control device is a bottom-mounted mechanical capacity control device.

[0010] Another aspect of this disclosure relates to a method of using a sealed liquid delivery system, the sealed liquid delivery system comprising: a mechanical capacity control device including a mechanical capacity control valve movable to change the amount of gas compressed by the screw compressor; a mechanical capacity control device housing including a cavity configured to receive the mechanical capacity control device, a gap being formed between the mechanical capacity control device housing and the mechanical capacity control valve; and a pressurized sealed liquid delivery member carried by the mechanical capacity control device housing and configured to supply a sealing liquid under pressure to the cavity of the mechanical capacity control device housing to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve, the method comprising: supplying the sealing liquid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealed liquid delivery member to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

[0011] One or more embodiments of the present disclosure described above include one or more of the following: the mechanical capacity control valve is a rotary slide valve, which rotates to open or close a passage to change the amount of gas compressed by the screw compressor, and the supply includes: supplying the sealing liquid under pressure to the cavity of the mechanical capacity control device while the rotary slide valve rotates to open or close the passage to change the amount of gas compressed by the screw compressor; the mechanical capacity control valve is one of a slide valve, a lift valve, and a gate valve, such valves having a clearance between their valve mechanism and their valve seat to open or close a passage to change the amount of gas compressed by the screw compressor, and the supply includes: supplying the sealing liquid under pressure to the cavity of the mechanical capacity control device while the slide valve, lift valve, and gate valve open or close the passage to change the amount of gas compressed by the screw compressor; the sealing liquid delivery system includes the sealing liquid, and the sealing liquid may be the same as or different from the sealing liquid used in the compressor, and the supply includes: supplying the same sealing liquid as the sealing liquid used in the compressor to the cavity of the mechanical capacity control device under pressure, or supplying the same sealing liquid as the sealing liquid used in the compressor to the cavity of the mechanical capacity control device under pressure. The compressor uses a different sealing fluid supplied under pressure to the cavity of the mechanical capacity control device; the pressurized sealing fluid delivery component includes a sealing fluid control orifice communicating with the cavity of the mechanical capacity control device housing to supply sealing fluid to the cavity of the mechanical capacity control device housing under pressure, and the supply includes: supplying the sealing fluid under pressure to the cavity of the mechanical capacity control device housing through the sealing fluid control orifice to suppress any leakage between the mechanical capacity control device housing and the mechanical capacity control valve. The pressurized sealing liquid delivery component includes an internally or externally arranged sealing liquid supply line, which is carried by the mechanical capacity control device housing and communicates with the sealing liquid control orifice to supply sealing liquid to the cavity of the mechanical capacity control device housing under pressure. The supply includes: supplying the sealing liquid to the cavity of the mechanical capacity control device housing under pressure through the sealing liquid supply line and the sealing liquid control orifice to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.The mechanical capacity control device housing includes an intake end and an exhaust end. The intake end is closer to the gas outlet of the screw compressor than the exhaust end, and the exhaust end is closer to the gas inlet of the screw compressor than the intake end. The intake end carries the pressurized sealing liquid delivery component, and the supply includes: supplying the sealing liquid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing liquid delivery component located at the intake end to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve; the mechanical capacity control device is a top-mounted mechanical capacity control device, and the supply includes: supplying the sealing liquid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing liquid delivery component located in the top-mounted mechanical capacity control device to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve. Leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve; the mechanical capacity control device is a side-mounted mechanical capacity control device, and the supply includes: supplying the sealing fluid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing fluid delivery element located in the side-mounted mechanical capacity control device to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve; and / or the mechanical capacity control device is a bottom-mounted mechanical capacity control device, and the supply includes: supplying the sealing fluid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing fluid delivery element located in the bottom-mounted mechanical capacity control device to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve. Attached Figure Description

[0012] The general architecture for implementing the various features of this disclosure will now be described with reference to the accompanying drawings. The drawings and related descriptions are provided to illustrate exemplary embodiments of this disclosure, and are not intended to limit the scope of this disclosure. Throughout the drawings, reference numerals are repeatedly used to indicate the correspondence between the elements involved.

[0013] Figure 1 This is a cross-sectional view of a prior art mechanical capacity control device located below the rotor housing in a screw compressor, wherein gravity causes sealing fluid to be delivered to and substantially fill the gap between the valve and the rotor housing.

[0014] Figure 2A This is a cross-sectional view of an embodiment of a screw compressor, wherein the mechanical capacity control device is located above the rotor housing; Figure 2B yes Figure 2A An enlarged area in which sealing fluid is delivered to and substantially fills the gap between the valve and the rotor housing; Figure 2CIt is along Figure 2A A cross-sectional view of a sealed liquid delivery system taken from line 2C-2C.

[0015] Figure 3 Another embodiment of a sealed liquid delivery system is shown, wherein the mechanical capacity control device is a side-mounted mechanical capacity control device.

[0016] Figure 4 This is yet another embodiment of a sealed liquid delivery system, wherein the mechanical capacity control device is a bottom-mounted mechanical capacity control device. Detailed Implementation

[0017] The following detailed description provides further details of the accompanying drawings and exemplary embodiments of this application. For clarity, reference numerals and descriptions of redundant elements between drawings have been omitted. The terminology used throughout the description is provided as an example and is not intended to be limiting. Ordinal terms, such as "first," "second," "third," etc., may be used for labelling purposes only in the specification and claims and should not be limited to referring to the described actions or items occurring in the described order. Actions or items may be arranged in a different order, or may be performed in parallel or dynamically, without departing from the scope of this application.

[0018] The exemplary embodiments described herein relate to a sealed liquid delivery system 100 for a mechanical capacity control device 110 of a screw compressor 120. (Refer to...) Figure 1 Before describing the sealed liquid delivery system 100, the mechanical capacity control device or valve 130 of a prior art screw compressor 140 will first be described to better understand the sealed liquid delivery system 100. When the mechanical capacity control valve 130 is open, gas is allowed to flow out from a window in the rotor housing 150, through the valve chamber 160, through a transfer pipe, and into the inlet, thereby reducing the compressor capacity. When the mechanical capacity control valve 130 is closed, the capacity increases. Even when the mechanical capacity control valve 130 is closed, some leakage always exists through the gap between the mechanical capacity control valve 130 and its mechanical capacity control valve housing 168, which reduces efficiency. If the sealed liquid is introduced into the gap, the efficiency is improved. The mechanical capacity control valve 130 is typically located below the rotor housing 150, allowing gravity or centrifugal force to move the sealed liquid into the gap.

[0019] Figures 2A to 2C An embodiment of a screw compressor 120 is shown, wherein the mechanical capacity control device 110 is located above the rotor housing 150, rather than as... Figure 1The rotor housing 150 is shown below the rotor housing. The mechanical capacity control device 110 is a mechanical capacity control valve (e.g., a rotary slide valve) 175, which is movable (e.g., rotatable) to open or close a passage to change the amount of gas compressed by the screw compressor 120. In an alternative embodiment, the mechanical capacity control valve 175 is one of a slide valve, lift valve, gate valve, or other valve device. The mechanical capacity control device housing 180 includes a cavity 190 configured to receive the mechanical capacity control device 110. A gap G is formed between the mechanical capacity control device housing 180 and the mechanical capacity control valve 175. The sealing fluid delivery system 100 includes a pressurized, internally or externally arranged sealing fluid delivery element or supply line 200 terminating at a sealing fluid control orifice 210. The sealing fluid control orifice 210 is carried by a mechanical capacity control device housing 180 and configured to supply sealing fluid under pressure to a cavity 190 of the mechanical capacity control device housing 180 to suppress leakage through a gap G between the mechanical capacity control device housing 180 and a mechanical capacity control valve 175, even if the mechanical capacity control valve 175 is not located in a position to supply unintentional sealing fluid. The mechanical capacity control device housing 180 includes an intake end (e.g., a screw valve chamber intake end) 220 and an outlet end (e.g., a screw valve chamber outlet end) 230, with the intake end 220 closer to the gas outlet of the screw compressor 120 than the outlet end 230, and the outlet end 230 closer to the gas inlet of the screw compressor 120 than the intake end 220. The intake end 220 carries the pressurized sealing fluid delivery element 200.

[0020] like Figure 2C As shown, the sealing fluid delivery system 100 can circulate / recycle the same sealing fluid used in the screw compressor 120. The sealing fluid used in the screw compressor 120 near the bottom of the rotor housing 150 can be drawn under pressure through inlet or orifice 232 to the pressurized sealing fluid delivery supply line 200 for delivery to the sealing fluid control orifice 210, whereby the sealing fluid is supplied under pressure to the cavity 190 of the mechanical capacity control device housing 180 to suppress leakage through the gap G between the mechanical capacity control device housing 180 and the mechanical capacity control valve 175. In an alternative embodiment, the sealing fluid supplied under pressure to the cavity 190 of the mechanical capacity control device housing 180 to suppress leakage through the gap G between the mechanical capacity control device housing 180 and the mechanical capacity control valve 175 is different from the sealing fluid used in the compressor.

[0021] In use, the sealing liquid delivery system 100 supplies sealing liquid under pressure to the cavity 190 of the mechanical capacity control device housing 180 through the pressurized sealing liquid delivery component 200 to suppress leakage through the gap G between the mechanical capacity control device housing 180 and the mechanical capacity control valve 175.

[0022] Although the sealing liquid control orifice 210 and the pressurized sealing liquid supply line 200 of the sealing liquid delivery system 100 have been combined Figures 2A to 2C The top-mounted mechanical capacity control device 110 is shown and described, but in alternative embodiments, the sealing liquid control orifice 210 and the pressurized sealing liquid delivery supply line 200 arranged inside or outside the sealing liquid delivery system 100 can be combined with the side-mounted mechanical capacity control device 110 of the screw compressor 120. Figure 3 ) and / or bottom-mounted mechanical capacity control device 110 ( Figure 4 )use.

[0023] By employing the proposed mechanical capacity control device 110 and sealing fluid delivery system 100, the leakage problem in the prior art—specifically, in top-mounted, side-mounted, and bottom-mounted mechanical capacity control devices (where gravity or centrifugal force does not cause the sealing fluid to move into the gap)—is alleviated without increasing cost and / or incurring functional degradation due to design trade-offs to reduce leakage (e.g., increasing overlap, increasing valve size, reducing rotor housing window area, reducing the gap between the valve and rotor housing, and designing the valve to open more abruptly). The proposed mechanical capacity control device 110 and sealing fluid delivery system 100 supply sealing fluid under pressure to the cavity 190 of the mechanical capacity control device housing 180 to suppress leakage through the gap G between the mechanical capacity control device housing 180 and the mechanical capacity control valve 175, even if the mechanical capacity control valve 175 is not located where unintentional sealing fluid is supplied.

[0024] While the invention is readily adaptable to various modifications and alternatives, specific embodiments thereof have been illustrated by way of example in the accompanying drawings and described in detail herein. However, it should be understood that the description of specific embodiments herein is not intended to limit the invention to the particular forms disclosed.

[0025] The foregoing detailed description has illustrated various exemplary embodiments of the apparatus and / or process using accompanying drawings, schematic diagrams, and examples. Where these drawings, schematic diagrams, and examples contain one or more functions and / or operations, each function and / or operation in these drawings or examples can be implemented individually and / or jointly by various structures. While certain exemplary embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of protection. In fact, the novel methods and apparatus described herein can be implemented in many other forms. Furthermore, various omissions, substitutions, and changes can be made to the form of the apparatus and systems described herein without departing from the spirit of protection. The appended claims and their equivalents are intended to cover these forms or modifications that fall within the scope and spirit of protection.

Claims

1. A sealed liquid delivery system for a mechanical capacity control device of a screw compressor, comprising: A mechanical capacity control device includes a mechanical capacity control valve that is movable to change the amount of gas compressed by the screw compressor; A mechanical capacity control device housing includes a cavity configured to accommodate the mechanical capacity control device, with a gap formed between the mechanical capacity control device housing and the mechanical capacity control valve; A pressurized sealing liquid delivery device, carried by the housing of the mechanical capacity control device, is configured to supply sealing liquid to the cavity of the mechanical capacity control device housing under pressure to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

2. The sealed liquid delivery system of claim 1, wherein, The mechanical capacity control valve is a rotary slide valve, which opens or closes the passage by rotation to change the amount of gas compressed by the screw compressor.

3. The sealed liquid delivery system of claim 1, wherein, The mechanical capacity control valve is one of a sliding valve, a lift valve, and a gate valve. Such valves have a clearance between their valve mechanism and their seat to open or close the passage to change the amount of gas compressed by the screw compressor.

4. The sealed liquid delivery system of any one of claims 1 to 3, wherein, The sealing liquid delivery system includes the sealing liquid, and the sealing liquid may be the same as or different from the sealing liquid used in the compressor.

5. The sealed liquid delivery system of any one of claims 1 to 4, wherein, The pressurized sealing liquid delivery component includes a sealing liquid control port that communicates with a cavity of the mechanical capacity control device housing to supply sealing liquid to the cavity of the mechanical capacity control device housing under pressure.

6. The sealed liquid delivery system according to claim 5, wherein, The pressurized sealing liquid delivery device includes a sealing liquid supply line arranged internally or externally. The sealing liquid supply line is carried by the housing of the mechanical capacity control device and communicates with the sealing liquid control port to supply sealing liquid to the cavity of the mechanical capacity control device housing under pressure.

7. The sealed liquid delivery system according to any one of claims 1 to 6, wherein, The housing of the mechanical capacity control device includes an intake end and an exhaust end. The intake end is closer to the gas outlet of the screw compressor than the exhaust end, and the exhaust end is closer to the gas inlet of the screw compressor than the intake end. The intake end carries the pressurized sealed liquid conveying component.

8. The sealed liquid delivery system according to any one of claims 1 to 7, wherein, The mechanical capacity control device is a top-mounted mechanical capacity control device.

9. The sealed liquid delivery system according to any one of claims 1 to 7, wherein, The mechanical capacity control device is a side-mounted mechanical capacity control device.

10. The sealed liquid delivery system according to any one of claims 1 to 7, wherein, The mechanical capacity control device is a bottom-mounted mechanical capacity control device.

11. A method of using the sealed liquid delivery system according to claim 1, comprising: The pressurized sealing liquid delivery device supplies sealing liquid under pressure to the cavity of the mechanical capacity control device housing to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

12. The method according to claim 11, wherein, The mechanical capacity control valve is a rotary slide valve, which opens or closes a passage by rotation to change the amount of gas compressed by the screw compressor, and the supply includes: supplying the sealing liquid under pressure to the cavity of the mechanical capacity control device while the rotary slide valve rotates to open or close the passage to change the amount of gas compressed by the screw compressor.

13. The method according to claim 11, wherein, The mechanical capacity control valve is one of a sliding valve, a lift valve, and a gate valve. Such valves have a clearance between their valve mechanism and their seat to open or close the passage to change the amount of gas compressed by the screw compressor. The supply includes supplying the sealing liquid to the cavity of the mechanical capacity control device under pressure while the sliding valve, lift valve, and gate valve open or close the passage to change the amount of gas compressed by the screw compressor.

14. The method according to any one of claims 11 to 13, wherein, The sealing liquid delivery system includes the sealing liquid, and the sealing liquid may be the same as or different from the sealing liquid used in the compressor, and the supply includes: supplying the same sealing liquid as the sealing liquid used in the compressor to the cavity of the mechanical capacity control device under pressure, or supplying the sealing liquid different from the sealing liquid used in the compressor to the cavity of the mechanical capacity control device under pressure.

15. The method according to any one of claims 11 to 14, wherein, The pressurized sealing liquid delivery component includes a sealing liquid control orifice communicating with a cavity of the mechanical capacity control device housing to supply sealing liquid to the cavity of the mechanical capacity control device housing under pressure, and the supply includes: supplying the sealing liquid to the cavity of the mechanical capacity control device housing under pressure through the sealing liquid control orifice to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

16. The method according to claim 15, wherein, The pressurized sealing liquid delivery device includes a sealing liquid supply line arranged internally or externally. The sealing liquid supply line is carried by the housing of the mechanical capacity control device and communicates with the sealing liquid control orifice to supply sealing liquid to the cavity of the mechanical capacity control device housing under pressure. The supply includes: supplying the sealing liquid to the cavity of the mechanical capacity control device housing under pressure through the sealing liquid supply line and the sealing liquid control orifice to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

17. The method according to any one of claims 11 to 16, wherein, The mechanical capacity control device housing includes an intake end and an exhaust end, the intake end being closer to the gas outlet of the screw compressor than the exhaust end, and the exhaust end being closer to the gas inlet of the screw compressor than the intake end. The intake end carries the pressurized sealing liquid delivery element, and the supply includes: supplying the sealing liquid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing liquid delivery element located at the intake end to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

18. The method according to any one of claims 11 to 17, wherein, The mechanical capacity control device is a top-mounted mechanical capacity control device, and the supply includes: supplying the sealing fluid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing fluid delivery element located in the top-mounted mechanical capacity control device to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

19. The method according to any one of claims 11 to 17, wherein, The mechanical capacity control device is a side-mounted mechanical capacity control device, and the supply includes: supplying the sealing fluid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing fluid delivery member located in the side-mounted mechanical capacity control device to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

20. The method according to any one of claims 11 to 17, wherein, The mechanical capacity control device is a bottom-mounted mechanical capacity control device, and the supply includes: supplying the sealing fluid under pressure to the cavity of the mechanical capacity control device housing through the pressurized sealing fluid delivery member located in the bottom-mounted mechanical capacity control device to suppress leakage through the gap between the mechanical capacity control device housing and the mechanical capacity control valve.

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