Air curtain system and steam turbine
By installing an air curtain system between the oil barrier of the turbine and the turbine body, compressed gas is used to form an air curtain to prevent the leakage of steam into the bearing box, the problem of lubricating oil quality decline caused by steam leakage in the turbine shaft seal is solved, and better results are achieved lubricating effect and lower production costs.
Patent Information
- Application Number
- CN202421108209.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-21
- Publication Date
- 2025-02-18
- Estimated Expiration
- 2034-05-21
AI Technical Summary
During the use of the turbine, due to the wear and large gap of the shaft seal, the leakage of steam into the bearing box, causing the lubricating oil to drop and the lubricating effect to drop sharply, affecting the safe operation of the unit.
Design an air curtain system, including an air supply device, a first air curtain device and a second air curtain device, by installing these devices between the oil barrier of the turbine and the turbine body, and forming an air curtain with compressed gas to block steam leakage Enter the bearing box.
It effectively prevents the shaft seal from leaking steam into the bearing box, avoids the deterioration of the lubricant oil quality, improves the lubricating effect of the unit, reduces the frequency of lubricant replacement, reduces production costs, and eliminates safety hazards.
Smart Images
Figure CN222501822U_ABST
Abstract
Description
Technical Field
[0001] The embodiments of this specification belong to the technical field of steam turbines, and specifically relate to an air curtain system and a steam turbine. Background Art
[0002] During the long-term use of steam turbines, the shaft seals will wear and the clearance will be too large, resulting in steam leakage at the shaft seals. The leaked steam can be easily sucked into the bearing box for the following reasons: first, the distance between the shaft seal and the bearing box is small; second, the oil baffle of the bearing box will also deform due to long-term operation at high temperatures, resulting in poor sealing effect; third, the bearing box is designed to operate at a slight negative pressure to facilitate oil return. After the leaked steam enters the bearing box, it condenses into water and enters the lubricating oil, causing the oil quality to deteriorate and the lubrication effect to drop sharply, seriously affecting the safe operation of the steam turbine. Stopping the unit to replace the lubricating oil will increase the economic cost. Therefore, there is an urgent need for a system to prevent the steam turbine shaft seal from leaking into the bearing box. Utility Model Content
[0003] The embodiments of this specification provide an air curtain system and a steam turbine, which can prevent the steam turbine shaft seal from leaking into the bearing box and prevent the lubricating oil from deteriorating, thereby ensuring the lubrication effect of the steam turbine.
[0004] In a first aspect, an embodiment of the present specification provides an air curtain system, which is applied to a steam turbine and includes an air supply device, a first air curtain device, and a second air curtain device;
[0005] The first air curtain device and the second air curtain device are connected to the air supply device respectively, and the first air curtain device and the second air curtain device are sequentially arranged between the oil baffle inside the steam turbine and the steam turbine body;
[0006] The first air curtain device is provided with a first air inlet connected to the air supply device, and the bottom of the first air curtain device is provided with a two-way flow guide structure for guiding the gas in the first air curtain device along the rotor surface in a direction away from the oil block and in a direction close to the oil block;
[0007] The second air curtain device is provided with a second air inlet connected to the air supply device, and the bottom of the second air curtain device is provided with a unidirectional flow guide structure for guiding the gas in the second air curtain device along the rotor surface away from the oil baffle.
[0008] As a preferred solution, the two-way air guide structure includes a first air outlet and a second air outlet arranged on the bottom plate of the first air curtain device, the opening directions of which are respectively inclined toward a side close to the oil block direction and a side away from the oil block direction.
[0009] As a preferred solution, a blocking structure arranged on the turbine rotor is further provided between the first air curtain device and the oil baffle.
[0010] As a preferred embodiment, the bottom of the first air curtain device is open, and the two-way guide structure includes a first guide strip arranged on the turbine rotor and extending from the bottom opening of the first air curtain device, and the first guide strip includes a first guide surface and a second guide surface for guiding the gas in the first air curtain device along the rotor surface in a direction away from the oil stop and in a direction close to the oil stop, respectively.
[0011] As a preferred solution, the one-way air guide structure includes a third air outlet arranged on the bottom plate of the second air curtain device, the opening direction of which is inclined away from the oil baffle direction.
[0012] As a preferred solution, at least one supporting rib is provided in the second air curtain device, and two ends of the supporting rib are respectively connected to two side walls of the second air curtain device.
[0013] As a preferred embodiment, the air supply device includes a connected air storage tank and a main pipeline, and the air supply device also includes a first branch pipeline and a second branch pipeline respectively connected to the main pipeline, the first branch pipeline and the second branch pipeline are respectively connected to the first air curtain device and the second air curtain device, and the first branch pipeline and the second branch pipeline are respectively installed with a first air intake regulating valve and a second air intake regulating valve; a third air intake regulating valve is also arranged on the main pipeline.
[0014] As a preferred solution, a dryer is also installed on the main pipeline, and the dryer is arranged at the upstream end of the third air intake regulating valve.
[0015] As a preferred embodiment, the first branch pipeline is also equipped with a first pressure detection device arranged at the upstream end of the first air intake regulating valve; the second branch pipeline is also equipped with a second pressure detection device arranged at the upstream end of the second air intake regulating valve.
[0016] In a second aspect, an embodiment of the present specification provides a steam turbine, comprising an oil baffle, a rotor, a steam turbine body, and an air curtain system based on the first aspect of the above embodiment, wherein the oil baffle and the steam turbine body are respectively connected to the rotor, and the air curtain system is arranged between the oil baffle and the steam turbine body;
[0017] The end of the oil baffle connected to the rotor is open and has an oil collecting groove formed inside. The oil baffle is also provided with an oil discharge port connected to the oil collecting groove at the end away from the rotor.
[0018] The rotor is provided with a second guide strip extending from the oil baffle opening into the oil collecting groove to guide the fluid flowing into the oil collecting groove to the oil discharge port.
[0019] The beneficial effects brought by the technical solutions provided by some embodiments of this specification include at least:
[0020] The utility model installs a first air curtain device and a second air curtain device between the oil baffle and the turbine body, and injects compressed gas into the first air curtain device and the second air curtain device through the air supply device to form an air curtain. When steam leaks from the shaft seal, it will be blocked by the double-layer air curtain from the first air curtain device and the second air curtain device, completely preventing the steam from leaking from the shaft seal from entering the bearing box, solving the problem of oil quality deterioration caused by steam from leaking from the shaft seal entering the bearing box, while reducing the frequency of lubricating oil replacement for the unit, and also allowing the unit to achieve better lubrication effects and eliminate safety hazards. At the same time, one of the air flows in the first air curtain device flows into the bearing box, which can better prevent oil leakage from the bearing box and reduce the amount of lubricating oil used in the turbine. Therefore, this system reduces production costs while ensuring the safe operation of the turbine. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In order to more clearly illustrate the technical solutions in the embodiments of this specification, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0022] Figure 1 It is a structural schematic diagram of an air curtain system provided in an embodiment of this specification applied to a steam turbine.
[0023] Figure 2 It is a structural schematic diagram of another air curtain system provided in an embodiment of this specification applied to a steam turbine.
[0024] In the figure: 1. air storage tank; 2. first air curtain device; 3. second air curtain device; 4. oil baffle; 5. rotor; 6. first air inlet; 7. second air inlet; 8. first air outlet; 9. second air outlet; 10. third air outlet; 11. blocking structure; 12. first guide strip; 13. first guide surface; 14. second guide surface; 15. supporting rib; 16. main pipeline; 17. first branch pipeline; 18. second branch pipeline; 19. first air intake regulating valve; 20. second air intake regulating valve; 21. third air intake regulating valve; 22. dryer; 23. first pressure detection device; 24. second pressure detection device; 25. oil collecting trough; 26. oil drain; 27. second guide strip; 28. bearing box; 29. shaft seal; 30. turbine body. DETAILED DESCRIPTION
[0025] The technical solutions in the embodiments of this specification will be described clearly and completely below in conjunction with the drawings in the embodiments of this specification.
[0026] The terms "first", "second", "third", etc. in the description and claims of this specification and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.
[0027] The following description provides examples and does not limit the scope, applicability or examples set forth in the claims. Changes may be made to the functions and arrangements of the elements described without departing from the scope of the present specification. Various processes or components may be appropriately omitted, substituted or added to each example. For example, the described method may be performed in an order different from the order described, and various steps may be added, omitted or combined. In addition, features described with respect to some examples may be combined in other examples.
[0028] See also Figure 1 , Figure 1 A schematic structural diagram of an air curtain system provided in an embodiment of the present specification applied to a steam turbine is shown.
[0029] like Figure 1 As shown, the system may at least include an air supply device, a first air curtain device 2, and a second air curtain device 3;
[0030] The first air curtain device 2 and the second air curtain device 3 are connected to the air supply device respectively, and the first air curtain device 2 and the second air curtain device 3 are sequentially arranged between the oil baffle 4 inside the steam turbine and the steam turbine body 30;
[0031] The first air curtain device 2 is provided with a first air inlet 6 connected to the air supply device, and the bottom of the first air curtain device 2 is provided with a two-way flow guide structure for guiding the gas in the first air curtain device 2 along the surface of the rotor 5 in a direction away from the oil baffle 4 and in a direction close to the oil baffle 4;
[0032] The second air curtain device 3 is provided with a second air inlet 7 connected to the air supply device, and the bottom of the second air curtain device 3 is provided with a unidirectional flow guide structure for guiding the gas in the second air curtain device 3 along the surface of the rotor 5 away from the oil baffle 4.
[0033] It can be seen that the air curtain device provided by the utility model is installed between the oil baffle 4 and the turbine body 30, and compressed gas is injected into the first air curtain device 2 and the second air curtain device 3 through the air supply device to form an air curtain. When the steam of the shaft seal 29 leaks and flows into the bearing box 28, the compressed air in the first air curtain device 2 is guided by the two-way flow guide structure, one of which flows toward the direction close to the oil baffle 4, preventing the oil in the bearing box 28 from flowing out, thereby preventing the bearing box 28 from leaking oil; the other air flows away from the oil baffle 4 to prevent high-temperature steam from entering the bearing box 28.
[0034] In order to avoid the situation where the shaft seal 29 has a large leakage and one air flow still cannot completely prevent the high-temperature steam from entering the bearing box 28, a second air curtain device 3 is installed outside the first air curtain device 2; the one-way flow guide structure of the second air curtain device 3 will guide the compressed gas to flow away from the oil baffle 4, further preventing the leaked steam from entering the bearing box 28. Under the dual effects of the first air curtain device 2 and the second air curtain device 3, the high-temperature steam can be better prevented from entering the bearing box 28.
[0035] There is a gap of 0.75-1 mm between the bottom of the first air curtain device 2 and the second air curtain device 3 and the rotor 5 to prevent the rotor 5 from rubbing against each other when rotating.
[0036] It is understandable that the temperature of the steam leaked from the shaft seal 29 is very high, and the high temperature will cause deformation and aging of the oil baffle 4. The newly installed first air curtain device 2 and the second air curtain device 3 can also help isolate the high-temperature steam from the oil baffle 4, slowing down the deformation and aging of the oil baffle 4 and extending the service life of the oil baffle 4.
[0037] See also Figure 1 As shown, in one embodiment of the present specification, the two-way air guide structure includes a first air outlet 8 and a second air outlet 9, whose opening directions are arranged on the bottom base plate of the first air curtain device 2, and are inclined toward a side close to the oil baffle 4 and a side away from the oil baffle 4, respectively.
[0038] It can be seen that because the first air outlet 8 is inclined toward the oil baffle 4, the airflow in the first air curtain device 2 can be guided to flow toward the oil baffle 4, thereby blocking the oil in the bearing box 28 from flowing out; similarly, the second air outlet 9 is inclined away from the oil baffle 4, which will guide the airflow in the first air curtain device 2 to flow away from the oil baffle 4, so as to block the high-temperature steam leaking from the shaft seal 29.
[0039] It is understandable that the first air outlet 8 and the second air outlet 9 can also be set to a nozzle shape that is wide at the top and narrow at the bottom, which can further squeeze the gas and allow the air curtain to form a larger positive pressure, better preventing the lubricating oil from leaking from the bearing box 28 and steam from entering the bearing box 28.
[0040] See also Figure 1 As shown, in one embodiment of the present specification, a blocking structure 11 arranged on the turbine rotor 5 is further provided between the first air curtain device 2 and the oil baffle 4 .
[0041] It can be understood that the side wall of the blocking structure 11 close to the oil baffle 4 can prevent the lubricating oil from flowing outward; the side of the blocking structure 11 away from the oil baffle 4 blocks part of the compressed gas from flowing toward the oil baffle. Although this will weaken the effect of preventing oil leakage, considering that the leaked oil has passed through the side wall close to the oil baffle 4, appropriately reducing the amount of compressed gas will not have much effect, and blocking part of the compressed gas can also prevent the compressed gas from rushing directly into the oil baffle 4, resulting in a higher pressure in the bearing box 28.
[0042] It can be understood that the side wall of the blocking structure 11 close to the oil baffle 4 can be perpendicular to the rotor 5, thereby achieving a better effect of blocking the oil; the side of the blocking structure 11 away from the oil baffle 4 can be a structure inclined toward the oil baffle 4, allowing part of the compressed gas to pass through.
[0043] See also Figure 2 , Figure 2 A schematic structural diagram of another air curtain system provided in an embodiment of this specification applied to a steam turbine is shown.
[0044] The first air curtain device 2 has an opening at the bottom, and the two-way flow guide structure is Figure 1 Different from that shown in the figure, it includes a first guide strip 12 arranged on the turbine rotor 5 and extending from the bottom opening of the first air curtain device 2, and the first guide strip 12 includes a first guide surface 13 and a second guide surface 14 for guiding the gas in the first air curtain device 2 along the surface of the rotor 5 away from the oil baffle 4 and close to the oil baffle 4 respectively.
[0045] It can be seen that there is an opening at the bottom of the first air curtain device 2, and the first guide strip 12 extends from the bottom opening into the first air curtain device 2. The first guide strip 12 can be, but is not limited to, in the shape of a triangular prism, and the gas in the first air curtain device 2 is divided into a first guide surface 13 and a second guide surface 14 that guide the gas along the surface of the rotor 5 in a direction away from the oil baffle 4 and in a direction close to the oil baffle 4, which are two surfaces of the triangular prism. The first guide surface 13 can guide the gas to prevent high-temperature steam from flowing into the bearing box 28, and the second guide surface 14 can guide the gas to deliver the lubricating oil to the bearing box 28.
[0046] In one embodiment of the present specification, the first guide surface 13 and the second guide surface 14 are arc-shaped, and the first guide surface 13 and the second guide surface 14 are concave, thereby playing a more gentle guiding role, thereby reducing the loss of the rotor 5.
[0047] It is understandable that if Figure 2 The first air curtain device 2 shown can be welded or bolted to the oil baffle 4, and the oil baffle 4 is used as a side wall of the first air curtain device 2; and the first guide bar 12 can be installed by itself or the copper teeth already on the rotor can be used as the first guide bar 12. Thus, the components of the steam turbine itself are fully utilized, and the production cost of the air curtain device is reduced.
[0048] See also Figure 1 or Figure 2 As shown, in one embodiment of the present specification, the one-way air guide structure includes a third air outlet 10 disposed on the bottom plate of the second air curtain device 3 and inclined in an opening direction away from the oil baffle 4 .
[0049] It can be seen that because the third air outlet 10 is inclined toward the side away from the oil baffle 4 , the airflow in the second air curtain device 3 can be guided to flow away from the oil baffle 4 , thereby blocking the high-temperature steam from flowing into the bearing box 28 .
[0050] See also Figure 1 or Figure 2 As shown, in one embodiment of the present specification, at least one supporting rib 15 is disposed in the second air curtain device 3 , and both ends of the supporting rib 15 are respectively connected to two side walls of the second air curtain device 3 .
[0051] It is understandable that, because the steam temperature leaking from the shaft seal 29 is relatively high, the first air curtain device 2 and the second air curtain device 3 are made of 5 mm steel plates, and the high-temperature steam easily causes the second air curtain device 3 to deform, so support ribs 15 are installed in the second air curtain device 3. Preferably, a plurality of evenly distributed support ribs 15 can be installed in the second air curtain device 3 to improve the support effect, such as 8 10 mm steel bars evenly distributed in the whole circle; support ribs 15 can also be installed in the first air curtain device 2 at the same time to prevent the first air curtain device 2 from deforming.
[0052] See also Figure 1 or Figure 2 As shown, in one embodiment of the present specification, the air supply device includes a connected air storage tank 1 and a main pipeline 16, and the air supply device also includes a first branch pipeline 17 and a second branch pipeline 18 respectively connected to the main pipeline 16, the first branch pipeline 17 and the second branch pipeline 18 are respectively connected to the first air curtain device 2 and the second air curtain device 3, and the first branch pipeline 17 and the second branch pipeline 18 are respectively installed with a first air intake regulating valve 19 and a second air intake regulating valve 20; the main pipeline 16 is also provided with a third air intake regulating valve 21.
[0053] It is understandable that the first branch pipe 17 and the second branch pipe 18 are equipped with air intake regulating valves, which are ball valves, and can control the intake volume of compressed air in the first air curtain device 2 and the second air curtain device 3 respectively, thereby achieving a better effect of blocking the flow of steam and lubricating oil. The third air intake regulating valve 21 on the main pipe 16 can uniformly control the compressed gas, and facilitate the rapid opening or closing of the air intake of the air curtain system through a valve.
[0054] See also Figure 1 or Figure 2 As shown, in one embodiment of the present specification, a dryer 22 is further installed on the main pipeline 16 , and the dryer 22 is arranged at the upstream end of the third intake regulating valve 21 .
[0055] It is understandable that, because the dryer 22 is installed on the main pipeline 16, the compressed gas entering the first air curtain device 2 and the second air curtain device 3 is dry gas, which can avoid the quality of the lubricating oil in the bearing box 28 being reduced due to the compressed air containing moisture.
[0056] See also Figure 1 or Figure 2 As shown, in one embodiment of the present specification, a first pressure detection device 23 arranged at the upstream end of the first air intake regulating valve 19 is also installed on the first branch pipe 17; and a second pressure detection device 24 arranged at the upstream end of the second air intake regulating valve 20 is also installed on the second branch pipe 18.
[0057] It can be understood that, because the first pressure detection device 23 and the second pressure detection device 24 are installed, the pressure of the compressed gas delivered by the gas tank 1 into the first branch pipe 17 and the second branch pipe 18 can be detected so as to adjust the air intake of the first air curtain device 2 and the second air curtain device 3.
[0058] As a preferred solution, the first air curtain device 2 and the second air curtain device 3 have holes opened in the chamber to connect to a compressed air pipe with a pressure greater than 0.1 MPa, and a pressure gauge is installed at the air inlet to detect the pressure.
[0059] See also Figure 1 or Figure 2 As shown, this specification also provides a steam turbine.
[0060] like Figure 1 or Figure 2 As shown, the steam turbine may at least include an oil baffle 4, a rotor 5, a steam turbine body 30, and an air curtain system based on any of the above embodiments, wherein the oil baffle 4 and the steam turbine body 30 are respectively connected to the rotor 5, and the air curtain system is arranged between the oil baffle 4 and the steam turbine body 30;
[0061] The end of the oil stopper 4 connected to the rotor 5 is open and has an oil collecting groove 25 formed therein. The oil stopper 4 is also provided with an oil discharge port 26 communicating with the oil collecting groove 25 at the end away from the rotor 5.
[0062] The rotor 5 is provided with a second guide bar 27 extending from the opening of the oil baffle 4 into the oil collecting groove 25 to guide the fluid flowing into the oil collecting groove 25 to the oil discharge port 26 .
[0063] It is understandable that the second guide strip 27 includes a third guide surface for guiding the lubricating oil flowing from the bearing box 28 toward the oil baffle 4 into the oil collection groove 25, and a fourth guide surface for guiding the lubricating oil flowing into the oil baffle 4 due to being blocked by the first air outlet 8 or the second guide surface 14 into the oil collection groove 25. The second guide strip 27 may be, but is not limited to, in the shape of a triangular prism, and the lubricating oil enters the bottom of the oil collection groove 25 after being guided by the third guide surface and the fourth guide surface, and is discharged into the bearing box 28 through the oil discharge port 26. Because the third guide surface and the fourth guide surface have a gathering effect on the lubricating oil, the lubricating oil can be efficiently discharged into the bearing box 28, thereby reducing the leakage of the lubricating oil.
[0064] The embodiments described above are merely preferred embodiments of this specification and are not intended to limit the scope of this specification. Without departing from the design spirit of this specification, various modifications and improvements made to the technical solutions of this specification by ordinary technicians in this field should fall within the scope of protection determined by the claims of this specification.
Claims
1. An air curtain system, applied to a steam turbine, characterized in that: It includes an air supply device, a first air curtain device, and a second air curtain device; The first air curtain device and the second air curtain device are connected to the air supply device respectively, and the first air curtain device and the second air curtain device are sequentially arranged between the oil baffle inside the steam turbine and the steam turbine body; The first air curtain device is provided with a first air inlet connected to the air supply device, and the bottom of the first air curtain device is provided with a two-way flow guide structure for guiding the gas in the first air curtain device along the rotor surface in a direction away from the oil block and in a direction close to the oil block; The second air curtain device is provided with a second air inlet connected to the air supply device, and the bottom of the second air curtain device is provided with a unidirectional flow guide structure for guiding the gas in the second air curtain device along the rotor surface away from the oil baffle.
2. The air curtain system according to claim 1, characterized in that: The two-way air flow guide structure includes a first air outlet and a second air outlet which are arranged on the bottom plate of the first air curtain device and have opening directions inclined toward a side close to the oil block direction and inclined away from the oil block direction, respectively.
3. The air curtain system according to claim 2, characterized in that: A blocking structure arranged on the turbine rotor is also provided between the first air curtain device and the oil baffle.
4. The air curtain system according to claim 1, characterized in that: The first air curtain device has an opening at the bottom, and the two-way flow guide structure includes a first guide strip arranged on the turbine rotor and extending from the bottom opening of the first air curtain device, and the first guide strip includes a first guide surface and a second guide surface for guiding the gas in the first air curtain device along the rotor surface in a direction away from the oil block and in a direction close to the oil block, respectively.
5. The air curtain system according to any one of claims 1 to 4, characterized in that: The one-way air guide structure includes a third air outlet disposed on the bottom plate of the second air curtain device, the opening direction of which is inclined toward a side away from the oil blocking direction.
6. The air curtain system according to claim 1, characterized in that: At least one supporting rib is disposed in the second air curtain device, and two ends of the supporting rib are respectively connected to two side walls of the second air curtain device.
7. The air curtain system according to claim 1, characterized in that: The air supply device includes a connected air storage tank and a main pipeline, and also includes a first branch pipeline and a second branch pipeline respectively connected to the main pipeline, the first branch pipeline and the second branch pipeline are respectively connected to the first air curtain device and the second air curtain device, and the first branch pipeline and the second branch pipeline are respectively installed with a first air intake regulating valve and a second air intake regulating valve; a third air intake regulating valve is also arranged on the main pipeline.
8. The air curtain system according to claim 7, characterized in that: A dryer is also installed on the main pipeline, and the dryer is arranged at the upstream end of the third air intake regulating valve.
9. The air curtain system according to claim 7, characterized in that: The first branch pipeline is also equipped with a first pressure detection device disposed at the upstream end of the first air intake regulating valve; the second branch pipeline is also equipped with a second pressure detection device disposed at the upstream end of the second air intake regulating valve.
10. A steam turbine, characterized in that: It comprises an oil baffle, a rotor, a steam turbine body and the air curtain system according to any one of claims 1 to 9, wherein the oil baffle and the steam turbine body are respectively connected to the rotor, and the air curtain system is arranged between the oil baffle and the steam turbine body; The end of the oil baffle connected to the rotor is open and has an oil collecting groove formed inside. The oil baffle is also provided with an oil discharge port connected to the oil collecting groove at the end away from the rotor. The rotor is provided with a second guide strip extending from the oil baffle opening into the oil collecting groove to guide the fluid flowing into the oil collecting groove to the oil discharge port.