High-safety operation device for stable operation of nuclear power circulating water pump
By designing the upper and lower bearing components and oil film lubrication and cooling structures in the nuclear power circulation water pump, the problem of pump bearing wear is solved, and the stable operation and service life of the pump are achieved.
Patent Information
- Application Number
- CN202420878491.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-25
- Publication Date
- 2024-12-24
- Estimated Expiration
- 2034-04-25
AI Technical Summary
The pump bearings of the circulating water pump in nuclear power plant are susceptible to thrust during long-term operation, resulting in increased wear and affecting the stable operation of the pump.
A high-safe operation device including an upper bearing assembly and a lower bearing assembly is designed to form an oil film by injecting oil into the oil supply member, lubricate the thrust tile and the upper thrust head, reduce wear, and pass through the upper radial tile and lower diameter. The radial force is subjected to the shingle to ensure the stable rotation of the pump shaft.
The service life of the upper thrust head is extended, the wear of the bearing assembly is reduced, the stable operation capability of the circulating water pump is improved, and the service life is further extended and the oil leakage is prevented through the cooling assembly and the labyrinth sealing structure.
Smart Images
Figure CN222228886U_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of water pumps, and in particular to a high-safety operation device for the stable operation of nuclear power circulating water pumps. Background Art
[0002] In the field of nuclear power plants, circulating water pumps are usually used to provide necessary cooling water to the condenser of the steam turbine and the auxiliary cooling water system. Circulating water pumps are efficient, reliable, and durable, and can work for a long time in harsh environments, providing important guarantees for the safe operation of nuclear power plants.
[0003] At present, water pumps are usually composed of components such as motors, gear boxes, pump bodies, pump shafts and impellers. The pump shafts are installed in the pump bodies through bearings. Since the flow rate of the circulating water pumps in nuclear power plants is extremely large, the pump shafts will be subjected to a large downward axial thrust when the circulating water pumps are running. The thrust is transmitted to the bearings through the pump shafts. After long-term use, the wear of the bearings will be aggravated, making the bearings prone to damage, thereby affecting the stable operation of the circulating water pumps. Utility Model Content
[0004] In order to reduce the wear of bearings during use and improve the stability of water pumps during operation, the present application provides a high-safety operation device for the stable operation of nuclear power circulating water pumps.
[0005] The present application provides a high-safety operation device for stable operation of a nuclear power circulating water pump, which adopts the following technical solution:
[0006] A high-safety operation device for stable operation of a nuclear power circulating water pump, comprising an upper bearing assembly and a lower bearing assembly arranged on a pump cover, the pump shaft is rotatably arranged in the pump cover through the upper bearing assembly and the lower bearing assembly, the upper bearing assembly comprises an upper bearing shell, an upper thrust head, a thrust washer, an upper radial washer and an oil supply member, the upper bearing shell is arranged on the pump cover, the upper thrust head is arranged on the pump shaft and is located in the upper bearing shell, the upper radial washer is arranged on the outer peripheral side of the upper thrust head, the thrust washer is arranged at the bottom end of the upper thrust head, the oil supply member is connected to the inner cavity of the upper bearing shell and supplies oil before the water pump is started, so that an oil film is formed between the thrust washer and the upper thrust head, the lower bearing assembly comprises a lower bearing shell, a lower sliding rotor and a lower radial washer, the lower bearing shell is arranged on the pump cover and is located below the upper bearing shell, the lower sliding rotor is arranged on the pump shaft and is located in the lower bearing shell, and the lower radial washer is arranged on the outer peripheral side of the lower sliding rotor.
[0007] By adopting the above technical solution, before the water pump is operated, the oil supply part injects oil into the inner cavity of the upper bearing shell, and the oil enters between the thrust pad and the upper thrust head and forms an oil film. On the one hand, the oil film lubricates the thrust pad and the upper thrust head to reduce the wear between the thrust pad and the upper thrust head. On the other hand, the thrust received by the upper thrust head is transmitted to the thrust pad through the oil film, and the thrust pad bears the thrust, thereby increasing the service life of the upper thrust head and making it difficult for the upper bearing assembly to be damaged. During the operation of the water pump, the pump shaft drives the upper thrust head and the sliding rotor to rotate, and the upper radial pad and the lower radial pad bear the radial force of the pump shaft, so that the circulating water pump can operate stably.
[0008] Preferably, an upper oil return channel is provided in the upper thrust head along the diameter direction of the pump shaft.
[0009] By adopting the above technical solution, the oil supply component supplies oil into the space between the upper thrust head and the thrust washer to form an oil film, and the oil flows back to the inner cavity of the upper bearing shell through the upper oil return channel, thereby accelerating the oil circuit circulation.
[0010] Preferably, a lower oil return channel is provided in the lower sliding rotor along the diameter direction of the pump shaft, and the lower oil return channel is connected to the gap between the lower sliding rotor and the lower radial pad at one end away from the pump shaft.
[0011] By adopting the above technical solution, the oil in the lower bearing shell enters the gap between the lower sliding rotor and the lower radial pad through the lower oil return channel, so as to lubricate the contact surface between the lower sliding rotor and the lower radial pad, thereby reducing the wear of the lower radial pad.
[0012] Preferably, the ends of the upper oil return channel and the lower oil return channel close to the pump shaft are both expanded.
[0013] By adopting the above technical solution, the expanded oil return channel facilitates oil to enter the upper oil return channel and the lower oil return channel.
[0014] Preferably, an upper cooling assembly is disposed in the upper bearing shell, and a lower cooling assembly is disposed in the lower bearing shell.
[0015] By adopting the above technical solution, the upper cooling assembly cools the oil in the upper bearing shell, and the lower cooling assembly cools the oil in the lower bearing shell, thereby increasing the service life of the upper bearing assembly and the lower bearing assembly.
[0016] Preferably, a breather is provided at the top end of the lower bearing shell, and the breather is communicated with the inner cavity of the lower bearing shell.
[0017] By adopting the above technical solution, when oil is injected into the lower bearing shell, the gas in the lower bearing shell is discharged from the inner cavity of the lower bearing shell through the breather, so that the oil can be smoothly injected into the lower bearing shell.
[0018] Preferably, an oil drain pipe is provided at the bottom end of the lower bearing shell, and the oil drain pipe is communicated with the inner cavity of the lower bearing shell.
[0019] By adopting the above technical solution, when the lower bearing assembly needs to be overhauled, the oil in the lower bearing shell can be discharged through the oil drain pipe, thereby facilitating the overhaul of the lower bearing assembly.
[0020] Preferably, a labyrinth sealing structure is provided on the inner side wall of the lower bearing shell close to the lower sliding rotor, and the labyrinth sealing structure includes a plurality of sealing teeth, and the plurality of sealing teeth are arranged at equal intervals along the axial direction of the pump shaft, a throttling gap is formed between the sealing teeth and the lower sliding rotor, and a slow flow cavity is formed between two adjacent sealing teeth.
[0021] By adopting the above technical solution, the labyrinth sealing structure seals the oil in the inner cavity of the lower bearing shell, and the oil enters the slow-flow cavity through the throttling gap. Kinetic energy loss will be generated in the process of the oil passing through the throttling gap and entering the slow-flow cavity, thereby achieving sealing of the oil.
[0022] Preferably, the sealing teeth are arranged at an end close to the sliding rotor and inclined toward the direction in which the oil enters.
[0023] By adopting the above technical solution, the sealing teeth are inclined so that the slow-flow cavity is inclined, which makes the kinetic energy loss of oil greater after entering the slow-flow cavity, thereby further improving the sealing effect of the labyrinth seal structure.
[0024] Preferably, a plurality of guide rings are arranged at equal intervals on the outer side of the downward sliding rotor along the axial direction of the pump shaft, the guide ring is located between two adjacent sealing teeth, the guide ring is arranged obliquely close to the side wall of the sealing tooth and is used to guide the oil into the slow flow cavity.
[0025] By adopting the above technical solution, the guide ring guides the oil flowing into the throttling gap, making it easier for the oil to enter the slow-flow cavity, thereby further improving the sealing effect of the labyrinth seal structure.
[0026] In summary, the present application includes at least one of the following beneficial technical effects:
[0027] 1. Use the oil supply part to inject oil into the inner cavity of the upper bearing shell to form an oil film between the thrust pad and the upper thrust head, reduce the wear between the thrust pad and the upper thrust head, and the thrust force received by the upper thrust head is transmitted to the thrust pad through the oil film, thereby increasing the service life of the upper thrust head and making the upper bearing assembly less prone to damage; during the operation of the water pump, the pump shaft drives the upper thrust head and the lower sliding rotor to rotate, and the upper radial pad and the lower radial pad bear the radial force of the pump shaft, so that the circulating water pump can operate stably;
[0028] 2. Use the upper cooling assembly and the lower cooling assembly to cool the oil in the upper bearing shell and the lower bearing shell, thereby increasing the service life of the upper bearing assembly and the lower bearing assembly;
[0029] 3. The oil in the inner cavity of the lower bearing shell is sealed by a labyrinth seal structure, making it difficult for the oil to leak. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 This is a cross-sectional view of the overall structure of a high-safety operation device for stable operation of a nuclear power circulating water pump in Example 1 of the present application;
[0031] Figure 2 For this application Figure 1 The enlarged schematic diagram at A in the middle;
[0032] Figure 3 For this application Figure 1 The enlarged schematic diagram of point B in the middle;
[0033] Figure 4 For this application Figure 3 The enlarged schematic diagram at C in the middle;
[0034] Figure 5 The highly safe operation device for stable operation of a nuclear power circulating water pump in Example 2 of the present application is a partial structural cross-sectional view highlighting the guide ring.
[0035] 1. Pump body; 2. Pump cover; 3. Pump shaft; 4. Impeller; 5. Upper bearing assembly; 51. Upper bearing shell; 52. Upper thrust head; 53. Thrust pad; 54. Upper radial pad; 55. Oil supply part; 6. Lower bearing assembly; 61. Lower bearing shell; 62. Lower slide rotor; 63. Lower radial pad; 7. Oil film; 8. Upper oil return channel; 9. Lower oil return channel; 10. Upper cooling assembly; 11. Lower cooling assembly; 12. Breathing device; 13. Oil drain pipe; 14. Sealing tooth; 15. Throttling gap; 16. Slow flow cavity; 17. Guide ring; 18. Bracket; 19. First key; 20. Second key; 21. Upper guide pad seat; 22. Lower guide pad seat; 23. Locking nut; 24. Sealing cover; 25. Locking ring; 26. Exhaust hood. DETAILED DESCRIPTION
[0036] The following is combined with Figure 1-5 This application is described in further detail.
[0037] The embodiment of the present application discloses a high-safety operation device for stable operation of a nuclear power circulating water pump.
[0038] Example 1
[0039] Reference Figure 1A high-safety operation device for stable operation of a nuclear power circulating water pump includes an upper bearing assembly 5 and a lower bearing assembly 6 mounted on a pump cover 2. The pump cover 2 is fixedly mounted on the top of a pump body 1. A bracket 18 is fixedly mounted on the pump cover 2. The upper bearing assembly 5 is mounted on the top of the bracket 18. The lower bearing assembly 6 is fixedly mounted on the pump cover 2 and is located directly below the upper bearing assembly 5. The pump shaft 3 is mounted in the upper bearing assembly 5 and the lower bearing assembly 6. The pump shaft 3 is rotatably mounted in the pump cover 2. The bottom end of the pump shaft 3 extends into the pump body 1, and the impeller 4 is fixedly mounted at the bottom end of the pump shaft 3. The driving motor drives the impeller 4 to rotate through the pump shaft 3, thereby operating the circulating water pump. The upper bearing assembly 5 and the lower bearing assembly 6 jointly support the pump shaft 3, so that the circulating water pump can operate stably.
[0040] Reference Figure 1 and Figure 2 Specifically, the upper bearing assembly 5 includes an upper bearing shell 51, an upper thrust head 52, a thrust washer 53, an upper radial washer 54 and an oil supply member 55. The upper bearing shell 51 is fixedly mounted on the top of the bracket 18. The upper thrust head 52 is located in the upper bearing shell 51 and connected to the pump shaft 3 through the first key 19. The upper thrust head 52 and the pump shaft 3 are fixed by a locking nut 23. The upper radial washer 54 is coaxially sleeved on the outer peripheral side of the upper thrust head 52. An upper guide washer seat 21 is coaxially mounted in the upper bearing shell 51. The upper guide washer seat 21 limits and fixes the upper radial washer 54. The pump shaft 3 drives the upper thrust head 52 to rotate through the first key 19. The upper radial washer 54 bears the radial force of the pump shaft 3, thereby making the water pump run more stably. A sealing cover 24 is fixedly mounted on the top of the upper guide washer seat 21. The inner peripheral side of the sealing cover 24 seals against the outer peripheral side of the upper thrust washer 53, thereby sealing the upper bearing shell 51.
[0041] The thrust washer 53 is installed in the upper bearing shell 51 and is coaxially located below the upper thrust head 52. The oil supply part 55 is connected to the oil hole of the thrust washer 53 through a pipeline. Before the water pump is started, the oil supply part 55 injects oil into the oil hole, and the oil enters between the upper thrust head 52 and the thrust washer 53 through the oil hole and forms an oil film 7. When the water pump is started, the oil film 7 lubricates the thrust washer 53 and the upper thrust head 52, reducing the wear between the thrust washer 53 and the upper thrust head 52. At the same time, the thrust force received by the upper thrust head 52 is transmitted to the thrust washer 53 through the oil film 7, and the thrust washer 53 bears the thrust force, thereby increasing the service life of the upper thrust head 52 and making the upper bearing assembly 5 less prone to damage.
[0042] An upper oil return channel 8 is provided inside the upper thrust head 52 along its diameter, and a plurality of upper oil return channels 8 are provided at equal intervals along the circumference of the upper thrust head 52, and the upper oil return channel 8 is expanded at one end close to the pump shaft 3. The oil at the oil film 7 can enter the upper oil return channel 8 through the expanded end of the upper oil return channel 8, and then flow from the upper oil return channel 8 into the upper bearing shell 51, thereby accelerating the oil circuit circulation.
[0043] An upper cooling assembly 10 is coaxially mounted in the upper bearing shell 51. The upper cooling assembly 10 is composed of a plurality of liquid supply pipes and is located outside the upper guide shoe seat 21. Cold water flows in the liquid supply pipes and absorbs the heat of the oil in the upper bearing shell 51, thereby cooling the oil in the upper bearing shell 51 and improving the service life of the upper bearing assembly 5.
[0044] Reference Figure 1 and Figure 3 The lower bearing assembly 6 includes a lower bearing shell 61, a lower lower rotor 62 and a lower radial bush 63. The lower bearing shell 61 is fixedly mounted on the pump cover 2. The lower lower rotor 62 is connected to the pump shaft 3 through the second key 20. The lower lower rotor 62 and the pump shaft 3 are fixed by a locking ring 25. The lower radial bush 63 is coaxially sleeved on the outer peripheral side of the lower lower rotor 62. A lower guide bush seat 22 is coaxially mounted in the lower bearing shell 61. The lower guide bush seat 22 limits and fixes the lower radial bush 63. The pump shaft 3 drives the lower lower rotor 62 to rotate through the second key 20. The lower radial bush 63 cooperates with the upper radial bush 54 to bear the radial force of the pump shaft 3, thereby further improving the stability of the water pump during operation. An exhaust hood 26 is fixedly mounted on the top of the lower guide bush seat 22. The inner peripheral side of the exhaust hood 26 is sealed against the outer peripheral side of the sealing ring, thereby sealing the lower bearing shell 61.
[0045] A lower oil return channel 9 is provided in the lower rotor 62 along its diameter, and a plurality of lower oil return channels 9 are provided at equal intervals along the circumference of the lower rotor 62, and the lower oil return channel 9 is expanded at one end close to the pump shaft 3. The oil in the lower bearing shell 61 can enter the lower oil return channel 9 through the expanded end of the lower oil return channel 9, and the oil then flows from the lower oil return channel 9 into the gap between the lower rotor 62 and the lower radial pad 63, so that the oil can lubricate the abutment between the lower rotor 62 and the lower radial pad 63.
[0046] A lower cooling assembly 11 is coaxially mounted in the lower bearing shell 61. The lower cooling assembly 11 is composed of a plurality of liquid supply pipes and is located outside the lower guide shoe seat 22. Cold water flows in the liquid supply pipes and absorbs the heat of the oil in the lower bearing shell 61, thereby cooling the oil in the lower bearing shell 61 and improving the service life of the lower bearing assembly 6.
[0047] An oil drain pipe 13 is installed on the bottom wall of the lower bearing shell 61, and the oil drain pipe 13 is connected to the inner cavity of the lower bearing shell 61. When the lower bearing assembly 6 needs to be repaired, the oil in the lower bearing shell 61 can be discharged through the oil drain pipe 13, so as to facilitate the repair of the lower bearing assembly 6. A respirator 12 is installed on the side wall of the exhaust hood 26, and the respirator 12 is connected to the inner cavity of the lower bearing shell 61. After the lower bearing assembly 6 is repaired, oil is injected into the lower bearing shell 61. At this time, the respirator 12 can remove the air in the lower bearing shell 61, so as to facilitate the smooth injection of oil into the lower bearing shell 61.
[0048] Reference Figure 4 A labyrinth seal structure is installed on the circumferential side wall of the inner cavity of the lower bearing shell 61 near the lower rotor 62. The sealing labyrinth structure is composed of a plurality of sealing teeth 14. The plurality of sealing teeth 14 are fixedly installed on the circumferential side wall of the inner cavity of the lower bearing shell 61 along the axial direction of the pump shaft 3. A rectangular slow-flow space is formed between each adjacent two sealing teeth 14. A throttling gap 15 is formed between the end of the sealing tooth 14 and the side wall of the lower rotor 62, and the throttling gap 15 is connected to the slow-flow space.
[0049] The labyrinth seal structure seals the oil in the inner cavity of the lower bearing shell 61, and the oil enters the slow-flow cavity 16 through the throttling gap 15. Kinetic energy loss will be generated in the process of the oil passing through the throttling gap 15 and entering the slow-flow cavity 16, thereby achieving sealing of the oil.
[0050] The implementation principle of a high-safety operation device for stable operation of a nuclear power circulating water pump in the embodiment of the present application is as follows: the driving motor drives the impeller 4 to rotate through the pump shaft 3, thereby operating the circulating water pump. Before the water pump is operated, the oil supply part 55 injects oil into the inner cavity of the upper bearing shell 51, and the oil enters between the thrust pad 53 and the upper thrust head 52 and forms an oil film 7. On the one hand, the oil film 7 lubricates the thrust pad 53 and the upper thrust head 52 to reduce the wear between the thrust pad 53 and the upper thrust head 52. On the other hand, the thrust received by the upper thrust head 52 is transmitted to the thrust pad 53 through the oil film 7, and the thrust pad 53 bears the thrust, thereby increasing the service life of the upper thrust head 52 and making it difficult for the upper bearing assembly 5 to be damaged. During the operation of the water pump, the pump shaft 3 drives the upper thrust head 52 and the lower rotor 62 to rotate, and the upper radial pad 54 and the lower radial pad 63 bear the radial force of the pump shaft 3, so that the circulating water pump can operate stably.
[0051] Example 2
[0052] Reference Figure 5 The difference between this embodiment and embodiment 1 is that the end of the sealing tooth 14 close to the lowering rotor 62 is installed tilted toward the oil inlet direction, and a plurality of guide rings 17 are fixedly installed on the outer wall of the lowering rotor 62 at equal intervals along its own axial direction. The plurality of guide rings 17 correspond one to one to the plurality of slow-flow cavities 16, and the guide rings 17 are located at the openings of the slow-flow cavities 16. The cross-section of the guide ring 17 is a right triangle, and the end of the guide ring 17 away from the oil inlet direction is tilted toward the slow-flow cavity 16.
[0053] The guide ring 17 guides the oil flowing into the throttling gap 15 to facilitate the oil to enter the inclined slow-flow cavity 16. The slow-flow cavity 16 is inclined, so that the kinetic energy loss of the oil after entering the slow-flow cavity 16 is greater, thereby further improving the sealing effect of the labyrinth seal structure.
[0054] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.
Claims
1. A high-safety operation device for stable operation of nuclear power circulating water pumps, characterized in that: The invention comprises an upper bearing assembly (5) and a lower bearing assembly (6) which are arranged on a pump cover (2); a pump shaft (3) is rotatably arranged in the pump cover (2) via the upper bearing assembly (5) and the lower bearing assembly (6); the upper bearing assembly (5) comprises an upper bearing shell (51), an upper thrust head (52), a thrust pad (53), an upper radial pad (54) and an oil supply member (55); the upper bearing shell (51) is arranged on the pump cover (2); the upper thrust head (52) is arranged on the pump shaft (3) and is located in the upper bearing shell (51); the upper radial pad (54) is arranged on the outer peripheral side of the upper thrust head (52); the thrust pad (53) is arranged on the outer peripheral side of the upper thrust head (52); the thrust pad (53) is arranged on the outer peripheral side of the upper thrust head (52); the thrust pad (53) is arranged on the outer peripheral side of the upper radial pad (54 ... 3) is arranged at the bottom end of the upper thrust head (52), the oil supply member (55) is connected to the inner cavity of the upper bearing shell (51) and supplies oil before the water pump is started, so that an oil film (7) is formed between the thrust pad (53) and the upper thrust head (52), the lower bearing assembly (6) includes a lower bearing shell (61), a lower rotor (62) and a lower radial pad (63), the lower bearing shell (61) is arranged on the pump cover (2) and is located below the upper bearing shell (51), the lower rotor (62) is arranged on the pump shaft (3) and is located in the lower bearing shell (61), and the lower radial pad (63) is arranged on the outer peripheral side of the lower rotor (62).
2. A high-safety operation device for stable operation of a nuclear power circulating water pump according to claim 1, characterized in that: An upper oil return passage (8) is provided in the upper thrust head (52) and penetrates along the diameter direction of the pump shaft (3).
3. A high-safety operation device for stable operation of a nuclear power circulating water pump according to claim 2, characterized in that: A lower oil return passage (9) is provided in the lower sliding rotor (62) along the diameter direction of the pump shaft (3), and the lower oil return passage (9) is connected to the gap between the lower sliding rotor (62) and the lower radial bush (63) at one end away from the pump shaft (3).
4. A high-safety operation device for stable operation of a nuclear power circulating water pump according to claim 3, characterized in that: The ends of the upper oil return channel (8) and the lower oil return channel (9) close to the pump shaft (3) are both expanded.
5. A high-safety operation device for stable operation of a nuclear power circulating water pump according to claim 1, characterized in that: An upper cooling assembly (10) is disposed in the upper bearing shell (51), and a lower cooling assembly (11) is disposed in the lower bearing shell (61).
6. A high-safety operation device for stable operation of nuclear power circulating water pumps according to claim 1, characterized in that: A respirator (12) is provided at the top end of the lower bearing shell (61), and the respirator (12) is communicated with the inner cavity of the lower bearing shell (61).
7. A high-safety operation device for stable operation of nuclear power circulating water pumps according to claim 1, characterized in that: An oil drain pipe (13) is provided at the bottom end of the lower bearing shell (61), and the oil drain pipe (13) is communicated with the inner cavity of the lower bearing shell (61).
8. A high-safety operation device for stable operation of nuclear power circulating water pumps according to claim 1, characterized in that: A labyrinth seal structure is provided on the inner side wall of the lower bearing shell (61) close to the lowering rotor (62), and the labyrinth seal structure comprises a plurality of sealing teeth (14), the plurality of sealing teeth (14) are arranged at equal intervals along the axial direction of the pump shaft (3), a throttling gap (15) is formed between the sealing teeth (14) and the lowering rotor (62), and a slow-flow cavity (16) is formed between two adjacent sealing teeth (14).
9. A high-safety operation device for stable operation of a nuclear power circulating water pump according to claim 8, characterized in that: The end of the sealing tooth (14) close to the sliding rotor (62) is arranged to be inclined toward the direction in which the oil enters.
10. A high-safety operation device for stable operation of nuclear power circulating water pumps according to claim 9, characterized in that: A plurality of guide rings (17) are arranged at equal intervals on the outer side of the sliding rotor (62) along the axial direction of the pump shaft (3); the guide ring (17) is located between two adjacent sealing teeth (14); the guide ring (17) is arranged obliquely close to the side wall of the sealing tooth (14) and is used to guide oil into the slow-flow cavity (16).