A check valve and a range hood using the same

Abstract

The application discloses a check valve and a range hood applying the check valve, wherein the check valve comprises a shell (1) and a valve piece (2); and further comprises a Laval tube (3) arranged in a channel (13) of the shell (1), two ends of the Laval tube (3) are respectively an air inlet pipe opening (31) and an air outlet pipe opening (32), the air inlet pipe opening (31) is in butt joint with a first port (11) of the shell (1); a middle part of the Laval tube (3) has a reduced diameter section (33) along an oil fume discharging direction; the valve piece (2) is arranged at the air outlet pipe opening (32) of the Laval tube (3) and is configured to be one-way rotated (32) under the action of oil fume flow to open the air outlet pipe opening (32). By arranging the Laval tube in the channel of the shell, the oil fume is accelerated after entering the Laval tube, and the oil fume disorder can be reduced, so that the oil fume is facilitated to be discharged from the check valve.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of check valve, in particular to a check valve and an extractor hood using the same. BACKGROUND

[0002] As an essential kitchen installation device for modern floor public flue, the check valve plays a decisive role in blocking the backflow of oil fume and preventing the backflow of oil fume. For example, the Chinese patent with the patent number CN106065964B discloses a check valve. The check valve comprises a cover body and a valve piece arranged in the cover body and capable of rotating relative to the cover body. A driving mechanism for driving the valve piece to rotate is arranged on the cover body. An installation cavity is arranged in the cover body. The driving mechanism is installed in the installation cavity. The driving mechanism comprises a driving rod extending out of the installation cavity and used for driving the valve piece to rotate.

[0003] However, the check valve in the above patent has the following problems:

[0004] Firstly, the oil fume does not have a certain flow direction in the cover body, which causes a certain disorder of the oil fume, thereby being not conducive to the discharge of the oil fume.

[0005] Secondly, in order to promote the discharge of the oil fume and prevent the backflow of the oil fume in the public flue, the fan of the extractor hood needs to be operated at a large power, which is not conducive to energy saving and the construction of a green exhaust mode.

[0006] Thirdly, when the pressure of the oil fume is large, the valve piece of the check valve may impact other parts when it is turned over and opened, thereby generating a large noise. SUMMARY

[0007] The first technical problem to be solved by the present application is to provide a check valve facilitating the discharge of oil fume.

[0008] The second technical problem to be solved by the present application is to provide a check valve conducive to energy saving.

[0009] The third technical problem to be solved by the present application is to provide a check valve with less noise.

[0010] The fourth technical problem to be solved by the present application is to provide an extractor hood.

[0011] To solve the first technical problem, the present application adopts the technical scheme of a check valve comprising a shell and a valve piece. The shell has a through channel. The two ends of the channel are respectively a first port and a second port.

[0012] The check valve further comprises a driving mechanism arranged in the shell and used for driving the valve piece to rotate.

[0013] A Laval tube is arranged in the passage of the shell, and two ends of the Laval tube are respectively an air inlet and an air outlet, and the air inlet is connected with the first port of the shell;

[0014] The middle part of the Laval tube has a reduced diameter section along the direction of the exhaust fume;

[0015] The valve plate is arranged at the air outlet of the Laval tube, and is configured to be rotated in one direction under the action of the exhaust fume to open the air outlet.

[0016] In order to further facilitate the exhaust fume, the Laval tube comprises a lower expanding diameter section downstream of the reduced diameter section along the direction of the exhaust fume;

[0017] The middle part of the lower expanding diameter section is provided with an annular limiting part adjacent to the air outlet, and the annular limiting part is located upstream of the valve plate along the direction of the exhaust fume, and is in abutment with the valve plate in the closed state of the air outlet.

[0018] In this way, by arranging the annular limiting part, on the one hand, the valve plate is abutted and limited, and on the other hand, the position of the annular limiting part corresponds to the reduced diameter section, and a small Laval tube is formed near the air outlet, thereby further facilitating the exhaust fume.

[0019] In order to further solve the second technical problem of the present application, preferably, the shell comprises

[0020] A cylindrical body;

[0021] An outer annular ring, the outer periphery of which is connected with the inner peripheral wall of the cylindrical body, and the outer annular ring has a windward surface;

[0022] An inner annular ring located in the space surrounded by the outer annular ring and connected with the inner periphery of the outer annular ring, the inner annular ring is bent towards the air outlet relative to the windward surface of the outer annular ring, the inner annular ring surrounds an air inlet cavity, and the free end of the inner annular ring is the first port;

[0023] The inner wall of the cylindrical body, the inner wall of the outer annular ring and the inner wall of the inner annular ring surround the passage, and the inner annular ring has a ventilation hole penetrating through the wall thickness thereof, and the ventilation hole is connected with the passage and the air inlet cavity respectively;

[0024] The inner annular ring movably constrains a shielding piece located in the air inlet cavity and used for adjusting the area of the first port; the back surface of the shielding piece is opposite to the ventilation hole, and the back surface of the shielding piece is acted on by the return air from the passage into the ventilation hole, and moves towards the position of reducing the area of the first port.

[0025] When the pressure inside the common flue is high, backflow of fumes (return air) may enter the casing's channel and reach the ventilation holes. This backflow acts on the back of the shielding component, causing it to move towards a position that reduces the area covered by the first port. The air inlet area of ​​the first port increases, and the airflow into the Laval tube increases. Correspondingly, the exhaust volume at the Laval tube's outlet increases, forming a larger aerosol wall at the outlet, which effectively blocks the backflow of fumes in the common flue. Thus, based on the backflow of fumes in the channel, the shielding component can adjust the area covered by the first port, automatically regulating the amount of fumes entering the Laval tube. This allows the fumes to reach the fan at the Laval tube's inlet, enabling the fumes to exit through the check valve at a lower operating power, thus contributing to energy conservation.

[0026] To facilitate pushing the shielding component, the shielding component is arc-shaped and moves circumferentially along the wall surface of the air inlet cavity after being subjected to force;

[0027] The ventilation hole is strip-shaped, and its length direction forms an acute angle with the tangent direction of the shielding member. The ventilation hole is inclined in the direction that the shielding member reduces the area of ​​the first port it covers.

[0028] This allows the backflow of oil fumes entering the ventilation holes to push the shielding parts to move.

[0029] To facilitate the movement of the shield, the back of the shield has a guide groove that communicates with the ventilation hole. By providing the guide groove, the backflowing fumes entering the ventilation hole are concentrated in the guide groove, which facilitates the movement of the backflowing fumes to push the shield.

[0030] To facilitate the movement of the shielding component, a guide vane is provided at the ventilation opening to partially block the ventilation opening. This guide vane divides the ventilation opening into a first half-through opening that is blocked and a second half-through opening that is not blocked. Along the direction of movement of the shielding component to reduce the area of ​​the first port being covered, the second half-through opening is located downstream of the first half-through opening. The guide vane guides the backflow of oil fumes from the common flue, causing the backflow of oil fumes to concentrate on one side of the second half-through opening, thereby facilitating the movement of the shielding component.

[0031] To facilitate the movement of the shielding component, a mounting tube is coaxially installed inside the ventilation hole. This mounting tube is opposite to the guide groove, and the guide vane is rotatably connected to the mounting tube, thus having at least two states:

[0032] In the first state, the guide vane blocks the first semi-through hole;

[0033] In the second state, the guide vane flips to open the first semi-through hole and flips to abut or approach the guide groove.

[0034] Thus, the guide vane is in abutment with or close to the guide groove, and the guide vane divides the guide groove into two sections, which is conducive to the concentration of the backflow of oil fume from the common flue in one section of the guide groove, thereby facilitating the pushing of the shielding member.

[0035] The cooperation structure of the shielding member and the inner annular ring can be various, preferably, a fixing member is arranged on the inner annular ring in the air inlet cavity, and an arc-shaped insertion slot is formed between the fixing member and the inner annular ring and opens in the circumferential direction of the inner annular ring.

[0036] The shielding member is arc-shaped, and is inserted into the arc-shaped insertion slot and moves along the arc-shaped insertion slot.

[0037] Thus, when the shielding member is inserted into the arc-shaped recess, the shielding of the first port by the shielding member is reduced, the air inlet area of the first port is increased, and the air inlet amount at the first port is increased.

[0038] In order to further facilitate the exhaust of oil fume, the fixing member and the shielding member are inclined towards the direction of expanding the first port against the flow direction of the oil fume.

[0039] Thus, the positions of the fixing member and the shielding member are similar to the expansion section, the first port is contracted, which is similar to the formation of a small Lafler tube, thereby further facilitating the exhaust of oil fume.

[0040] In order to facilitate the automatic resetting of the shielding member, the shielding member has a first position and a second position reached by the movement of the back surface of the shielding member under the action of the return air from the channel into the air inlet hole.

[0041] The non-return valve further comprises a first elastic member acting on the shielding member, and the first elastic member is in an energy storage state when the shielding member is in the second position, and the first elastic member has a tendency to release energy and make the shielding member return to the first position from the second position.

[0042] The automatic resetting of the shielding member is facilitated by the first elastic member.

[0043] In order to further solve the third technical problem of the present application, preferably, a noise reduction ring is arranged between the Lafler tube and the first port of the shell, the noise reduction ring extends into the channel, or the Lafler tube is sleeved with a noise reduction ring located in the channel.

[0044] The noise reduction ring is adjacent to the first port of the shell, and has a noise reduction hole in communication with the channel at the position located in the channel.

[0045] The noise reduction ring is arranged to facilitate the reduction of noise.

[0046] There are various mounting structures for the valve plate. Preferably, a connecting shaft is provided in the air outlet, and the valve plate is rotatably mounted on the connecting shaft. A second elastic element is provided on the connecting shaft to release energy and cause the valve plate to return to the tendency to close the air outlet.

[0047] The technical solution adopted by the present invention to solve the fourth technical problem mentioned above is: a range hood, characterized in that: a check valve as described above is used.

[0048] Compared with the prior art, the advantages of the present invention are as follows: by setting a Laval tube in the channel of the shell, the oil fumes are accelerated after entering the Laval tube, which can reduce the turbulence of oil fumes and facilitate the discharge of oil fumes from the check valve; at the same time, the oil fumes form an aerosol wall at the air outlet of the Laval tube, which helps to block the backflow of oil fumes in the public flue. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the check valve according to Embodiment 1 of the present invention;

[0050] Figure 2 This is a schematic diagram of the check valve from another angle according to Embodiment 1 of the present invention;

[0051] Figure 3 This is a cross-sectional view of the check valve according to Embodiment 1 of the present invention;

[0052] Figure 4 This is an exploded view of the check valve according to Embodiment 1 of the present invention;

[0053] Figure 5 This is another exploded view of the check valve according to Embodiment 1 of the present invention;

[0054] Figure 6 This is an assembly diagram of the shielding component and the fixing component in Embodiment 1 of the present invention;

[0055] Figure 7 for Figure 6 A schematic diagram of the middle component from another angle;

[0056] Figure 8 for Figure 6 Exploded view of the components;

[0057] Figure 9 This is an exploded view of the check valve of Embodiment 1 of the present invention from another angle;

[0058] Figure 10 for Figure 9 Enlarged schematic diagram of part I in the middle;

[0059] Figure 11 This is another cross-sectional view of the check valve according to Embodiment 1 of the present invention;

[0060] Figure 12 forFigure 11 Enlarged view of the middle part II;

[0061] Figure 13 As Figure 11 an exploded view;

[0062] Figure 14 As Figure 11 another exploded view;

[0063] Figure 15 As a further sectional view of the check valve of the embodiment of the present application;

[0064] Figure 16 As a schematic view of the relationship between the oil fume sprayed by the Laval tube and the oil fume in the public flue;

[0065] Figure 17 As an assembly view of the middle shielding member, the fixing member and the first elastic member of the second embodiment of the present application. DETAILED DESCRIPTION

[0066] The present application will be further described in detail below with reference to the accompanying drawings.

[0067] Embodiment 1:

[0068] Referring to Figures 1-16 , the preferred embodiment of the present application. The check valve comprises a housing 1, a valve plate 2, a Laval tube 3, a shielding member 4, a fixing member 5, a first elastic member 6, a flow guide vane 7, a noise reduction ring 9 and the like main components.

[0069] Among them, referring to Figures 1-5 , Figures 11-15 , the housing 1 has a through channel 13, the two ends of the channel 13 are respectively a first port 11 and a second port 12, the first port 11 is used for air inlet. The housing 1 is divided into a first part 17 and a second part 18 connected together, the first part 17 comprises a cylindrical body 14, an outer annular ring 15 and an inner annular ring 16, and the housing 1 can also be an integral piece. Specifically, the outer annular ring 15 is connected with the inner peripheral wall surface of the cylindrical body 14 at its outer periphery, and the outer annular ring 15 has a windward surface 151; the inner annular ring 16 is located in the space surrounded by the outer annular ring 15 and connected with the inner periphery of the outer annular ring 15, and the inner annular ring 16 is bent towards the air outlet 32 relative to the windward surface 151 of the outer annular ring 15, and the inner annular ring 16 surrounds an air inlet cavity 162 Figure 3 , Figure 15), the free end of the inner annular ring 16 is the first port 11; the inner wall surface of the cylindrical body 14, the inner wall surface of the outer annular ring 15 and the inner wall surface of the inner annular ring 16 form the channel 13, the inner wall surface of the cylindrical body 14 forms a first space, which is the channel 13 after removing the air inlet cavity 162, the inner annular ring 16 has a ventilation hole 161 penetrating through the wall thickness thereof, which is in communication with the channel 13 and the air inlet cavity 162 respectively.

[0070] Referring to Figure 2 , the valve piece 2 is arranged at the air outlet port 32 of the Laval tube 3 and is configured to be one-way rotated 32 to open the air outlet port 32 under the action of the oil fume flow. Specifically, the air outlet port 32 is provided with a connecting shaft 30, the valve piece 2 is rotationally arranged on the connecting shaft 30, the connecting shaft 30 is provided with a second elastic member 20 which releases energy to make the valve piece 2 return to the trend of closing the air outlet port 32, and the second elastic member 20 is for example a torsion spring.

[0071] Referring to Figures 1-5 , Figures 11-15 , the Laval tube 3 is arranged in the channel 13 of the shell 1, the two ends of the Laval tube 3 are respectively the air inlet port 31 and the air outlet port 32, the air inlet port 31 is in butt joint with the first port 11 of the shell 1; along the oil fume flow direction, the middle part of the Laval tube 3 has a reduced diameter section 33; the Laval tube 3 includes a lower diameter expanding section 35 located downstream of the reduced diameter section 33 and an upper diameter expanding section 34 located upstream of the reduced diameter section 33; the middle part inner wall surface of the lower diameter expanding section 35 is provided with an annular limiting part 351 at a position adjacent to the air outlet port 32, along the oil fume flow direction, the annular limiting part 351 is located upstream of the valve piece 2 and abuts against the valve piece 2 in the closed state of the air outlet port 32.

[0072] Referring to Figure 1 , Figures 3-9 , the shielding piece 4 is movably constrained in the air inlet cavity 162 of the inner annular ring 16, and the shielding piece 4 is used to adjust the area size of covering the first port 11. Specifically, the fixed piece 5 is arranged on the inner annular ring 16 and located in the air inlet cavity 162, and the fixed piece 5 and the inner annular ring 16 form an arc-shaped insertion slot 10 which is open along the circumferential direction of the inner annular ring 16; the shielding piece 4 is arc-shaped, the shielding piece 4 is inserted into the arc-shaped insertion slot 10 and moves along the arc-shaped insertion slot 10; the inner annular ring 16 is provided with a guide rail 40 Figure 4), the shielding piece 4 is movably sleeved on the guide rail 40. The back surface of the shielding piece 4 is opposite to the air vent 161, and the back surface of the shielding piece 4 is acted on by the backflow oil fume from the channel 13 into the air vent 161, and is moved towards a position of reducing the area of covering the first port 11, that is, the first port 11 of the shell 1 is enlarged. The shielding piece 4 is moved along the wall surface where the air inlet cavity 162 is located in a circumferential direction after being acted on. The air vent 161 is in a strip shape, the length direction of the air vent 161 is at an acute angle with the tangent direction of the shielding piece 4, and the air vent 161 is inclined towards the direction in which the shielding piece 4 reduces the area of covering the first port 11. See Figure 7 、 Figure 8 , Figure 12 The back surface of the shielding piece 4 has a flow guide groove 41 which is in communication with the air vent 161. Against the direction of the flow of the oil fume, the fixed piece 5 and the shielding piece 4 are both inclined towards the direction of enlarging the first port 11, so that the shielding piece 4 is similar to a small Laval tube, and the Laval tube is beneficial to promoting the oil fume to be discharged.

[0073] See Figures 7-10 See Figures 12-14 The air vent 161 is provided with a flow guide piece 7 which partially shields the air vent 161, and the flow guide piece 7 divides the air vent 161 into a first half air vent 1611 which is shielded and a second half air vent 1612 which is not shielded. Along the moving direction of the shielding piece 4 in which the shielding piece 4 reduces the area of covering the first port 11, the second half air vent 1612 is located downstream of the first half air vent 1611. Specifically, the air vent 161 is coaxially provided with a mounting pipe 8 which is opposite to the flow guide groove 41, and the flow guide piece 7 is rotationally connected with the mounting pipe 8 and has two states: see Figure 8 In the first state, the flow guide piece 7 shields the first half air vent 1611; in the second state, the flow guide piece 7 is turned to open the first half air vent 1611, and is turned to abut or be close to the flow guide groove 41. After the backflow oil fume from the channel 13 enters the air vent 161, the flow guide piece 7 is turned to abut the flow guide groove 41 to divide the flow guide groove 41 into two sections, the backflow oil fume is concentrated in one of the two sections of the flow guide groove 41, and the shielding piece 4 is facilitated to be moved.

[0074] See Figures 2-5 , Figures 11-14 The noise reduction ring 9 is abutted between the Laval tube 3 and the first port 11 of the shell 1, the noise reduction ring 9 extends into the channel 13, the noise reduction ring 9 is adjacent to the first port 11 of the shell 1, and the noise reduction ring 9 has a noise reduction hole 91 which is in communication with the channel 13 at the position in the channel 13. Alternatively, the noise reduction ring 9 is sleeved on the outer periphery of the Laval tube 3.

[0075] The embodiment further includes a range hood which adopts the check valve. The check valve is installed on a vertically extending wall, and the installation position is as shown in Figure 1, the backflow oil fume into the public flue overcomes the gravity to drive the shielding piece 4 to rotate, and the shielding piece 4 resets by the gravity. In order to maintain the shielding piece 4 in the required position without falling when the fan of the range hood does not work, a limiting block (not shown in the figure) is arranged on the inner annular ring 16 below the shielding piece 4 to prevent the shielding piece 4 from falling, or a first magnetic piece is arranged at the lower end of the shielding piece 4, and a second magnetic piece repelling the first magnetic piece is arranged on the inner annular ring 16, so that the shielding piece 4 does not fall by the repelling force between the two magnetic pieces. Figure 1

[0076] The working principle and use process are as follows.

[0077] After the oil fume enters the Laval tube 3, it is accelerated and pushes the valve piece 2 of the Laval tube 3 out of the air outlet pipe 32 to open the second port 12 of the shell 1 in one direction, so that the oil fume is discharged. The check valve is provided with a reduced diameter section 33, an annular limiting part 351, and the fixed piece 5 and the shielding piece 4 are inclined to the direction of expanding the first port 11 against the flow direction of the oil fume, which is equivalent to three reduced diameter positions and three small Laval tubes, so as to facilitate the discharge of the oil fume. At the same time, the oil fume forms an aerosol wall at the air outlet pipe 32 of the Laval tube 3, which is beneficial to block the backflow of the oil fume in the public flue.

[0078] The jet angle of the oil fume at the air outlet pipe 32 of the Laval tube 3 is related to the inlet conditions (such as pressure, temperature), the nature of the gas, the expected jet speed, the environmental conditions (such as outlet pressure), and the jet angle. The outlet pressure of the air outlet pipe 32 of the Laval tube 3 can be obtained by the continuity equation, Bernoulli equation, and isentropic flow relationship.

[0079] The oil fume outlet pressure of the air outlet pipe 32 of the Laval tube 3 is denoted as Pa, and the environmental pressure of the public flue is denoted as Pe. According to the relative size of Pa / Pe and the outlet inclination angle, the flow state of the oil fume in the Laval tube 3 is divided into the following three cases, as shown in Figure 16 .

[0080] 1) When the oil fume outlet pressure of the air outlet pipe 32 of the Laval tube 3 is greater than the public flue pressure, that is, Pa>Pe, it is in a supersaturated state, and the area and boundary of the oil fume discharged from the Laval tube 3 are in the state shown by number A. At this time, the fan for sending the oil fume to the check valve can work at a smaller power, and the air volume can be reduced, or the shielding piece 4 is moved to cover the first port 11 of the shell 1 to increase the area, so as to reduce the air inlet, and the oil fume discharged from the air outlet pipe 32 gradually tends to the state shown by number B.

[0081] ​2) When the oil fume outlet pressure at the air outlet pipe opening 32 of the Venturi tube 3 is equal to the common flue pressure, i.e., Pa = Pe, it is in a saturated state. The area and boundary of the oil fume discharged from the Venturi tube 3 are in the state shown by the number B. At this time, the fan of the range hood is in a balanced state, and the energy consumption of the fan reaches the optimal state.

[0082] 3) When the oil fume outlet pressure at the air outlet pipe opening 32 of the Venturi tube 3 is less than the common flue pressure, i.e., Pa < Pe, it is in an unsaturated state. The area and boundary of the oil fume discharged from the Venturi tube 3 are in the state shown by the number C. At this time, the oil fume in the common flue may flow back into the passage 13 of the housing 1. The path of the backflowing oil fume is as Figure 12 shown by the hollow arrow in the figure. The backflowing oil fume passes through the noise reduction hole 91, enters the ventilation hole 161, and then reaches the diversion groove 41, which pushes the shielding member 4 to move. The area of the shielding member 4 covering the first port 11 of the housing 1 decreases, which is beneficial to increasing the air intake volume into the Venturi tube 3. The area and boundary of the oil fume gradually tend to the state shown by the number B. At this time, the operating power of the fan does not need to be adjusted, which is beneficial to energy conservation. In the prior art in this case, the power of the fan needs to be increased to increase the air intake volume into the Venturi tube 3, resulting in higher fan energy consumption and being unfavorable for energy conservation.

[0083] In this way, the check valve can automatically adjust the position of the shielding member 4 according to the common flue environment and other conditions, and automatically adjust the size of the area covering the first port 11 of the housing 1, so as to adjust the air intake volume into the Venturi tube 3 to maintain the best operating state.

[0084] In addition, by providing the Venturi exhaust pipe 3, the valve piece 2 is relatively far from the first port 11 of the housing 1, so the noise when the valve piece 2 opens and closes is relatively behind. The noise reduction ring 9 is provided, which is beneficial to absorbing noise.

[0085] Embodiment 2:

[0086] Based on the check valve in Embodiment 1, a first elastic member 6 is added. The shielding member 4 has a first position and a second position where it moves under the action of the回风 (return air) entering the ventilation hole 161 from the passage 13 on its back surface. The first elastic member 6 acts on the shielding member 4. Refer to Figure 17 , the two ends of the first elastic member 6 are respectively connected to the shielding member 4 and the fixing member 5. When the shielding member 4 is in the second position, the first elastic member 6 is in an energy storage state, and the first elastic member 6 has a tendency to release energy and make the shielding member 4 return from the second position to the first position. The first elastic member 6 is a spring or a spring sheet. In this way, in addition to being installed on a vertically extending wall in the direction shown by [[ID=二十]] Figure 1 the figure, the check valve can also be adjusted to other installation directions according to needs.

Claims

1. A check valve comprising a housing (1) and a valve plate (2), the housing (1) having a channel (13) therethrough, the channel (13) having a first port (11) and a second port (12) at opposite ends thereof; characterized in that Further comprising a Laval tube (3) disposed in the channel (13) of the housing (1), the Laval tube (3) having an air inlet tube opening (31) and an air outlet tube opening (32) at opposite ends thereof, the air inlet tube opening (31) being in abutment with the first port (11) of the housing (1); the Laval tube (3) having a reduced diameter section (33) at a middle portion thereof in the direction of flow of the oil fume; the valve plate (2) being disposed at the air outlet tube opening (32) of the Laval tube (3) and being configured to rotate unidirectionally under the action of the oil fume to open the air outlet tube opening (32); the housing (1) comprising a cylindrical body (14); an outer annular ring (15) having an outer periphery connected to an inner peripheral wall surface of the cylindrical body (14), the outer annular ring (15) having a windward surface (151); an inner annular ring (16) disposed in a space surrounded by the outer annular ring (15) and connected to an inner periphery of the outer annular ring (15), the inner annular ring (16) being bent towards the air outlet tube opening (32) relative to the windward surface (151) of the outer annular ring (15), the inner annular ring (16) surrounding an air inlet cavity (162), a free end of the inner annular ring (16) being the first port (11); the inner wall surface of the cylindrical body (14), the inner wall surface of the outer annular ring (15) and the inner wall surface of the inner annular ring (16) surrounding the channel (13), the inner annular ring (16) having a ventilation hole (161) penetrating through a wall thickness thereof, the ventilation hole (161) being in communication with the channel (13) and the air inlet cavity (162) respectively; the inner annular ring (16) movably constraining a shielding member (4) in the air inlet cavity (162) and used for adjusting the area size of the shielding of the first port (11); a back surface of the shielding member (4) being opposite to the ventilation hole (161), and the back surface of the shielding member (4) being acted upon by the return air from the channel (13) into the ventilation hole (161) and moving towards a position of reducing the area of the shielding of the first port (11).

2. The check valve of claim 1, wherein: in the direction of flow of the oil fume, the Laval tube (3) comprising a lower expanded diameter section (35) downstream of the reduced diameter section (33); the lower expanded diameter section (35) having an annular limiting portion (351) at a middle portion of an inner wall surface thereof at a position adjacent to the air outlet tube opening (32), the annular limiting portion (351) being upstream of the valve plate (2) in the direction of flow of the oil fume and being in abutment with the valve plate (2) in a state of closing the air outlet tube opening (32).

3. The check valve of claim 1, wherein: the shielding member (4) being arc-shaped and moving along a wall surface of the air inlet cavity (162) in a circumferential direction under force; the ventilation hole (161) being strip-shaped, a length direction of the ventilation hole (161) being at an acute angle with a tangential direction of the shielding member (4), and the ventilation hole (161) being inclined towards a direction of reducing the area of the shielding of the first port (11) by the shielding member (4).

4. The check valve of claim 1, wherein: the back surface of the shielding member (4) having a flow guide groove (41) in communication with the ventilation hole (161).

5. The check valve of claim 4, wherein: The air vent (161) is provided with a guide vane (7) partially shielding the air vent (161), which divides the air vent (161) into a first half air vent (1611) being shielded and a second half air vent (1612) being unshielded, and the second half air vent (1612) is located downstream of the first half air vent (1611) along a moving direction of the shielding piece (4) reducing the area of the first port (11).

6. The check valve of claim 5, wherein: The air vent (161) is provided with a mounting pipe (8) coaxially mounted in the air vent (161), which is opposite to the guide groove (41), and the guide vane (7) is rotationally connected with the mounting pipe (8) and has at least two states: In the first state, the guide vane (7) shields the first half air vent (1611); In the second state, the guide vane (7) is flipped to open the first half air vent (1611), and is flipped to abut against or close to the guide groove (41).

7. The check valve of claim 1, wherein: The inner annular ring (16) is provided with a fixing piece (5) located in the air inlet cavity (162), which forms an arc-shaped insertion slot (10) opening along the circumference of the inner annular ring (16) with the inner annular ring (16); The shielding piece (4) is arc-shaped, which is inserted into the arc-shaped insertion slot (10) and moves along the arc-shaped insertion slot (10).

8. The check valve of claim 7, wherein: Against the flow direction of the oil fume, the fixing piece (5) and the shielding piece (4) are both inclined to the direction of expanding the first port (11).

9. The check valve of claim 1, wherein: The shielding piece (4) has a first position and a second position reached by moving under the action of the return air from the channel (13) into the air vent (161) on the back surface thereof; The non-return valve further comprises a first elastic piece (6) acting on the shielding piece (4), the shielding piece (4) is in the second position, the first elastic piece (6) is in an energy storage state, and the first elastic piece (6) has a tendency to release energy and make the shielding piece (4) return to the first position from the second position.

10. The check valve of claim 1, wherein: The Laval tube (3) and the first port (11) of the shell (1) are abutted by a noise reduction ring (9) extending into the channel (13), or the Laval tube (3) is sleeved with a noise reduction ring (9) located in the channel (13); The noise reduction ring (9) is adjacent to the first port (11) of the shell (1), and has a noise reduction hole (91) communicating with the channel (13) at the position located in the channel (13).

11. The check valve of claim 1, wherein: The air outlet pipe (32) is provided with a connecting shaft (30), and the valve piece (2) is rotationally arranged on the connecting shaft (30), and the connecting shaft (30) is provided with a second elastic piece (20) releasing energy to make the valve piece (2) return to the closed air outlet pipe (32).

12. A range hood characterized by: The non-return valve as claimed in any one of claims 1-11 is adopted.

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