A volatile organic compound detection device with built-in cleaning function and its sampling method

Abstract

This invention discloses a volatile organic compound (VOC) detection device with a built-in cleaning function, comprising an upper cylinder and a lower cylinder integrally connected. A first isolation plate, a second isolation plate, and a third isolation plate are installed in the upper cylinder. An air outlet is provided on the side wall of the upper cylinder between the first and second isolation plates. A first detection tube or a second detection tube is installed in each through slot on the first isolation plate, with the bottom end of the first detection tube penetrating downwards through the second isolation plate and extending below it. An air extraction assembly and a driving assembly are provided between the second and third isolation plates. An air inlet filter assembly is provided on the lower surface of the third isolation plate, and a collection tube and a cleaning tube are also provided through the third isolation plate. A cleaning frame is fixedly installed between all the clamps. This invention also discloses a sampling method for VOC detection. The device and method of this invention achieve gas sampling and ensure the long-term effective use of the air inlet filter assembly.

Description

Technical Field

[0001] This invention belongs to the field of atmospheric environmental monitoring technology, and relates to a volatile organic compound (VOC) detection device with a built-in cleaning function. This invention also relates to a sampling method for VOC detection. Background Technology

[0002] Volatile organic compounds (VOCs) are important precursors to secondary pollutants such as fine particulate matter and ozone, which in turn cause atmospheric environmental problems such as haze and photochemical smog. Detection of VOCs in the air is a crucial indicator in environmental monitoring. Outdoors, portable detection instruments are often used for direct measurement. However, because suspended impurities in the air easily clog the instrument's detection port, it is necessary to initially filter atmospheric impurities, but not the analytes themselves. This can be achieved by using a sparsely pored filter. However, current detection devices cannot clean the filter in a timely manner, leading to severe filter clogging after a period of operation and a decrease in detection accuracy.

[0003] In the prior art, application number 202110285955.6, entitled "An Automatic Sampling and Detection Device for Volatile Organic Compounds in Air," utilizes a cleaning mechanism. A motor drives two cams to rotate, and the interaction between the cams and a sliding plate causes a push rod to move up and down repeatedly. A rack on the push rod interacts with a transmission gear on the rotating rod, causing a cleaning block to swing back and forth around the rod. Brushes on the cleaning block clean the filter frame during this swinging motion, allowing the device to operate for longer periods. However, this cleaning block design only cleans the surface of the filter frame, failing to effectively clean impurities accumulated between the filter mesh openings, easily leading to mesh clogging. Furthermore, the detection of volatile organic compounds is often limited to simple on-site testing, lacking space for gas storage and sample retention.

[0004] Therefore, there is an urgent need to develop a volatile organic compound detection device with a built-in cleaning function to significantly solve the technical problem of mesh clogging. Summary of the Invention

[0005] The purpose of this invention is to provide a volatile organic compound (VOC) detection device with a built-in cleaning function, which solves the problem that existing technologies are prone to mesh clogging and have significant limitations in conventional VOC detection.

[0006] Another object of the present invention is to provide a sampling method for detecting volatile organic compounds.

[0007] The technical solution adopted in this invention is a volatile organic compound (VOC) detection device with a built-in cleaning function, comprising an upper cylinder and a lower cylinder snapped together as one unit; a first isolation plate, a second isolation plate, and a third isolation plate are fixedly installed in the upper cylinder from top to bottom; an air outlet is provided on the side wall of the upper cylinder between the first and second isolation plates; multiple through slots are opened on the first isolation plate, and a first detection tube or a second detection tube is slidably installed in each through slot; the bottom ends of all the first detection tubes penetrate downward through the second isolation plate and extend to the bottom of the second isolation plate; an air extraction component and a driving component are provided between the second and third isolation plates; an air inlet filter component is provided on the lower surface of the third isolation plate; a collection tube and a cleaning tube are also provided through the third isolation plate; and a cleaning frame is fixedly installed between all the clamps.

[0008] Another technical solution adopted in this invention is a sampling method for detecting volatile organic compounds, which utilizes the aforementioned volatile organic compound detection device with built-in cleaning function and is implemented according to the following steps:

[0009] Step 1: Position the upper and lower cylinders and install the testing instruments;

[0010] Step 2: Continuously feed in the sampling gas and perform sampling gas detection;

[0011] Step 3: Remove dust from the outer surface of the filter screen;

[0012] Step 4: Perform dust removal on the filter screen.

[0013] The beneficial effects of the present invention include the following aspects:

[0014] 1) This invention, through the cooperation of the driving component, the gas extraction component and the air intake filter component, ensures effective gas delivery, provides convenient conditions for the detection of volatile organic compounds in the gas, realizes gas sampling, achieves the purpose of sampling and retention, and can also ensure the long-term effective use of the air intake filter component, thus having a wide range of applications.

[0015] 2) This invention utilizes the combination of insert plate, slot, pin, spring, limiting plate and positioning hole to ensure effective adjustment of the distance between the lower cylinder and the upper cylinder, which is convenient to use and can provide more detection environment for the detection of volatile organic compounds.

[0016] 3) This invention utilizes the coordinated arrangement of a motor, crankshaft, and drive gear to not only drive the air extraction assembly for gas delivery but also drive the filter screen to rotate. Combined with the cleaning frame, this effectively ensures the cleanliness of the filter screen surface.

[0017] 4) This invention utilizes the back-and-forth movement of the piston plate to achieve the circulation and transportation of gas between the second and third isolation plates, thereby achieving the purpose of on-site sampling. Furthermore, during the gas exchange process, the replaced gas is sprayed out from the cleaning nozzle to blow off impurities in the mesh of the rotating filter screen. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the external structure of the device of the present invention after the upper and lower cylinders are connected.

[0019] Figure 2 This is a cross-sectional view of the internal structure of the upper and lower cylinders after they are joined together in the device of the present invention;

[0020] Figure 3 This is a bottom view of the cross-section of the third isolation plate in the device of the present invention;

[0021] Figure 4 This is a schematic diagram showing the connection of the drive gear, teeth, and limiting ring in the device of the present invention.

[0022] Figure 5 This is a top view showing the connection between the card holder and the cleaning frame in the device of the present invention.

[0023] In the diagram, 1. Detection box; 2. Upper cylinder; 3. Lower cylinder; 4. Snap-fit ​​assembly; 5. First isolation plate; 6. Second isolation plate; 7. Third isolation plate; 8. Air extraction assembly; 9. First detection tube; 10. Second detection tube; 11. Plug; 12. Air intake filter assembly; 13. Drive assembly; 14. Insert plate; 15. Pin; 16. Slot; 17. Limiting plate; 18. Spring; 19. Positioning hole; 20. 21. Air extraction cylinder; 22. Piston plate; 23. Drive rod; 24. T-shaped pipe; 25. Air supply pipe; 26. Air inlet pipe; 27. Air outlet; 28. Motor; 29. ​​Crankshaft; 30. Collar; 31. Drive gear; 32. Limiting ring; 33. Filter screen cover; 34. Annular groove; 35. Clip; 36. Sweeping frame; 37. Collection pipe; 38. Sweeping pipe; 39. Sweeping nozzle; 40. Cover; 51. Hook. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0025] Reference Figure 1 , Figure 2 The volatile organic compound (VOC) detection device of the present invention includes an upper cylinder 2 and a lower cylinder 3, which are fixed together by a snap-fit ​​assembly 4 to form a detection box 1. The cross-section of the detection box 1 can be cylindrical, square, or rectangular. Figure 3 That is, a square cylindrical body;

[0026] The upper cylinder 2 is fixedly installed with a first isolation plate 5, a second isolation plate 6 and a third isolation plate 7 from top to bottom. An air outlet 26 is provided on the side wall of the upper cylinder 2 between the first isolation plate 5 and the second isolation plate 6. The first isolation plate 5 has multiple through slots. A first detection tube 9 or a second detection tube 10 is slidably installed in each through slot. All first detection tubes 9 and second detection tubes 10 are provided with plugs 11. The bottom end of all first detection tubes 9 passes through the second isolation plate 6 downward and extends to the bottom of the second isolation plate 6.

[0027] An air extraction assembly 8 and a drive assembly 13 are provided between the second isolation plate 6 and the third isolation plate 7. The drive assembly 13 is used to drive the air extraction assembly 8 to extract air. The air extraction assembly 8 delivers outside air from below the third isolation plate 7 to the space between the first isolation plate 5 and the second isolation plate 6.

[0028] The structure of the air extraction assembly 8 includes an air extraction cylinder 20, in which a piston plate 21 is slidably installed, and the outer end face of the piston plate 21 ( Figure 2 The left side shown is connected to the inner end of the drive rod 22 via a coupling, and the inner end of the piston plate 21 ( Figure 2 The air chamber (shown on the right) is connected to the three-way pipe 23. The other two ports of the three-way pipe 23 are connected to the air supply pipe 24 and the air inlet pipe 25 respectively. The air supply pipe 24 extends upward beyond the second isolation plate 6, and the air inlet pipe 25 penetrates downward through the third isolation plate 7 and extends into the interior of the air inlet filter assembly 12. A first one-way valve is installed in the pipe of the air inlet pipe 25, and a second one-way valve is installed in the pipe of the air supply pipe 24 to ensure the directional flow of air from bottom to top and to ensure a continuous supply of detection gas.

[0029] The structure of the drive assembly 13 includes a motor 27, which is a servo motor and is electrically connected to an external power source. It is controlled by a control switch. The motor 27 is fixedly installed on the lower surface of the first isolation plate 5. The output shaft of the motor 27 is connected to the crankshaft 28. A collar 29 is sleeved on the bent end of the crankshaft 28. The collar 29 is fixedly connected to the outer end of the drive rod 22. When the motor 27 works, it drives the crankshaft 28 to rotate. The collar 29 drives the drive rod 22 to move back and forth, thereby realizing the reciprocating motion of the piston plate 21.

[0030] Reference Figure 3 , Figure 4The lower surface of the third isolation plate 7 is provided with an air intake filter assembly 12. The structure of the air intake filter assembly 12 includes multiple brackets 34 and a limiting ring 31. All brackets 34 are fixedly connected upward to the lower surface of the third isolation plate 7. The inner surface of all brackets 34 is adapted to the outer surface of the limiting ring 31. All brackets 34 encircle and support the limiting ring 31. The lower part of the inner wall of the limiting ring 31 is fixedly connected downward to a filter screen cover 32. The upper part of the inner wall of the limiting ring 31 is stepped and called an annular groove 33. A ring of teeth is evenly arranged on the inner wall of the annular groove 33. The bottom end of the crankshaft 28 passes downward through the third isolation plate 7 and is fixedly connected to a drive gear 30. The drive gear 30 meshes with the ring of teeth of the annular groove 33. The drive gear 30 drives the limiting ring 31 and the filter screen cover 32 to rotate through the teeth.

[0031] A collection pipe 36 and a cleaning pipe 37 are also installed through the third isolation plate 7. Both the collection pipe 36 and the cleaning pipe 37 are located inside the filter screen cover 32 and are used to transport outside air to the top of the third isolation plate 7. A third one-way valve is installed in the pipe of the collection pipe 36 and a fourth one-way valve is installed in the pipe of the cleaning pipe 37. Several cleaning nozzles 38 are connected to the side of the cleaning pipe 37 near the filter screen cover 32. The cleaning nozzles 38 can blow away the dust on the filter screen cover 32 to achieve deep cleaning of the filter screen cover 32 from the inside out.

[0032] Reference Figure 5 A cleaning frame 35 is fixedly installed between all the card holders 34. The cleaning frame 35 is adapted to the shape of the filter screen cover 32. The filter screen cover 32 rotates and is scraped by the cleaning frame 35 in order to clean the outer surface of the filter screen cover 32.

[0033] The top of the upper cylinder 2 is fastened with a cover 39, and a hook 40 is fixedly installed on the upper end face of the cover 39 to facilitate the hoisting and transportation of the entire device.

[0034] Reference Figure 1 , Figure 2 , Figure 3The structure of the snap-fit ​​assembly 4, taking a square cylinder as an example, includes four insert plates 14, four slots 16, and two pins 15. The four slots 16 are respectively located on the lower part of the four sides of the upper cylinder 2, and the four insert plates 14 are respectively located on the top of the four sides of the lower cylinder 3. A pin 15 is provided near the bottom of each of the two opposite slots 16. Multiple positioning holes 19 are opened on the two insert plates 14 below the two slots 16. The positioning holes 19 are opened sequentially from top to bottom and are adapted to the pins 15. Each insert plate 14 has at least upper, middle, and lower positioning holes. The upper cylinder 2 has three positioning holes 19 at different heights. Each pin 15 is fitted with a spring 18 around its outer periphery. Each pin 15 has a limiting plate 17 fixedly installed at its outer end. The two ends of each spring 18 are fixedly connected to the limiting plate 17 on its side and the adjacent side of the upper cylinder 2, respectively. When the upper cylinder 2 and the lower cylinder 3 are connected, four insert plates 14 are inserted into four slots 16, and two pins 15 are inserted into positioning holes 19 at the same height on the two insert plates 14, so as to adjust and fix the vertical position between the upper cylinder 2 and the lower cylinder 3.

[0035] Taking a circular cylinder as an example, the insert plate 14, slot 16, and pin 15 in the snap-fit ​​assembly 4 are evenly arranged along the outer circular surface of the cylinder, with 3-4 of each component, and all corresponding to each other at the top and bottom. The structure and working principle of each component are the same as those of the square cylinder.

[0036] The motor 27 is connected to an external controller and power supply, providing power for air pressurization and cleaning / dust removal.

[0037] The first detection tube 9 and the second detection tube 10 have different lengths. The first detection tube 9 can detect the gas in two spaces: the first isolation plate 5 and the second isolation plate 6, and the second isolation plate 6 and the third isolation plate 7. The second detection tube 10 can only detect the gas in the space between the first isolation plate 5 and the second isolation plate 6.

[0038] When there are four card holders 34, the four scraper arms of the sweeping frame 35 are arranged in a cross shape; when there are three card holders 34, the sweeping frame 35 has three scraper arms arranged equally along the circumference.

[0039] The sampling method for detecting volatile organic compounds of the present invention is implemented using the above-mentioned volatile organic compound detection device according to the following steps:

[0040] Step 1: Position the upper cylinder 2 and lower cylinder 3, and install the testing instruments.

[0041] Place the test box 1 on a horizontal surface and pull each limiting plate 17 outwards. Each limiting plate 17 overcomes the tension of its respective spring 18. All the limiting plates 17 drive all the pins 15 to disengage from the insert plate 14, and the upper cylinder 2 and lower cylinder 3 are released from their limits.

[0042] Lift the hook 40 upwards. The hook 40 will drive the cover 39 and the upper cylinder 2 to rise. After the upper cylinder 2 is a certain distance away from the lower cylinder 3, release the limiting plate 17. The spring 18 will pull the limiting plate 17 to insert the pin 15 into the positioning hole 19 on the insert plate 14.

[0043] Then unscrew the cap 39, unscrew the plug 11 on the second detection tube 10, place the detection head of the detection instrument into the second detection tube 10, and close the cap 39.

[0044] It can perform continuous real-time sampling and detection, or it can be covered with the cap 39 to detect gas in a closed space. The gas sample can be preserved after the cap 39 is covered.

[0045] Step 2: Continuously supply sampling gas and perform sampling gas detection.

[0046] The motor 27 is started, which drives the crankshaft 28 to rotate. The crankshaft 28 drives the collar 29 to rotate, and the collar 29 drives the drive rod 22 to reciprocate. The drive rod 22 drives the piston plate 21 to reciprocate within the vacuum pump 20; the piston plate 21 moves outward ( Figure 2 During the pulling-out process (left side), a negative pressure appears in the air chamber of the suction cylinder 20, and outside air flows through the filter screen 32 into the air inlet pipe 25, and is drawn into the suction cylinder 20 (right side air chamber) through the three-way pipe 23; the piston plate 21 moves inward ( Figure 2 (As shown on the right) During the pushing process, the air in the air chamber of the air extraction cylinder 20 is compressed and called pressurized air. The pressurized air enters the space between the first isolation plate 5 and the second isolation plate 6 through the three-way pipe 23 and the air delivery pipe 24, and is used by the detection head of the detection instrument for detection. Finally, it is discharged from the air outlet 26.

[0047] After starting the motor 27, set the detection time, use the air between the second isolation plate 6 and the third isolation plate 7 as the sampling gas, open the plug 11 on the first detection tube 9, and place the detection head of the detection instrument into the first detection tube 9 to detect the volatile organic compounds in the sampling gas between the second isolation plate 6 and the third isolation plate 7.

[0048] Step 3: Remove dust from the outer surface of the filter screen 32.

[0049] In step 2, while the crankshaft 28 drives the piston plate 21, the crankshaft 28 also drives the drive gear 30 to rotate. The drive gear 30 meshes with the teeth on the annular groove 33, causing the limiting ring 31 to drive the filter screen 32 to rotate. When the outside turbid air enters the filter screen 32, large impurities are intercepted. As the filter screen 32 rotates, the large impurities on the filter screen 32 are swept off into the lower cylinder 3 by the cleaning frame 35.

[0050] Step 4: Perform dust removal on the filter screen 32.

[0051] In step 2, as the crankshaft 28 drives the piston plate 21 to move inward, the air pressure between the second isolation plate 6 and the third isolation plate 7 decreases. The outside turbid air, after being filtered by the filter screen 32, enters the space between the second isolation plate 6 and the third isolation plate 7 through the collection pipe 36. In step 2, as the piston plate 21 is pulled outward, the air filtered between the second isolation plate 6 and the third isolation plate 7 is compressed and the air pressure increases rapidly. The compressed air enters the cleaning pipe 37 and is then quickly sprayed out from the cleaning nozzle 38, blowing off the impurities in the mesh of the filter screen 32.

[0052] Example 1

[0053] At a joint testing station in Yan'an City, Changqing Oilfield, the device of this invention was used for continuous VOCs gas detection, and the data recorded are as follows:

[0054]

[0055] By comparing this value with the detection data and usage time of existing technology equipment, it is determined that the detection results of the device of the present invention are accurate and the usage time is longer.

[0056] Example 2

[0057] At a joint testing station in Qingyang City, Changqing Oilfield, the device of this invention was used for continuous VOCs gas detection, and the data recorded are as follows:

[0058]

[0059] By comparing this value with the detection data and usage time of existing technology equipment, it is determined that the detection results of the device of the present invention are accurate and the usage time is longer.

[0060] Example 3

[0061] At a joint testing station in Qingyang City, Changqing Oilfield, the device of this invention was used for continuous VOCs gas detection, and the data recorded are as follows:

[0062]

[0063] By comparing this value with the detection data and usage time of existing technology equipment, it is determined that the detection results of the device of the present invention are accurate and the usage time is longer.

[0064] Example 4

[0065] At a wastewater monitoring point in Qingyang City, Changqing Oilfield, the device of this invention was used for continuous VOCs gas detection, and the data were recorded as follows:

[0066]

[0067]

[0068] The values ​​for days 4-14 and 16-29 in the above four embodiments are omitted and not displayed.

[0069] By comparing this value with the detection data and usage time of existing technology equipment, it is determined that the detection results of the device of the present invention are accurate and the usage time is longer.

[0070] As can be seen from the above four embodiments, in accordance with the "Technical Requirements and Detection Methods for Portable Monitors of Total Hydrocarbons, Methane and Non-Methane Hydrocarbons in Ambient Air and Exhaust Gas" (HJ 1012-2018), high-concentration VOCs samples were collected from the oil inlet of the storage tank using a gas collection bag. The same VOCs sample was tested using a commonly used portable gas detector (FID) and the volatile organic compound detection device with built-in cleaning function of the present invention. The results showed that the initial error of the non-methane total hydrocarbon detection results of the two instruments was 1%-2%. After continuous detection for 30 days, the error of the non-methane total hydrocarbon detection results of the two instruments was 5%-10%. Among them, the volatile organic compound detection device with built-in cleaning function of the present invention was more stable and had higher accuracy.

Claims

1. A volatile organic compound (VOC) detection device with built-in cleaning function, characterized in that: The upper cylinder (2) and the lower cylinder (3) are snapped together as one unit; the upper cylinder (2) is fixedly installed with a first isolation plate (5), a second isolation plate (6) and a third isolation plate (7) from top to bottom; an air outlet (26) is provided on the side wall of the upper cylinder (2) between the first isolation plate (5) and the second isolation plate (6); multiple through slots are opened on the first isolation plate (5); a first detection tube (9) or a second detection tube (10) is slidably installed in each through slot; the bottom ends of all the first detection tubes (9) penetrate downward through the second isolation plate (6) and extend to the bottom of the second isolation plate (6); an air extraction assembly (8) and a drive assembly (13) are provided between the second isolation plate (6) and the third isolation plate (7); an air intake filter assembly (12) is provided on the lower surface of the third isolation plate (7); a collection tube (36) and a cleaning tube (37) are also provided through the third isolation plate (7); a cleaning frame (35) is fixedly installed between all the brackets (34); The structure of the air extraction assembly (8) includes an air extraction cylinder (20), a piston plate (21) is slidably installed inside the air extraction cylinder (20), the outer end face of the piston plate (21) is connected to the inner end of the drive rod (22), the air chamber at the inner end of the piston plate (21) is connected to the three-way pipe (23), the other two ports of the three-way pipe (23) are connected to the air supply pipe (24) and the air inlet pipe (25) respectively, the air supply pipe (24) extends upward beyond the second isolation plate (6), the air inlet pipe (25) passes downward through the third isolation plate (7) and extends into the interior of the air inlet filter assembly (12), a first one-way valve is provided in the pipe of the air inlet pipe (25), and a second one-way valve is provided in the pipe of the air supply pipe (24); The structure of the drive assembly (13) includes a motor (27), which is fixedly installed on the lower surface of the first isolation plate (5). The output shaft of the motor (27) is connected to the crankshaft (28) for transmission. A collar (29) is sleeved on the bent end of the crankshaft (28), and the collar (29) is fixedly connected to the outer end of the drive rod (22). The structure of the intake filter assembly (12) includes multiple brackets (34) and a limiting ring (31). All brackets (34) are fixedly connected to the lower surface of the third isolation plate (7) upwards. The inner surface of all brackets (34) is adapted to the outer surface of the limiting ring (31). All brackets (34) hug and support the limiting ring (31). The lower part of the inner wall of the limiting ring (31) is fixedly connected to the filter screen (32). The upper part of the inner wall of the limiting ring (31) is stepped and called an annular groove (33). A ring of teeth is evenly arranged on the inner wall of the annular groove (33). The bottom end of the crankshaft (28) passes through the third isolation plate (7) downwards and is fixedly connected to the drive gear (30). The drive gear (30) meshes with the ring of teeth of the annular groove (33). The drive gear (30) drives the limiting ring (31) and the filter screen (32) to rotate through the teeth.

2. The volatile organic compound detection device with built-in cleaning function according to claim 1, characterized in that: The upper cylinder (2) and the lower cylinder (3) are fixed together by a snap-fit ​​assembly (4). The structure of the snap-fit ​​assembly (4) is as follows, for a square cylinder, including four insert plates (14), four slots (16), and two pins (15); the four slots (16) are respectively located on the lower part of the four sides of the upper cylinder (2), and the four insert plates (14) are respectively located on the top of the four sides of the lower cylinder (3). A pin (15) is provided near the bottom of each of the two opposite slots (16). Multiple positioning holes (19) are opened on the two insert plates (14) below the two slots (16). The positioning holes (19) are opened sequentially from top to bottom and are adapted to the pins (15). Each insert plate (14) has multiple positioning holes (19). At least three positioning holes (19) at the upper, middle and lower height positions are provided on the plate (14); a spring (18) is sleeved on the outer periphery of each pin (15), and a limiting plate (17) is fixedly installed on the outer end of each pin (15). The two ends of each spring (18) are fixedly connected to the limiting plate (17) on this side and the adjacent upper cylinder (2) side respectively; when the upper cylinder (2) and the lower cylinder (3) are connected, the four insert plates (14) are inserted into the four slots (16) respectively, and two pins (15) are inserted into the positioning holes (19) at the same height on the two insert plates (14).

3. The volatile organic compound detection device with built-in cleaning function according to claim 2, characterized in that: The collection pipe (36) and the cleaning pipe (37) are both located inside the filter screen cover (32). The cleaning pipe (37) is connected to several cleaning nozzles (38) on the side near the filter screen cover (32). A third one-way valve is installed in the pipe of the collection pipe (36), and a fourth one-way valve is installed in the pipe of the cleaning pipe (37).

4. A sampling method for detecting volatile organic compounds, utilizing the volatile organic compound detection device with a self-cleaning function as described in claim 2 or 3, characterized in that, Follow these steps: Step 1: Position the upper cylinder (2) and the lower cylinder (3) and install the testing instruments; Step 2: Continuously feed in the sampling gas and perform sampling gas detection; Step 3: Remove dust from the outer surface of the filter screen (32); Step 4: Perform dust removal on the filter screen (32).

5. The sampling method for detecting volatile organic compounds according to claim 4, characterized in that, In step 1, the specific process is as follows: Place the test box (1) on a horizontal ground and pull each limiting plate (17) outward. Each limiting plate (17) overcomes the tension of its own spring (18), and all the limiting plates (17) drive all the pins (15) to disengage from the insert plate (14), and the upper cylinder (2) and lower cylinder (3) are released from their limits. Lift the hook (40) upwards again. The hook (40) will drive the cover (39) and the upper cylinder (2) to rise. After the upper cylinder (2) is a certain distance away from the lower cylinder (3), release the limiting plate (17). The spring (18) will pull the limiting plate (17) to make the pin (15) insert into the positioning hole (19) on the insert plate (14). Then unscrew the cap (39), unscrew the plug (11) on the second detection tube (10), place the detection head of the detection instrument into the second detection tube (10), and close the cap (39).

6. The sampling method for detecting volatile organic compounds according to claim 4, characterized in that, Step 2, the specific process is as follows: Start the motor (27), which drives the crankshaft (28) and collar (29) to rotate. The collar (29) drives the drive rod (22) to reciprocate. The drive rod (22) drives the piston plate (21) to reciprocate in the vacuum cylinder (20). During the process of the piston plate (21) being pulled outward, the air chamber of the vacuum cylinder (20) experiences negative pressure. Outside air flows through the filter screen (32) into the air inlet pipe (25) and is sucked into the vacuum cylinder (20) through the three-way pipe (23). During the process of the piston plate (21) being pushed inward, the air in the air chamber of the air extraction cylinder (20) is compressed and called pressurized air. The pressurized air enters the space between the first isolation plate (5) and the second isolation plate (6) through the three-way pipe (23) and the air delivery pipe (24) for detection by the detection head of the detection instrument, and is finally discharged from the air outlet (26). After starting the motor (27), set the detection time, use the air between the second isolation plate (6) and the third isolation plate (7) as the sampling gas, open the plug (11) on the first detection tube (9), place the detection head of the detection instrument in the first detection tube (9), and the volatile organic compounds in the sampling gas between the second isolation plate (6) and the third isolation plate (7) can be detected.

7. The sampling method for detecting volatile organic compounds according to claim 4, characterized in that, Step 3, the specific process is as follows: While the crankshaft (28) drives the piston plate (21), the crankshaft (28) also drives the drive gear (30) to rotate. The drive gear (30) meshes with the teeth on the annular groove (33) to drive the limit ring (31) to rotate the filter screen (32). When the outside turbid air enters the filter screen (32), large pieces of impurities are intercepted. As the filter screen (32) rotates, the large pieces of impurities on the filter screen (32) are swept off into the lower cylinder (3) by the cleaning frame (35).

8. The sampling method for detecting volatile organic compounds according to claim 4, characterized in that, Step 4, the specific process is as follows: As the crankshaft (28) drives the piston plate (21) to move inward, the air pressure between the second isolation plate (6) and the third isolation plate (7) decreases. After being filtered by the filter screen (32), the outside turbid air enters the space between the second isolation plate (6) and the third isolation plate (7) through the collection pipe (36). During the process of the piston plate (21) being pulled outward, the air filtered between the second isolation plate (6) and the third isolation plate (7) is compressed and the air pressure increases rapidly. The compressed air enters the cleaning pipe (37) and is then quickly sprayed out from the cleaning nozzle (38), blowing off the impurities in the mesh of the filter screen (32).

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