A two-position three-way valve for air pressure and liquid level

Abstract

The present invention discloses a two-position, three-way valve for pneumatic and liquid level control, comprising a valve body. The inner cavity of the valve body is divided into a liquid level cavity and an air cavity by a diaphragm. The liquid level cavity is provided with a hydraulic opening, which is sealedly connected to a conduit having one end extending into the liquid. The air cavity is provided with an air opening, which is connected to the external atmosphere. A pneumatic chamber is also provided within the air cavity. The pneumatic chamber is provided with a communication port communicating with the air cavity and an interface valve port communicating with an interface valve. A negative pressure channel is provided between the pneumatic and liquid level control chambers, connecting an external negative pressure gas source to the pneumatic chamber. A switch assembly is provided within the negative pressure channel to control the connection between the pneumatic chamber and the negative pressure gas source. The switch assembly closes the negative pressure channel in an initial state. When the diaphragm moves downward to a first position, the diaphragm closes the communication port. When the diaphragm continues to move downward to a second position, the diaphragm pushes the switch assembly to connect the pneumatic chamber and the negative pressure gas source. No electricity is required, and the opening and closing of the interface valve can be set according to the liquid level.

Description

Technical Field

[0001] The present invention relates to the technical field of valves, in particular to a two-position three-way valve for air pressure and liquid level. Background Art

[0002] Negative pressure drainage systems use negative pressure to collect wastewater from negative pressure intelligent collectors distributed at the end of a tree-like negative pressure collection network and funnel it to a negative pressure power center at the end of the system. Existing negative pressure intelligent collectors consist of a water collection terminal, a sewage suction pipe, an interface valve, a pilot valve, and a level switch. The pilot valve is typically a solenoid valve or a mechanical valve.

[0003] When a solenoid valve is used as the pilot valve, switching between atmospheric pressure and negative pressure is required to open and close the interface valve. Current two-position, three-way solenoid valves suffer from relatively high operating voltages, high operating currents, and high energy consumption. This creates high power requirements and hinders future maintenance. Furthermore, when the pilot valve is a solenoid valve, a liquid level switch must still be used in conjunction.

[0004] Using a mechanical pilot valve presents two major challenges. First, when the liquid level is at the critical conduction point, all three ports are simultaneously connected, preventing the interface valve from opening smoothly. Second, the control interface valves all open and close at the same critical point. This means that when the liquid level reaches the conduction interface valve, the interface valve closes immediately upon a slight decrease in level. Currently, delaying valve closure by adjusting the flow rate in the control air path of the interface valve does not directly reflect the liquid level. Summary of the Invention

[0005] In order to overcome the above shortcomings, the purpose of the present invention is to provide a two-position three-way valve for air pressure liquid level, which does not require electricity and the opening and closing of the interface valve can be set according to the liquid level, thereby improving the existing technology of controlling the opening and closing of the interface valve at the same liquid level.

[0006] To achieve the above objectives, the present invention employs a technical solution comprising: a pneumatic, two-position, three-way valve comprising a valve body, the inner cavity of the valve body being divided into a liquid level chamber and an air chamber by a diaphragm, the valve body being characterized in that the liquid level chamber is provided with a hydraulic opening, the hydraulic opening being sealedly connected to a conduit having one end extending into the liquid, and the air chamber is provided with an air opening, the air opening being connected to the external atmosphere. A pneumatic chamber is further provided within the air chamber, the pneumatic chamber being provided with a communication port communicating with the air chamber and an interface valve port communicating with an interface valve, a negative pressure channel being provided between the pneumatic chamber and the air chamber, connecting an external negative pressure gas source to the pneumatic chamber, and a switch assembly being provided within the negative pressure channel for controlling the connection between the pneumatic chamber and the negative pressure gas source. The switch assembly initially closes the negative pressure channel, and when the diaphragm moves downward to a first position, the diaphragm closes the communication port. When the diaphragm continues to move downward to a second position, the diaphragm pushes the switch assembly to connect the pneumatic chamber to the negative pressure gas source.

[0007] The beneficial effect of the present invention is that when the liquid level rises, the air pressure in the liquid level cavity increases, and the diaphragm moves toward the air cavity. In the process of gradually rising liquid level, the diaphragm first reaches the first position, seals the connecting port, and the external atmosphere no longer enters the air pressure cavity. As the liquid level continues to rise, the diaphragm pushes the switch assembly to move, connecting the air pressure cavity and the negative pressure air source. The entire process first disconnects the air pressure cavity from the air cavity connected to the external atmosphere, and then connects the negative pressure channel, connecting the air pressure cavity and the external negative pressure air source. The external negative pressure air source enters the interface valve from the interface valve port, and the interface valve opens. When the interface valve is closed, the process is reversed. The opening and closing of the entire cross-sectional valve completely relies on the mechanical structure and does not require electricity. At the same time, the cooperation of the diaphragm, the air pressure cavity and the switch assembly allows the opening and closing of the interface valve to be located at different liquid levels, improving the problem of controlling the opening and closing of the interface valve at the same liquid level in the prior art, so that the opening and closing of the interface valve can be set according to the liquid level.

[0008] Specifically, the diaphragm includes two diaphragms, one positioned corresponding to the communication port and the other to the negative pressure channel. Diaphragm one is located directly above the communication port and can open and close the communication port during its vertical movement. Diaphragm two is located directly above the air pressure channel and can push the switch assembly. This dual-diaphragm structure allows diaphragms one and two to push the communication port and switch assembly, respectively, during their vertical movement, improving stability.

[0009] Furthermore, the negative pressure channel includes a guide tube, which includes a first opening and a second opening located at both ends, the first opening extends into the air cavity and communicates with the air cavity, the second opening extends into the air pressure cavity and communicates with the air pressure cavity, the guide tube is also connected to an air source port located between the first opening and the second opening, the air source port is connected to a negative pressure air source, the switch assembly can slide in the guide tube, the switch assembly always closes the first opening and can connect or disconnect the second opening and the air source port during movement.

[0010] Furthermore, the switch assembly includes a push rod and a sliding rod, the push rod is fixed on diaphragm 2 and can extend from the first opening into the guide pipe, the sliding rod includes a sliding rod part that can slide in the guide tube and a frustum part located at the end of the sliding rod part, the sliding rod part is outer-circularly connected with a first sealing ring, the first sealing ring can always close the first opening, the large circular surface of the frustum part is located outside the guide pipe and can abut against the second opening under the pressure of a spring to close the second opening, the frustum part can be separated from the second opening under the push of the push rod, and when the frustum part and the second opening are separated, the air source port and the second opening are connected.

[0011] Furthermore, a bolt is threadedly connected to the valve body, one end of the bolt extends into the air pressure chamber, one end of the spring abuts against the bolt, and the other end abuts against the large circular surface of the frustum.

[0012] Furthermore, in the initial state, the gap between the push rod and the slide rod portion is larger than the gap between the diaphragm 1 and the communication port, ensuring that when the diaphragms 1 and 2 move downward synchronously, the diaphragm 1 first closes the communication port, and then the push rod pushes the slide rod to move, thus achieving a sequential order.

[0013] Specifically, the switch assembly includes a lifting rod fixed to diaphragm 2 and capable of extending from the first opening into the guide conduit. The lifting rod is capable of sliding within the guide conduit. A second sealing ring and a third sealing ring are sleeved on the lifting rod, with the air source port located between the second and third sealing rings. The second sealing ring always seals the first opening. In its initial state, the third sealing ring seals the second opening and can connect the second opening to the air source port during downward movement. The switch assembly, comprising the lifting rod and two sealing rings, has a simple structure.

[0014] Furthermore, the sliding distance of the lifting rod sliding downward to connect the second opening and the air source port is greater than that of the lifting rod, and in the initial state, a gap is left between the diaphragm 1 and the communication port.

[0015] Furthermore, the liquid level chamber, air chamber and air pressure chamber are commonly penetrated by a partition, which divides the liquid level chamber into chamber one and chamber two that are interconnected, the partition divides the air chamber into chamber three and chamber four that are interconnected, and the partition divides the air pressure chamber into chamber five and chamber six that are interconnected. Chamber one, chamber three and chamber five are located on the same side of the partition, and chamber two, chamber four and chamber six are located on the other side of the partition. The negative pressure channel is located on the diaphragm one that seals and isolates chamber one and chamber three, and diaphragm two that seals and isolates chamber two and chamber four.

[0016] Specifically, the hydraulic opening is provided in at least one of chambers 1 and 2, the air opening is provided in at least one of chambers 3 and 4, and the interface valve port is provided in at least one of chambers 5 and 6. Chambers 1 and 2 are always connected and maintain the same pressure, while chambers 3 and 4 are always connected and maintain the same pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of an initial state of an embodiment of the present invention;

[0019] Figure 3 This is a structural schematic diagram of an embodiment of the present invention when the diaphragm moves downward to the first position;

[0020] Figure 4 This is a structural schematic diagram of an embodiment of the present invention when the diaphragm moves downward to the second position;

[0021] Figure 5 This is a schematic diagram of an initial state of an embodiment of the present invention;

[0022] Figure 6 This is a structural schematic diagram of an embodiment of the present invention when the diaphragm moves downward to the first position;

[0023] Figure 7 This is a structural diagram of an embodiment of the present invention when the diaphragm moves downward to the second position.

[0024] In the picture:

[0025] 1. Valve body; 2. Liquid level cavity; 2a. Chamber 1; 2b. Chamber 2; 21. Hydraulic opening; 3. Air cavity; 3a. Chamber 3; 3b. Chamber 4; 31. Air opening; 4. Air pressure cavity; 4a. Chamber 5; 4b. Chamber 6; 41. Connecting port; 42. Interface valve port; 5. Negative pressure channel; 51. First opening; 52. Second opening; 6. Switch assembly; 61. Push rod; 62. Sliding rod; 621. Sliding rod portion; 622. Cone portion; 63. First sealing ring; 64. Spring; 65. Bolt; 66. Lifting rod; 67. Second sealing ring; 68. Third sealing ring; 71. Diaphragm 1; 72. Diaphragm 2; 8. Air source port; 9. Partition; 91. Port 1; 92. Port 2; 93. Port 3 DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0027] See attached Figure 1 As shown, a two-position three-way valve of air pressure and liquid level of the present invention comprises a valve body 1, the inner cavity of the valve body 1 is divided into a liquid level cavity 2 and an air cavity 3 by a diaphragm. The pressure difference between the liquid level cavity 2 and the air cavity 3 will push the diaphragm to deform and move up and down.

[0028] The liquid level chamber 2 is provided with a hydraulic opening 21, and the hydraulic opening 21 is sealed and connected to a conduit with one end extending into the liquid. One end of the conduit extends below the liquid level. When the liquid level changes, the gas in the conduit will change, and thus the gas in the liquid level chamber 2 will be changed. The air chamber 3 is provided with an air opening 31, and the air opening 31 is connected to the external atmosphere. An air pressure chamber 4 is also provided in the air chamber 3, and a connecting port 41 communicating with the air chamber 3 and an interface valve port 42 communicating with the interface valve are provided on the air pressure chamber 4. A negative pressure channel 5 connecting an external negative pressure gas source and the air pressure chamber 4 is also provided between the air pressure chamber 4 and the air chamber 3. A switch component 6 for controlling the on-off of the air pressure chamber 4 and the negative pressure gas source is provided in the negative pressure channel 5. The switch component 6 closes the negative pressure channel 5 in the initial state. See the attached Figure 3As shown in FIG, when the diaphragm moves down to the first position, the diaphragm can close the communication port 41 to disconnect the air pressure chamber 4 and the air chamber 3. Figure 4 As shown, when the diaphragm continues to move downward to the second position, the diaphragm can push the switch assembly 6 to move to connect the air pressure chamber 4 and the negative pressure air source.

[0029] As the liquid level rises, the pressure in liquid level chamber 2 increases, causing the diaphragm to move toward air chamber 3. As the liquid level gradually rises, the diaphragm first reaches its first position, sealing communication port 41 and preventing the outside air from entering pneumatic chamber 4. As the liquid level continues to rise, the diaphragm pushes switch assembly 6 to move, connecting pneumatic chamber 4 to the negative pressure air source. This process first disconnects pneumatic chamber 4 from air chamber 3, which is connected to the outside atmosphere. Then, negative pressure channel 5 is opened, connecting pneumatic chamber 4 to the external negative pressure air source. The external negative pressure air source enters the interface valve through interface valve port 42, causing the interface valve to open.

[0030] After the interface valve opens, the liquid level begins to drop. As the liquid level gradually decreases, the air pressure in liquid level chamber 2 decreases, causing the diaphragm to move in the opposite direction. First, switch assembly 6 resets, closing negative pressure passage 5 and disconnecting the negative pressure air source from air pressure chamber 4. At this point, the diaphragm still closes communication port 41, leaving the interface valve open. As the liquid level continues to drop, the diaphragm moves away from communication port 41, connecting air chamber 3 to air pressure chamber 4. External air can enter the interface valve through interface valve port 42, closing the interface valve.

[0031] The opening and closing of the entire cross-sectional valve is entirely mechanical, requiring no electricity. The diaphragm, air pressure chamber 4, and switch assembly 6 work together to allow the interface valve to open and close at different liquid levels, resolving the existing problem of controlling the opening and closing of the interface valve at the same liquid level. This allows the interface valve to be opened and closed based on the liquid level.

[0032] In one embodiment, see the attached Figure 1 and 2 As shown, the diaphragms include diaphragm 1 71 and diaphragm 2 72, respectively positioned corresponding to the communication port 41 and the negative pressure channel 5. Together, these two diaphragms separate the liquid level chamber 2 and the air chamber 3. Diaphragm 1 71 is located directly above the communication port 41 and can open and close the communication port 41 during its vertical movement. Diaphragm 2 72, located directly above the air pressure channel, can push the switch assembly 6. The two diaphragms allow diaphragms 1 71 and 72 to push the communication port 41 and switch assembly 6, respectively, during their vertical movement, improving stability.

[0033] See attached Figure 2As shown, the negative pressure channel 5 includes a guide tube, which includes a first opening 51 and a second opening 52 at both ends. The first opening 51 extends into the air cavity 3 and communicates with the air cavity 3, and the second opening 52 extends into the air pressure cavity 4 and communicates with the air pressure cavity 4. The guide tube is also connected to an air source port 8 located between the first opening 51 and the second opening 52. The air source port 8 is connected to a negative pressure air source. The switch assembly 6 can slide within the guide tube. The switch assembly 6 always closes the first opening 51 and can connect or disconnect the second opening 52 and the air source port 8 during movement. That is, the negative pressure channel 5 is a three-way channel defined by a three-way pipe. The first opening 51, the second opening 52, and the air source port 8 are respectively the three openings of the three-way channel. The air source port 8 extends out of the valve body 1 and can be connected to a negative pressure air source.

[0034] See attached Figure 2 As shown, in one embodiment, the switch assembly 6 includes a push rod 61 and a sliding rod 62. The push rod 61 is fixed to the second diaphragm 72 and can extend from the first opening 51 into the guide pipe. The sliding rod 62 includes a sliding rod portion 621 and a frustum portion 622 located at the end of the sliding rod portion 621. The sliding rod portion 621 can slide within the guide pipe. The large circular surface of the frustum portion 622 is located outside the guide pipe and can abut against the second opening 52 to close the second opening 52. A first sealing ring 63 is connected to the outer surface of the sliding rod portion 621. The first sealing ring 63 can always close the first opening 51. The gas source port 8 is always located between the first sealing ring 63 and the frustum portion 622. When the push rod 61 moves downward synchronously with the diaphragm 2 72, it can abut against the slide rod portion 621 of the sliding rod 62 and push the sliding rod 62 downward. When the frustum portion 622 moves downward and away from the end of the second opening 52, the second opening 52 opens, and the second opening 52 is connected to the air source port 8, that is, the air pressure chamber 4 is connected to the external negative pressure air source.

[0035] The small circular surface of the truncated cone portion 622 is connected to the sliding rod portion 621 and can extend into the guide pipe. The large circular surface of the truncated cone portion 622 has a diameter greater than the diameter of the second opening 52. The outer wall of the truncated cone portion 622 can abut against the second opening 52, closing the second opening 52. In this case, the gas source port 8 is disconnected from the second opening 52. The sliding rod 62 is integrally formed, and the sliding rod portion 621 is inserted into the guide pipe through the second opening 52.

[0036] The truncated cone 622 is pressed against the second opening 52 by the spring 64. Initially, the spring 64 pushes the truncated cone 622 upward, closing the second opening 52. At this point, the spring 64 is compressed. As the push rod 61 moves downward, the thrust exceeds the spring 64's force, causing the spring 64 to continue compressing. This pushes the sliding rod 62, causing the outer wall of the truncated cone 622 to move away from the second opening 52. This connects the second opening 52 to the air source port 8, connecting the air pressure chamber 4 to the negative pressure air source.

[0037] In one embodiment, to facilitate adjustment of the elastic force exerted by the spring 64 on the truncated cone portion 622, a bolt 65 is threadedly connected to the valve body 1, one end of the bolt 65 extending into the air pressure chamber 4. One end of the spring 64 abuts against the bolt 65, and the other end abuts against the large circular surface of the truncated cone portion 622.

[0038] In the initial state, see the attached Figure 2 As shown, when the air cavity 3 and the liquid level cavity 2 are balanced and the diaphragm does not move up or down, a gap of one exists between the push rod 61 and the slide portion 621, and a gap of two exists between the diaphragm and the communication port 41, with gap one being larger than gap two. This ensures that when the diaphragm moves downward, it first seals against the communication port 41, and then the push rod 61 abuts against the slide portion 621, pushing the slide portion 621 to move. When the diaphragm moves upward to reset, the push rod 61 also first leaves the push rod portion, and then the diaphragm leaves the communication port 41.

[0039] See attached Figure 5 As shown, in another embodiment, the switch assembly 6 includes a lifting rod 66 fixed on the diaphragm 2 72 and capable of extending from the first opening 51 into the guide pipe, and the lifting rod 66 can slide in the guide pipe. A second sealing ring 67 and a third sealing ring 68 are sleeved on the lifting rod 66, and the gas source port 8 is located between the second sealing ring 67 and the third sealing ring 68. The second sealing ring 67 always seals the first opening 51, and the third sealing ring 68 seals the second opening 52 in the initial state, disconnecting the second opening 52 from the gas source port 8, and can open the second opening 52 during the downward movement, connecting the second opening 52 with the gas source port 8. The second opening 52 is opened on the end side wall of the guide pipe, and the third sealing ring 68 is always located in the guide pipe and will not slide out of the guide pipe. In this embodiment, the switch assembly 6 is a lifting rod 66 and a sealing ring, which move directly with the diaphragm 2, and the structure is simpler.

[0040] The sliding distance of the lifting rod 66 sliding downward to connect the second opening 52 and the third opening 93 is greater than the gap 2, that is, in the initial state, the distance from the third sealing ring 68 to the second opening 52 is greater than the gap 2.

[0041] In one embodiment, see the attached Figure 2 and 5 As shown, a partition 9 runs through the liquid level chamber 2, air chamber 3, and air pressure chamber 4. This partition 9 divides the liquid level chamber into chamber 1 2a and chamber 2 2b, the air chamber 3 into chamber 3 3a and chamber 4 3b, and the air pressure chamber 4 into chamber 5 4a and chamber 6 4b. Chambers 1 2a, 3a, and 5 4a are located on the same side of the partition 9, while chambers 2 2b, 4b, and 6 4b are located on the other side of the partition 9.

[0042] Diaphragm 1 71 seals and isolates chamber 1 2a from chamber 3 3a, while diaphragm 2 72 seals and isolates chamber 2 2b from chamber 4 3b. A communication port 41 is provided on chamber 5 4a, directly below the center of diaphragm 1 71. Negative pressure channel 5 is provided between chamber 4 3b and chamber 6 4b, with its first opening 51 located directly below the center of diaphragm 2 72. Because the diaphragms are fixed at both ends, their center position allows for vertical displacement, corresponding to the communication port 41 and the first opening 51.

[0043] The hydraulic opening 21 is provided on at least one of chamber 1 2a and chamber 2 2b. When only one of chamber 1 2a and chamber 2 2b is provided with the hydraulic opening 21, the partition 9 is further provided with a port 1 91 for connecting chamber 1 2a and chamber 2 2b, thereby ensuring that chamber 1 2a and chamber 2 2b are connected and the pressure in the two is always the same.

[0044] The air opening 31 is provided on at least one of the chamber three 3a and the chamber four 3b. When only one of the chamber three 3a and the chamber four 3b is provided with the air opening 31, the partition 9 is also provided with a second port 92 for connecting the chamber three 3a and the chamber four 3b, thereby ensuring that the chamber three 3a and the chamber four 3b are connected and the pressure inside the two is always the same.

[0045] The interface valve port 42 is provided in at least one of chambers 5 4a and 6 4b, and the communication port 41 is provided in one of these chambers 5 and 6 4b, with the negative pressure channel 5 provided in the other. If only one of chambers 5 and 6 4b is provided with an interface valve port 42, the partition plate 9 is also provided with a port 3 93 that connects chambers 5 and 6 4b, ensuring communication between chambers 5 4a and 6 4b, with one interface valve port 42 connected to the interface valve. If chambers 5 4a and 6 4b are provided with interface valve port 1 and interface valve port 2, respectively, both interfaces are connected to the interface valves.

[0046] The conduit is connected to the opening 1 91 and the hydraulic opening 21. As the liquid level rises, the pressure in chamber 1 2a and chamber 2 2b increases, and diaphragms 1 71 and 2 72 move toward chamber 3 3a and chamber 4 3b. As the liquid level gradually rises, diaphragm 1 71 first contacts the communication port 41 and seals it. Figure 3 and 6 As the liquid level continues to rise, the diaphragm 2 72 drives the push rod 61 to contact the sliding rod 62 (or the lifting rod 66 continues to move downward), connecting the air source port 8 and the second opening 52, that is, connecting the interface valve port 42 and the external negative pressure air source, and the interface valve opens. At this time, the state is shown in the attached figure. Figure 4 and 7After the interface valve is opened, the liquid level begins to drop. As the liquid level gradually decreases, the push rod 61 separates from the sliding rod 62 (or the lifting rod 66 moves upward). The push rod 61 (or the lifting rod 66) seals the second opening 52, closing the air source port 8 and the second opening 52, thereby disconnecting the interface valve port 42 from the external negative pressure air source. At this time, the diaphragm 1 71 still closes the connecting port 41, and the interface valve is in the open state. The liquid level continues to drop, and the diaphragm 1 71 leaves the connecting port 41. The air entering the air cavity 3 from the air opening 31 can enter the air pressure cavity 4 from the connecting port 41. The air in the air pressure cavity 4 enters the interface valve from the interface valve port 42, and the interface valve opens.

[0047] The above embodiments are only for illustrating the technical concept and features of the present invention. Its purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A two-position, three-way pneumatic-liquid-level valve, comprising a valve body, wherein the inner cavity of the valve body is divided into a liquid level cavity and an air cavity by a diaphragm, characterized in that: The liquid level cavity is provided with a hydraulic opening, the hydraulic opening is sealedly connected to a conduit having one end extending into the liquid, and the air cavity is provided with an air opening, the air opening being connected to the external atmosphere; An air pressure chamber is also provided in the air chamber, and a connecting port connected to the air chamber and an interface valve port connected to the interface valve are provided on the air pressure chamber. A negative pressure channel connecting an external negative pressure air source and the air pressure chamber is also provided between the air pressure chamber and the air chamber. A switch component for controlling the connection and disconnection of the air pressure chamber and the negative pressure air source is provided in the negative pressure channel. The switch component closes the negative pressure channel in the initial state. When the diaphragm moves down to the first position, the diaphragm can close the connecting port. When the diaphragm continues to move down to the second position, the diaphragm can push the switch component to move to connect the air pressure chamber and the negative pressure air source.

2. The pneumatic liquid level two-position three-way valve according to claim 1, characterized in that: The diaphragm includes diaphragm 1 and diaphragm 2, which are respectively arranged corresponding to the connecting port and the negative pressure channel. Diaphragm 1 is located directly above the connecting port and can open and close the connecting port during the up and down movement. Diaphragm 2 is located directly above the air pressure channel and can push the switch assembly to move.

3. The pneumatic liquid level two-position three-way valve according to claim 2, characterized in that: The negative pressure channel includes a guide tube arranged along the second moving direction of the diaphragm, and the guide tube includes a first opening and a second opening at both ends, the first opening extends into the air cavity and is communicated with the air cavity, the second opening extends into the air pressure cavity and is communicated with the air pressure cavity, the guide tube is also connected to an air source port located between the first opening and the second opening, the air source port is connected to a negative pressure air source, the switch assembly can slide in the guide tube, the switch assembly always closes the first opening and can connect or disconnect the second opening and the air source port during movement.

4. The pneumatic liquid level two-position three-way valve according to claim 3, characterized in that: The switch assembly includes a push rod and a sliding rod. The push rod is fixed on diaphragm 2 and can extend from the first opening into the guide pipe. The sliding rod includes a sliding rod part that can slide in the guide tube and a frustum part located at the end of the sliding rod part. The sliding rod part is outer-circularly connected with a first sealing ring. The first sealing ring can always close the first opening. The large circular surface of the frustum part is located outside the guide pipe and can abut against the second opening under the pressure of a spring to close the second opening. The frustum part can be separated from the second opening under the push of the push rod.

5. The pneumatic liquid level two-position three-way valve according to claim 4, characterized in that: The valve body is also threadedly connected with a bolt, one end of the bolt extends into the air pressure chamber, one end of the spring abuts against the bolt, and the other end abuts against the large circular surface of the truncated cone portion.

6. The pneumatic liquid level two-position three-way valve according to claim 4, characterized in that: In the initial state, a gap between the push rod and the sliding rod portion is larger than a gap between the diaphragm 1 and the communication port.

7. The pneumatic liquid level two-position three-way valve according to claim 3, characterized in that: The switch assembly includes a lifting rod fixed on diaphragm 2 and capable of extending from the first opening into the guide pipe. The lifting rod can slide in the guide pipe. A second sealing ring and a third sealing ring are sleeved on the lifting rod. The air source port is located between the second sealing ring and the third sealing ring. The second sealing ring always seals the first opening. In the initial state, the third sealing ring seals the second opening and can connect the second opening and the air source port during the downward movement.

8. The pneumatic liquid level two-position three-way valve according to claim 7, characterized in that: The sliding distance of the lifting rod sliding downward to connect the second opening and the air source port is greater than the gap left between the diaphragm 1 and the communication port in the initial state.

9. The pneumatic liquid level two-position three-way valve according to claim 2, characterized in that: The liquid level chamber, air chamber and air pressure chamber are commonly penetrated by a partition, which divides the liquid level chamber into chamber one and chamber two that are interconnected, the partition divides the air chamber into chamber three and chamber four that are interconnected, and the partition divides the air pressure chamber into chamber five and chamber six that are interconnected. Chamber one, chamber three and chamber five are located on the same side of the partition, and chamber two, chamber four and chamber six are located on the other side of the partition. The negative pressure channel is located on the diaphragm one that seals and isolates chamber one and chamber three, and diaphragm two that seals and isolates chamber two and chamber four.

10. The pneumatic liquid level two-position three-way valve according to claim 9, characterized in that: The hydraulic opening is provided on at least one of chamber one and chamber two, the air opening is provided on at least one of chamber three and chamber four, and the interface valve port is provided on at least one of chamber five and chamber six.

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