A negative pressure maintaining system and method for a moisture-proof vacuum loading machine

Abstract

The present application belongs to the technical field of material conveying, and relates to a negative pressure maintaining system and method for a moisture-proof vacuum feeding machine, comprising a feeding machine cavity, a conveying pipeline, a vacuum power source, a discharging device and a controller; the controller controls the vacuum power source and executes the following control strategy: in the feeding stage, the vacuum power source operates to draw the pressure in the negative pressure circuit to a preset feeding target negative pressure; during the opening of the discharging device and the discharge operation, the vacuum power source continuously operates to maintain the negative pressure circuit in a first negative pressure state; after the completion of the discharge and the closing of the discharging device, the vacuum power source maintains the pressure in the negative pressure circuit in a preset moisture-proof negative pressure interval. The negative pressure maintaining system and method for the moisture-proof vacuum feeding machine provided by the present application can effectively realize material moisture-proofing and guarantee product quality, and has the advantages of low cost, simple system, safety and reliability, convenient maintenance and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of material conveying, and relates to a negative pressure maintaining system and method for a moisture-proof vacuum feeder. Background Technology

[0002] In industrial production processes such as chemical, food, and pharmaceutical manufacturing, many powder materials exhibit extremely high hygroscopicity. During vacuum feeding, if these materials come into contact with humid air, they are highly susceptible to agglomeration, denaturation, and degradation. This not only severely impacts the quality stability of the final product but can also cause blockages in conveying pipelines, equipment malfunctions, disrupt production continuity, and increase production costs and maintenance workload.

[0003] Currently, the industry commonly employs nitrogen protection as a moisture-proof solution for vacuum feeding of hygroscopic powder materials. The core idea of ​​this method is to fill the pipes and containers of the vacuum feeder with nitrogen to create a sealed environment isolated from the external humid air, thereby preventing the material from absorbing moisture.

[0004] The existing nitrogen protection technology mainly implements two types of processes: one is the intermittent mode of "feeding - nitrogen balancing - discharging", that is, after feeding is completed, nitrogen is introduced into the system cavity to make the internal pressure of the cavity rise to normal pressure or slightly positive pressure, and then the discharging device is turned on to discharge the material; the other is the continuous nitrogen balancing mode, that is, during the entire vacuum feeding cycle, a small amount of nitrogen is continuously introduced into the system to maintain a slightly positive pressure state inside the cavity to prevent the entry of external humid air.

[0005] However, the aforementioned existing technologies have many obvious shortcomings in practical applications and are difficult to meet the core requirements of "high efficiency, economy, safety, and reliability" in industrial production, as follows: 1. High cost: Whether it is intermittent or continuous nitrogen filling, high-purity nitrogen needs to be consumed continuously or intermittently. For large-scale continuous production, the purchase and storage costs of nitrogen are extremely high. At the same time, the continuous consumption of nitrogen will also lead to high production energy consumption, further increasing production costs.

[0006] 2. Complex system and high failure rate: The nitrogen protection system requires additional nitrogen sources (such as liquid nitrogen storage tanks and nitrogen generators), precision pressure regulating valves, gas filtration devices, dedicated nitrogen pipelines and control components, which significantly increases the initial investment in equipment; and the complex structure of multiple components working together significantly increases the failure rate of the system, and the workload and maintenance costs also increase accordingly.

[0007] 3. Safety hazards exist: Nitrogen is an inert gas, colorless and odorless. If there is a nitrogen leak in the system, it will lead to a decrease in the oxygen concentration in the local space, creating an oxygen-deficient environment, which can easily cause asphyxiation accidents of operators and pose a serious threat to safe production. At the same time, nitrogen leaks will also cause nitrogen waste, further increasing cost losses.

[0008] 4. Limited moisture-proof effect: During continuous nitrogen filling, the flow of nitrogen will inevitably bring in a small amount of external moisture, affecting the moisture-proof effect; during intermittent nitrogen filling mode, the internal pressure of the system fluctuates greatly during nitrogen filling balance and material discharge, which may cause a small amount of humid air to seep in, making it impossible to achieve complete isolation. Summary of the Invention

[0009] This invention addresses the shortcomings of existing technologies by providing a negative pressure maintaining system and method for a moisture-proof vacuum feeder. This system effectively prevents material moisture and ensures product quality, while also offering advantages such as low cost, simple system, safety and reliability, and convenient maintenance.

[0010] To solve the above-mentioned technical problems, the objective of this invention is achieved through the following technical solution: A negative pressure maintaining system for a moisture-proof vacuum feeder includes a feeder cavity, a conveying pipeline, a vacuum power source, a discharging device, and a controller. The conveying pipeline connects the feeder cavity to the inlet end, and the vacuum power source is connected to the feeder cavity to provide negative pressure suction. The system also includes a negative pressure sensor installed in the negative pressure loop formed by the feeder cavity, the conveying pipeline, the vacuum power source, and the discharging device. The negative pressure sensor is used to detect the pressure value in the loop in real time, and the negative pressure sensor is electrically connected to the controller. The controller controls the vacuum power source and executes the following control strategy: During the feeding stage, the vacuum power source operates to draw the pressure in the negative pressure circuit to the preset feeding target negative pressure; During the material feeding device being turned on and the material discharge operation being carried out, the vacuum power source continues to operate to maintain the negative pressure circuit in the first negative pressure state; After the material discharge is completed and the feeding device is turned off, the controller adjusts the operating parameters of the vacuum power source according to the pressure signal fed back by the negative pressure sensor, so as to maintain the pressure in the negative pressure circuit within the preset moisture-proof negative pressure range.

[0011] As a further improvement of the present invention, during the material discharge period, the controller reduces the operating power or speed of the vacuum power source to a preset material discharge maintenance value, so that a dynamic balance is formed between the pumping rate of the vacuum power source and the depressurization rate formed by the opening of the material discharge device, thereby maintaining the first negative pressure state.

[0012] As a further improvement of the present invention, the controller also dynamically adjusts the power or speed of the vacuum power source according to the feedback signal of the negative pressure sensor in the standby state, so that the system pressure is maintained within the moisture-proof negative pressure range.

[0013] As a further improvement of the present invention, the controller continuously receives the pressure signal fed back by the negative pressure sensor in the standby state and dynamically adjusts the operating power or speed of the vacuum power source to compensate for pressure fluctuations caused by micro-leakage in the system and maintain the pressure in the negative pressure circuit within the moisture-proof negative pressure range; preferably, the controller adopts a PID adjustment algorithm.

[0014] As a further improvement of the present invention, it also includes a material level sensor installed in the feeding machine cavity, the material level sensor being electrically connected to the controller for detecting the material height in the feeding machine cavity; the controller determines whether feeding and unloading are completed based on the signal from the material level sensor.

[0015] As a further improvement of the present invention, the controller also compares the pressure value detected by the negative pressure sensor with a preset safety threshold. When the pressure value exceeds the safety threshold, the controller triggers an alarm signal.

[0016] As a further improvement of the present invention, the moisture-proof negative pressure range is a relative pressure value of -15kPa to -25kPa.

[0017] As a further improvement of the present invention, the vacuum power source is a frequency-controlled Roots blower, liquid ring pump or screw vacuum pump; the feeding device is a pneumatic disc valve, rotary valve or gate valve; the negative pressure sensor is installed on the top of the feeding machine cavity or on the main conveying pipeline.

[0018] The present invention also provides a negative pressure maintaining method for the negative pressure maintaining system of the above-mentioned moisture-proof vacuum feeder, comprising the following steps: Step 1, Feeding stage: The controller receives the feeding command, opens the feed valve and starts the vacuum power source to draw the system pressure to the target negative pressure for feeding. The material is sucked into the feeding machine cavity under the action of negative pressure until the material level sensor detects that feeding is complete. Step 2, Material Discharge and Negative Pressure Maintenance Stage: After the material is fed, close the feed valve and start the discharge device to discharge the material; at the same time, the controller reduces the operating power or speed of the vacuum power source to the material discharge maintenance value, so that the system pressure is maintained in the first negative pressure state until the material level sensor detects that the material discharge is complete; Step 3, Moisture-proof negative pressure maintenance stage: After the material is fed, the feeding device is turned off. The controller adjusts the operating parameters of the vacuum power source according to the pressure signal fed back by the negative pressure sensor in real time, so that the system pressure is stabilized in the preset moisture-proof negative pressure range. Step 4, Standby Stage: The system enters standby mode. The controller continuously monitors the pressure signal of the negative pressure sensor and adjusts the vacuum power source to maintain the system pressure within the moisture-proof negative pressure range until the next feeding command is received.

[0019] As a further improvement of the present invention, during the feeding and negative pressure maintenance stage, the power or speed of the vacuum power source is reduced to balance its pumping capacity with the pressure relief rate formed by the opening of the feeding device, so as to maintain the first negative pressure state.

[0020] As a further improvement of the present invention, the negative pressure value of the first negative pressure state is lower than the negative pressure value of the loading target negative pressure, and the negative pressure value of the first negative pressure state falls within the moisture-proof negative pressure range.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a negative pressure maintenance system for a moisture-proof vacuum feeder, replacing nitrogen consumption with negative pressure maintenance, significantly reducing operating costs and simplifying the system structure. This invention completely abandons the traditional approach of relying on high-purity nitrogen for moisture protection, instead utilizing the system's own vacuum power source to maintain a specific negative pressure state throughout the entire process. This change directly eliminates all nitrogen-related facilities such as nitrogen procurement, nitrogen generation equipment, gas storage tanks, pressure regulating valve groups, and dedicated pipelines, significantly reducing initial equipment investment and long-term operating material costs. The system only requires adding a negative pressure sensor and optimizing the control program to the existing vacuum feeder, resulting in a simple structure, fewer components, and fewer potential failure points. Daily maintenance only requires routine maintenance of the vacuum source and sensor.

[0022] 2. This invention achieves reliable moisture protection through full-process negative pressure isolation: Firstly, the system maintains negative pressure in a sealed state, preventing external humid air from entering the cavity via convection. Even if a trace amount of moisture seeps in due to minor sealing defects, the continuous pumping capacity of the vacuum power source far exceeds the seepage rate, ensuring that the seeped moisture is immediately pumped out, keeping the cavity in a constantly renewed, rarefied state. Secondly, due to the reduced absolute pressure, the absolute content of water molecules per unit volume decreases simultaneously, resulting in extremely low water vapor partial pressure in the gaseous environment of the material, far below the equilibrium water vapor partial pressure at the material surface. This thermodynamically suppresses the material's tendency to absorb moisture. Compared to the positive pressure fluctuations caused by nitrogen balance and humidity disturbances caused by gas replacement in traditional nitrogen protection, this invention features a smooth pressure curve throughout the entire process, remaining consistently in a negative pressure zone, resulting in a more stable and reliable moisture protection effect.

[0023] 3. During the standby phase, the system actively locks the pressure inside the cavity in the moisture-proof negative pressure range through closed-loop regulation. When the next feeding command arrives, the cavity is already in a low-humidity negative pressure ready state. Unlike traditional nitrogen filling schemes, there is no need for time-consuming gas replacement or pressure balancing. Feeding can be started directly and the vacuum level can be increased to the feeding target value. The single cycle is significantly shortened, making it especially suitable for continuous, high-frequency production conditions. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the system hardware of the present invention; Figure 2 This is a flowchart (I) of the control method of the present invention; Figure 3 This is a flowchart (II) of the control method of the present invention; Figure 4 This is a flowchart (III) of the control method of the present invention; Figure 5 This is a comparison chart of the pressure-time curves of the working cycle of this invention and the traditional nitrogen protection cycle; Reference numerals in the attached drawings: 1. Feeding machine cavity; 2. Conveying pipeline; 3. Vacuum power source; 4. Discharging device; 5. Controller; 6. Negative pressure sensor; 7. Feed valve; 8. Material level sensor. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. See also: Figure 1-5 : Comparison Appendix Figure 1 The negative pressure maintaining system of this embodiment includes the following components: a feeding machine cavity 1, a conveying pipeline 2, a vacuum power source 3, a discharging device 4, a controller 5, a negative pressure sensor 6, a feed valve 7, and a material level sensor 8. Wherein: The feeding machine chamber 1 is a vertical, sealed stainless steel container with a volume of approximately 500L. It has a feed inlet at the top and a feed valve 7 installed thereon. The feed valve 7 is connected to a distant powder storage silo via a conveying pipeline 2. A negative pressure sensor 6 is also installed at the top of the feeding machine chamber 1 to continuously collect the real-time pressure value of the gas phase space inside the chamber. A capacitive level sensor 8 is installed on the inner side wall of the feeding machine chamber 1 near the preset maximum material level. The discharge port at the bottom of the feeding machine chamber 1 is connected to a discharge device 4. In this embodiment, a pneumatic disc valve is used, which has good airtightness when closed.

[0026] Vacuum power source 3 is a variable frequency driven Roots blower with a rated power of 7.5kW and a frequency adjustment range of 15Hz to 50Hz. The blower's intake port is connected to the top of the feeding machine cavity 1 via a vacuum pipeline, and the exhaust port is open to the atmosphere. Controller 5 uses a PLC (Programmable Logic Controller) and is equipped with a touch-screen human-machine interface. The signal input terminals of controller 5 are connected to the negative pressure sensor 6 and the material level sensor 8, respectively, and the control output terminals are connected to the frequency converter of vacuum power source 3, the drive element of feed valve 7, and the drive element of unloading device 4, respectively. Controller 5 is also connected to an external audible and visual alarm for abnormal indication.

[0027] The above components together form a completely sealed negative pressure circuit except for the feed valve 7 and the discharge valve which are briefly open.

[0028] The key parameters for this embodiment are set as follows: The following operating parameters can be preset in controller 5 via the human-machine interface: Target negative pressure for material feeding: -50 kPa (relative to atmospheric pressure, the same below); Feeding frequency: 20Hz (corresponding to the power reduction operation point of vacuum power source 3 during feeding, the actual measured system pressure is about -20kPa, which is recorded as the first negative pressure state); Moisture-proof negative pressure target range: -15kPa to -25kPa; Safety alarm threshold: -5kPa (i.e., if the system pressure rises above this value, it is judged as a sealing abnormality); Control parameters: PID algorithm is used, with a proportional coefficient of 2.5, integral time of 10s, and derivative time of 2s.

[0029] Comparison Appendix Figure 2 To be continued Figure 4 The workflow of this embodiment is as follows: 1. Material feeding stage The operator triggers the feeding command via the touchscreen. Controller 5 first outputs a start signal to the Roots blower frequency converter, causing the blower to run at full frequency of 50Hz. Gas is rapidly extracted from the feeding chamber 1 and conveying pipeline 2, and the pressure value monitored by the negative pressure sensor 6 drops sharply. When the pressure reaches the preset -50kPa, controller 5 opens the feed valve 7. External powder material is then drawn into the feeding chamber 1 along the conveying pipeline 2 under negative pressure. As material accumulates, once the level sensor 8 detects that the material has reached the set height, controller 5 immediately closes the feed valve 7, ending the feeding phase.

[0030] 2. Material feeding stage – dynamic negative pressure maintenance After feeding is completed, controller 5 first delays briefly to ensure that feed valve 7 is completely closed, and then opens discharge device 4 (pneumatic disc valve), and the material begins to be discharged from the bottom. At the same time, controller 5 lowers the operating frequency of the Roots blower from 50Hz to the preset 20Hz.

[0031] Even with the pressure relief channel open via the discharge valve, the Roots blower does not stop but continues to operate at a low pumping rate. This pumping rate and the venting rate caused by the opening of the discharge valve reach a dynamic balance at a specific frequency, maintaining the system pressure stably at a first negative pressure state of approximately -20 kPa. Once the level sensor 8 detects that material has been discharged, the controller 5 determines that discharging is complete and immediately shuts off the discharge device 4.

[0032] 3. Moisture-proof negative pressure establishment and standby maintenance stage After the feeding device 4 is shut down, the negative pressure circuit returns to a completely sealed state. Since the Roots blower continues to pump air at a frequency of 20Hz, the system pressure will further decrease from -20kPa. The controller 5 reads the pressure value from the negative pressure sensor 6 in real time and uses a PID algorithm to dynamically adjust the blower frequency. When the pressure is below -25 kPa, the fan frequency should be increased appropriately to reduce the pumping intensity. When the pressure is higher than -15 kPa, the fan frequency should be appropriately reduced to enhance the pumping strength.

[0033] Through the aforementioned closed-loop regulation, the system pressure is precisely stabilized within the target range of -15 kPa to -25 kPa, and the system enters a moisture-proof standby state. During standby, even if there are minor, unavoidable seal leaks in the system, the controller 5 continues to perform the aforementioned regulation actions to actively compensate for pressure drift and ensure that the system always maintains a preset negative pressure dry environment.

[0034] 4. Abnormal alarms and protection Throughout the operation, the negative pressure sensor 6 continuously monitors the pressure. If leakage worsens due to aging seals, loose pipes, or other reasons, the system pressure will continue to approach atmospheric pressure. Once the pressure rises above the safety threshold of -5 kPa, the controller 5 immediately triggers an audible and visual alarm, displays a fault code and maintenance prompts on the touchscreen, and records the pressure curve data at the time of the fault for subsequent troubleshooting.

[0035] 5. Start the next cycle When a new feeding instruction is received, since the system is already in a negative pressure drying state of -15kPa to -25kPa, controller 5 does not need to perform any gas replacement steps. It directly increases the frequency of the Roots blower to 50Hz, and opens the feed valve 7 after the pressure drops to -50kPa to start a new round of feeding. This instant-on feature greatly shortens the standby switching time between adjacent batches.

[0036] Comparison Appendix Figure 5 The graph uses a standard coordinate curve format, with the horizontal axis representing time (t) and the vertical axis representing the pressure value of the system relative to atmospheric pressure (kPa), to clearly present the complete change process between the negative pressure zone and the positive pressure zone. The graph contains two pressure change curves, corresponding to the negative pressure maintenance system of this invention and the traditional nitrogen protection process, respectively.

[0037] The pressure change trajectory of the negative pressure maintaining system of the present invention within a complete working cycle is as follows: Initially, the system is at atmospheric pressure (0 kPa). When the feeding command is issued, the vacuum power source 3 starts and operates at full power, and the system pressure rapidly drops to a stable level near the target negative pressure of -50 kPa. During this stage, the feed valve 7 opens, and the material is sucked into the feeding chamber 1. After feeding is completed, the feed valve 7 closes, and the discharge device 4 opens, and the system enters the discharge stage. At this time, the vacuum power source 3 operates at a reduced frequency, and the pumping rate and the pressure relief rate formed by the opening of the discharge device 4 reach a dynamic balance. The system pressure rises back to a first negative pressure state of approximately -20 kPa and maintains a small fluctuation around this value throughout the entire discharge period. After discharge is completed, the discharge device 4 closes, the system returns to a sealed state, and the controller 5 performs closed-loop adjustment based on feedback from the negative pressure sensor 6, further fine-tuning and stabilizing the system pressure within the moisture-proof negative pressure range of -15 kPa to -25 kPa. During the subsequent standby phase, the curve remained within this range and fluctuated smoothly, without any stage of rising back to normal or positive pressure.

[0038] The pressure change trajectory of a traditional nitrogen-protected process within a complete working cycle is as follows: Initially, the system is at atmospheric pressure (0 kPa). After the feeding phase begins, the system pressure drops to the feeding negative pressure (approximately -50 kPa). After feeding is completed, the traditional process requires nitrogen to be introduced into the system to balance the pressure or establish a slightly positive pressure environment. At this time, the system pressure rapidly rises, crossing the 0 kPa line and entering the positive pressure zone, reaching a maximum of approximately 5 kPa in a slightly positive pressure state. During the unloading phase, the system pressure is maintained near this slightly positive pressure. After unloading is completed, as nitrogen supply stops and the system naturally leaks, the pressure slowly drops back to near atmospheric pressure along the curve. The curve shows a clear positive / atmospheric pressure phase in the cycle, which contrasts sharply with the curve corresponding to this invention.

[0039] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A negative pressure maintaining system for a moisture-proof vacuum feeding machine, comprising a feeding machine cavity, a conveying pipeline, a vacuum power source, a discharging device and a controller, the conveying pipeline connecting the feeding machine cavity and a feeding end, and the vacuum power source being in communication with the feeding machine cavity to provide a negative pressure suction force; characterized in that, The system also includes a negative pressure sensor, which is installed in a negative pressure circuit consisting of a feeding machine cavity, a conveying pipeline, a vacuum power source, and a feeding device. The negative pressure sensor is used to detect the pressure value in the circuit in real time. The negative pressure sensor is electrically connected to the controller. The controller controls the vacuum power source and executes the following control strategy: During the feeding stage, the vacuum power source operates to draw the pressure in the negative pressure circuit to the preset feeding target negative pressure; During the material feeding device being turned on and the material discharge operation being carried out, the vacuum power source continues to operate to maintain the negative pressure circuit in the first negative pressure state; After the material discharge is completed and the feeding device is turned off, the controller adjusts the operating parameters of the vacuum power source according to the pressure signal fed back by the negative pressure sensor, so as to maintain the pressure in the negative pressure circuit within the preset moisture-proof negative pressure range.

2. The negative pressure maintaining system for a moisture-proof vacuum feeder according to claim 1, characterized in that, During the material discharge period, the controller reduces the operating power or speed of the vacuum power source to a preset material discharge maintenance value, so that a dynamic balance is formed between the pumping rate of the vacuum power source and the depressurization rate formed by the opening of the material discharge device, thereby maintaining the first negative pressure state.

3. The negative pressure maintaining system for a moisture-proof vacuum feeder according to claim 1, characterized in that, The controller also dynamically adjusts the power or speed of the vacuum power source based on the feedback signal from the negative pressure sensor in standby mode, so that the system pressure is maintained within the moisture-proof negative pressure range.

4. A negative pressure maintaining system for a moisture-proof vacuum feeder according to claim 3, characterized in that, In standby mode, the controller continuously receives pressure signals from the negative pressure sensor and dynamically adjusts the operating power or speed of the vacuum power source to compensate for pressure fluctuations caused by micro-leakage in the system, and maintains the pressure in the negative pressure circuit within the moisture-proof negative pressure range.

5. A negative pressure maintaining system for a moisture-proof vacuum feeder according to claim 1, characterized in that, It also includes a material level sensor installed in the feeding machine cavity. The material level sensor is electrically connected to the controller and is used to detect the material height in the feeding machine cavity. The controller determines whether feeding and unloading are completed based on the signal from the material level sensor.

6. A negative pressure maintaining system for a moisture-proof vacuum feeder according to claim 1, characterized in that, The controller also compares the pressure value detected by the negative pressure sensor with a preset safety threshold. When the pressure value exceeds the safety threshold, the controller triggers an alarm signal.

7. A negative pressure maintaining system for a moisture-proof vacuum feeder according to claim 1, characterized in that, The moisture-proof negative pressure range is a relative pressure value of -15kPa to -25kPa.

8. A method for maintaining negative pressure in the negative pressure maintaining system according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1, Feeding stage: The controller receives the feeding command, opens the feed valve and starts the vacuum power source to draw the system pressure to the target negative pressure for feeding. The material is sucked into the feeding machine cavity under the action of negative pressure until the material level sensor detects that feeding is complete. Step 2, Material Discharge and Negative Pressure Maintenance Stage: After the material is fed, close the feed valve and start the discharge device to discharge the material; at the same time, the controller reduces the operating power or speed of the vacuum power source to the material discharge maintenance value, so that the system pressure is maintained in the first negative pressure state until the material level sensor detects that the material discharge is complete; Step 3, Moisture-proof negative pressure maintenance stage: After the material is fed, the feeding device is turned off. The controller adjusts the operating parameters of the vacuum power source according to the pressure signal fed back by the negative pressure sensor in real time, so that the system pressure is stabilized in the preset moisture-proof negative pressure range. Step 4, Standby Stage: The system enters standby mode. The controller continuously monitors the pressure signal of the negative pressure sensor and adjusts the vacuum power source to maintain the system pressure within the moisture-proof negative pressure range until the next feeding command is received.

9. A negative pressure maintaining method for a negative pressure maintaining system according to claim 8, characterized in that, During the feeding and negative pressure maintenance phase, the power or speed of the vacuum power source is reduced to balance its pumping capacity with the pressure relief rate formed by the opening of the feeding device, so as to maintain the first negative pressure state.

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