Shaft heater steam trap with self-cleaning function and control method thereof

Abstract

The invention discloses a shaft heater steam trap with a self-cleaning function and a control method of the shaft heater steam trap. A filter screen is arranged in a shaft heater steam trap body, a fluid inlet end and a fluid outlet end are arranged, and the shaft heater steam trap further comprises an inlet pipeline, an outlet pipeline, a backwashing pipeline, a drainage pipeline, a bypass pipeline, a monitoring assembly and a valve control assembly; the monitoring assembly is in communication connection with the valve control assembly, when the operation state parameters meet the preset blocking condition, the water conveying path is switched to the bypass pipeline to conduct drainage based on the valve control assembly, and the backwashing process based on the backwashing pipeline and the drainage pipeline is started. By integrating the monitoring assembly and the valve control assembly, the blockage of the steam trap can be automatically identified and switched to bypass operation in a linkage manner, and meanwhile, back flushing is started, so that unmanned and rapid online treatment on the blockage problem of the shaft heater steam trap is realized, and equipment faults and unit operation risks caused by blockage are fundamentally avoided.

Description

Technical Field

[0001] This invention relates to the field of gas turbine technology, and in particular to a shaft steam trap with self-cleaning function and its control method. Background Technology

[0002] The turbine shaft seal heater (hereinafter referred to as "shaft heater") is a key piece of equipment in the turbine system. Its function is to use the heat from the steam returning from the turbine shaft seal to heat the condensate, while the condensate formed by the condensation of the shaft seal steam needs to be recovered to the condenser. In this system, the shaft heater condensate trap serves as a critical filtration device, used to remove solid impurities such as rust from the condensate, preventing them from entering the condenser and ensuring the clean and stable operation of the steam-water circulation system.

[0003] However, existing shaft seal condensate systems have significant drawbacks. First, the shaft seal steam contains numerous impurities. With prolonged unit operation, these impurities accumulate at the condensate filter screen, easily leading to filter blockage. Filter blockage directly hinders condensation, causing the water level inside the shaft seal heater to rise. Excessive water level triggers the shaft seal heater's emergency condensate function, affecting normal unit operation. If the water level rises further to the height of the shaft seal fan, it will cause the fan motor to overload or even burn out. More seriously, if the water level continues to rise to the turbine shaft seal, the steam may carry moisture into the main engine oil system, causing oil emulsification and rendering the lubricating oil ineffective in lubrication and cooling. This ultimately leads to accelerated bearing wear, increased bearing temperature and vibration, potentially triggering unit protection tripping and posing a serious threat to unit safety.

[0004] Secondly, blockage of the steam trap can also cause poor steam discharge from the shaft seal, forcing the steam to be discharged into the condenser, resulting in increased condenser back pressure, reduced unit operating efficiency, and impact on condenser vacuum, thus jeopardizing the unit's economy and safety.

[0005] Currently, to address steam trap blockage, the system has a bypass pipe that can directly discharge the condensate into the ditch. However, the switching operation of this bypass cannot be completed automatically and must be manually performed on-site by operators. This method has significant limitations: on the one hand, it relies on inspection personnel to promptly detect blockage alarms; on the other hand, manual operation cannot be performed immediately when a fault occurs. Therefore, existing technology cannot provide a rapid and automatic response and handling of shaft-mounted steam trap blockage, making it difficult to guarantee the continuous, stable, and safe operation of the unit. Summary of the Invention

[0006] The purpose of this invention is to provide a shaft steam trap with self-cleaning function and its control method. By integrating monitoring components and valve control components, it can automatically identify steam trap blockage and switch to bypass operation in conjunction with the reverse flushing, thereby realizing unmanned and rapid online processing of shaft steam trap blockage problem, fundamentally avoiding equipment failure and unit operation risks caused by blockage.

[0007] To address the aforementioned technical problems, a first aspect of this invention provides a shaft-mounted steam trap with a self-cleaning function, comprising a shaft-mounted steam trap body, wherein a filter screen is disposed within the shaft-mounted steam trap body, and a fluid inlet end and a fluid outlet end are provided, further comprising: An inlet pipe is provided, with its inlet connected to the condensate outlet of the shaft seal heater and its outlet connected to the fluid inlet end of the shaft seal heater body. The outlet pipe has its inlet connected to the fluid outlet end of the shaft-mounted steam trap body, and its outlet is used to connect to the condenser. The backwash pipe has an inlet for connecting to a flushing water source and an outlet for connecting to the fluid outlet end of the shaft-mounted steam trap body. A drainage pipe, the inlet of which is connected to the fluid inlet end of the shaft-mounted drainage pipe body, and the outlet of which is connected to the sewage discharge point; A bypass pipe, the inlet of which is connected to the inlet pipe, and the outlet of which is connected to the sewage discharge point; A monitoring component is used to detect operating status parameters that characterize the clogging state of the filter screen in real time; Valve control assembly, comprising multiple control valves installed on various pipelines; The monitoring component is communicatively connected to the valve control component. When the operating status parameters meet the preset blockage conditions, the valve control component switches the water supply path to the bypass pipeline to facilitate drainage and initiates the backwashing process based on the backwash pipeline and the drainage pipeline.

[0008] Furthermore, the monitoring components include: a shaft-mounted steam trap inlet temperature transmitter and a shaft-mounted steam trap outlet temperature transmitter; The shaft-mounted steam trap inlet temperature transmitter is installed on the inlet pipe to detect the steam trap temperature value at the inlet end of the fluid flowing in. The shaft-mounted condensate outlet temperature transmitter is installed on the outlet pipe to detect the condensate temperature value flowing out from the fluid outlet end.

[0009] Furthermore, the monitoring component also includes a differential pressure transmitter; The differential pressure transmitter is connected to the shaft-mounted condensate drain body to detect the pressure difference between its fluid inlet and fluid outlet ends.

[0010] Furthermore, the monitoring component also includes a differential pressure transmitter; The differential pressure transmitter is mounted on the shaft seal heater to detect the vacuum level of the shaft seal heater.

[0011] Furthermore, the preset blocking condition is any combination of the following conditions: The vacuum level of the shaft seal heater detected by the differential pressure transmitter is less than or equal to a preset pressure value; The pressure difference between the fluid inlet and the fluid outlet detected by the differential pressure transmitter is greater than or equal to a preset differential pressure value; The temperature difference detected by the inlet temperature transmitter and the outlet temperature transmitter of the shaft-mounted steam trap is greater than or equal to a preset temperature difference value.

[0012] Furthermore, the valve control assembly includes a shaft-mounted steam trap inlet valve and a shaft-mounted steam trap outlet valve; The shaft-mounted steam trap inlet valve is installed on the inlet pipe; The outlet valve of the shaft-mounted steam trap is installed on the outlet pipe; During the backwashing process, the inlet valve and outlet valve of the shaft-mounted steam trap are set to the closed state to isolate the fluid communication between the shaft-mounted steam trap body and the inlet and outlet pipes.

[0013] Furthermore, the valve control assembly includes: a shaft-mounted steam trap flushing door and a shaft-mounted steam trap drain door; The shaft-mounted steam trap flushing gate is installed on the backwash pipe to control the flow of the flushing medium during the backwashing process; The drain valve of the shaft-mounted steam trap is installed on the steam duct to control the discharge of sewage during backwashing.

[0014] Furthermore, the valve control assembly also includes a shaft-mounted steam trap bypass valve, which discharges condensate from the inlet pipe when the shaft-mounted steam trap body is blocked or backflushing is performed.

[0015] Accordingly, a second aspect of the present invention provides a method for controlling a shaft-mounted steam trap with a self-cleaning function, which controls the aforementioned shaft-mounted steam trap with a self-cleaning function, including the following steps: The vacuum level, pressure difference between fluid inlet and fluid outlet, and temperature difference of the shaft seal heater are obtained in real time by monitoring components. The vacuum degree, the pressure difference, and the temperature difference are compared with the corresponding thresholds. When at least two operating status parameters meet the preset blockage conditions, a switching and cleaning command is generated. Based on the switching and cleaning commands, the valve control component is controlled to switch the drainage path to bypass operation, so that the drainage is discharged through the bypass pipe. Initiate a backwashing process based on the backwashing pipe and the drainage pipe. After backwashing for a preset duration, control the valve control component to switch the drainage path back to normal operation.

[0016] Furthermore, initiating the backwashing process based on the backwashing pipe and the drain pipe includes: The control valve connected to the backwash pipe is opened to allow the flushing medium to be introduced; The control valve connected to the drainage pipe is opened to discharge the flushing wastewater; The flushing medium is kept flowing into the backwash pipe for the preset duration. After the preset time period is reached, the control valves connected to the backwash pipe and the drainage pipe are closed.

[0017] The above-described technical solutions of the embodiments of the present invention have the following beneficial technical effects: 1. By integrating monitoring components to track key parameters such as differential pressure, temperature difference, and vacuum in real time, the system can automatically diagnose and trigger the cleaning program immediately when blockage occurs. The system then links the valve control components to precisely switch to the bypass to maintain unobstructed drainage and simultaneously initiates reverse flushing of the filter screen. The entire "detection-judgment-switching-cleaning" process is completed automatically, completely solving the response delay problem caused by the reliance on manual on-site operation in traditional methods. This effectively prevents a series of operational accidents that may be caused by untimely handling, such as abnormal shaft water level, fan overload, or even unit tripping.

[0018] 2. The system comprehensively utilizes three criteria: the inlet and outlet differential pressure of the condensate trap body, temperature changes, and the vacuum degree of the shaft seal heater. Only when any two of these parameters exceed the threshold is a blockage confirmed and subsequent operations executed. This multi-dimensional, cross-validated intelligent diagnostic strategy greatly avoids system malfunctions caused by false alarms from a single sensor or signal fluctuations, ensuring that backwashing operations are only initiated when necessary, thereby improving the overall decision-making intelligence and operational reliability of the self-cleaning system.

[0019] 3. By setting up an independent bypass pipeline and linking it with the backwashing process in a programmed manner, the condensate draining task can be seamlessly switched to bypass execution during self-cleaning, ensuring that the condensate draining output of the shaft seal heater is continuous and uninterrupted. This design ensures that maintenance operations do not affect the core functions of the main system at all, promptly cleaning impurities from the filter screen and eliminating the risk of increased shaft seal water level or decreased condenser vacuum due to the drainer being taken out of operation. Thus, while maintaining the overall operational stability of the unit, the equipment itself is maintained efficiently. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the principle of the shaft-mounted steam trap with self-cleaning function provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the shaft-adding hydrophobic operation logic provided in an embodiment of the present invention; Figure 3 This is a flow chart of the shaft-mounted condensate trap control method with self-cleaning function provided in the embodiments of the present invention.

[0021] Figure label: 1. Shaft-mounted steam trap inlet isolation door; 2. Shaft-mounted steam trap inlet temperature transmitter; 3. Shaft-mounted steam trap inlet door; 4. Shaft-mounted steam trap drain door; 5. Shaft-mounted steam trap; 6. Shaft-mounted steam trap inlet and outlet differential pressure transmitter; 7. Shaft-mounted steam trap outlet door; 8. Shaft-mounted steam trap outlet temperature transmitter; 9. Shaft-mounted steam trap flushing door; 10. Shaft-mounted steam trap bypass isolation door; 11. Shaft-mounted steam trap bypass door. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0023] Reference Figure 1 and Figure 2 The first aspect of the present invention provides a shaft-mounted steam trap with self-cleaning function, including a shaft-mounted steam trap body 5, a filter screen is provided inside the shaft-mounted steam trap body 5, and a fluid inlet end and a fluid outlet end are provided. It also includes: a backwash pipe, a drain pipe, a bypass pipe, an inlet pipe, an outlet pipe, a monitoring component and a valve control component.

[0024] Specifically, the inlet pipe connects to the condensate outlet of the shaft seal heater, and its outlet connects to the fluid inlet end of the shaft seal condensate body 5. The outlet pipe connects to the fluid outlet end of the shaft seal condensate body 5, and its outlet connects to the condenser. The backwash pipe connects to the backwash water source, and its outlet connects to the fluid outlet end of the shaft seal condensate body 5. The condensate pipe connects to the fluid inlet end of the shaft seal condensate body 5, and its outlet connects to the drain point. The bypass pipe connects to the inlet pipe, and its outlet connects to the drain point. The monitoring component is used to detect operating status parameters characterizing the filter clogging status in real time. The valve control component includes multiple control valves installed on each pipe.

[0025] The monitoring component is connected to the valve control component. When the operating status parameters meet the preset blockage conditions, the valve control component switches the water delivery path to the bypass pipeline to drain the water and starts the backwashing process based on the backwashing pipeline and the drain pipeline.

[0026] The shaft-mounted steam trap with self-cleaning function provided in this embodiment of the invention involves the coordinated cooperation and systematic integration of multiple key components. The shaft-mounted steam trap body 5 serves as the core filtration unit, containing a metal filter screen to intercept solid particles such as rust and welding slag in the condensate. The body structure clearly distinguishes between the fluid inlet and outlet ends, forming the basic path for the forward flow of the medium. In actual installation, the fluid inlet end is sealed to the inlet pipe via a flange, and the fluid outlet end is similarly connected to the outlet pipe via a flange, ensuring the system's sealing reliability under pressure.

[0027] The inlet pipe is responsible for introducing the condensate generated by the shaft seal heater into the steam trap body. One end of this pipe is fixed to the condensate outlet port of the shaft seal heater via welding or flange connection, while the other end connects to the fluid inlet port of the steam trap body. The pipe material is typically corrosion-resistant carbon steel or stainless steel, and the pipe diameter is determined based on the system's condensate flow rate to ensure that the flow resistance is within acceptable limits. The outlet pipe is used to transport the clean condensate, filtered by the filter screen, to the condenser. The inlet end of this pipe connects to the fluid outlet port of the steam trap body, and the outlet end connects to the corresponding port on the condenser. During normal operation, the condensate flows from the inlet pipe through the filter screen under pressure differential, trapping solid impurities, while the clean condensate enters the condenser through the outlet pipe, completing a closed-loop recycling process.

[0028] The backwash pipe is a key component designed to enable the filter screen's self-cleaning function. Its inlet end connects to the plant's demineralized water main pipe to obtain a stable and clean flushing water source; the outlet end connects to the fluid outlet end of the condensate trap body, i.e., the downstream side of the filter screen. This arrangement creates a reverse flow path opposite to the normal condensate flow direction; when backwashing is performed, high-pressure demineralized water flows backward through this pipe from the back of the filter screen, effectively flushing and removing blockages adhering to the filter screen surface.

[0029] The drainage pipe is specifically designed to guide wastewater containing impurities out of the system during the backwashing phase. The inlet end of this pipe connects to the fluid inlet end of the condensate trap body, upstream of the filter screen; the outlet end connects to the power plant's drainage ditch or wastewater collection system. During backwashing, impurities detached from the filter screen are carried by the flushing water into this pipe and ultimately discharged into the drainage ditch, preventing secondary pollution.

[0030] The bypass pipeline serves as an emergency and maintenance channel. Its inlet is connected to the inlet pipeline via a tee, located between the condensate outlet of the shaft seal heater and the inlet valve of the steam trap; the outlet is directly connected to the sewage discharge point. This pipeline forms a flow path that bypasses the steam trap body. When the steam trap is clogged or backflushing is required, the condensate can be discharged directly into the ditch through this pipeline by switching valves, thus ensuring that the condensate output of the shaft seal heater will not be interrupted even during maintenance, effectively preventing abnormal rises in its water level.

[0031] The monitoring component is a sensing unit responsible for real-time acquisition of operating parameters characterizing the filter clogging status. Specifically, this component includes an inlet temperature transmitter 2 for the shaft seal heater installed on the inlet pipe, an outlet temperature transmitter 8 for the shaft seal heater installed on the outlet pipe, a differential pressure transmitter bridging the fluid inlet and outlet ends of the heater body, and a differential pressure transmitter 6 installed on the shaft seal heater. The temperature transmitters use platinum resistance thermometers, with their protective sleeves directly inserted into the pipeline medium; the differential pressure transmitters are connected to the pressure taps at the fluid inlet and outlet ends via pressure taps; and the differential pressure transmitter 6 is directly installed on the vacuum interface of the shaft seal heater. All transmitters use a 4-20mA standard signal output and are connected to the power plant's distributed control system.

[0032] The valve control assembly is the actuator unit, consisting of multiple shut-off valves installed on various pipelines. An inlet valve 3 (shaft-assisted steam trap inlet valve) is installed on the inlet pipeline, and an outlet valve 7 (shaft-assisted steam trap outlet valve) is installed on the outlet pipeline. Both are gate valves or ball valves driven by electric actuators, used to isolate the steam trap body during backwashing. A flush valve 9 (shaft-assisted steam trap flushing valve) is installed on the backwash pipeline, and a drain valve 4 (shaft-assisted steam trap drain valve) is installed on the drain pipeline. Both are shut-off valves driven by pneumatic actuators, offering fast response and precise control of the backwashing process. A bypass valve 11 (shaft-assisted steam trap bypass valve), an electric gate valve, is installed on the bypass pipeline for controlling the bypass flow. All valve actuators receive switching commands from the control system.

[0033] The system's workflow is managed by preset control logic. When the monitoring component detects that the inlet pipe pressure is below -2 kPa, the differential pressure across the steam trap is above 1 kPa, or the inlet-outlet temperature difference is above 10°C, the control system determines that the filter is clogged if any two of these conditions are met simultaneously. Subsequently, the bypass valve 11 of the steam trap is automatically opened, and the inlet valve 3 and outlet valve of the steam trap are closed, switching the drainage path to the bypass. Next, the flushing valve 9 and drain valve 4 of the steam trap are opened, and demineralized water is injected from the backwash pipe at a specific flow rate. After flushing for 5 minutes, the flushing valve 9 and drain valve are closed, completing the filter cleaning. Finally, the valve status is switched again, the bypass valve 11 is closed, and the inlet and outlet valves are opened, restoring the steam trap to normal operation. If the monitoring parameters do not return to normal after the first flush, the flushing process can be repeated.

[0034] By optimizing pipeline configuration and integrating multi-parameter monitoring and programmed valve control, the system achieves automatic detection of shaft seal condensate blockage, automatic switching of condensate routes, and backwashing of filters. This effectively avoids a series of operational problems caused by poor condensate drainage, such as rising water level in shaft seal heaters, overload of shaft seal fans, and drop in condenser vacuum. This significantly improves the automation level and safety and reliability of the unit operation.

[0035] Furthermore, in the shaft-added hydrophobic system described in this invention, as shown in the attached... Figure 1 As shown, the shaft seal heater inlet isolation gate 1 is installed on the inlet pipe, located between the shaft seal heater drain outlet and the shaft seal heater body. It is driven by an electric actuator and remains open during normal system operation to allow drainage to pass smoothly. When the system enters backwash mode, the gate receives a control signal and closes reliably to achieve physical isolation from the upstream piping system.

[0036] In one specific embodiment of the present invention, the monitoring component includes: a shaft-mounted steam trap inlet temperature transmitter 2 and a shaft-mounted steam trap outlet temperature transmitter 8; the shaft-mounted steam trap inlet temperature transmitter 2 is disposed on the inlet pipe to detect the condensate temperature value at the inlet end of the fluid flowing in; the shaft-mounted steam trap outlet temperature transmitter 8 is disposed on the outlet pipe to detect the condensate temperature value at the outlet end of the fluid flowing out.

[0037] The shaft-mounted steam trap inlet temperature transmitter 2 is vertically inserted into the pipe wall of the inlet pipe through a temperature sensing sleeve with threads or flanges. Its temperature sensing element directly contacts the medium flowing in the center of the pipe to accurately detect the condensate temperature value at the inlet end of the fluid. Correspondingly, the shaft-mounted steam trap outlet temperature transmitter 8 is fixed on the outlet pipe in the same way. Its temperature sensing element extends into the pipe to detect the condensate temperature value flowing out from the outlet end of the fluid.

[0038] Both temperature transmitters can use Pt100 platinum resistance thermometers as sensing elements. These elements are connected to the temperature transmitter module via three-wire or four-wire wiring, converting the resistance signal into a 4-20mA standard current signal output to the DCS control system. During actual installation, the temperature sensing sleeve material is selected from 304 or 316 stainless steel depending on the medium characteristics, and sufficient straight pipe section is reserved at the installation location to ensure measurement accuracy. During system operation, the DCS continuously collects and calculates the measured values ​​from the two temperature transmitters to obtain real-time temperature difference data between the inlet and outlet of the steam trap. When this temperature difference consistently exceeds a preset threshold, it is used in conjunction with other parameters as an important basis for judging filter blockage.

[0039] Through the above implementation method, the temperature changes at the inlet and outlet of the condensate trap can be monitored in real time to accurately detect the decrease in heat exchange efficiency and abnormal flow caused by filter clogging. This provides a reliable temperature parameter basis for automatically judging the clogging status and triggering the cleaning program, thereby enhancing the diagnostic accuracy and response timeliness of the entire self-cleaning system.

[0040] Furthermore, the monitoring component also includes a differential pressure transmitter; the differential pressure transmitter is connected to the shaft-mounted steam trap body 5 to detect the pressure difference between its fluid inlet end and fluid outlet end.

[0041] Furthermore, the monitoring component also includes a differential pressure transmitter. The differential pressure transmitter is connected via two sets of pressure taps to specially designed pressure tapping interfaces at the fluid inlet and outlet ends of the shaft-mounted condensate trap body 5. The high-pressure side tap connects to the pressure tapping point at the fluid inlet, and the low-pressure side tap connects to the pressure tapping point at the fluid outlet. The pressure taps are made of stainless steel, with isolation valves and drain valves installed along the route for maintenance and repair. A U-shaped bend is formed near the transmitter to achieve condensate sealing and prevent steam from directly impacting the sensor. The differential pressure transmitter uses a capacitive or silicon piezoresistive measurement principle, and its diaphragm material is selected from Hastelloy or tantalum metal to ensure corrosion resistance, depending on the characteristics of the medium. During operation, as condensate flows through the filter screen, impurities accumulate on the filter screen surface, gradually increasing the resistance of the fluid passing through the filter screen, resulting in a corresponding increase in the pressure difference between the fluid inlet and outlet ends. The differential pressure transmitter detects this pressure difference in real time and converts it into a 4-20mA standard signal for transmission to the DCS control system. The control system compares the measured differential pressure value with a preset 1kPa threshold. When the differential pressure continues to exceed the threshold and is combined with other monitoring parameters, the system can accurately determine the degree of filter clogging.

[0042] By configuring a differential pressure transmitter to continuously monitor the pressure difference between the inlet and outlet of the condensate drain body, the actual flow status of the filter screen can be directly reflected. This detection method has high sensitivity to filter screen blockage and provides the most direct differential pressure parameter basis for automatically judging the cleaning time. It effectively avoids malfunctions that may be caused by judging based on a single parameter and significantly improves the reliability and accuracy of the entire self-cleaning system.

[0043] Furthermore, the monitoring component also includes a differential pressure transmitter 6; the differential pressure transmitter 6 is mounted on the shaft seal heater to detect the vacuum level of the shaft seal heater.

[0044] The differential pressure transmitter 6 is directly installed on the vacuum interface at the top of the shaft seal heater via flange or threaded connection, with its pressure tap directly connected to the internal steam space of the shaft seal heater. The differential pressure transmitter 6 employs the absolute pressure measurement principle, with a measurement range of -100 kPa to 0 kPa (absolute pressure) and an accuracy class of 0.5, enabling precise detection of the vacuum level inside the shaft seal heater. The transmitter's sensing element uses diffused silicon or ceramic capacitor technology, providing excellent adaptability to vacuum environments. During system operation, when the shaft seal steam trap filter becomes clogged, the steam discharge from the shaft seal is obstructed, leading to an increase in non-condensable gases accumulated inside the shaft seal heater, resulting in increased pressure and a corresponding decrease in vacuum. The differential pressure transmitter 6 monitors this change in real time, transmitting the detected vacuum signal to the DCS control system via a 4-20mA analog signal or PROFIBUS-PA fieldbus. The control system compares this vacuum value with a preset -2 kPa (gauge pressure) threshold. When the vacuum level falls below this threshold and other monitoring conditions are met simultaneously, an anomaly in the steam trap system is confirmed.

[0045] By adding 6 differential pressure transmitters to continuously monitor the vacuum level of the shaft seal heater, the working status of the condensate trap can be indirectly judged from the perspective of the operating status of upstream equipment. This multi-directional monitoring method provides an important auxiliary basis for judging filter blockage, enhances the comprehensiveness and reliability of the entire self-cleaning system diagnosis, and ensures that timely countermeasures can be taken when the condensate trap is blocked, so as to avoid affecting the stable operation of the unit's vacuum system.

[0046] Furthermore, the preset blockage condition is any combination of the following conditions: the vacuum degree of the shaft seal heater detected by the differential pressure transmitter 6 is less than or equal to the preset pressure value; the pressure difference between the fluid inlet end and the fluid outlet end detected by the differential pressure transmitter is greater than or equal to the preset differential pressure value; and the temperature difference detected by the shaft seal condensate inlet temperature transmitter 2 and the shaft seal condensate outlet temperature transmitter 8 is greater than or equal to the preset temperature difference value.

[0047] In practical applications, these three criteria parameters are set as follows: when the vacuum degree of the shaft seal heater is lower than -2 kPa (gauge pressure), or the differential pressure across the condensate drain body is higher than 1 kPa, or the inlet and outlet temperature difference is higher than 10°C, the system enters an early warning state. The control system adopts a "two out of three" logical judgment principle, that is, only when any two of the above three conditions are met simultaneously will the filter blockage be finally confirmed and the automatic cleaning program be triggered. This multi-criteria design fully considers various operating condition fluctuations during unit operation, such as normal fluctuations in vacuum degree or occasional false signals from a single sensor, avoiding system malfunctions caused by abnormalities in a single parameter. In specific implementation, each preset threshold can be modified and set through the DCS operation interface to adapt to the characteristic requirements of different units or different operating stages. At the same time, an appropriate delay judgment function is also set to avoid malfunctions triggered by instantaneous fluctuations.

[0048] By establishing this preset clogging condition based on multi-parameter fusion judgment, the working status of the steam trap can be comprehensively evaluated from three dimensions: vacuum system status, flow resistance characteristics, and heat exchange efficiency. This significantly improves the accuracy and reliability of clogging judgment, ensuring timely activation of protective measures in real clogging situations while effectively preventing malfunctions under normal operating conditions. This gives the entire self-cleaning system a higher level of intelligence and adaptability.

[0049] Furthermore, the valve control assembly includes a shaft-fed steam trap inlet valve 3 and a shaft-fed steam trap outlet valve 7; the shaft-fed steam trap inlet valve 3 is installed on the inlet pipe; the shaft-fed steam trap outlet valve 7 is installed on the outlet pipe; during backwashing, the shaft-fed steam trap inlet valve 3 and shaft-fed steam trap outlet valve 7 are set to the closed state, isolating the fluid communication between the shaft-fed steam trap body 5 and the inlet and outlet pipes.

[0050] The inlet valve 3 of the shaft seal steam trap adopts an electric gate valve structure, vertically installed on the inlet pipe near the fluid inlet end of the shaft seal steam trap body 5 via flange connection. Its valve body is made of cast steel, and the valve stem seal uses graphite packing. The outlet valve 7 of the shaft seal steam trap is also an electric gate valve, fixed to the outlet pipe near the fluid outlet end in the same installation method. Both valves' electric actuators are equipped with local / remote control switching functions. The rated torque is calculated based on the pipe diameter and medium pressure, and valve position limit switches and torque protection devices are provided. During normal operation, both valves remain fully open, allowing the condensate from the shaft seal heater to flow smoothly through the steam trap body to complete the filtration process. When entering backwash mode, the control logic first sends a closing command to the actuators of both valves. The electric actuators drive the valve plates to fall completely, forming a reliable metal-to-metal seal, thereby mechanically isolating the shaft seal steam trap body 5 from the inlet and outlet pipes, creating the necessary isolation conditions for subsequent backwashing operations.

[0051] By configuring these electrically operated isolation valves and precisely controlling their closing state during backwashing, the condensate drain body to be cleaned can be effectively isolated from the operating system. This ensures that the backwash water flow can be concentrated through a dedicated pipeline for efficient cleaning, while preventing wastewater from flowing back into the main pipeline system during the flushing process. At the same time, it ensures that the continuous operation of the main pipeline system is not affected during maintenance, thus achieving safe isolation between cleaning operations and system operation.

[0052] Furthermore, the valve control assembly includes: a shaft-mounted steam trap flushing gate 9 and a shaft-mounted steam trap drain gate 4; the shaft-mounted steam trap flushing gate 9 is installed on the backwashing pipe and controls the flow of the flushing medium during the backwashing process; the shaft-mounted steam trap drain gate 4 is installed on the drainage pipe and controls the discharge of wastewater during the backwashing process.

[0053] The shaft-fed steam trap flushing gate 9 adopts a pneumatic angle gate valve structure, vertically installed at the inlet section of the backwash pipeline via a flange connection, located between the demineralized water header interface and the shaft-fed steam trap body 5. Its valve body is made of 304 stainless steel, with Stellite alloy overlaid on the valve seat sealing surface, and flexible graphite packing used for the valve stem seal. The valve's pneumatic actuator is equipped with a double-acting cylinder and dual solenoid valves, receiving switching signals from the DCS system to operate, with a total stroke time not exceeding 10 seconds. The shaft-fed steam trap drain gate 4 adopts a pneumatic ball valve structure, installed on the vertical section of the drain pipeline via a flange. Its valve body is made of carbon steel, the ball surface is chrome-plated, and the valve seat is made of reinforced PTFE. Its actuator is equipped with a single-acting spring return cylinder to ensure a safe closed position in case of air loss. During normal system operation, both valves remain closed, forming physical isolation. When the backwashing phase begins, the DCS control logic first detects that the inlet valve 3 and outlet valve of the shaft-mounted steam trap are completely closed. Then, it synchronously outputs control signals to open the flushing valve 9 and drain valve of the shaft-mounted steam trap simultaneously. At this time, 0.3-0.5MPa pressurized water supplied by the demineralized water header flows through the backwash pipe into the shaft-mounted steam trap body 5. After backwashing the filter screen, it carries impurities and is discharged into the drain through the drain pipe. Throughout the backwashing process, the DCS monitors the opening and closing signals of the two valves in real time to ensure reliable execution of the flushing process.

[0054] By configuring these pneumatic valves with fast response characteristics and establishing strict interlocking control logic, the start and termination of the backwashing process can be precisely controlled, ensuring that the flushing medium continuously flushes the filter screen for a predetermined time under the set pressure, while ensuring that the wastewater containing impurities is completely discharged from the system. This coordinated control mechanism effectively improves the thoroughness of filter screen cleaning and the degree of automation of system operation.

[0055] Furthermore, the valve control assembly also includes a shaft-assisted steam trap bypass valve 11, which discharges condensate from the inlet pipe when the shaft-assisted steam trap body 5 is blocked or backflushed.

[0056] The bypass valve 11 of the shaft-driven steam trap adopts an electric gate valve structure and is horizontally installed in the middle section of the bypass pipeline via a flange connection. Its valve body is made of cast steel, with hard alloy overlay on the sealing surface, and the valve stem features an anti-blowout design. The electric actuator of the bypass valve 11 is equipped with an integrated controller, capable of receiving 4-20mA analog signals from the DCS system to achieve precise opening control, while also providing torque protection and valve position feedback functions. During normal operation, the bypass valve 11 remains fully closed, at which point all condensate is filtered through the shaft-driven steam trap body 5. When filter blockage is detected or the system enters a backwashing procedure, the bypass valve 11 is first confirmed to be operable, and then an opening command is issued. The actuator drives the gate to the fully open position. At this time, the condensate from the inlet pipeline changes its flow direction under pressure differential, enters the bypass pipeline through the tee port connected to the inlet pipeline, flows through the fully open bypass valve 11, and is directly discharged to the designated discharge point. During this process, the DCS system continuously monitors the opening signal of the bypass door 11 to ensure that it is fully opened to the 100% position, thereby establishing a stable bypass drainage channel.

[0057] Meanwhile, the bypass isolation door 10 of the shaft-assisted steam trap is installed at the inlet of the bypass pipe. It adopts the same type of electric actuator and automatically opens when the steam trap is blocked or backwashing is performed, guiding the condensate from the inlet pipe to the bypass channel and directly discharging it into the ditch. The two achieve safe switching and reliable isolation between the main pipeline and the bypass through programmed linkage control.

[0058] By setting a bypass door 11 for the shaft seal heater and incorporating it into a programmed control system, the drain path can be automatically switched to bypass operation when the drain body becomes clogged or needs maintenance and cleaning. This design ensures that the drain output of the shaft seal heater remains unobstructed, effectively preventing abnormal rise in equipment water level due to poor draining. At the same time, it provides the necessary time window for backwashing operations, ensuring continuous and stable operation of the unit during maintenance.

[0059] Accordingly, refer to Figure 3 The second aspect of the present invention provides a control method for a shaft-mounted steam trap with self-cleaning function, which controls the aforementioned shaft-mounted steam trap with self-cleaning function, including the following steps: Step S100: The vacuum level of the shaft seal heater, the pressure difference between the fluid inlet and the fluid outlet, and the temperature difference are obtained in real time by the monitoring component.

[0060] Key operating parameters are continuously collected through multiple dedicated sensors. Specifically, a differential pressure transmitter 6 installed on the shaft seal heater monitors its internal vacuum level in real time, which directly reflects the smoothness of the steam discharge system; a differential pressure transmitter connected between the fluid inlet and outlet ends of the steam trap continuously detects the pressure loss generated by the fluid before and after passing through the filter screen; and temperature transmitters installed on the inlet and outlet pipes simultaneously measure the inlet and outlet condensate temperatures. These sensors all use a 4-20mA standard signal output, connected to the DCS analog input module via shielded cables, with a sampling period set to 100 milliseconds to ensure data real-time performance and accuracy. The DCS system performs digital filtering on the collected raw data to eliminate field interference and calculates the inlet and outlet temperature difference every second, forming an effective data packet that can be used for logical judgment.

[0061] Step S200: The vacuum degree, pressure difference and temperature difference are compared with the corresponding thresholds. When at least two operating status parameters meet the preset blockage conditions, a switching and cleaning command is generated.

[0062] The system compares real-time collected vacuum, differential pressure, and temperature difference values ​​with preset thresholds: when the vacuum is below -2 kPa (gauge pressure), the differential pressure is above 1 kPa, or the temperature difference exceeds 10°C, the corresponding parameter flag is set. The system employs a "two-out-of-three" voting logic, meaning a valid blockage signal is confirmed only when at least two of the three parameters simultaneously exceed the set threshold. To avoid misjudgments caused by fluctuations in operating conditions, this state must be maintained for at least 10 seconds before the control system generates a formal switching and cleaning command. This judgment logic effectively improves system reliability, ensuring timely response to actual blockage situations while avoiding malfunctions caused by a single abnormal parameter.

[0063] In step S300, based on the switching and cleaning commands, the valve control component is controlled to switch the condensate path to bypass operation, so that the condensate is discharged through the bypass pipe.

[0064] Upon receiving the switching and cleaning commands, the initial status of each valve is first checked to confirm that the inlet and outlet valves of the shaft seal steam trap are in the open position, and the bypass valve 11 is in the closed position. Then, control commands are issued according to a predetermined sequence: first, the bypass valve 11 of the shaft seal steam trap is opened; the electric actuator reaches the fully open position within 5 seconds of receiving the command, and the valve position feedback signal confirms that the opening is complete. Next, the inlet and outlet valves of the shaft seal steam trap are simultaneously closed; these two electric valves complete the closing action within 8 seconds, and their respective limit switches issue closing confirmation signals. This series of operations ensures that during the switching process, the condensate from the inlet pipe can be continuously discharged to the sewage point through the newly established bypass channel, avoiding condensate interruption due to the switching operation, thereby effectively preventing abnormal rises in the water level of the shaft seal heater.

[0065] Step S400: Start the backwashing process based on the backwashing pipe and the drainage pipe. After backwashing for a preset time, control the valve control component to switch the drainage path back to normal operation.

[0066] After confirming that the condensate has been stably discharged through the bypass, simultaneously open the flushing valve 9 and the drain valve of the shaft-mounted steam trap. These two pneumatic valves reach full open within 2 seconds. 0.4MPa pressurized water supplied by the demineralized water header flows through the backwash pipe, entering from the bottom of the steam trap body, penetrating the filter screen in reverse, and carrying away the detached impurities through the condensate pipe into the drainage ditch. The backwashing process lasts 300 seconds, during which the DCS system monitors and maintains the flushing water pressure. After the preset time is reached, sequentially close the flushing valve 9 and the drain valve. After confirming they are fully closed, open the inlet valve 3 and the outlet valve of the shaft-mounted steam trap, and finally close the bypass valve 11. A 3-second buffer time is set between each valve action to ensure a stable transition. After resuming normal operation, continue monitoring all parameters. If the blockage indicators are still not cleared, the cleaning process can be repeated.

[0067] By establishing a complete monitoring, judgment, execution, and recovery mechanism, the automatic identification and handling of the blockage status of the shaft steam trap has been realized. This not only significantly improves maintenance efficiency, but also ensures the consistency and reliability of operation through programmed control, effectively guaranteeing the continuous and stable operation of the unit's related systems.

[0068] Furthermore, the initiation of the backwashing process based on the backwashing pipe and the drain pipe in step S400 includes: Step S410: Open the control valve connected to the backwash pipeline to introduce the flushing medium.

[0069] First, an opening command is sent to the electromagnetic control unit of the shaft-mounted steam trap flushing gate 9. Upon receiving the control signal, the pneumatic actuator drives the cylinder piston rod to complete its full movement within 1.5 seconds, switching the valve from a fully closed to a fully open state. During valve opening, a limit switch continuously monitors the valve stem position. When a fully open signal is detected, this signal is fed back to the DCS system via a digital input module. At this time, flushing medium from the demineralized water header enters the backwash pipeline at a working pressure of 0.4 MPa. The medium flow rate is monitored in real time by an orifice plate flow meter on the pipeline to ensure that the flushing intensity meets design requirements.

[0070] In step S420, the control valve connected to the drainage pipe is opened to discharge the flushing wastewater.

[0071] After confirming that flushing gate 9 is open, an opening command is immediately sent to the drain gate 4 of the shaft-mounted steam trap. The actuator of the pneumatic ball valve adopts a single-acting spring return design. After receiving compressed air power, the ball is driven to complete a 90-degree rotation within 1 second, achieving a fully open state. After the valve opens, a smooth discharge channel is established between the drain pipe and the trench. At this time, the inlet and outlet channels of the backwashing process are fully established, and the flushing medium can flow continuously through the entire cleaning circuit.

[0072] Step S430: Maintain the flushing medium flowing into the backwash pipe for a preset duration.

[0073] After confirming that both the flushing gate 9 and the drain gate are fully open, the DCS system initiates a 300-second timer. During this period, the control system continuously monitors the flushing water pressure and stabilizes it within the range of 0.35-0.45 MPa by adjusting the main pipe outlet regulating valve. Simultaneously, it monitors the flow signal in the drain pipe, indirectly judging the filter cleaning effect through flow rate trends. Throughout the entire flushing process, the control system maintains the status of all valves unchanged to ensure a continuous flow of flushing media.

[0074] Step S440: After the preset time is reached, the control valves connected to the backwash pipe and the drain pipe are closed.

[0075] Once the preset 300-second flushing duration is reached, the control system first sends a closing command to the shaft-mounted steam trap flushing gate 9, cutting off the flushing medium supply. After confirming that flushing gate 9 is completely closed, a 3-second delay is made before sending a closing command to the drain gate. This time delay ensures that any residual sewage in the pipeline is completely discharged. During the closing process of both valves, their closing feedback signals are received in real time. Only after confirming that both valves are completely closed is the backwashing process officially considered complete.

[0076] By precisely controlling the backwashing process, the washing intensity and time are ensured to meet technical requirements, while a strict interlocking protection mechanism prevents misoperation. At the same time, a comprehensive status monitoring system ensures the reliability of the process, thus effectively guaranteeing the cleaning effect of the filter screen.

[0077] The embodiments of the present invention aim to protect a shaft-mounted steam trap with self-cleaning function and its control method, which has the following effects: 1. By integrating monitoring components to track key parameters such as differential pressure, temperature difference, and vacuum in real time, it can automatically diagnose and trigger the cleaning program immediately when blockage occurs; then it will link the valve control components to precisely switch to the bypass to maintain unobstructed drainage, and simultaneously start the reverse flushing of the filter screen. The entire "detection-judgment-switching-cleaning" process is completed automatically, which completely solves the response delay problem caused by the reliance on manual on-site operation in the traditional method, and effectively prevents a series of operational accidents such as abnormal shaft water level, fan overload, and even unit tripping that may be caused by untimely handling.

[0078] 2. The system comprehensively utilizes three criteria: the inlet and outlet differential pressure of the condensate trap body, temperature changes, and the vacuum degree of the shaft seal heater. Only when any two of these parameters exceed the threshold is a blockage confirmed and subsequent operations executed. This multi-dimensional, cross-validated intelligent diagnostic strategy greatly avoids system malfunctions caused by false alarms from a single sensor or signal fluctuations, ensuring that backwashing operations are only initiated when necessary, thereby improving the overall decision-making intelligence and operational reliability of the self-cleaning system.

[0079] 3. By setting up an independent bypass pipeline and linking it with the backwashing process in a programmed manner, the condensate draining task can be seamlessly switched to bypass execution during self-cleaning, ensuring that the condensate draining output of the shaft seal heater is continuous and uninterrupted. This design ensures that maintenance operations do not affect the core functions of the main system at all, promptly cleaning impurities from the filter screen and eliminating the risk of increased shaft seal water level or decreased condenser vacuum due to the drainer being taken out of operation. Thus, while maintaining the overall operational stability of the unit, the equipment itself is maintained efficiently.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A shaft trap with self-cleaning function, comprising a shaft trap body (5), a filter screen is arranged in the shaft trap body (5), and a fluid inlet end and a fluid outlet end are arranged, characterized in that, Also comprising: an inlet pipe, the inlet of which is connected to the drain outlet of the shaft seal heater, and the outlet of which is connected to the fluid inlet end of the shaft drain body (5); an outlet pipe, the inlet of which is connected to the fluid outlet end of the shaft drain body (5), and the outlet of which is connected to the condenser; a backwash pipe, the inlet of which is connected to a source of flushing water, and the outlet of which is connected to the fluid outlet end of the shaft drain body (5); a drain pipe, the inlet of which is connected to the fluid inlet end of the shaft drain body (5), and the outlet of which is connected to a drain point; a bypass pipe, the inlet of which is connected to the inlet pipe, and the outlet of which is connected to the drain point; a monitoring assembly for detecting in real time an operating state parameter representing the clogging state of the filter screen; a valve control assembly comprising a plurality of control valves arranged on the pipes; wherein the monitoring assembly is communicatively connected to the valve control assembly, and when the operating state parameter meets a preset clogging condition, the valve control assembly switches the water supply path to the bypass pipe to drain water, and initiates a backwashing process based on the backwash pipe and the drain pipe.

2. The shaft with a self-cleaning function according to claim 1, wherein The monitoring assembly comprises a shaft drain inlet temperature transmitter (2) and a shaft drain outlet temperature transmitter (8); The shaft drain inlet temperature transmitter (2) is arranged on the inlet pipe and detects the temperature of the water flowing into the fluid inlet end; The shaft drain outlet temperature transmitter (8) is arranged on the outlet pipe and detects the temperature of the water flowing out of the fluid outlet end.

3. The shaft with a self-cleaning function according to claim 2, wherein, The monitoring assembly further comprises a differential pressure transmitter; The differential pressure transmitter is connected to the shaft drain body (5) and detects the pressure difference between the fluid inlet end and the fluid outlet end.

4. The shaft with a self-cleaning function according to claim 3, wherein The monitoring assembly further comprises a differential pressure transmitter (6); The differential pressure transmitter (6) is arranged on the shaft seal heater and detects the vacuum degree of the shaft seal heater.

5. The shaft with a self-cleaning function according to claim 4, wherein The preset clogging condition is any combination of the following conditions: The vacuum degree of the shaft seal heater detected by the differential pressure transmitter (6) is less than or equal to a preset pressure value; The pressure difference between the fluid inlet end and the fluid outlet end detected by the differential pressure transmitter is greater than or equal to a preset differential pressure value; The temperature difference detected by the shaft drain inlet temperature transmitter (2) and the shaft drain outlet temperature transmitter (8) is greater than or equal to a preset temperature difference value.

6. The shaft with self-cleaning function according to any one of claims 1-5, characterized in that, The valve control assembly comprises a shaft drain inlet valve (3) and a shaft drain outlet valve (7); The shaft drain inlet valve (3) is arranged on the inlet pipe; The shaft drain outlet valve (7) is arranged on the outlet pipe; During the backwashing process, the shaft drain inlet valve (3) and the shaft drain outlet valve (7) are set to a closed state to isolate the fluid communication between the shaft drain body (5) and the inlet pipe and the outlet pipe.

7. The shaft with a self-cleaning function according to claim 6, wherein The valve control assembly comprises a shaft drain flushing valve (9) and a shaft drain drain valve (4); The shaft drain flushing valve (9) is arranged on the backwash pipe and controls the on-off of the flushing medium during the backwashing process; The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing.

8. The shaft with a self-cleaning function according to claim 7, wherein, The valve control assembly further comprises a shaft trap bypass door (11) which discharges the trap from the inlet pipeline when the shaft trap body (5) is blocked or backwashing.

9. A control method of a steam trap-equipped shaft with a self-cleaning function, characterized by, The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing.

10. The method of claim 9, wherein the control method is characterized by, The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (4) is arranged on the trap pipeline and controls the discharge of sewage during backwashing. The shaft trap blowdown door (

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