Method for preventing shutdown material leakage caused by internal leakage of oil pressure of hydraulic cylinder

Abstract

The invention discloses a method for preventing shutdown and material leakage caused by internal leakage of oil pressure of a hydraulic cylinder, which comprises the following steps of: (1) firstly, additionally arranging a protection position limit switch I at a position in front of a position where a hydraulic push rod normally extends out in place, and connecting a signal line of the protection position limit switch I to a PLC (Programmable Logic Controller) control system; opening protection of the hydraulic push rod is carried out through a protection position limiting switch I; (2) a protection position limiting switch II is additionally arranged at the position in front of the position where the hydraulic push rod normally retracts in place, a signal line of the protection position limiting switch II is connected to the PLC control system, and then the protection position limiting switch II is used for conducting off-position protection on the hydraulic push rod; and (3) the position of the hydraulic push rod is judged in a logic judgment mode, and alarming and resetting are conducted in time when the oil pressure is internally released. Under the condition that an original system is not greatly changed, the problem of shutdown and material leakage caused by internal leakage of the oil cylinder is effectively avoided in a most economical and rapid mode.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, and in particular to a method for preventing machine shutdown and material leakage caused by internal leakage of hydraulic cylinder oil pressure. Background Art

[0002] Hydraulic push rods are widely used in industrial sites. They are suitable for linear (or reciprocating rotation at a certain angle) motions that require reciprocating push and pull, and can also be used to control the opening and closing of hopper valves; hopper valves can be divided into straight-through valves (used to control the switch of stored materials) and three-way valves (used to control the falling direction of flowing materials). Hydraulic push rods are composed of a hydraulic cylinder and a push rod. There is a piston inside the hydraulic cylinder. When hydraulic oil enters the hydraulic cylinder through the oil inlet of the hydraulic cylinder, the piston will move outward due to the pressure of the oil; the piston and the seal in the hydraulic cylinder are tightly matched, so that the hydraulic oil cannot leak from between the piston and the hydraulic cylinder, thereby ensuring the working effect of the system.

[0003] At present, our coal yard has five main material receiving processes, namely, receiving coal and coke by rail transport line, receiving coal and coke by car, and receiving coal by wharf. In addition, there are five coal supply processes, namely, direct supply process of self-produced coke (coke discharged from dry quenching is directly transported to blast furnace for use), process of supplying blast furnace by silo, process of putting self-produced coke into coke silo, process of supplying coal for blast furnace pulverization and process of supplying coal for coke oven blending. In addition, there are more than twenty auxiliary processes of various sizes.

[0004] In order to meet the functions of each process, a large number of flaps and straight-through valves are set up on site to change the direction of the drop point at the tail end of the belt to meet the material flow direction of the process, thereby completing the switching between the processes; among them, the direction of the drop point at the tail end of the belt is controlled by a hydraulic push rod, and all coal yard processes are controlled in a fully automatic intelligent manner. You only need to select the starting and end points of the material, and the system can automatically open the corresponding belt in sequence and automatically control the valve flap. It can be seen that the valve flap signal plays a very important role, which can indicate the direction of the belt material flow and allow the program to judge the correctness of the process.

[0005] Due to the frequent movement of the hydraulic push rod, the sealing effect of the seal inside the hydraulic cylinder is easily reduced over time, resulting in internal leakage of oil pressure, and the piston will slowly retract, causing the valve to open a gap and then cause the position signal to be lost. If the program does not receive the position signal, it will be judged that the condition is not met, and the process will be stopped to cause a production accident; if no one finds it for a long time, the oil cylinder will continue to release pressure, which will cause the valve to slowly open and cause leakage, thereby causing environmental pollution and increasing labor costs; in addition, because the valve signal participates in the process control, if the valve switch is in place signal is lost for a long time, it will cause the system to interlock and shut down. Therefore, the above problems need to be solved urgently. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preventing shutdown and leakage caused by internal leakage of hydraulic cylinder oil pressure, which effectively avoids the shutdown and leakage caused by internal leakage of hydraulic cylinder in the most economical and fast way without making major changes to the original system.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for preventing material leakage caused by hydraulic cylinder oil pressure leakage includes a PLC control system, an extension position limit switch for monitoring the extension of the hydraulic push rod, and a retraction position limit switch for monitoring the retraction of the hydraulic push rod; the innovation point is that it also includes the following steps: (1) First, a protection position limit switch I is installed in front of the normal extended position of the hydraulic push rod, and the signal line of the protection position limit switch I is connected to the PLC control system, and then the opening position protection of the hydraulic push rod is performed through the protection position limit switch I; (2) Then, a protection position limit switch II is installed in front of the normal retracted position of the hydraulic push rod, and the signal line of the protection position limit switch II is connected to the PLC control system, and then the closed position protection of the hydraulic push rod is performed through the protection position limit switch II; (3) The position of the hydraulic push rod is determined through logical judgment, and an alarm is promptly reset when oil pressure leaks.

[0008] Preferably, in the above step (1), the protection position limit switch I is installed 2 cm before the normal extended position of the hydraulic push rod.

[0009] Preferably, in the above step (2), the protection position limit switch II is installed 2 cm before the normal retracted position of the hydraulic push rod.

[0010] Preferably, in the above step (3), a binary point method is adopted, and 1 is set to represent that the extension position limit switch, the retracted position limit switch, the protection position limit switch I and the protection position limit switch II receive a signal, and 0 is set to represent that the extension position limit switch, the retracted position limit switch, the protection position limit switch I and the protection position limit switch II lose the signal.

[0011] Preferably, in the above step (3), assuming that the initial state of the hydraulic push rod is the retracted state, at this time the signal of the retracted position limit switch is 1, then the position logic determination of the hydraulic push rod is specifically: (3.1.1) When there is no need to perform the valve opening action, if the signal of the retracting position limit switch changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the retracting action until the signal of the retracting position limit switch changes from 0 to 1; (3.1.2) When the valve opening action needs to be executed, the hydraulic push rod extends at a constant speed, the signal of the retracting position limit switch changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, then the hydraulic push rod is judged to be in the operating state, and the protection action is not executed; If the signal of the protection position limit switch II does not change to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs a retraction action until the signal of the retraction position limit switch changes from 0 to 1; after the hydraulic push rod retraction action command is issued, if the signal of the retraction position limit switch still does not change to 1 after 10s, a valve closing timeout alarm is issued, and the action is stopped and wait for subsequent disposal; (3.1.3) When it is determined that the hydraulic push rod is still in the operating state, the hydraulic push rod continues to perform the extension action, the signal of the protection position limit switch II changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, followed by the signal of the protection position limit switch I changes from 1 to 0, and the signal of the extension position limit switch changes from 0 to 1, then it is determined that the valve opening action is completed, and the extension action of the hydraulic push rod is stopped.

[0012] Preferably, in the above step (3.1.1), after the hydraulic push rod retract action command is issued, if the signal of the retracted position limit switch has not changed to 1 after 10 seconds, a valve closing timeout alarm is issued, and the action is stopped to wait for subsequent processing.

[0013] Preferably, in the above step (3.1.3), if the signal of the extension position limit switch has not changed to 1 after 30 seconds, a valve opening timeout alarm is issued, and the action is stopped and waits for subsequent processing.

[0014] Preferably, in the above step (3), assuming that the initial state of the hydraulic push rod is the extended state, at this time the signal of the extended position limit switch is 1, then the position logic determination of the hydraulic push rod is specifically: (3.2.1) When there is no need to execute the valve closing action, if the signal of the extension position limit switch changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the extension action until the signal of the extension position limit switch changes from 0 to 1; (3.2.2) When the valve closing action needs to be executed, the hydraulic push rod retracts at a uniform speed, the signal of the extension position limit switch changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, then the hydraulic push rod is judged to be in the operating state, and the protection action is not executed; If the signal of the protection position limit switch I does not change to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the extension action until the signal of the extension position limit switch changes from 0 to 1; after the hydraulic push rod extension action command is issued, if the signal of the extension position limit switch still does not change to 1 after 10s, a valve opening timeout alarm is issued, and the action is stopped and wait for subsequent disposal; (3.2.3) When it is determined that the hydraulic push rod is still in the operating state, the hydraulic push rod continues to retract, the signal of the protection position limit switch I changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, followed by the signal of the protection position limit switch II changes from 1 to 0, and the signal of the retraction position limit switch changes from 0 to 1, then it is determined that the valve closing action is completed, and the retraction action of the hydraulic push rod is stopped.

[0015] Preferably, in the above step (3.2.1), when the hydraulic push rod extension action command is issued, if the signal of the extension position limit switch has not changed to 1 after 10 seconds, a valve opening timeout alarm is issued, and the action is stopped to wait for subsequent processing.

[0016] Preferably, in the above step (3.2.3), if the signal of the retracted position limit switch has not changed to 1 after 30 seconds, a valve closing timeout alarm is issued, and the action is stopped and waits for subsequent processing.

[0017] Beneficial effects of the present invention: (1) The present invention effectively avoids the problem of shutdown and material leakage caused by oil cylinder leakage in the most economical and fast way without making major changes to the original system; (2) The present invention can monitor the position of the hydraulic push rod in real time, and when the hydraulic pressure leaks and causes the position of the hydraulic push rod to change, it will immediately alarm and automatically control the valve to move to the original position, thereby avoiding leakage; (3) The present invention avoids replacing all hydraulic cylinders with hydraulic cylinders equipped with 4-20mA analog position sensors, thereby saving costs and avoiding major changes to the original system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is a logic diagram when the initial state of the hydraulic push rod of the present invention is a retracted state.

[0020] Figure 2 This is a logic diagram when the initial state of the hydraulic push rod of the present invention is the extended state. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be clearly and completely described below through specific implementation methods.

[0022] A method for preventing material leakage caused by hydraulic cylinder oil pressure leakage includes a PLC control system, an extension position limit switch for monitoring the extension of a hydraulic push rod, and a retraction position limit switch for monitoring the retraction of the hydraulic push rod; Figure 1 , Figure 2 As shown, the following steps are included: (1) First, a protective position limit switch I is installed 2 cm before the normal extended position of the hydraulic push rod, and the signal line of the protective position limit switch I is connected to the PLC control system, and then the open position protection of the hydraulic push rod is performed through the protective position limit switch I.

[0023] (2) Then, a protection position limit switch II is installed 2 cm before the hydraulic push rod normally retracts to its initial position, and the signal line of the protection position limit switch II is connected to the PLC control system, thereby performing closed position protection of the hydraulic push rod through the protection position limit switch II.

[0024] (3) The position of the hydraulic push rod is determined through logical judgment, and an alarm is promptly reset when oil pressure leaks.

[0025] In the above steps, the binary point method is used, and 1 is set to represent that the extension limit switch, retraction limit switch, protection limit switch I and protection limit switch II receive the signal, and 0 is set to represent that the extension limit switch, retraction limit switch, protection limit switch I and protection limit switch II lose the signal.

[0026] The present invention assumes that the initial state of the hydraulic push rod is the retracted state, and the signal of the retracted limit switch is 1. Figure 1 As shown in the figure, the logic determination of the position of the hydraulic push rod is as follows: (3.1.1) When there is no need to perform the valve opening action, if the signal of the retracting position limit switch changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the retracting action until the signal of the retracting position limit switch changes from 0 to 1; In the above steps, when the hydraulic push rod retraction action command is issued, if the signal of the retraction limit switch has not changed to 1 after 10 seconds, a valve closing timeout alarm is issued, and the action is stopped waiting for subsequent processing.

[0027] (3.1.2) When the valve opening action needs to be executed, the hydraulic push rod extends at a constant speed, the signal of the retracting position limit switch changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, then the hydraulic push rod is judged to be in the operating state, and the protection action is not executed; If the signal of the protection position limit switch II does not change to 1, the hydraulic push rod is judged to be abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically retracts until the signal of the retraction position limit switch changes from 0 to 1; after the hydraulic push rod retraction action command is issued, if the signal of the retraction position limit switch still does not change to 1 after 10s, a valve closing timeout alarm is issued, and the action is stopped waiting for subsequent disposal.

[0028] (3.1.3) When it is determined that the hydraulic push rod is still in the operating state, the hydraulic push rod continues to perform the extension action, the signal of the protection position limit switch II changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, followed by the signal of the protection position limit switch I changes from 1 to 0, and the signal of the extension position limit switch changes from 0 to 1, then it is determined that the valve opening action is completed, and the extension action of the hydraulic push rod is stopped; In the above steps, if the signal of the extension position limit switch has not changed to 1 after 30 seconds, a valve opening timeout alarm is issued, and the action is stopped and wait for subsequent treatment. The valve opening time of the present invention is set to 30 seconds. If the signal of the extension position limit switch has not changed to 1 after 30 seconds of the hydraulic push rod extension action signal, an alarm is issued to prompt the valve opening timeout.

[0029] The present invention assumes that the initial state of the hydraulic push rod is the extended state, and the signal of the extended position limit switch is 1. Figure 2 As shown in the figure, the logic determination of the position of the hydraulic push rod is as follows: (3.2.1) When there is no need to execute the valve closing action, if the signal of the extension position limit switch changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the extension action until the signal of the extension position limit switch changes from 0 to 1; In the above steps, when the hydraulic push rod extension action command is issued, if the signal of the extension position limit switch has not changed to 1 after 10 seconds, a valve opening timeout alarm is issued, and the action is stopped and wait for subsequent processing.

[0030] (3.2.2) When the valve closing action needs to be executed, the hydraulic push rod retracts at a uniform speed, the signal of the extension position limit switch changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, then the hydraulic push rod is judged to be in the operating state, and the protection action is not executed; If the signal of the protection position limit switch I does not change to 1, the hydraulic push rod is judged to be abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the extension action until the signal of the extension position limit switch changes from 0 to 1; after the hydraulic push rod extension action command is issued, if the signal of the extension position limit switch still does not change to 1 after 10s, a valve opening timeout alarm is issued, and the action is stopped waiting for subsequent disposal.

[0031] (3.2.3) When it is determined that the hydraulic push rod is still in the operating state, the hydraulic push rod continues to retract, the signal of the protection position limit switch I changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, followed by the signal of the protection position limit switch II changes from 1 to 0, and the signal of the retraction position limit switch changes from 0 to 1, then it is determined that the valve closing action is completed, and the retraction action of the hydraulic push rod is stopped.

[0032] In the above steps, if the signal of the retracted position limit switch has not changed to 1 after 30 seconds, a valve closing timeout alarm is issued, and the action is stopped and wait for subsequent disposal. The valve closing time of the present invention is set to 30 seconds. If the signal of the retracted position limit switch has not changed to 1 after 30 seconds of the hydraulic push rod retracting action signal, an alarm is issued to prompt the valve closing timeout.

[0033] Beneficial effects of the present invention: (1) The present invention effectively avoids the problem of shutdown and material leakage caused by oil cylinder leakage in the most economical and fast way without making major changes to the original system; (2) The present invention can monitor the position of the hydraulic push rod in real time, and when the hydraulic pressure leaks and causes the position of the hydraulic push rod to change, it will immediately alarm and automatically control the valve to move to the original position, thereby avoiding leakage; (3) The present invention avoids replacing all hydraulic cylinders with hydraulic cylinders equipped with 4-20mA analog position sensors, thereby saving costs and avoiding major changes to the original system.

[0034] The embodiments described above are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary engineering technicians in the field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have been fully recorded in the technical requirements.

Claims

1. A method for preventing material leakage caused by hydraulic cylinder oil pressure leakage, comprising a PLC control system, an extension position limit switch for monitoring the extension of a hydraulic push rod, and a retraction position limit switch for monitoring the retraction of the hydraulic push rod; characterized in that The following steps are also included: (1) First, a protection position limit switch I is installed in front of the normal extended position of the hydraulic push rod, and the signal line of the protection position limit switch I is connected to the PLC control system, and then the opening position protection of the hydraulic push rod is performed through the protection position limit switch I; (2) Then, a protection position limit switch II is installed in front of the normal retracted position of the hydraulic push rod, and the signal line of the protection position limit switch II is connected to the PLC control system, and then the closed position protection of the hydraulic push rod is performed through the protection position limit switch II; (3) The position of the hydraulic push rod is determined through logical judgment, and an alarm is promptly reset when oil pressure leaks.

2. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as described in claim 1, characterized in that: In the above step (1), the protection position limit switch I is installed 2 cm before the normal extended position of the hydraulic push rod.

3. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 1, characterized in that: In the above step (2), the protection position limit switch II is installed 2 cm before the normal retracted position of the hydraulic push rod.

4. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 1, characterized in that: In the above step (3), a binary point method is used, and 1 is set to represent that the extension position limit switch, the retraction position limit switch, the protection position limit switch I and the protection position limit switch II receive a signal, and 0 is set to represent that the extension position limit switch, the retraction position limit switch, the protection position limit switch I and the protection position limit switch II lose a signal.

5. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 4, characterized in that: In the above step (3), assuming that the initial state of the hydraulic push rod is the retracted state, at this time the signal of the retracted limit switch is 1, then the position logic determination of the hydraulic push rod is specifically: (3.1.1) When there is no need to perform the valve opening action, if the signal of the retracting position limit switch changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the retracting action until the signal of the retracting position limit switch changes from 0 to 1; (3.1.2) When the valve opening action needs to be executed, the hydraulic push rod extends at a constant speed, the signal of the retracting position limit switch changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, then the hydraulic push rod is judged to be in the operating state, and the protection action is not executed; If the signal of the protection position limit switch II does not change to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs a retraction action until the signal of the retraction position limit switch changes from 0 to 1; after the hydraulic push rod retraction action command is issued, if the signal of the retraction position limit switch still does not change to 1 after 10s, a valve closing timeout alarm is issued, and the action is stopped and wait for subsequent disposal; (3.1.3) When it is determined that the hydraulic push rod is still in the operating state, the hydraulic push rod continues to perform the extension action, the signal of the protection position limit switch II changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, followed by the signal of the protection position limit switch I changes from 1 to 0, and the signal of the extension position limit switch changes from 0 to 1, then it is determined that the valve opening action is completed, and the extension action of the hydraulic push rod is stopped.

6. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 5, characterized in that: In the above step (3.1.1), when the hydraulic push rod retract action command is issued, if the signal of the retracted position limit switch has not changed to 1 after 10 seconds, a valve closing timeout alarm will be issued, and the action will be stopped waiting for subsequent processing.

7. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 5, characterized in that: In the above step (3.1.3), if the signal of the extension position limit switch has not changed to 1 after 30 seconds, a valve opening timeout alarm will be issued and the action will be stopped waiting for subsequent processing.

8. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 4, characterized in that: In the above step (3), assuming that the initial state of the hydraulic push rod is the extended state, at this time the signal of the extended position limit switch is 1, then the position logic determination of the hydraulic push rod is specifically: (3.2.1) When there is no need to execute the valve closing action, if the signal of the extension position limit switch changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the extension action until the signal of the extension position limit switch changes from 0 to 1; (3.2.2) When the valve closing action needs to be executed, the hydraulic push rod retracts at a uniform speed, the signal of the extension position limit switch changes from 1 to 0, and then the signal of the protection position limit switch I changes from 0 to 1, then the hydraulic push rod is judged to be in the operating state, and the protection action is not executed; If the signal of the protection position limit switch I does not change to 1, it is determined that the hydraulic push rod is abnormal and an internal leakage alarm is issued; at this time, the PLC control system issues a closing command, and the hydraulic push rod automatically performs the extension action until the signal of the extension position limit switch changes from 0 to 1; after the hydraulic push rod extension action command is issued, if the signal of the extension position limit switch still does not change to 1 after 10s, a valve opening timeout alarm is issued, and the action is stopped and wait for subsequent disposal; (3.2.3) When it is determined that the hydraulic push rod is still in the operating state, the hydraulic push rod continues to retract, the signal of the protection position limit switch I changes from 1 to 0, and then the signal of the protection position limit switch II changes from 0 to 1, followed by the signal of the protection position limit switch II changes from 1 to 0, and the signal of the retraction position limit switch changes from 0 to 1, then it is determined that the valve closing action is completed, and the retraction action of the hydraulic push rod is stopped.

9. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 8, characterized in that: In the above step (3.2.1), when the hydraulic push rod extension action command is issued, if the signal of the extension position limit switch has not changed to 1 after 10 seconds, a valve opening timeout alarm will be issued, and the action will be stopped and wait for subsequent processing.

10. A method for preventing material leakage due to hydraulic cylinder oil pressure leakage as claimed in claim 8, characterized in that: In the above step (3.2.3), if the signal of the retracted limit switch has not changed to 1 after 30 seconds, a valve closing timeout alarm will be issued and the action will be stopped waiting for subsequent processing.

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