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Introduction of the commissioning of pneumatic control valve in the production process

1. The regulating valve is used in conjunction with other instruments in the modern factory. It can realize the automatic adjustment and remote control functions of process parameters such as flow, liquid level, pressure, temperature and other media such as liquid, gas and steam during the production process. . ... 1. The regulating valve is used in conjunction with other instruments in the modern factory. It can realize the automatic adjustment of process parameters such as flow, liquid level, pressure, temperature and other media such as liquid, gas and steam during the production process. Remote control function. Among them, the pneumatic diaphragm regulating valve is the final implementation of the automatic regulating system. The regulating valve is used in the modern factory. The pneumatic regulating valve is used with other instruments to realize the process parameters such as flow, liquid level, pressure and temperature during the production process. Automatic adjustment and remote control of liquids, gases, steam, etc. Among them, the pneumatic diaphragm regulating valve plays an important role as the final actuator of the automatic regulating system. The application of the regulating valve is directly related to the quality and safety of production. Second, the common fault of the regulating valve, the cause analysis and solution (1) the regulating valve does not work. Cause: There is no signal pressure or diaphragm cracking, the diaphragm leaks, the diaphragm thrust is reduced; the valve core is stuck with the valve seat or bushing, the valve stem is bent, etc., and the regulating valve cannot be operated. Solution: Connect the signal cable and air supply connector firmly or replace the diaphragm; straighten the valve stem or replace the valve stem. (2) The regulating valve works normally, but it does not adjust. Cause: The spool is loose or the pipe is blocked. Solution: The spool is disconnected from the valve stem and the valve stem is firmly connected. The piping department is in contact with the competent department to clear the pipeline. (3) The regulating valve is slow or beating. Reason: The aging or dryness of the sealing packing increases the friction between the valve stem and the packing; the valve body contains viscous dirt and clogging, coking, etc.; the diaphragm and the "O"-shaped sealing ring leak. Solution: Replace the sealing packing, re-adjust; remove dirt, coke, etc.; fasten the film head, or replace the diaphragm, O-ring. (4) The regulating valve is unstable or oscillates. Cause: The adjustment valve diameter is too large; the single seat valve medium flows in the same direction as the closing direction. The spool and guide sleeve are heavily worn. Solution: Replace the valve with the proper valve diameter; adjust the valve direction; improve the joint surface (grinding) or replace the valve core and guide sleeve. Third, the typical failure repair program of the regulating valve The "regulation valve works normally, but can not adjust the role" failure as an example to illustrate the maintenance program: a chemical plant vinyl chloride workshop, the use of valves for the single-seat control valve of Sichuan Instrument No. 11 plant. The production line has an annual output of 100,000 tons of plastic pellets. There are two production lines in the compression, conversion and fractionation sections of the vinyl chloride workshop. In addition to compression, the conversion and fractionation sections use a large number of regulating valves. The working environment of each regulating valve is completely different, and each pipe usually has only one regulating valve. Some regulating valves are also provided with a bypass. Manual valve control. If the regulator valve fails, the bypass valve can be opened to ensure normal production. Therefore, before the dismantling, it is necessary to carefully analyze the cause of the failure of the regulating valve and formulate a sound maintenance plan. 1. Inspection methods and standards. Maintenance method: (1) According to the operation rules, the replacement is required, the maintenance worker carries the canister, the vinyl chloride scent sensor, and the guardian of the gas defense station can only dismantle the valve. (2) Turn off the air supply, remove the positioner and air supply tube, disassemble the valve (.3) connect the valve stem, check the connection status of the valve stem, check whether the connecting pin can be removed, not Remove it with a special tool, or change the hole. 2. Assembly of the valve after inspection. (1) Before assembly, all the components of the valve should be cleaned and inspected. The assembly sequence should be from bottom to top. The added gasket should be greased, and the added filler should be filled evenly. (2) All fastening bolts and packings should be greased before assembly for the next inspection and lubrication. 3. Adjustment of the valve. After the valve is assembled, the positioner is installed and the air supply tube is adjusted. The calibration point should not be less than 5 points, 0%, 25%, 50%, 75%, 100%. Slowly input each point signal into the positioner in turn, and observe whether the stroke pointer corresponds to the scale scale. Otherwise, it should be adjusted repeatedly until the standard is reached. 4. Commissioning and acceptance. (1) After the valve adjustment standard is installed on the pipeline, notify the process workshop after confirming that there is no problem, and handle the handover procedure. (2) Cooperate with the craftsman to change from on-site manual operation to total control operation. (3) Check whether the records and documents after the inspection are complete and accurate. (4) When the valve is introduced into the medium, check the packing and the flanges on both sides for leakage. (5) After the normal operation of the regulating valve for 72 hours, it shall be accepted by the relevant technical supervisor. 5. Safety precautions. (1) Maintenance safety precautions: Maintenance must be carried out by more than two people; the required protective equipment must be worn when entering the on-site maintenance; if the electric valve is found to be abnormal, it must be approved by the craftsman and take safety measures before operation. (2) Safety precautions for inspection: the valve used for online maintenance must be handed over; the process medium must be drained before the online valve is disassembled, and the operation is confirmed to be free of leakage; the air source should be shut down during maintenance; When using special tools, the parts must not be damaged; the removed parts and the exposed valve body should be covered with soft material. (3) Precautions for operation and safety: Before the operation, the craftsman should be notified to handle the handover procedures; when commissioning, the technical and maintenance personnel should cooperate closely. Fourth, the disassembly process of the regulating valve (1) cut off the power supply, gas source; remove the power line and signal line and then remove the gas pipe; (2) connect the gas pipe (via the pressure reducing valve, the fixed value to the membrane head), set the pressure reducing valve The pressure is the minimum working pressure of the spring on the nameplate; (3) then remove the split nut, remove and remove the air source after removal; (4) loosen the pointer block and lock nut; (5) loosen the bracket round nut (6) Loosen and remove the bonnet nut diagonally, remove the upper bonnet, valve core, guide sleeve and toothed gasket in turn; after disassembly, check the cause of the fault, the valve plug and the valve stem reconnect. The valve body is then assembled in the reverse order of disassembly.

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