How to repair pneumatic control valve?

Control point is different. Therefore, the working environment of each control valve is not exactly the same, it can be said that there is usually only one control valve on each road, if there is a malfunction of the control valve, you have to open the bypass valve, so as to ensure the normal production. Now, pneumatic actuator valve is applied to many modern factories. When we use it with other instrumentations, it can achieve the function of automatic adjustment and remote control of the flow, liquid level, pressure, temperature and other technological parameters during productive process and other media such as liquid, gas, steam,etc. Air actuated diaphragm valve as the final actuator of the automatic pneumatic actuator control system plays a very important role, control valve application is directly related to the quality and safety of production.

 

To guarantee its quality and safety, we will tell you about the common fault, reason analysis and solutions of air actuator control valve, for example:

 

Firstly, the control valve does not operate, because there is no signal pressure or diaphragm crack, diaphragm air leakage, the thrust of the diaphragm decreases. The valve core is jammed with the angle seat valves or liner and the valve rod is bent so that the regulator cannot operate. We can connect the signal wire and air source joint firmly or replace the diaphragm; Straighten valve rod or replace it.

 

Secondly, the control valve works normally but has no regulating effect. Because valve core spool off or pipe blocked. If the spool falls off, it can connect the valve core with the valve rod firmly, or if the pipeline problem, it can contact with competent department to dredge the pipeline.

 

Thirdly, if the control valve works slowly or jump frequently, it may be the friction between valve rod and filling increases due to aging or drying of sealing packing or because the valve contains viscous dirt, blockage, coking and other conditions appear, as well as diaphragm leakage. We can replace seal packing and readjust, remove dirt and coking, etc. Also it can tighten the diaphragm head, or replace the diaphragm.

 

Fourthly, the valve is unstable or oscillate. In this situation, it can be the size of the regulating valve is too large, the single acting actuator valve medium flows in the same direction as the closing direction. The valve core and guide sleeve are badly worn. We can replace with the right air operated gate valve size, adjust the valve direction and improve the joint surface or replace the valve core and guide sleeve.

 

Apart from above,let me share you some of pneumatic actuator valve 's typical fault maintenance plans.

 

Taking the failure of actuator pneumatic valve works normally, but it has no regulating effect" as an example, the maintenance plan is elaborated: in a chemical plant vinyl chloride workshop, the valve is a single-seat control valve of a well-known enterprise in China. The production line has an annual output of 100,000 tons of plastic particles, and there are two sets of production lines in the compression, conversion and fractionation section of vinyl chloride workshop. In addition to compression, conversion and fractionation section largely use pneumatic control valves, the working environment of each control valve is completely different, and there is usually only one control valve in each pipe line, some control valves also set bypass beside, it can be controlled by manual valve. If the regulator fails, the bypass valve can be opened to ensure normal production.Therefore, before the pneumatic control valve overhaul, it is necessary to carefully analyze the failure reasons of the control valve  and  develop a perfect maintenance plan.

 

Here are maintenance methods and standards. According to the operation rules, the replacement is required to be qualified, maintenance workers carry the canisters, vinyl chloride smell sensor, and the valve can be dismantled and inspected only when under the guardianship of gas station staff. Turn off the air source, remove the actuator with positioner and air source pipe, and disassemble the valve. Check the connection condition of valve core and valve rod, check whether the connecting pin can be removed, or use a special tool to remove or change the hole. We must assembe the valves after maintenance. All components of the valve should be cleaned and inspected before assembly, the assembly sequence should be from bottom to top, the added gaskets should be lubricated, and the added packing should be full and even. All fastening bolts and packing should be lubricated before assembly to facilitate the next maintenance and lubrication.

   

We should know valve adjustment. After the valve is assembled, we install positioner and air source pipe for adjustment. Calibration points should not be less than 5 points, 0%, 25%, 50%, 75%, 100%. Input each point signal into the positioner in turn slowly, and observe whether the route index corresponds to the scale label. Otherwise, and then make repeated adjustments until the standard is reached.

 

Then we have a trial run and acceptance. To install the standard valve into the pipeline, we inform the craft workshop after confirming that there is no problem, and handle the handing over procedure. Next we cooperate with the technician to change the on-site manual operation to the general control operation. And check whether the records and archives are complete and accurate after maintenance. Later we check whether the packing and both sides of the flange are leaking when the valve is introduced into the medium. After 72 hours of normal operation, the pneumatic control valve shall be signed and accepted by the relevant technical supervisor.

 

We should also consider safety precautions in all aspects. In terms of maintenance safety, maintenance must be carried out by more than two people. To enter the site for maintenance, they are required wear prescribed protective articles. If the air actuator valves is found to be abnormal, it must be approved by the technician and safety measures shall be taken before operation. In the aspect of overhaul safety, when repairing valves used online, the certificate must be handed over. Before the on-line valve disassembly, the process medium must be discharged and confirmed not to leak before the operation. The air source should be turned off during maintenance. Special tools must be used during maintenance and important parts must not be damaged. The removed parts and exposed body shall be covered with soft material. In operation safety's aspect. The technician shall be notified to handle the hand-over procedures before operation. Both process and maintenance staff should cooperate closely during operation .