Two ways to adjust valve on site
The regulating valve is an indispensable terminal control instrument in the automatic control loop. Because there are many technological factors affecting its operation, and if a certain factor is neglected, the regulating valve is often far from the working point at the time of design, and even cannot work normally. Since 1987, our factory has undertaken overhaul tasks for a number of large-scale petrochemical plants. We often find that a small number of on-site control valves, including a small number of imported valves, have good quality, but users report that these valves are not operating properly. , I want to repair the factory; we opened the refurbishment to the original post, but after the operation of the old "disease" recurrence, the common phenomenon is the adjustment instability, vibration, noise, etc., can not meet the regulatory requirements of the system, some valves only abandoned Instead, change hands. Later, we had to suspect that there was a problem with the original selection and requested the user to provide the process parameters and operating requirements for these valves. After calculations were made, they were found to operate under a small opening and could not achieve normal regulation.
We have analyzed two reasons for this phenomenon:
1, the valve diameter calculation and improper selection.
2. The difference between the actual process parameters and the data used during the operation is large. To this end, we propose reform measures. For these on-site control valves, the user generally requires not to change the flange on the pipeline, nor to replace the valve body, the reason is very simple, it can save manpower and material resources, more importantly, remove the welding installation process a lot of trouble. For different situations, we use two methods of restructuring, the first is to change the flow characteristics of the valve from the straight line characteristics to equal percentage characteristics. The second is to reduce the diameter of the valve seat or reduce the area of ​​the window on the sleeve under the same condition of the valve body, and reduce the rated flow coefficient. Sometimes used in combination. Both reduce the seat diameter and change the flow characteristics.
The following is a typical example to illustrate the situation before and after restructuring. In October 1989, a joint venture in Shanghai used a DN50, C=30 straight-line sleeve valve for water supply regulation of a 20t industrial boiler. It was found that the operation was unstable and accompanied by strong vibration and noise. To repair, but still can not be used normally, had to exercise by hand.
Boiler is often operated near the rated value, then the opening of the regulating valve is below 10%. We all know that the linear characteristic of the regulating valve can not be stable under 10%; according to the above situation, we propose that the valve body should not be removed. Next, adjust the sleeve with an equal percentage characteristic, the nominal C value is still 30, so that the opening degree of the valve can be increased. Taking the adjustable ratio R=30 as an example, under the same working conditions, the working point moves to the right, and the calculated opening degree is “rated point Cnorm=3.5Knorm=37% (irrespective of distortion factor). Maximum point Cmax=7.1Kmax =58%, Figure 1 is reasonable in this range of opening, but after the automatic adjustment, it is found that the regulating valve still can not work stably, but in the two-position switching operation, it is obviously not the regulating valve itself. The problem, but the problem of automatic control instrument matching, has been gradually checked and found that for boiler water level upper limit, the set value on the regulator is too small, that is, the liquid level fluctuation is allowed to be too small, when the liquid level is at a low water level, Regulator ordered the valve to open, due to the larger flow capacity of the valve, the amount of water supply, as long as a few seconds straight, the liquid level that reaches the upper limit, due to the regulator has integration time, until it sends a signal and quickly turn off The water supply is rapidly reduced, the liquid level in the boiler quickly reaches the lower limit value, and when the regulator is forced to open the valve, the valve is already in the fully closed position, thus forming frequent switches. Based on the above analysis, we propose on the spot Liquid level fluctuations allow The degree of relaxation was appropriate, so that the regulating valve could operate smoothly and immediately. After we had spent an hour in the control room, both parties were satisfied that they would leave. After a month, I called and asked about the operation of the regulating valve. The factory answered the operation. Normal, it is still in use.Since small and medium-sized enterprises use industrial boilers with 20t/h evaporation, common problems still occur in the selection of water supply control valves. We recommend the use of DN25~40, equal percentage sleeve valves. More appropriate.
The second example is Yangzi Petrochemical Company’s XX plant. The two electric single seat valves have a nominal diameter of DN6â€, a valve seat diameter of dN3â€, a C value of 150, and a linear characteristic, which is a product of the German Gulde company and is used to regulate oxygen. flow. When I went to visit in March 1991, the factory reflected that the two valves were frequently turned on and off to form continuous air supply. The motors in the electric actuators were burned out due to frequent start-ups. Our factory still sent people to fix it, but it was still old after reusing it. Look like.
Rated working condition: Cnorm=7.08.K=4.7%, maximum operating condition Cmax=1.77.Kmax=11.8% Such a small opening degree, the regulating valve cannot of course work stably. We propose to replace the regulating valve, but the factory requires that the system be changed without changing the valve body. We immediately designed and processed a special set of valve seats. We want to use the opportunity for summer overhaul, but due to the long time the original valve seat. Rust can not be unscrewed on the valve body, the factory was determined to remove the valve body, turning the original valve seat with a vertical turning off, and then install the special design of the valve seat poppet, dN is 50.C value 32, equal percentage characteristics, so that the C value is almost one-fifth of the original, and it is equal percentage characteristics, and the opening degree is 83% when the opening degree is 56% of the maximum working condition under the rated working condition (irrespective of the calculation of the distortion factor. Value), has been installed in the original post operation has been stable operation, so far no fault. (Shanghai Automation Instrument No.7, No.202150) Xue Wenbin has made great progress in the selection of control valves for the selection of control valves and power plants in the design institutes of various industries and our manufacturing facilities. In the project, the selection of regulating valves has become more standardized. However, in small and medium-sized enterprises or units that have used regulating valves for the first time, due to various reasons, there may still be improper selection. If we find the situation mentioned in this article, I would like to adopt The above two methods for restructuring are simple and save trouble.
We have analyzed two reasons for this phenomenon:
1, the valve diameter calculation and improper selection.
2. The difference between the actual process parameters and the data used during the operation is large. To this end, we propose reform measures. For these on-site control valves, the user generally requires not to change the flange on the pipeline, nor to replace the valve body, the reason is very simple, it can save manpower and material resources, more importantly, remove the welding installation process a lot of trouble. For different situations, we use two methods of restructuring, the first is to change the flow characteristics of the valve from the straight line characteristics to equal percentage characteristics. The second is to reduce the diameter of the valve seat or reduce the area of ​​the window on the sleeve under the same condition of the valve body, and reduce the rated flow coefficient. Sometimes used in combination. Both reduce the seat diameter and change the flow characteristics.
The following is a typical example to illustrate the situation before and after restructuring. In October 1989, a joint venture in Shanghai used a DN50, C=30 straight-line sleeve valve for water supply regulation of a 20t industrial boiler. It was found that the operation was unstable and accompanied by strong vibration and noise. To repair, but still can not be used normally, had to exercise by hand.
Boiler is often operated near the rated value, then the opening of the regulating valve is below 10%. We all know that the linear characteristic of the regulating valve can not be stable under 10%; according to the above situation, we propose that the valve body should not be removed. Next, adjust the sleeve with an equal percentage characteristic, the nominal C value is still 30, so that the opening degree of the valve can be increased. Taking the adjustable ratio R=30 as an example, under the same working conditions, the working point moves to the right, and the calculated opening degree is “rated point Cnorm=3.5Knorm=37% (irrespective of distortion factor). Maximum point Cmax=7.1Kmax =58%, Figure 1 is reasonable in this range of opening, but after the automatic adjustment, it is found that the regulating valve still can not work stably, but in the two-position switching operation, it is obviously not the regulating valve itself. The problem, but the problem of automatic control instrument matching, has been gradually checked and found that for boiler water level upper limit, the set value on the regulator is too small, that is, the liquid level fluctuation is allowed to be too small, when the liquid level is at a low water level, Regulator ordered the valve to open, due to the larger flow capacity of the valve, the amount of water supply, as long as a few seconds straight, the liquid level that reaches the upper limit, due to the regulator has integration time, until it sends a signal and quickly turn off The water supply is rapidly reduced, the liquid level in the boiler quickly reaches the lower limit value, and when the regulator is forced to open the valve, the valve is already in the fully closed position, thus forming frequent switches. Based on the above analysis, we propose on the spot Liquid level fluctuations allow The degree of relaxation was appropriate, so that the regulating valve could operate smoothly and immediately. After we had spent an hour in the control room, both parties were satisfied that they would leave. After a month, I called and asked about the operation of the regulating valve. The factory answered the operation. Normal, it is still in use.Since small and medium-sized enterprises use industrial boilers with 20t/h evaporation, common problems still occur in the selection of water supply control valves. We recommend the use of DN25~40, equal percentage sleeve valves. More appropriate.
The second example is Yangzi Petrochemical Company’s XX plant. The two electric single seat valves have a nominal diameter of DN6â€, a valve seat diameter of dN3â€, a C value of 150, and a linear characteristic, which is a product of the German Gulde company and is used to regulate oxygen. flow. When I went to visit in March 1991, the factory reflected that the two valves were frequently turned on and off to form continuous air supply. The motors in the electric actuators were burned out due to frequent start-ups. Our factory still sent people to fix it, but it was still old after reusing it. Look like.
Rated working condition: Cnorm=7.08.K=4.7%, maximum operating condition Cmax=1.77.Kmax=11.8% Such a small opening degree, the regulating valve cannot of course work stably. We propose to replace the regulating valve, but the factory requires that the system be changed without changing the valve body. We immediately designed and processed a special set of valve seats. We want to use the opportunity for summer overhaul, but due to the long time the original valve seat. Rust can not be unscrewed on the valve body, the factory was determined to remove the valve body, turning the original valve seat with a vertical turning off, and then install the special design of the valve seat poppet, dN is 50.C value 32, equal percentage characteristics, so that the C value is almost one-fifth of the original, and it is equal percentage characteristics, and the opening degree is 83% when the opening degree is 56% of the maximum working condition under the rated working condition (irrespective of the calculation of the distortion factor. Value), has been installed in the original post operation has been stable operation, so far no fault. (Shanghai Automation Instrument No.7, No.202150) Xue Wenbin has made great progress in the selection of control valves for the selection of control valves and power plants in the design institutes of various industries and our manufacturing facilities. In the project, the selection of regulating valves has become more standardized. However, in small and medium-sized enterprises or units that have used regulating valves for the first time, due to various reasons, there may still be improper selection. If we find the situation mentioned in this article, I would like to adopt The above two methods for restructuring are simple and save trouble.
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