Can a valve operating at a low opening degree achieve automatic control by closing the upstream manual valve?
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There are two scenarios here for everyone to discuss: 1. There is a tower stiller with steam jacket heating; the feed flow rate is low and the temperature is high, with the process controlled at around 110 degrees, and the steam temperature at 160 degrees. When the valve is slightly opened (to about 10-20% of its full opening), the temperature rises rapidly, and since there is no place for heat to dissipate, the cooling process is slow. Can automatic PID control be achieved this way? 2. Still steam heating, with a tubular preheater; the steam temperature is 160 degrees. It is necessary to keep the material temperature around 60 degrees, as the material boils at 20 degrees and tends to vaporize easily. When the valve is opened to 80% of its capacity, the temperature rises rapidly, and it is necessary to close it completely within 5 seconds. After three to five minutes of cooling, someone needs to open the valve again. Automatic operation at such a small opening degree should not be possible. In both cases, it is likely that the pipeline valves designed are too large, preventing the control valves from achieving precise control. In this case, can reducing the size of the manual valve achieve the goal of increasing the valve opening for automatic control?
It is completely possible to do so by closing the upstream valve and allowing the control valve to operate within its adjustable range.
By selecting an appropriate flow coefficient for the control valve, automatic control can be achieved.
In this way, the scouring of the manual valve will increase, but control should still be possible
This approach is advisable; if it is a single-seat valve, it is best to replace the valve internals in order to reduce the size of the valve seat
I believe that adding a pilot valve can increase the opening degree of the control valve accordingly, but it cannot achieve the goal of ideal automatic control, as the characteristics of the valve remain unchanged.
I believe that adding a pilot valve can increase the opening degree of the control valve accordingly, but it cannot achieve the goal of ideal automatic control, as the characteristics of the valve remain unchanged.
It’s possible in the short term. It is recommended to replace the entire set of valve cores and seat over the long term
If the flow rate is too low, it’s likely impossible to avoid replacing the valve internals; opening the large valve just a little results in it closing almost immediately, which is similar to the behavior of a small on-off valve. The flow characteristics in such cases can be considered those of an on-off valve.