What are the reasons why pneumatic control valves operate at a low opening degree for extended periods of time?
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What are the reasons why pneumatic control valves operate at a low opening degree for extended periods of time?
1. Improper selection; the parameters provided by the process are too high； 2. When the plant operates at reduced capacity and low load ； 3. Leakage in the control valve bypass line ； 4. The valve spool of the control valve is severely worn, resulting in high leakage.
1. There is an issue with the selection of the control valve； The CV value is calculated too high ； Incorrect process parameter provided ； 2. The process operation conditions have changed, resulting in changes in the process parameters ； 3. Leakage in the line connected to the control valve ； 4. Changes have occurred in the process flow.
If it is the first reason, how should it be handled? Is it possible to replace the valve core?
Use another one, and take the old one to another place. Replacing just the valve core does not solve the problem.
1. The design selection was incorrect; the current operating conditions do not match the design conditions. If this is the case, it’s best to create a new unit. 2. Check whether the process load is set at a medium-to-high level
Recalculate the CV value based on the process parameters, and then select an appropriate spool for replacement.
1. There is an issue with the selection of the control valve； The CV value was calculated incorrectly ； Incorrect process parameter provided ； 2. The process operation conditions have changed, resulting in changes in the process parameters ； 3. Leakage in the control valve ； 4. Changes in the process flow. 5. The production load is too low.
1. The valve spool of the control valve is severely worn, resulting in leakage from the control valve； There is an issue with the selection of the 2 valves ； The CV value was calculated incorrectly ；
Check whether the original parameters match the current process; it’s advisable to calculate the Cv value and opening degree of the control valve. If the requirements are not met, the valve must be replaced. If the conditions are satisfied and the bypass valve is closed, then it’s very likely that there is internal leakage in the valve.
There is an issue with the selection of the control valve； The CV value is calculated too high ； Incorrect process parameter provided