I saw one P&ID 6" control valve has been connected with 8"
process line, and 2" valve also connected in parallel with
6" valve. why the 2" valve connected in parallel, Is there
any technical reason. please clarify. With Regards-Kittu
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Answer Posted / divyang
There can be many reasons to provide two CV-
1. Case where flow controllability is extremly important.
Hence to get better control at lower load 2" CV will be
operated & once plant reaches cerain load higher size
control valve comes into picture.
2. Higher size CV is kept on certain value of manual
opening, and fine control is done by smaller valve. eg if
flow requried is 10000 kg/hr and controlling limits are +/-
200 kg, smaller CV will give fine control.
3. During revamp of the plant capacity instead of
increasing the existing CV, if a samller size CV is
available in spare same can be installed in parallel
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