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

Answer Posted / ajith294

above answer is split range controller. what is a split
range control? two control valves are controled by a
controller is split range. for eg: 50% of controller out
put both of the valve will be close condition , see below
table.

% input Valve A opening %, Valve B opening&
0 0 100
25 0 50
50 0 0
75 50 0
100 100 0

but in your question on 2" valve is connected parrallel
with 6" Control valve. means for the bypassing 6" control
valve, they are using 2" valve.

for technically it is very very improtant. becasue at the
time of maintance of the control valve, there will be no
disturbance in process.

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