G
Hi all
We shall receive Steam from a steam header by one of our contractor companies. They have engineered 2 x parallel control valves (A and B) regulated by an upstream pressure transducer (PT).
<pre>
40barg>------|---A_Valve---|--PT---->30barg
ooooooooooo|ooooooooooo|oooooooo
oooooooooooo---B_Valve---ooooooooo
</pre>
Their control philosophy is basically the A valve has a higher setpoint than the B valve. The A valve is normally in service @30 barg and the B valve regulates if the downstream pressure controlled by A valve drops below the setpoint to the B valve setpoint(lets say 29barg).
Now, I think these valves will fight each other if a process disruption goes below the setpoint of the B valve SP of 29barg! As both valves will be open and trying to regulate the pressure with overshoot..am I wrong?
After a HAZOP we are encouraging our Contractor to install PSV's downstream of the PT to maintain system pressure below the piping spec of 34 barg as I am not entirely convinced tha their "parallel pressure control" will work
Thanks
Graham
We shall receive Steam from a steam header by one of our contractor companies. They have engineered 2 x parallel control valves (A and B) regulated by an upstream pressure transducer (PT).
<pre>
40barg>------|---A_Valve---|--PT---->30barg
ooooooooooo|ooooooooooo|oooooooo
oooooooooooo---B_Valve---ooooooooo
</pre>
Their control philosophy is basically the A valve has a higher setpoint than the B valve. The A valve is normally in service @30 barg and the B valve regulates if the downstream pressure controlled by A valve drops below the setpoint to the B valve setpoint(lets say 29barg).
Now, I think these valves will fight each other if a process disruption goes below the setpoint of the B valve SP of 29barg! As both valves will be open and trying to regulate the pressure with overshoot..am I wrong?
After a HAZOP we are encouraging our Contractor to install PSV's downstream of the PT to maintain system pressure below the piping spec of 34 barg as I am not entirely convinced tha their "parallel pressure control" will work
Thanks
Graham