3 replies to this topic

[sparsha]

Dear All

 

I have a Vacuum Residue feed drum whose design pressure is 25 barg. A PSV is provided for the drum. I have N2 blanketing to that drum to maintain its pressure @ 16 barg. I have a control valve with bypass on the N2 line. N2 used is HP Nitrogen @ 170 barg. The bypass line contains a restriction orifice and a globe valve in the same order . The main control valve doesn't have a RO.

 

1) I would like to  know why both globe valve(control valve ) and RO are needed on bypass line.

 

2) If it is to reduce the PSV size during the inadvertent bypass opening case, then we should also have an RO       on main control valve line as the CV can fail open.

 

3) I have a split range control between the N2 inlet and a valve on vent line(split range blanketing system). What     is the purpose of by pass lines on control valves of a split range blanketing. Does the operator control the           blanketting manually in case any one of the main valve fails?

 

4) I was thinking the bypass valve will be an indentical to main valve except that it is manually operate. Please       correct me if i am wrong.

 

Attaching the diagram for reference.

Attached Files

•  0308_001.pdf   225.85KB   70 downloads

[shan]

The bypass RO is needed to make the bypass overall Cv the same as or similar to the main line overall Cv.

[sparsha]

The bypass RO is needed to make the bypass overall Cv the same as or similar to the main line overall Cv.

But why we need an RO to meet the Cv. Can't we meet the Cv with the valve alone. I am of the opinion that bpass valve and main valve should be of same size.

[shan]

You have 4 valves (1 control valve + 3 gate valves) on the main line, but just 2 valves (1 globe valve + 1 gate valve) on the bypass line.  Therefore, the bypass line RO is needed to achieve the same combined Cv for the main line and the bypass line.