3 replies to this topic

[process101]

Hi every one:
What should be the minimum distance between a valve and a vessel? The valve could be a flow control valve, a pressure control valve or a level control valve. Is there any rule of thumb for installing a valve at some distance? because I have seen in P&Id that for some vessel the level valve is installed very close to the vessel's outlet and in some cases they are installed at some distance
For example: In order to control liquid level in Flash tank the level control valve is installed after lean and rich Amine heat exchanger. why the valve is not installed close to the flash tank?

Thank you very much in advance.

[djack77494]

If you have a liquid that is flashing across the control valve, I like to locate the valve as close to its ultimate destination as possible. Ideally, mount the valve on the vessel nozzle. This is done for a number of reasons, perhaps most simply explained by saying it's much easier to deal with a liquid than a two phase mixture. By similar reasoning, you may want to keep the valve low (for higher static head) or close to its origin (for less hydraulic losses). You may also want to located the valve downstream of a heat exchanger if the fluid is cooled in the exchanger. This would lessen the liklihood and/or severity of flashing. Beyond this, I don't think there would be much of a reason for preferences (except layout issues).

[Art Montemayor]

Process:

I want to reinforce the strong reasons that Doug has pointed out as to where one places a control valve within a process. I hope that you note that Doug has stressed the common sense value of making such a decision. It is important that you always be aware of and consider what is going through the valve, the subsequent product, its temperature, pressure, and composition. Adding to that information the need for maintenance, repairs, or physical support (in the case of large valves) winds up being the ingredients needed to make a sound engineering judgment about ultimate placement and location.

I also want to stress that the P&ID you are looking at has no merit or accuracy in depicting exactly where the control valve is placed – except the relative location. Therefore, your statement "I have seen in P&Id that for some vessel the level valve is installed very close to the vessel's outlet and in some cases they are installed at some distance" is totally erroneous. Neither you or anyone can accurately make that statement with only the P&ID to guide you. You need a layout plan or a detailed piping isometric with distances to make that judgment.

And do not make multiple postings of the same query. I have deleted your second posting on this Forum. Please READ THE FORUM GUIDELINES regarding posting queries. These guidelines are readily found at the beginning of the Forum page.

[process101]

Good Morning Mr. Art:
I apologize for posting two times. actually it was done by mistake. I try to
remove one of the post but i couldn't.It won't happen again.
But Thank you very much for answering my question.