3 replies to this topic

[T&E]

Hi all.

 

I'm an engineer working in the chemical engineering field for several years.

 

Recently, I designed the firewater system and there are PSV's at firewater pump discharges.

 

Thus, I searched NFPA 20, and I saw the sentence,

 

"Relief valve discharge piping returning water back to the supply source, such as an aboveground storage tank, shall be run independently and not be combined with the discharge from other relief valves." (5.18.6.3)

 

From my humble experience, I'd never seen the system like this. If I follow the Code, PSV discharge lines are connected separately to the firewater storage tank.

 

Please advise that I should follow this.

[fallah]

T&E,

 

Actually, it means with a common supply source the PSVs discharge header of one parallel set of pumps cannot be combined with that of the another parallel set of pumps and each PSVs discharge header shall be terminated separately to the supply source. Obviously, the discharge pipes of the PSVs included in the same set of parallel pumps can be combined before terminating to the supply source...

[T&E]

fallah

 

Thank you for your comment. 

 

I agree with your comment but, actually, I proceed the PSV discharge design as per the NFPA 20 code (all separate discharge lines). Because, I cannot find the sentence (or meaning) in the Code that you are mentioned. Thus if the Owner or Company wants to follow the Code strictly, I have no base data to protect the single PSV discharge line design.

 

[fallah]

Because, I cannot find the sentence (or meaning) in the Code that you are mentioned. Thus if the Owner or Company wants to follow the Code strictly, I have no base data to protect the single PSV discharge line design.

 

 

T&E,

 

Ok, no problem. You have to follow the code regarding PSV discharge line as per NFPA 20. Then if the PSVs on parallel pumps discharge lines might simultaneously be in relieving status consider dedicated discharge line for each PSV up to supply source, otherwise considering common discharge header for them not only wouldn't have any contradiction with the code but also having economical benefits due to lesser pipework and reduction in tank nozzles.