NFPA 20 - suction/discharge pipe sizing
NFPA 20 - suction/discharge pipe sizing
(OP)
I am in need of a fire pump history lesson.
In the past two weeks, I have looked at two separate fire pump installations where 2,000gpm pumps had been installed with 8" suction and discharge piping, instead of the minimum 10" piping required by NFPA 20. The first time, I was quick to point it out as an error - but the second time, I started to wonder if it was more than just a coincidence.
Both pumps were installed in the early 80's, meaning that the design would have been governed by an early-to-mid 70's edition of NFPA 20. The oldest edition of 20 I have access to is '87, which lists minimum suction and discharge piping as 10" for a 2,000gpm pump.
Was there ever a time when NFPA 20 permitted 8" piping for 2,000gpm pumps?
Thanks in advance.
In the past two weeks, I have looked at two separate fire pump installations where 2,000gpm pumps had been installed with 8" suction and discharge piping, instead of the minimum 10" piping required by NFPA 20. The first time, I was quick to point it out as an error - but the second time, I started to wonder if it was more than just a coincidence.
Both pumps were installed in the early 80's, meaning that the design would have been governed by an early-to-mid 70's edition of NFPA 20. The oldest edition of 20 I have access to is '87, which lists minimum suction and discharge piping as 10" for a 2,000gpm pump.
Was there ever a time when NFPA 20 permitted 8" piping for 2,000gpm pumps?
Thanks in advance.





RE: NFPA 20 - suction/discharge pipe sizing
RE: NFPA 20 - suction/discharge pipe sizing
If you go to NFPA20 you can choose your edition.
http://www.nfpa.org/codes-and-standards/all-codes-...
Well sort of - the 1976 revision shows table 2-16 and 2000 gpm is 10" suction and discharge.
The 1974 edition is the "full" code and also shows it as 10"
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: NFPA 20 - suction/discharge pipe sizing
RE: NFPA 20 - suction/discharge pipe sizing
RE: NFPA 20 - suction/discharge pipe sizing
I thank you all for the replies.
RE: NFPA 20 - suction/discharge pipe sizing
I have encountered this same scenario with water main end-suction pumps used as fire pumps.
RE: NFPA 20 - suction/discharge pipe sizing
We witnessed a test of the first pump - flowed at 2000 gpm for about 3 minutes before the engine got so hot that coolant started boiling out of the tank, so it's safe to say that undersized suction/discharged piping is but one of the issues.
Quite the scene to witness, though.
RE: NFPA 20 - suction/discharge pipe sizing
About three years ago I used a 1,250 gpm fire pump where I had to have a 12" suction in order to maintain a minimum 20 psi residual pressure at the "pump inlet flange" with the pump operating at 150%. This is downstream the backflow assembly. Long suction line, off my memory I think it was 800 feet, and calculations were showing we should have 23 psi @ 150% and during the test we got 24 psi residual.
For the C900 I used a C-Value of 140 which is more realistic given tests that have been conducted. Yeah, you can use the 150 for calculations but to be safe you better use 140 for something like this.
Also, while the pipe was 12" used reducers to install an 8" backflow because it had the lowest friction loss at 1,875 gpm. What I do on something like this I don't shop on price I want whatever provides the lowest pressure loss at 1,875.
Oh, and in Georgia if you don't have the 20 psi @ 150% you fail the acceptance test and how do you fix that, re-bore the four lane highway and install 800' of 12" to replace the 8" installed because "the book" said you could? After you tell the owner this you commit Hari-Kari to atone for the sin of not properly doing your job?