NFPA 13 7psi minimum

[Gogo707]

Hello all,

Working on a project in which a private water tank (located at elevation) is the main supply for a NFPA 13 Fire Sprinkler System. NFPA 13 states that the minimum PSI is 7. I am currently getting a residual pressure at the source of only 5psi. With the elevation, I will get a PSI at BOR of 49.7. Is the NFPA 13 minimum (7) strictly for what is needed at BOR or do I need to get increased pressure at the supply source?

Thanks in advance!

 

[steveray]

7psi?

 

[Paul Sweet]

Sprinkler heads won't produce the required coverage and pattern at less than 7 PSI.

 

[steveray]

go go mentioned pressure at the source….never heard the heads referred to as the source…

 

[Yankee Chronicler]

Hello all,

Working on a project in which a private water tank (located at elevation) is the main supply for a NFPA 13 Fire Sprinkler System. NFPA 13 states that the minimum PSI is 7. I am currently getting a residual pressure at the source of only 5psi. With the elevation, I will get a PSI at BOR of 49.7. Is the NFPA 13 minimum (7) strictly for what is needed at BOR or do I need to get increased pressure at the supply source?

What is "BOR"?

Where does NFPA 13 specify a minimum pressure of 7 psi? I can't find it in my copy of NFPA 13-2013.

 

[Yankee Chronicler]

Table 11.2.2.1 indicates a minimum residual pressure of 15 psi for light hazard systems, and 20 psi for ordinary hazard systems. The table also requires minimum flow rates and minimum durations. It then says

11.2.2.6.1 The residual pressure requirement of Table 11.2.2.1 shall be met at the elevation of the highest sprinkler.

 

[IJHumberson]

The 7 psi minimum required in NFPA 13 is the minimum pressure required at the hydraulically remote sprinkler with the required design flowing. This minimum pressure was added into the NFPA 13 standard about 35 years ago, because the sprinkler manufacturer's kept designing sprinklers with lower and lower design pressure requirements to meet the minimum coverage requirements (especially for residential sprinklers). The NFPA 13 technical committees determined that a minimum pressure at the hydraulically remote sprinkler was necessary, because having a very low minimum pressure at the hydraulically remote sprinkler could cause the sprinkler to fall below the minimum with a very minor issue in the sprinkler piping.

Without knowing the occupancy and size of the building, from what you've described, it MIGHT be possible to design a sprinkler system to supply the minimum required flow (at the minimum 7 psi at the hydraulically remote sprinkler) without a fire pump. That would have to be evaluated by a sprinkler system designer.

 

[blugosi]

@Yankee Chronicler , BOR is the Base of Riser in the building
@OP , for many sprinkler types 7 psi is all you need for a sprinkler to provide its nominal flow and develop the expected wetting pattern.
However, how and where did you measure the residual pressure of 5 psi?
Are you sure this is not the static pressure?