NFPA 409 Design Pump Capacity

[worravit]

Dear All

I have question about design of fire water pump in Hangar NFPA 409
Refer from hydrauliac calculation, system is designed 6000 GPM @ 7 barg. So vendor select both pump, 3,000 GPM for each pump. But in my understand, the system should design for 6000 GPM for each pump or not?

Best Regards
WVt

 

[skdesigner]

NFPA 409-04 6.2.10.8.2 The total pumping capacity shall be such that maximum demand can be met with the largest fire pump out of service.

If you were going to use a 6,000 usgpm pump, you would be correct in that NFPA 409 would require a redundant backup.

Keep in mind that NFPA 20 requires a fire pump be able to flow at least 150% of it's rated capacity. For a 6,000 usgpm pump, that would be 9,000 usgpm (slightly overkill). You would probably be better off installing something like four 1,500 usgpm pumps in parallel. 1,500*1.5 = 2,250 usgpm @ 150% capacity. With the 4th pump as a redundant backup you would have 3*2,250 = 6,750 usgpm available (which works out to 133% of each pump's rated capacity)

NFPA 20-2010 4.8.3 also requires that centrifugal fire pumps with ratings over 5,000 usgpm must be subject to individual review by either the AHJ or a listing laboratory.