American Fire Sprinkler Association
12750 Merit Dr., Suite 350 Dallas TX 75251
Ph: (214) 349-5965 Fax: (214) 276-0908
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TECHNICAL UPDATE
January 3, 2008
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What is the minimum section pressure for a centrifugal pump when
tested at 150 percent?"
We have reviewed the 2007 Edition of NFPA 20 as the applicable
Standard. Our informal interpretation is that gauge pressure at the
suction flange shall be 0 psi or higher at 150 percent of the rated
capacity of the pump.
Some AHJ's or water companies will set a minimum of 10 to 20 psi
residual pressure for the city main. This is to avoid the potential
for ground water seeping into the distribution supply. There is no
such requirement in NFPA 20 for 10 or 20 psi on city mains. Section
5.14.3.1 does establish that the gauge pressure at the pump suction
flanges shall be 0 psi or higher with the pump operating at 150
percent of rated capacity. Some AHJ's are also requiring backflow
prevention devices in the suction line. Section 5.26.4 indicates that
where a backflow prevention device is installed, the final arrangement
shall provide effective pump performance with a minimum suction
pressure of 0 psi at the gauge at 150 percent of the rated capacity.
If the suction supplies do not permit flowing at 150 percent, the
final arrangement shall provide effective pump performance at the
maximum allowable discharge. However, the discharge shall exceed the
fire protection system design flow. Suction pressures are also
indicated for conducting an acceptance test. Section 14.2.7.2.2 will
allow for test flows lower than 150 percent if the available suction
supplies do not permit the flowing of 150 percent. The reduced
capacity shall constitute an acceptable test, provided that the pump
discharge exceeds the fire protection system design flow and pressure
requirements. Another factor to consider in the suction pipe is
velocity. The velocity in the suction pipe cannot exceed 15 ft/sec as
indicated in section 5.14.3.3. Using the pipe sizes established in
Table 5.25 will assure that the velocity of 15 ft/sec in the suction
pipe will not be exceeded.
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Technical Update is prepared by the Technical Services Dept. of the
AFSA: Vice President of Engineering and Technical Services Roland
Huggins, a PE registered in fire protection engineering; Phill Brown,
a NICET IV certified automatic sprinkler technician and NFPA Certified
Fire Protection Specialist (CFPS) and Tom Wellen, a degreed fire
protection engineering technologist. This is provided with the
understanding that the AFSA assumes no liability for this opinion or
actions taken on it and they are not to be considered the official
position of the NFPA or its technical committees.
Copyright (c) 2008, American Fire Sprinkler Association. All Rights
Reserved
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