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
May 21, 2008
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An elevation diagram was provided showing the piping arrangement for
suction and discharge of the fire pump. You asked the following
question:
“Is it acceptable to have one tee, which is less than 10 diameters of
the suction pipe to the inlet flange of the fire pump with center line
plane of the tee parallel to the fire pump split-case pump shaft? This
is based on the situation that the water goes straight through the tee
and the side outlet of the tee is to feed the by-pass which is closed
when fire pump is in service.”
We have reviewed the 2007 edition of NFPA 20 that you indicated as the
applicable Standard. Our informal interpretation is that the tee
fitting will not affect the water going into the fire pump. However,
when a bypass is provided the valves shall be in the open position.
The purpose of the tee is to supply water through the side outlet to
supply the fire pump bypass. The tee fitting does not feed water from
the side outlet into the suction line of the fire pump thus the
requirements of Section 5.14.6.3 do not apply. As you said, the water
will flow straight through the tee fitting. Another tee fitting is
shown upstream of the tee fitting in question and connects with an
existing 8 in. city water supply. The tee fitting outlet centerline is
located to be perpendicular to the split-case fire pump shaft. This
tee fitting orientation meets the requirements of Section 5.14.6.3.
This requirement is to help prevent turbulence from the water exiting
the elbow or tee from exerting undue stress on the fire pump’s
impeller. If the centerline of the elbow or tee is vertical
(perpendicular) to the pump shaft, this stress is significantly
reduced. This issue is clarified in Section 5.14.6.3.3 that states,
“Elbows with a centerline plane perpendicular to the horizontal split-
case pump shaft shall be permitted at any location in the pump suction
intake.” This is further illustrated in Figure A.5.14.6, which shows
an acceptable piping arrangement as having a suction supply dropping
down to an elbow that is directly attached to the suction side flange
of the pump.
Regarding the valve for the bypass connection, it shall always be open
according to Section 5.16.1. If a bypass is provided, the valves shall
be supervised in the open position. The loss of the pump can occur not
only from maintenance, but also equipment or power failure where the
bypass connection would be beneficial. In addition, since some of the
suction and discharge piping is not as cleanly arranged as a new
installation, it may be worthwhile passing along the design
arrangement to the pump manufacturer’s representative to ensure the
existing piping arrangement would not effect the operation of the pump.
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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 © 2008, American Fire Sprinkler Association. All Rights
Reserved
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