Xylem 9100 Series Base Mounted Centrifugal Fire Pumps AC8585 REV.C - Manual (Page 16)

Suction Piping
When installing the suction piping, observe
the following precautions (See Figure 7).
The sizing and installation of the suction
piping is extremely important. It must be
selected and installed so that pressure losses
are minimized and sufficient liquid will flow
into the pump when started and operated.
Many NPSH (Net Positive Suction Head)
problems can be attributed directly to
improper suction piping systems.
Friction losses caused by undersized suction
piping can increase the fluid’s velocity into the
pump. As recommended by the Hydraulic
Institute Standard ANSI/HI 1.1-1.5-1994,
suction pipe velocity should not exceed the
velocity in the pump suction nozzle. In some
situations pipe velocity may need to be
further reduced to satisfy pump NPSH
requirements and to control suction line
losses. Pipe friction can be reduced by using
pipes that are one to two sizes larger than the
pump suction nozzle in order to maintain pipe
velocities less than 5 feet/second.
Suction piping should be short in length, as
direct as possible, and never smaller in
diameter than the pump suction opening. If
the suction pipe is short, the pipe diameter
can be the same size as the suction opening.
If longer suction pipe is required, pipes
should be one or two sizes larger than the
opening depending on piping length.
Suction piping for horizontal double suction
pumps should not be installed with an elbow
close to the suction flange of the pump
except when the suction elbow is in the
vertical plane. A suction pipe of the same size
as the suction nozzle approaching at any
angle other than straight up or straight down
must have the elbow located 10 pipe
diameters from the suction flange of the
pump. Vertical mounted pumps and other
space limitations require special piping.
CHECK VALVE
GATE VALVE
SUCTION PIPE INSTALLED WITH A
GRADUAL RISE TO PUMP
INCREASER
LEVEL
CORRECT CENTER LINE
OF PIPE
AIR POCKET
INCORRECT
AIR POCKET
INCORRECT
AIR POCKET
INCORRECT
GRADUAL RISE
TO PUMP
NO AIR
POCKETS
CORRECT
GRADUAL RISE
TO PUMP NO AIR
POCKETS
ECCENTRIC
REDUCER
CORRECT
DISTANCE PLUS
ECCENTRIC REDUCER
STRAIGNTENS FLOW
CORRECT
PATH OF WATER
INCORRECT
FIGURE 7 – SUCTION PIPE INSTALLATIONS
(PIPING SUPPORTS NOT SHOWN)
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