Xylem Bell & Gossett VSX Series, Instruction Manual

Page: 15 / 44

1
Suction Piping
When installing the suction piping, refer to the
Hydraulics Institute Standards and observe
the following precautions. (See Figure 14.)
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 directly attributed to
improper suction piping systems.
Friction losses caused by undersized suction
piping can increase the fluid’s velocity into the
pump. Refer to the
Hydraulic Institute
Standards for inlet pipe sizing and velocity
requirements.
Elbows in the suction piping for horizontal
double suction pumps should be installed per
the
Hydraulics Institute Standards as there is
always an uneven turbulent flow around an
elbow. When it is in a position other than the
vertical (in relation to the pump suction
nozzle) it causes more liquid to enter one
side of the impeller than the other. (See
Figure 15.) This results in high unequalized
thrust loads that will overheat the bearings
and cause rapid wear, in addition to affecting
hydraulic performance.
For pipe reducers on the inlet side, no more
than one pipe diameter reduction in a single
reducer should be used.
Figure 14: Suction Pipe Installations
(Piping supports not shown)