Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Vertical Pumps 125
Wet Pit Pumps
The most common applications for wet pit pumps are:
• Water supply pumps for municipalities and industry. The pumps are
mounted in intake structures on lakes or rivers.
» Condenser cooling water pumps for central power plants. The pumps
take suction from a natural body of either fresh or salt water.
• Cooling tower pumps. Take suction from a cooling tower basin and circulate
water through a closed system.
» Flood control pumps mounted at dams and in collection basins, often as
part of large flood control systems.
« Transfer pumps for central irrigation districts and water treatment facilities,
Water Supply Pumps
This pump type is normally installed as multiple, parallel operating
units in a simple intake structure or as a stand-alone pumping plant located
on a reservoir, lake, or river and discharging into a pipeline or an
open canal. Depending on the system requirements, multi-stage pumps
or single-stage pumps of the desired specific speed are used. A combination
of fixed and variable speed drivers may be desirable to obtain optimum
system efficiency. While structural integrity and cost are critical
items in design of intake structures, hydraulic considerations and protection
of the pumping equipment are equally important. The structure
should be physically located so that a minimum of debris and silt will be
diverted toward it. Trash racks and rotating screens, which can routinely
be cleaned, must be provided to keep foreign objects from entering the
pumps. The intake structure must be designed for low approach velocity
and with dividing walls forming individual bays as required [5]. The
pumps should be located within the structure in such a fashion that uniform
velocity distribution is provided at each pump suction bell. Obstructions,
changes in flow direction, or velocity changes that may cause
formation of vortices and air entrainment must be avoided. Flow patterns
within the structure, when one or more pumps are idle, must also be considered.
Pump settings, the distance from the mounting floor to the suction
intake, typically vary from 15 feet to 80 feet. The discharge may be
located above or below the mounting floor, depending on the system requirement.
In either case, the discharge pipe should be anchored downstream
from the pump discharge flange to prevent pump misalignment
from pipe reaction forces. When a flexible discharge piping connector is
used, tie bars must be provided across the connector to restrain the hydraulic
separating forces and prevent pump misalignment. Figure 9-11