Page 149 - Centrifugal Pumps Design and Application

Vertical Pumps 127

• Fresh water bearing lubrication is preferred, but salt water injection is
acceptable as long as it is filtered and continuous. If a pump sits idle for
extended periods without injection, accelerated corrosion may take
place as well as the build-up of harmful crystals and marine life.
• Care must be taken in the selection of base materials for salt water,
Consideration should be given to the average temperature of the water
and the potential absence of oxygen.

Cooling Tower Pumps

These pumps typically have short settings, less than 20 feet, operate
against a fixed head, and are connected to fixed speed drivers. The cool-
ing tower basin and associated sump for pump installation are usually
very limited in depth and area, requiring specific precautions to avoid
vortices and ensure uniform velocity distribution [5]. Model structure
testing is recommended where design margins are small. Water quality
tends to become questionable in this type of closed system, warranting
caution in material selection.

Flood Control Pumps

These are typically low lift, short setting pumps, but vary greatly in
size depending on historic demands. A 2,000 to 3,000 gpm sump pump
may be adequate for protecting a small area, while a large flood control
district may require multiple pumps of several hundred-thousand gpm ca-
pacity each. Such large pumps can partly be formed in concrete at the
site. This can be a major cost advantage, particularly if the water quality
demands high alloy metals. Figure 9-12 shows a propeller pump where
the suction bell, column, and discharge elbow have been formed in con-
crete.
Pump efficiency is not the primary consideration for flood control
pumps because operating time and therefore power consumption is lim-
ited. Reliability is the main concern, and the pumps must be capable of
handling large amounts of silt and sand. Serious flood conditions may be
connected with loss of electric power, and flood control pumps are there-
fore often driven by diesel engines through right angle gear drives,

Transfer Pumps

This general category of pumps covers a wide variety of applications,
from highly efficient central irrigation pumps and canal lift pumps, to
simple, non-clog pumps in sewage and water treatment plants. Com-
monality in design is therefore minimal. When efficiency is one of the