Environmental Engineering Reference
In-Depth Information
is increased, the quantity of water/wastewater pumped is reduced.
Also, centrifugal pumps can be operated for short periods with the
discharge valve closed.
nonclog pumping
—Specifically designed centrifugal pumps utilize
closed impellers with, at most, two to three vanes. They are usually
designed to pass solids or trash up to 3 inches in diameter.
•
dry-pit pump
—Depending on the application, the dry-pit pump may
be either a large-volume pump or a nonclog pump. It is located in a
dry pit that shares a common wall with the wet well. This pump is
normally placed in such a position as to ensure that the liquid level
in the wet well is sufficient to maintain the prime of the pump.
•
Wet-pit or submersible pump
—This type of pump is usually a non-
clog pump that can be submerged, with its motor, directly in the
wet well. In a few instances, the pump may be submerged in the wet
well while the motor remains above the water level. In these cases,
the pump is connected to the motor by an extended shaft.
•
underground pump stations
—Utilizing a wet-well/dry-well design,
these pumps are located in an underground facility. Wastes are col-
lected in a separate wet well, then pumped upward and discharged
into another collector line or manhole. This system normally uses
a nonclog type of pump and is designed to add sufficient head to
water/wastewater flow to allow gravity to move the flow to the plant
or the next pump station.
•
recycle or recirculation pumps
—Because the liquids being trans-
ferred by the recycle or recirculation pump normally do not contain
any large solids, the use of the nonclog type of centrifugal pump is
not always required. A standard centrifugal pump may be used to
recycle trickling filter effluent, return activated sludge, or digester
supernatant.
•
Service water pumps
—The wastewater plant effluent may be used
for many purposes, such as to clean tanks, water lawns, provide
water to operate the chlorination system, and backwash filters.
Because the plant effluent used for these purposes is normally
clean, the centrifugal pumps used in this case closely parallel the
units used for potable water. In many cases, the double-suction,
closed-impeller, or turbine type of pump is used.
•
3.3.7 Pump Control systems
Pump operations usually control only one variable: flow, pressure, or
level. All pump control systems have a measuring device that compares
a measured value with a desired one. This information relays to a con-
trol element that makes the changes. …The user may obtain control with
manually operated valves or sophisticated microprocessors. Economics
dictate the accuracy and complication of a control system.
Wahren (1997)
Most centrifugal pumps require some form of pump control system.
The only exception to this practice is when the plant pumping facilities
are designed to operate continuously at a constant rate of discharge. The
