TM 5-814-2/AFM 88-11, Vol. 2
CHAPTER 4
WASTEWATER PUMPING EQUIPMENT
furnished with vertical shaft having a bottom suction,
4-1.
WASTEWATER PUMPS
with the propeller mounted near the bottom of the shaft
a Centrifugal pumps. The centrifugal pump is the
and enclosed in a bowl.
The propeller is totally
predominate type of wastewater pump used. These
submerged and can be clogged by large solids, rags or
pumps are available in three variations, radial flow,
trash. Therefore, this pump will only be used for clear
mixed flow, and axial flow. Centrifugal pumps will not
well applications. Axial flow centrifugal pumps are
be used in capacities of less than 100 gallons per
available in 8-inch through 72-inch discharge sizes. The
minute.
recommended capacity range for these pumps is 500 to
(1) Radial flow pumps.
The radial flow
100,000 gpm. Pumps are available to operate from 1 to
centrifugal pump is the major type used for pumping raw
40 feet TDH.
wastes. In a radial flow pump, the fluid enters the
(4) Pump
construction.
Centrifugal
impeller axially and is discharged at right angles to the
wastewater pumps will normally be constructed of cast
shaft. Two types of radial flow pumps are available,
iron with bronze or stainless steel trim, and with either
single suction and double suction. In a single-end
cast iron or bronze impellers. When operating' ill
suction pump, fluid enters the impeller from one side.
wastewater containing substantial quantities of grit,
The shaft does not extend into the suction passage, and
impellers made of bronze, cast steel or stainless steel
because of this, rags and trash do not clog the pump.
will be required. Enclosed impellers will be specified for
The single-end suction pump will be suitable for
wastewater pumps required to pass solids. Pump
handling untreated wastewater. For a double suction
casings of the volute type will be used for pumping raw
pump, fluid enters the impeller from both sides, however
untreated wastes and wastewaters containing solids.
the shaft extends into the suction passage, thereby
Diffusion of turbine type casings may be utilized for
limiting its use to handling only clear water. Radial flow
effluent or clear water service at waste treatment
centrifugal pumps are available in discharge sizes of 2
facilities. Pump shafts will be high grade forged steel,
to 20 inches. However, pumps with a capacity to pass
and will be protected by renewable bronze or stainless
3-inch minimum solids will be required.
The
steel sleeves where the shaft passes through the
recommended capacity range for these pumps is 100 to
stuffing box. Stuffing boxes will utilize either packing
20,000 gpm. Pumps are available in discharge heads of
glands or mechanical type seals.
25 to 200 feet total dynamic head (TDH). Peak design
(5) Stuffing box seals. The stuffing box will
efficiency ranges from 60 percent for smaller pumps to
be lubricated and sealed against leakage of wastewater
85 percent for larger pumps. Radial flow pumps are
(into the box) by grease, potable water, or another clear
suitable for either wet well or dry well applications. They
fluid. The lubricating and sealing sealing medium will
can be installed with horizontal or vertical shafting,
be supplied to the stuffing box at a pressure of 5 to 10
however, vertical shaft pumps require considerably less
psi greater than the pump shutoff head. Grease seals
space.
are usually provided by cartridges which are either
(2) Mixed flow pumps.
The mixed flow
spring loaded or pressurized by connections off the
centrifugal pump is an intermediate design between the
pump discharge. These arrangements generally do not
radial flow type and the axial flow type, and has
maintain sufficient seal pressure on the stuffing box.
operating characteristics of both. The mixed flow pump
However, they will be acceptable for low head pumps
is designed with wide unobstructed passages, and is
and where the wastewater contains little grit, as when
therefore suitable for handling wastewater or clear
pumping treated effluent. When pumping raw untreated
water. Mixed flow centrifugal pumps are available in 8-
wastes containing the usual quantities of grit, a potable
inch through 84-inch discharge sizes.
The
water seal system with seal pump will be required if a
recommended capacity range for these pumps is 1,000
potable water line is assessable within a reasonable
to 80,000 gpm. Pumps are available to operate at 10 to
distance. The Later seal system will be capable of
60 feet TDH. Peak design efficiency depends on the
supplying 3 gpm per pump minimum. The principal
size and characteristics of the individual pump, but
advantage of a water seal over a grease seal is the
generally ranges from 80 to 90 percent. The mixed flow
positive pressure maintained on the stuffing box by the
centrifugal pump is normally used only in dry well
seal pump, and small amount of water which flows from
applications, with either horizontal or vertical shafting
the stuffing box into the pump casing. Grit and other
configuration.
abrasive materials that may be in the wastewater are
(3) Axial flow pumps. Axial flow centrifugal
pumps will not be used to pump raw untreated
wastewater. This pump is designed primarily for clear
water service and for wet well installations. The pump is
4-1
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