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............................................. Special Pumps

shaft, and the casing is bolted to
the motor. As a consequence of
this design, the motor shaft must
be able to resist all the impeller
radial and axial forces, and the
motor bearings must carry the
pump impeller loads in addition to
normal motor electromagnetic
and torsional loads.
The submersible pump in-
corporates a motor that is
designed so that the entire unit
can operate while immersed in the
pumped liquid. The compact
design and maneuverability of this
pump results in very flexible usage
in a variety of applications, but
mostly in drainage types of service.
In the water and waste treatment Figure 9.2: Typical submersible pump
industry, these pumps are (Reproduced with permission of ITT Flygt)
occasionally secured in a fixed
position at the bottom of the wet well and attached to the fixed
discharge piping. More frequently they are used in conjunction with a
set of slide rails and a special discharge flange connection that allows
them to be drawn up from the bottom of the wet well for service.
Sometimes they are used as portable units and simply lowered into
place as required. As with other submerged suction pumps, a variety of
float switches are available for automatic on/off control.
If these pump types are used in a critical application, it is worthwhile to
remember that all the usual cautionary signs of pump failure such as
vibration, noise and overheating, will go undetected because the pumps
are operating under water. Under these conditions, it is recommended
that some kind of alarms be included to indicate such problems.

.1.3 Priming the pump
Pump styles which do not operate with a submerged suction can also be
utilized. These pumps will be located above the sump, with only a
suction line being lowered into the sump, and with the liquid source
below the level of the pump. This is known as operating on a suction
lift and, under these conditions, it is important to be able to 'Prime' the
pump to ensure that it starts to pump.

Priming the pump requires removing all the air from the suction line
and the pump, and filling them with water. This is usually achieved

145 m