Environmental Engineering Reference
In-Depth Information
3.3.9.1.3 advantages
In addition to the advantages discussed earlier for a conventional
centrifugal pump, the submersible pump has additional advantages:
•
It is located below the surface of the liquid, so it is not as likely that
the pump will lose its prime, develop air leaks on the suction side
of the pump, or require initial priming.
•
The pump or the entire assembly is located in the well, so costs
associated with the construction and operation of this system are
reduced. It is not necessary to construct a dry well or a large struc-
ture to hold the pumping equipment and necessary controls.
3.3.9.1.4 disadvantages
The major disadvantage associated with the submersible pump is
the lack of access to the pump or pump and motor. The performance of
any maintenance requires either drainage of the wet well or extensive
lift equipment to remove the equipment from the wet well, or both. This
may be a major factor in determining if a pump receives the attention it
requires. Also, in most cases, all major maintenance on close-coupled
submersible pumps must be performed by outside contractors due to
the need to reseal the motor to prevent leakage.
3.3.9.2 Recessed Impeller or Vortex Pumps
The recessed impeller or vortex pump
uses an impeller that is
either partially or wholly recessed into the rear of the casing (see Figure
3.15). The spinning action of the impeller creates a vortex or whirlpool.
This whirlpool increases the velocity of the material being pumped. As
in other centrifugal pumps, this increased velocity is then converted to
increased pressure or head.
3.3.9.2.1 applications
The recessed impeller or vortex pump is used widely in applica-
tions where the liquid being pumped contains large amounts of solids or
debris and slurries that could clog or damage the impeller of the pump.
It has found increasing use as a sludge pump in facilities that withdraw
sludge continuously from their primary clarifiers.
3.3.9.2.2 advantages
The major advantage of this modification is the increased ability to
handle materials that would normally clog or damage the pump impel-
ler. Because the majority of the flow does not come in direct contact with
the impeller, the potential for problems is reduced.
