Page 82 - Know and Understand Centrifugal Pumps

Pump Classification

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DIAMETER AND

HEIGHTOFTHE
VANESANDSPEED
DETERMINE
THE FLOW
Figure 6-13 -~
them is the way that the impeller receives the liquid from the suction
piping. A classic pump impeller receives the liquid at the impeller’s ID.
By centrifugal force and blade design, the liquid is moved through the
blades fi-om the ID to the OD of the impeller where it expels the liquid
into the volute channel.

Tu r b i ne i m pel I ers
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On the other hand, turbine impellers receive the liquid at the outside
diameter of the impeller, add velocity fi-om the motor, and then expel
the liquid, also at the OD to the discharge nozzle. Because these
impellers have little available area at the OD, these impellers don’t
move large quantities of liquid. Rut, because the liquid’s velocity is
jerked instantly and violently to a very high speed (remember that a
classic centrifugal pump has to accelerate the liquid across the blades
from the ID to the OD), a lot of energy is added to the fluid and these
type pumps are capable of generating a lot of head at a low flow.
Additionally, because all the action occurs at the impeller’s OD
(Remember that there are friction losses and drag as the liquid in a
centrifugal pump traverses the impeller blades from ID to OD), there
are minimal losses in a turbine pump impeller, which further adds to its
high-pressure capacity, see Figure 6-14.
In the case of a regenerative turbine pump, any high-energy liquid
that doesn’t leave the pump through the discharge nozzle is imme-
diately re-circulated back toward the suction where it combines with
any new liquid entering into the blades. In this case even more energy is
added to already high-energy liquid (thus the name ‘regenerative’).
This type pump continues to regenerate and compound its pressure or