Environmental Engineering Reference
In-Depth Information
Discharge
Volute
Nozzle
Impeller
figure 3.8 Cross-sectional diagram showing the features of a centrifu-
gal pump.
Shut-off head
—The head or pressure at which the centrifugal pump
will stop discharging. It is also the pressure developed by the pump
when it is operated against a closed discharge valve. This is also
known as a
cut-off head
.
Slinger ring
—A device to prevent pumped liquids from traveling along
the shaft and entering the bearing assembly. A slinger ring is also
called a
deflector.
.
Wearing ring
—Device that is installed on stationary or moving parts
within the pump casing to protect the casing and the impeller
from wear due to the movement of liquid through points of small
clearances.
•
Casing ring
—A wearing ring installed in the casing of the pump.
A casing ring is also known as a
suction head ring
.
•
Impeller ring
—A wearing ring installed directly on the impeller.
•
Stuffing box cover ring
—A wearing ring installed at the impeller
in an end suction pump to maintain the impeller clearances and
to prevent casing wear.
3.3.3 Pump Theory
The
volute-cased centrifugal pump
(see Figure 3.8) provides the
pumping action necessary to transfer liquids from one point to another.
First, the drive unit (usually an electric motor) supplies energy to the
pump impeller to make it spin. This energy is then transferred to the
water by the impeller. The vanes of the impeller spin the liquid toward
the outer edge of the impeller at a high rate of speed or velocity. This
action is very similar to that which would occur when a bucket full of
water with a small hole in the bottom is attached to a rope and spun.
When the bucket is sitting still, the water in it will drain out slowly; how-
ever, when the bucket is spinning, the water will be forced through the
hole at a much higher rate of speed.
