ESSOM COMPANY LIMITED
Section 2: Theory
5
Figure 2- 4
:
Schematic diagram of a Pelton
-
type impulse turbine
.
The basic construction of the Pelton turbine is as shown in
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.
The turbine runner
consists of buckets placed radically side by side
.
Each bucket has two identical and adjacent spoons as shown in
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.
The free jet strikes buckets on a rotating wheel
.
In practice these buckets are usually spoon
-
shaped, with a central ridge
splitting the incoming jet into two halves which are deflected backward through an angle of about 165 degrees as shown
in
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.
Complete reversal of 180 degrees is desirable but it is not possible because the
water must be thrown out sidewise to clear for the following bucket
.
▪
Cross Flow Turbine
This Cross Flow or Through Flow Turbine is considered to be the same type of Impulse turbine, it consists of two
parts, a turbine runner and a nozzle
.
Water with high
-
pressure head is released through a nozzle, whose cross
-
section is
rectangular
.
The wheel or runner is made up of two circular disks jointed together at the rim with a series of curved blades
.
This type of turbine, which is also known as Banki turbine, is provided with a gate vane with lever linkage to regulate the
flow rates by increasing or decreasing the thickness of the jet for change in power requirements, as shown in
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Reference source not found.
.
The nozzle discharges the water jet in full width of the wheel and the jet is forced to enter
the wheel at an angle of certain degree to the wheel periphery
.
The water strikes the blade on the rim of the wheel, flow
over the blade, leaving it, passing through the empty space between the inner rims, enters a blade on the inner side of the
rim, and discharges at the outer rim
.
The wheel is therefore an inward jet wheel and the flow is essentially radial flow
type
.
Typical path of water through cross flow
(
Banki
)
turbine and the velocity diagram are shown in
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source not found.
.
D
B
C
E
A
Water Outlet
Water Inlet