Page 185 - Water and wastewater engineering

4-40 WATER AND WASTEWATER ENGINEERING

Curve no. 4-15
Size 1 Rpm 1750
Single- stage lab head and horse-power with
enameled cast iron bowls and bronze impeller
Effieciency shown for 2 or more stages Impeller B
No. Eff. Material Eff. Impeller A
stages change change 4.0
1 1 Imp.-C.I. 0 3.0
2 0 Imp.-C.I. Enn 0 Head per stage, m 2.0 A
3 0 Bowl -C.I. 1
4 0 Bowl -Brz. 1 1.0 B
Eye area 32 cm
Thurst constang - A 2.3 2
Thurst constang - B 2.3
Thurst constang - C 2.3 NPSH required
1 NPSH required at pump inlet, m
Max. no. std. stages 35 80 0
Max. operating pressure 3,900 kPa
Std. lateral .375
Std. shaft dia. 2.0 cm 60
Impeller number P-2397-10 A
Impeller wt. 3.6 kg
Bowl conn. - flanged Efficiency % 40
Add 10.6 cm per additional stage
Enclosed line shaft 20
33 cm 0
10.0 20.0 30.0 40.0
3
13 cm Discharge, m /h

FIGURE 4-15
Vertical turbine head—discharge curve for Example 4-7.

in the problem data (i.e., 5 C and altitude of 500 m), the NPSH A is greater than 9.6 m.
If the pump intake is set 1.0 m below the maximum 100 day drawdown as shown in
Figure 4-16 , it will meet both requirements.
m. Check the dimension drawing for the diameter to see if the pump will fit in the casing. Its
diameter is 13 cm, and the casing inside diameter is 15 cm. While the pump will fit, the
recommended minimum clearance of 5 cm is not met. The next larger diameter casing
of 20 cm should be chosen and the calculations reworked for screen length, velocity, and
drawdown. Because the estimates with the smaller diameter casing met the guidelines
for screen length and velocity with a substantial margin of safety, in this instance they do
not need to be reevaluated. However, the drawdown calculation and TDH will need to be
adjusted to account for the larger diameter.

Comments:
1. The number of stages for the pump is very high. A more reasonable number would be on
the order of three to five stages. A more extensive search of available pumps should be
conducted.
2. For some well systems, a submersible pump may be more appropriate than a line pump.
These should also be investigated.