Water Treatment Processes - Mathematics and Statistics for the Environment - page 610

The general equation used in calculating percent efficiency is shown below:

Part
Whole

% = × 100 (23.13)

Vertical turbine pump bowl efficiency is easily determined using a pump performance curve chart
provided by the pump manufacturer. Field efficiency is determined using Equation 23.14:

Fieldhead (ft)Capaci × ty (gpm)

Total bhp

Fieldefficiency (%) = × 100 (23.14)

3960 ×

■ EXAMPLE 23.15
Problem: Given the data below, calculate the field efficiency of the deep well turbine pump:

Field head—180 ft
Capacity—850 gpm
Total bhp—61.3 bhp

Solution:

Fieldhead (ft)Capaci × ty (gpm)

Total bhp

Fieldefficiency (%) = × 100

3960 ×

180 ft ×

960

850 gpm

= ×= 100 63 %

3 × 61.3

Overall efficiency is a comparison of the horsepower output of the system with that entering the
system. Equation 23.15 is used to calculate overall efficiency:

Fieldefficiency (%) × Motorefficiency (%)

100

Overallefficiency (%) = (23.15)

■ EXAMPLE 23.16
Problem: The efficiency of a motor is 90%. If the field efficiency is 83%, what is the overall effi-
ciency of the unit?

Solution:

Fieldefficiency (%) Motorefficiency (%)

100

×

Overallefficiency (%) =

83% 90%
100

×

= = 74 .%

23.3 WATER STORAGE
Water storage facilities for water distribution systems are required primarily to provide for fluctuat-
ing demands of water usage (to provide a sufficient amount of water to average or equalize daily
demands on the water supply system). In addition, other functions of water storage facilities include