Pumping Calculations - Basic Mathematics for Water and Wastewater Operators - page 208

■ Example 14.24
Problem: If a single-phase motor pulls 12 amperes at 220 volts and has a power fac-
tor of 1.1, how many kilowatts of power does it use?

Solution:

Volts × AmperesPower factor

1000 watts/kW

× 220 volts × 12 amperes × 1.1

= = 2.9 kW

1000 watts/kW

■ Example 14.25
Problem: How many watts of power does a three-phase motor use if it pulls 25
amperes at 440 volts and has a power factor of 0.94?

Solution: In the following, 1.732 is the square root of 3, a value used in many three-
phase calculations.

Volt s × Amperes × Power factor × 1.732 = 440 volts × 25 amperes × 0.94 × 1.732)

= 17,909 watts

■ Example 14.26
Problem: A pump must pump 3200 gpm against a total head of 22 ft. What horse-
power (water horsepower) will be required to do the work?

Solution:

Flow (gpm)Head (ft)
3960

× 3200 gpm ×

3960

22 ft

whp = = = 17.8 hp

■ Example 14.27
Problem: A flow of 540 gpm must be pumped against a head of 42 ft. What is the
horsepower required?

Solution:

Flow (gpm)Head (ft)
3960

× 540 gpm ×

960

42 ft

whp = = = 5.73 hp

3

■ Example 14.28
Problem: A pump is pumping a total head of 73.4 ft. If 875 gpm are to be pumped,
what is the water horsepower requirement?

Solution:

Flow (gpm)Head (ft)
3960

× 875 gpm × 73.4 f t

whp = = = 16.22 hp

3960