Water/Wastewater Laboratory Calculations - Basic Mathematics for Water and Wastewater Operators - page 232

Solution: Calculate the flow rate from the faucet:

Flow = Volume (gal) ÷ Time (min) = 1 gal ÷ 0.80 min = 1.25 gpm

■ Example 16.2
Problem: The flow from a faucet filled up a gallon container in 55 sec. What was the
flow rate from the faucet in gallons per minute?

Solution:

55 sec ÷ 60 sec/min = 0.92 minute

Calculate the flow rate:

Flow = Volume (gal) ÷ Time (min) = 1 gal ÷ 0.92 min = 1.1 gpm

SERVICE LINE FLUSHING TIME
To d et e r m i n e the quality of potable water delivered to the consumer, a sample is
taken from the customer's outside faucet—water that is typical of the water deliv-
ered. To obtain an accurate indication of the system water quality, this sample must
be representative. Further, to ensure that the sample taken is typical of water deliv-
ered, the service line must be flushed twice. Equation 16.2 is used to calculate flush-
ing time:

2 3 × 2

0.785 ×× × D 48 gal/ft

Flow rate (gpm)

Length (ft)7.

Flushing time(min) = (16.2)

■ Example 16.3
Problem: How long (in minutes) will it take to flush a 40-ft length of a 1/2-in.-
diameter service line if the flow through the line is 0.5 gpm?

Solution: Calculate the diameter of the pump in feet:

0.50 in. ÷ 12 in./ft = 0.04 ft

Calculate the flushing time:

2 3

0.785 ×× × D Length (ft) 7.48 gal /ft × 2

Flushing time =

Flow rate (gpm)

2 3 ×

0.785 × (. ) 004 × 40 ft × 7.48 gal/ft 2

=

0.5 gpm

= 1.5 min