Basic Units of Measurement and Conversions - Basic Mathematics for Water and Wastewater Operators - page 20

Problem: The flow in a channel is determined to be 3.89 cfs. What is the flow rate in
million gallons per day?

Solution:

Flow (cfs)
1.55 cfs/MG

3.89 cfs
1.55 cfs

Flow = = = 2. MGD

/MG

■ Example 2.22
Problem: The water in a tank weighs 675 lb. How many gallons does it hold?

Solution: Water weighs 8.34 lb/gal; therefore,

675 lb ÷ 8.34 lb/gal = 80.9 gal

■ Example 2.23
Problem: A liquid chemical weighs 62 lb/ft 3 . How much does a 5-gal can of it weigh?

Solution: Solve for specific gravity, determine lb/gal, and multiply by 5:

3

Weight of chemical
Weight of

62 lb/ft
62.4 lb/ft

Specificgravity = = = 099 .

3

ffwater

Weight of chemical
Weight of

Specificgravity =

ffwater
Weight of chemical
8.34 lb/gal

099 . =

0 .99 × 8.34 lb/gal = Weight of chemical

8.26 lb/gal = Weight of chemical

8.25 lb/gal × 5gal = 41 .. 3lb

■ Example 2.24
Problem: The weight of a wooden piling with a diameter of 16 in. and a length of 16
ft is 50 lb/ft 3 . If it is inserted vertically into a body of water, what vertical force is
required to hold it below the water surface?

Solution : If this piling had the same weight as water, it would rest just barely sub-
merged. Find the difference between its weight and that of the same volume of
water—that is the weight required to keep it down:

62.4 lb/ft 3 (water) - 50.0 lb/ft 3 (piling) = 12.4 lb/ft 3

Volume of piling = 0.785 × (1.33 ft) 2 × 16 ft = 22.22 ft 3

12.4 lb/ft 3 × 22.22 ft 3 = 275.5 lb