Environmental Engineering Reference
In-Depth Information
62.4 lb
of
water
1 ft
1 ft
1 ft
FIGURE 4.2
One cubic foot of water weighs 62.4 pounds.
Thus,
1 gal water = 8.34 lb
Note:
Convert cubic feet to gallons simply by multiplying the number of cubic feet
by 7.48 gal/ft
3
.
■
Example 4.1
Problem:
Find the number of gallons in a reservoir that has a volume of 855.5 ft
3
.
Solution:
855.5 ft
3
× 7.48 gal/ft
3
= 6399 gal (rounded)
Note:
The term
head
is used to designate water pressure in terms of the height of
a column of water in feet; for example, a 10-ft column of water exerts 4.3 psi. This
can be referred to as 4.3-psi pressure or 10 feet of head.
s
tevIn
'
s
L
aw
Stevin's law deals with water at rest. Specifically, it states: “The pressure at any point
in a fluid at rest depends on the distance measured vertically to the free surface and
the density of the fluid.” Stated as a formula, this becomes
p
=
w
×
h
(4.1)
where
p
= Pressure in pounds per square foot (lb/ft
2
, or psf).
w
= Density in pounds per cubic foot (lb/ft
3
).
h
= Vertical distance in feet.
