Page 225 - Water Engineering Hydraulics, Distribution and Treatment

hydrant individually or multiple hydrants flowing
6.9.4 Velocity Requirements
simultaneously; (c) in residential areas, fire hydrants
Velocity of flow is another factor recommended by the State
shall be placed a maximum of 500 ft (152.4 m) apart
of Iowa in determining the flow of water pipes and, therefore,
along the right-of-way with a maximum of 500 ft
the required pipe diameter. Velocities should normally be
(152. m) to the last lot, and the minimum flow from
5 ft/s (1.52 m/s) or less, due to high friction losses occurring
each hydrant shall be 750 gpm (2,839 L/min).
at greater velocities. Of course, this velocity requirement may
be exceeded under fire flow conditions.
The Ten-State Standards recommends that dead-end
6.9.7 Air Relief Valve Requirements
mains be equipped with a means to provide adequate flush-
At high points in water mains where air can accumulate,
ing and flushing devices be sized to provide flows which will
provisions shall be made to remove the air by means of air
give a velocity of at least 2.5 ft/s (0.762 m/s) in the water
relief valves (Fig. 5.26; Section 5.9.3). Use of manual air
main being flushed. 6.9 Practical Design and Analysis of Water Distribution Systems 203
relief valves is recommended. Automatic air relief valves
may be used in situations where floods of the manhole or
6.9.5 Pipes and Valves Spacing Requirements chamber may not occur.
A sufficient number of valves shall be provided on water
mains to minimize inconvenience and hazards during water 6.9.8 Depth of Cover Requirements
system repairs. Common standards on the pipe spacing and
gate valve spacing can be found from Section 6.2. Water mains shall be covered with sufficient earth or other
insulation to prevent freezing. In Florida, cover as measured
from finished grade to top of the pipeline shall be a min-
6.9.6 Hydrant Spacing, Location, and Fire Flow
imum of 36 in. (914.4 mm) for pipe diameters up to and
Requirements
including 12 in. (304.8 mm). Depth of cover for pipes 14 in.
There are two kinds of hydrants: (a) fire hydrants and (b) (355.6 mm) or greater in diameter shall be a minimum of
flushing hydrants. Fire hydrants should be provided at each 48 in. (1219.2 mm). Deeper cover depth is needed when
street intersection and at intermediate points between inter- automatic air release valves are used.
sections as recommended by the Ten-State Standards. Gener- Section 5.7.3 introduces the authors’ engineering equa-
ally, fire hydrant spacing ranges from 150 to 1,000 ft (45.72– tions for determination of the depth of cover in cold weather
304.8 m) depending on the area being served and the location regions.
where the water system is constructed. The following is a
summary of three sources of standards:
6.9.9 Separation of Water Mains from Sources
1. Common standards: The number, spacing distribu- of Contamination
tion, and fire flow requirements of fire hydrants are
In accordance with the Ten-State Standards, water mains
presented in Table 6.1.
shall be laid at least 10 ft (3.05 m) horizontally from any
2. The Ten-State Standards: (a) Fire hydrant spacing existing or proposed gravity sanitary sewer, gravity storm
ranges from 350 to 600 ft (106.7–182.9 m) depend- sewer, sanitary sewer force main, septic tank, sewer man-
ing on the area being served; and (b) flushing hydrants holes, or subsoil treatment system. The horizontal separation
(instead of fire hydrants) are provided on the water distance shall be measured edge to edge. In cases where it is
systems not designed to carry any fire flows and not practical to maintain a 10 ft (3.05 m) separation distance,
should give a velocity of at least 2.5 ft/s (0.76 m/s) in the reviewing authority may allow deviation on a case-by-
water main during flushing. case basis, if supported by data from the design engineer.
3. The State of Florida Hillsborough County Stan- Water mains crossing gravity sanitary sewer, gravity
dards: (a) In manufacturing and industrial areas, storm sewer, or sanitary sewer force main shall be laid to
fire hydrants shall be placed every 300 ft (91.4 m) provide a minimum vertical separation distance of 18 in.
along the right-of-way with a maximum of 150 ft (45.72 cm) between the outside of the water main and the
(45.7 m) to the last lot, and the minimum required outside of the sewer. This shall be the case where the water
fire flow shall be 1,000 gpm (3,785 L/min) main is either above or below the sewer with preference to the
provided by either each hydrant individually or water main located above the sewer. Besides, one full length
multiple hydrants flowing simultaneously; (b) in of water pipe shall be located at crossings, so both joints
commercial and apartment areas, fire hydrants shall will be as far from the sewer as possible. Special structural
be placed every 500 ft (152.4 m) along the right- support for the water and sewer pipes may be required.
of-way with a maximum of 250 ft (76.2 m) to the When it is impossible to obtain the minimum speci-
last lot, and the minimum required fire flow shall be fied horizontal separation distances, the reviewing author-
1,000 gpm (3,785 L/min) provided by either each ity must specifically approve any variance from the above