Water Hydraulics - Wastewater Operators - page 78

2.10.4 Minor head loss
In addition to the head loss caused by friction between the fluid and
the pipe wall, losses also are caused by turbulence created by obstruc-
tions (i.e., valves and fittings of all types) in the line, changes in direc-
tion, and changes in flow area.
Note: In practice, if minor head loss is less than 5% of the total head
loss, it is usually ignored.
2.11 basiC PiPing hydrauliCs
Water, regardless of the source, is conveyed to the waterworks for
treatment and distribution to the users. Conveyance from the source to
the point of treatment occurs by aqueducts, pipelines, or open channels,
but the treated water is normally distributed in pressurized closed con-
duits. After use, whatever the purpose, the water becomes wastewater,
which must be disposed of somehow but almost always ends up being
conveyed back to a treatment facility before being outfalled to some
water body to begin the cycle again. We call this an urban water cycle ,
because it provides a human-generated imitation of the natural water
cycle. Unlike the natural water cycle, however, without pipes, the cycle
would be nonexistent or, at the very least, short circuited.
For use as water mains in a distribution system, pipes must be
strong and durable in order to resist applied forces and corrosion. The
pipe is subjected to internal pressure from the water and to external
pressure from the weight of the backfill (soil) and vehicles above it. The
pipe may also have to withstand water hammer. Damage due to corro-
sion or rusting may also occur internally because of the water quality
or externally because of the nature of the soil conditions. Pipes used in
a wastewater system must be able to resist the abrasive and corrosive
properties of the wastewater. Like water pipes, wastewater pipes must
also be able to withstand the stresses caused by the soil backfill mate-
rial and the effect of vehicles passing above the pipeline. Joints between
wastewater collection and interceptor pipe sections should be flexible
but tight enough to prevent excessive leakage, either of sewage out of the
pipe or groundwater into the pipe. Of course, pipes must be constructed
to withstand the expected conditions of exposure, and pipe configura-
tion systems for water distribution or wastewater collection and inter-
ceptor systems must be properly designed and installed in terms of water
hydraulics. Because the water/wastewater operator should have a basic
knowledge of water hydraulics related to commonly used standard piping
configurations, piping basics are briefly discussed in this section.
2.11.1 Pipe networks
It would be far less costly and much more efficient if municipal water
and wastewater systems were built with individual, single-pipe networks
extending from the treatment plant to each user's residence or from the
user's sink or bathtub drain to the local wastewater treatment plant.