Environmental Engineering Reference
In-Depth Information
4.8.5.2.1 expansion and flexibility
Because of thermal expansion, water/
wastewater systems (which are rigid and
laid out in specified lengths) must have
adequate flexibility. In water/wastewater
systems without adequate flexibility, thermal expansion may lead to fail-
ure of piping or anchors. Moreover, it may also lead to joint leakage and
excessive loads on appurtences. The thermal expansion of piping can be
controlled by properly locating anchors, guides, and snubbers. Where
expansion cannot be controlled, flexibility is provided by use of bends,
loops, or expansion joints (Gigliardi and Liberatore, 2000).
Key Point:
Metals expand or contract according
to temperature variations. Over a long run (length
of pipe), the effects can cause considerable strain
on the lines—damage or failure may result.
4.8.5.2.2 Pipe Support Systems
Pipe supports are normally used to carry dead weight and ther-
mal expansion loads. These pipe supports may loosen in time, so they
require periodic inspection. Along with normal expansion and contrac-
tion, vibration (water hammer or fluids traveling at high speeds and
pressures) can cause the supports to loosen.
4.8.5.2.3 valve Selection
Proper valve selection and routine preventive maintenance are
critical to the proper operation and maintenance of any piping system.
In wastewater piping systems, valves are generally used for isolating a
section of the wastewater collection line, draining the wastewater line,
throttling liquid flow, regulating wastewater storage levels, controlling
water hammer, bleeding off air, or preventing backflow.
4.8.5.2.4 Isolation
Various valves are used in piping systems to provide for isolation;
for example, gate valves are used to isolate specific areas (valve closed)
of the system during repair work or to reroute wastewater flow (valve
open) throughout the collection system. Service stop valves are com-
monly used to shut off service lines to individual homes or industries.
Butterfly valves are also used for isolation purposes.
4.8.5.2.5 Preventing Backflow
Backflow, or reversed flow, could result in contaminated or polluted
water entering the potable water system. Water distribution systems
have numerous places where unsafe water may be drawn into the potable
water mains if a temporary vacuum should occur in the system. In addi-
tion, contaminated water from a higher pressure source can be forced
through a water system connection that is not properly controlled. A
typical backflow condition from a recirculated system is illustrated in
Figure 4.4.
