Environmental Engineering Reference
In-Depth Information
simple and straight for ward, but it can be complicated. If the pipe is rela-
tively short, no more than 20 to a few hundred feet in length, then we
may decide to replace the pipe. But, what
would we do if the pipe were 3 to 5 miles
or more in length? In this case, cleaning
such a length of pipe probably makes
more sense than replacing its entire
length. Each situation is different, requir-
ing remedial choices based on practical-
ity and expense.
Key Point:
After reading the previous example,
you might ask: “Why couldn't the pump be
slowed down so the chemical solution could
pass more slowly through the system, thus avoid-
ing the effect of increased friction?” The lower
pressure that results as pump speed is reduced
causes other problems as well. Pumps that run
at a speed other than that for which they are
designed do so with a reduction in efficiency.
4.5.2 Piping system Maintenance
Maintaining a piping system can be an involved process; however,
good maintenance practices can extend the life of piping system compo-
nents, and rehabilitation can further prolong their life. The performance
of a piping system depends on the ability of the pipe to resist unfavorable
conditions and to operate at or near the capacity and efficiency that it
was designed for. This performance can be checked in several ways: flow
measurement, fire flow tests, loss-of-head tests, pressure tests, simul-
taneous flow and pressure tests, tests for leakage, and chemical and
bacteriological water tests. These tests are an important part of system
maintenance. They should be scheduled as part of the regular operation
of the system (AWWA, 1996).
Most piping systems are designed with various protective fea-
tures included to minimize wear and catastrophic failure, as well as
the amount of maintenance required. Such protective features include
pressure-relief valves, blow-off valves, and clean-out plugs:
Pressure-relief valve
—A valve that opens automatically when the fluid
pressure reaches a preset limit to relieve the stress on a piping
system.
Blow-off valve
—A valve that can be opened to blow out any foreign
material in a pipe.
Clean-out plug
—A threaded plug that can be removed to allow access
to the inside of the pipe for cleaning.
Note:
Use caution when removing a clean-out plug from a piping system.
Before removing the plug, pressure must be cut off and the system bled
of residual pressure. Many piping systems (including wastewater lines
and interceptors) can be cleaned either by running chemical solvents
through the lines or by using mechanical clean-out devices.
4.6 PiPing sysTeM aCCessories
Depending on the complexity of the piping system, the number of
valves included in a system can range from no more than one in a small,
simple system to a large number in very complex systems such as water
distributions systems. Valves are necessary for both the operation of a
