Environmental Engineering Reference
In-Depth Information
piping system and control of the system and system components. In
wastewater treatment, this control function is used to control various
unit processes, pumps, and other equipment. Valves also function as
protective devices; for example, valves used to pro-
tect a piping system may be designed to open auto-
matically to vent fluid out of the pipe when the
pressure in the lines becomes too high. In lines
that carry liquids, relief valves preset to open at a
given pressure are commonly used. The size and type of valve are
selected depending on its intended use. Most valves require periodic
inspection to ensure that they are operating properly.
Key Point:
Not all valves function
as safety valves; for example, hand-
operated gate and globe valves
function primarily as control valves.
Along with valves, piping systems typically include accessories
such as pressure and temperature gauges, filters, strainers, pipe hang-
ers, and supports:
Pressure gauges
indicate the pressure in the piping system.
Temperature gauges
indicate the temperature in the piping system.
filters
and
strainers
are installed in piping systems to help keep flu-
ids clean and free from impurities.
Pipe hangers and supports
support piping to keep the lines straight
and prevent sagging, especially in long runs. Various types of pipe
hangers and supports are shown in Figure 4.2.
4.7 PiPing sysTeMs: TeMPeraTure
effeCTs and insulaTion
Most materials, especially metals, expand as the temperature
increases and contract as the temperature decreases. This can be a sig-
nificant problem in piping systems. To combat this problem and to allow
for expansion and contraction in piping systems,
expansion joints
must
be installed in the line between sections of rigid pipe. An expansion joint
absorbs thermal expansion and terminal movement; as the pipe sections
expand or contract with changing temperatures, the expansion joint
expands or compresses accordingly, eliminating stress on the pipes.
Piping system temperature requirements also have an impact on
how pipes are insulated; for example, we do not have to wander too far
in most plant sites to find pipes covered with layers of piping insulation.
Piping insulation amounts to wrapping the pipe in an envelope of insu-
lating material. The thickness of the insulation depends on the appli-
cation. Under normal circumstances, heat passes from a hot or warm
surface to a cold or cooler one. Insulation helps prevent hot fluid from
cooling as it passes through the system. For systems conveying cold
fluid, insulation helps keep the fluid cold. Materials used for insulation
vary, and they are selected according to the requirements of the appli-
cation. Various types of insulating materials are also used to protect
underground piping against rusting and corrosion caused by exposure
to water and chemicals in the soil.
