Environmental Engineering Reference
In-Depth Information
devices include strainers, filters, and traps. In this section, we describe
the design and function of strainers, filters, and traps. The major main-
tenance considerations of these protective devices also are explained.
4.14.1 applications
Filters, strainers, and traps are normally
thought of in terms of specific components used
in specific systems; however, it is important to
keep in mind that the basic principles apply in
many systems. Although the examples used in this chapter include
applications found in wastewater treatment, collection, and distribution
systems, the applications are also found in almost every plant—hot and
cold water lines, lubricating lines, pneumatic and hydraulic lines, and
steam lines. With regard to steam lines, it is important to point out that
in our discussion of traps, their primary application is in steam sys-
tems, where they remove unwanted air and condensate from lines.
Key Point:
A very large percentage
(estimated to be >70%) of all plant
facilities in the United States make use
of steam in some type of application.
Other system applications of piping protective devices include the
conveyance of hot and chilled water for heating and air conditioning and
lines that covey fluids for various processes. Any foreign contamination
in any of these lines can cause potential trouble. Piping systems can
become clogged, thereby causing greatly increased friction and lower
line pressure. Foreign contaminants (dirt and other particles) can also
damage valves, seals, and pumping components.
Note:
Foreign particles in a high-pressure line can damage a valve by
clogging the valve so it cannot close tightly. In addition, foreign par-
ticles may wear away the closely machined valve parts.
4.14.2 strainers
Strainers, usually wire mesh screens, are used in piping systems
to protect equipment sensitive to contamination that may be carried
by the fluid. Strainers can be used in pipelines conveying air, gas, oil,
steam, water, wastewater, and nearly any other fluid conveyed by pipes.
Generally, strainers are installed ahead of valves, pumps, regulators,
and traps to protect them against the damaging effects of corrosion
products that may become dislodged and conveyed throughout the pip-
ing system (Geiger, 2000).
A common strainer is shown in Figure 4.38. This type of strainer
is generally used upstream of traps, control valves, and instruments.
This strainer resembles a lateral branch fitting with the strainer ele-
ment installed in the branch. The end of the lateral branch is remov-
able to permit servicing of the strainer. In operation, the fluid passes
through the strainer screen, which catches most of the contaminants.
Then the fluid passes back into the line. Contaminants in the fluid are
caught in two ways—either they do not make it through the strainer
screen or they do not make the sharp turn that the fluid must take as it
leaves the unit. The bottom of the unit serves as a sump where the solids
