are to be joined. The purpose of dielectric fittings
uniform plastic state, joining the components
is to curtail galvanic or electrolytic action. The
together, and then allowing the two surfaces to
most common dielectric fittings are the union,
fuse into a homogeneous bond as the materials cool
coupling, and bushing.
to room temperature.
Fittings are identified by the sizes of pipe that
are connected to their openings. For example, a
3- by 3- by 1 1/2-in. tee is one that has two
openings for a 3-in. run of pipe and a 1 1/2-in.
reduced outlet. If all openings are the same size,
only one nominal diameter is designated. For
example, a 3-in. tee is one that has three 3-in.
Joints and Connections
There are various methods of joining pipes for
water distribution systems. Each method used is
designed to withstand internal (hydrostatic)
pressure in the pipe and normal soil loads if joints
and connections are belowground. Some of these
methods produce the types of joints and
connections described below.
FLARED AND SWEATED JOINTS. These
joints are generally used with copper pipe and
tubing. The end of a copper pipe is formed into
a funnellike shape so that it can be held in a
threaded fitting when a line joint is being made.
This method is called FLARING, and the result
is called a FLARED JOINT. A SWEATED
JOINT is made with soft solder instead of threads
or flares. In plumbing, copper pipe or tubing is
occasionally fused by heating with a gas flame and
silver-aIloy filler metal called SILVER BLAZING
(also called HARD SOLDERING).
SOLVENT WELDED, FUSION WELDED,
FILLET WELDED, THREADED, AND
FLANGED JOINTS. These types of joints are
common to plastic pipes. In the production of
a SOLVENT WELDED JOINT, a solvent cement
with a primer is used. Before solvent is applied,
the pipe and fitting must be thermally balanced
(caused to have similar temperatures). This
process should not be undertaken when the
temperature is below 40°F or above 90°F or when
the pipes are exposed to direct sunlight.
FUSION WELDED JOINTS are produced by
the use of a gas- or an electric-heated welding tool.
The process consists of simultaneously heating the
meeting surfaces of the pipe and fitting to a
FILLET WELDED JOINTS are made by the
use of a uniform heat and pressure on the welding
rod during application of the bead. This process
can also be applied to repair leaks in
In plastic pipes, THREADED JOINTS are
commonly used for temporary and low-pressure
piping since threading reduces the pipe wall
thickness. Only certain heavy pipes can be
threaded with a special strap wrench. Teflon tape
is often used for pipe joint compound when this
method of joining pipes is used.
FLANGED JOINTS are extensively used for
process lines that are dismantled frequently.
Plastic pipes are joined together by the use of
plastic flanges with soft rubber gaskets.
BELL-AND-SPIGOT AND MECHANICAL
JOINTS. These types of joints are most
commonly used with cast-iron pressure pipe and
fittings for water mains. These service lines are
joined by the use of lead, lead wool, or sometimes
a sulfur compound. Mechanical joints are made
with rubber sealing rings held in place by metal
follower rings that are bolted to the pipe. These
are designed to permit expansion and contraction
of the pipe without injury to the joints.
THREADED PIPE JOINTS are commonly
used on galvanized steel, galvanized wrought
and black-iron pipe. The process
includes connecting threaded male and female
ends. Nontoxic compounds are used for t bread
lubricant on water pipes, while powdered graphite
and oil are used for steam pipes.
Valves are devices that are used to stop, start,
or regulate the flow of water into, through, or
from pipes. Essentially, valves consist of a body
containing an opening and a means of closing the
opening with a valve disk or plug that can be
tightly pressed against a seating surface around
or within the opening. Many different valve
designs are available; however, only the three most
common types of valves will be discussed here.
They are the gate, check, and globe valves.