Figure 8-4.-Comparison of pressure and recessed (Durham)
types of fittings.
also be adapted to metal pipe fittings. The fittings
used on either steel pipe or wrought iron are
generally made of malleable iron or cast
iron. There are two types of iron pipe fittings
used: the PRESSURE type and the RECESSED
type (fig. 8-4).
The pressure type of fitting is the standard
fitting used on water pipe. The recessed type of
fitting, also known as a cast-iron drainage or
Durham fitting, is generally required on all
drainage lines. The recessed type is most suitable
for a smooth joint; it reduces the probability of
grease or foreign material remaining in the joint
and causing a stoppage in the line. Recessed
fittings are designed so that horizontal lines
entering them will have a slope of one-fourth in.
per foot.
ELBOWS (OR ELLS) 90° AND 45°.— These
fittings (fig. 8-5, close to middle of figure) are used
to change the direction of the pipe either 90 or
45 degrees. REGULAR elbows have female
threads at both outlets. STREET elbows change
the direction of a pipe in a close space where it
would be impossible or impractical to use an
elbow and nipple. Both 45- and 90-degree street
elbows are available with one female and one male
threaded end. The REDUCING elbow is similar
to the 90-degree elbow except that one opening
is smaller than the other.
TEES.— A tee is used for connecting pipes of
different diameters or for changing the direction
of pipe runs. A common type of pipe tee is the
STRAIGHT tee, which has a straight-through
portion and a 90-degree takeoff on one side. All
three openings of the straight tee are of the same
size. Another common type is the REDUCING
tee, similar to the straight tee just described,
except that one of the threaded openings is of a
different size than the other.
UNIONS.— There are two types of pipe
unions. The GROUND JOINT UNION consists
of three pieces, and the FLANGE UNION is
made in two parts. Both types are used for
joining two pipes together and are designed so that
they can be disconnected easily.
COUPLINGS.— The three common types of
couplings are straight coupling, reducer, and
eccentric reducer. The STRAIGHT COUPLING
is for joining two lengths of pipe in a straight run
that does not require additional fittings. A run
is that portion of a pipe or fitting continuing in
a straight line in the direction of flow. A
REDUCER is used to join two pipes of different
sizes. The ECCENTRIC REDUCER (also called
a BELL REDUCER) has two female (inside)
threads of different sizes with centers so designed
that when they are joined, the two pieces of pipe
will not be in line with each other, but they can
be installed so as to provide optimum drainage
of the line.
CAPS.— A pipe cap is a fitting with a female
(inside) thread. It is used like a plug, except that
the pipe cap screws on the male thread of a pipe
or nipple.
PLUGS.— Pipe plugs are fittings with male
(outside) threads. They are screwed into other
fittings to close openings. Pipe plugs have various
types of heads, such as square, slotted, and
hexagonal sockets.
NIPPLES.— A nipple is a short length of pipe
(12 in. or less) with a male thread on each end.
It is used for extension from a fitting.
At times, you may use the DIELECTRIC or
INSULATING TYPE of fittings. These fittings
connect underground tanks or hot-water tanks.
They are also used when pipes of dissimilar metals
8-4
