To prevent seizing, you can apply a suitable pipe
thread compound to the threads. When a compound is
applied to the threads, the two end threads are to be kept
free of the compound so that it will not contaminate the
fluid. Pipe compound, when improperly applied, may get
inside lines and harm pumps and control equipment.
Because of this reason many manufacturers forbid the
use of such compounds when fabricating the piping for a
Another material used on pipe thread is sealant
tape, made by TEFLONTM. This tape is made of
polytetraflouroethylene (PTFE), which provides an
effective means of sealing pipe connections and
eliminates the need of having to torque connections to
excessively high values to prevent leakage. It also
provides for ease in maintenance whenever it is necessary
to disconnect pipe joints.
connectors are commonly used in circulatory systems
consisting of lines made of tubing. These connectors
provide safe, strong, dependable connections without the
necessity of threading, welding, or soldering the tubing.
The connector consists of a fitting, a sleeve, and a nut (fig.
The fittings are made of steel, aluminum alloy, or
bronze. The fitting used in a connection should be
made of the same material as that of the sleeve, the nut,
and the tubing. For example, use steel connectors with
steel tubing and aluminum alloy connectors with
aluminum alloy tubing. Fittings are made in union, 45-
degree and 90-degree elbows, tees and various other
shapes (fig. 3-40).
Tubing used with flare connectors must be flared
before assembly. The nut fits over the sleeve, and when
tightened, draw the sleeve and tubing flare tightly against
the male fitting to form a seal.
The male fitting has a cone-shaped surface with the
same angle as the inside of the flare. The sleeve supports
the tube so vibration does not concentrate at the edge of
the flare and distributes the shearing action over a wider
area for added strength. Correct and incorrect methods
of installing flared-tube connectors are shown in figure
3-41. Tubing nuts should be tightened with a torque
wrench to the value specified in applicable technical
flareless-tube connector eliminates all tube flaring, yet
provides a safe, strong, and dependable tube connection.
This connector consists of a fitting, a sleeve or ferrule,
and a nut (fig. 3-42).
Flareless-tube connectors are available in many of
the same shapes and threaded combinations as flared-
tube connectors (fig. 3-40). The fitting has a counterbore
shoulder for the end of the tubing to rest against. The
angle of the counterbore causes the cutting edge of the
sleeve or ferrule to cut into the outside surface of the tube
when the two are assembled.
The nut presses on the bevel of the sleeve and causes
it to clamp tightly to the tube. Resistance to vibration is
concentrated at this point, rather than at the sleeve cut.
When fully tightened, the sleeve or ferrule is bowed
Figure 3-39.Flared-tube connector.
Figure 3-40.Flared-tube fittings.