Figure 5-12.Hose assembly
Flexible hose must
identification tags (aircraft).
not be twisted during
installation, since this reduces the life of the hose
considerably and may cause the fittings to loosen
as well. You can determine whether or not a hose
is twisted by looking at the layline that runs along
the length of the hose. If the layline does not spiral
around the hose, the hose is not twisted. If the
layline does spiral around the hose, the hose is
twisted (fig. 5-13, view B) and must be untwisted.
Flexible hose should be protected from chafing
by using a chafe-resistant covering wherever
The minimum bend radius for flexible hose
varies according to the size and construction of
the hose and the pressure under which the
system operates. Current applicable technical
publications contain tables and graphs showing
minimum bend radii for the different types of
installations. Bends that are too sharp will reduce
the bursting pressure of flexible hose considerably
below its rated value.
Flexible hose should be installed so that it will
be subjected to a minimum of flexing during
operation. Support clamps are not necessary with
short installations; but for hose of considerable
length (48 inches for example), clamps should be
placed not more than 24 inches apart. Closer
Figure 5-13.Correct and incorrect installation of flexible
supports are desirable and in some cases may be
A flexible hose must never be stretched tightly
between two fittings. About 5 to 8 percent of the
total length must be allowed as slack to provide
freedom of movement under pressure. When
under pressure, flexible hose contracts in length
and expands in diameter. Examples of correct and
incorrect installations of flexible hose are
illustrated in figure 5-13.
PFTE hose should be handled carefully during
removal and installation. Some PFTE hose is pre-
formed during fabrication. This type of hose tends
to form itself to the installed position in the sys-
tem. To ensure its satisfactory function and reduce
the likelihood of failure, anyone who works with
PFTE hose should observe the following rules:
Do not exceed recommended bend limits.
Do not exceed twisting limits.
Do not straighten a bent hose that has
taken a permanent set.
Do not hang, lift, or support objects from