TESTING HOSE ASSEMBLIES
Prior to installation, all field fabricated hose assemblies must be
pressure-tested.
This applies regardless of whether they were just
fabricated or were previously fabricated, tested, and placed in
storage.
All factory or depot fabricated assemblies must be
pressure-tested prior to installation.
Hose assemblies to be used in hydraulic, pneumatic, fuel, oil, or
coolant systems are tested on a hydrostatic test unit filled with
hydraulic fluid conforming to military specification MIL-H-5606, MIL-
H-83282, or MIL-H-6083; lubricating oil conforming to military
specification MIL-H-6082; or water.
Hose assemblies to be used in
instrument systems are tested using dry, oil-free air, or nitrogen,
federal specification 1313-N-411, grade A, type 1.
The steps involved in the testing process are explained in detail in
TM 1-1500-204-23-2.
INSTALLING HOSE ASSEMBLIES
During operation, the hose assemblies changes in length from +2
percent to -4 percent because of pressurization.
To compensate for
this, slack equal to at least five percent of the hose length must be
allowed for expansion and shrinkage. The five percent allowance must
be provided during cutting and fabricating.
In addition to hose
length, care must be taken not to twist the hose or to exceed the
allowed bend radius.
Supports and grommets must be used, fittings
lubricated, and protection against temperature provided.
Each of
these is discussed in the paragraphs that follow and illustrated in
Figure 2-17.
Twisting. Most hose is marked with a lengthwise solid line (lay
strip) for ease in detecting any twists of the line during
installation.
A twisted hose tends to untwist when pressurized
causing the end fitting to become loosened or sheared.
To avoid
twisting hose assemblies when connecting the second end, use two
wrenches: one to hold the stationary fitting and one to turn the
swivel nut.
Bend Radius.
Hose, like rigid tubing, has a limit to its bend
allowance.
Bends exceeding the permissible limit lead to early
failure of the hose assembly.
The radius of the sharpest bend
permissible for a hose is referred to as the minimum bend radius for
that hose.
This bend radius is measured in the same manner as the
minimum bend radius of rigid tubing as described in the paragraph of
this lesson entitled "routing of lines".
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AL0907
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