FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 9. Aircraft Systems and Components | 2. Hydraulic Systems | 9-30. Hydraulic Lines and Fittings
AC 43.13-1B CHG 1
9/27/01
fabricated as described in figure 9-8. Refer to
figure 9-10 for minimum bend radii. When a
hose assembly is removed, the ends should be
tied as shown in figure 9-11, so that the pre
formed shape will be maintained. Refer to
figure 9-12 for minimum bend radii for teflon
hose.
(3) All flexible hose installations should
be supported at least every 24 inches. Closer
supports are preferred. They should be care
fully routed and securely clamped to avoid
abrasion, kinking, or excessive flexing. Ex
cessive flexing may cause weakening of the
hose or loosening at the fittings.
e. O-Ring Seals. An understanding of O-
ring seal applications is necessary to determine
when replacement should be made. The sim
plest application is where the O-ring merely
serves as a gasket when it is compressed
within a recessed area by applying pressure
with a packing nut or screw cap. Leakage is
not normally acceptable in this type of instal
lation. In other installations, the O-ring seals
depend primarily upon their resiliency to ac
complish their sealing action. When moving
parts are involved, minor seepage may be
normal and acceptable. A moist surface found
on moving parts of hydraulic units is an indi
cation the seal is being properly lubricated.
In pneumatic systems, seal lubrication is pro
vided by the installation of a grease-
impregnated felt wiper ring. When systems
are static, seepage past the seals is not nor
mally acceptable.
f. Storage of replacement seals.
(1) Store O-ring seals where tempera
ture does not exceed 120° F.
(2) Keep seals packaged to avoid expo
sure to ambient air and light, particularly sun
light.
g. During inspection, consider the fol
lowing to determine whether seal replacement
is necessary.
(1) How much fluid is permitted to seep
past the seals? In some installations minor
seepage is normal. Refer to the manufacturer’s
maintenance information.
(2) What effect does the leak have on
the operation of the system? Know the sys
tem.
(3) Does the leak of fluid create a haz
ard or affect surrounding installations? A
check of the system fluid and a knowledge of
previous fluid replenishment is helpful.
(4) Will the system function safely
without depleting the reservoirs until the next
inspection?
h. Do’s and Don’ts that apply to O-ring
seals.
(a) Correct all leaks from static seal
installations.
(b) Don’t retighten packing gland
nuts; retightening will, in most cases, increase
rather than decrease the leak.
(c) Never reuse O-ring seals because
they tend to swell from exposure to fluids, and
become set from being under pressure. They
may have minor cuts or abrasions that are not
readily discernible by visual inspection.
(d) Avoid using tools that might
damage the seal or the sealing surface.
(e) Do not depend upon color-coding.
Coding may vary with manufacturer
(f) Be sure that part number is correct
(g) Retain replacement seals in their
package until ready for use. This provides
proper identification and protects the seal from
damage and contamination.
(h) Assure that the sealing surfaces
are clean and free of nicks or scratches before
installing seal.
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