aluminum; however, tools made from phenolic rod,
plastics, and wood may also be used.
When removing or installing O-rings, avoid using
pointed or sharp-edged tools that might cause
scratching or marring of hydraulic component
surfaces or cause damage to the O-rings. While using
the seal removal and the installation tools, contact
with cylinder walls, piston heads, and related
precision components is not desirable. With practice,
you should become proficient in using these tools.
Notice in view A of figure 2-46 how the
hook-type removal tool is positioned under the
O-ring, and then lifted to allow the extractor tool, as
well as the removal tool, to pull the O-ring from its
cavity. View B of figure 2-46 shows the use of
another type of extractor tool in the removal of
internally installed O-rings. In view C of figure 2-46,
notice the exterior tool positioned under both O-rings
at the same time. This method of manipulating the
tool positions both O-rings, which allows the
hook-type removal tool to extract both O-rings with
View D of figure 2-46 shows
practically the same removal as view C, except for the
use of a different type of extractor tool.
The removal of external O-rings is less difficult
than the removal of internally installed O-rings.
Views E and F of figure 2-46 shows two accepted
View E shows the use of a
spoon-type extractor, which is positioned under the
seal. After the O-ring is dislodged from its cavity, the
spoon is held stationary while simultaneously rotating
and withdrawing the piston. View F of figure 2-46 is
similar to view E, except only one O-ring is installed,
and a different type of extractor tool is used. The
wedge-type extractor tool is inserted beneath the
O-ring; the hook-type removal tool hooks the O-ring.
A slight pull on the latter tool removes the O-ring
from its cavity.
After the removal of all O-rings, it is mandatory
that you clean the affected parts that will receive new
Ensure that the area used for such
installations is clean and free from all contamination.
Each replacement O-ring should be removed from
its sealed package and inspected for defects such as
blemishes, abrasions, cuts, or punctures. Although an
O-ring may appear perfect at first glance, slight
surface flaws may exist. These are often capable of
preventing satisfactory O-ring performance under the
variable operating pressures of aircraft systems.
O-rings should be rejected for flaws that will affect
Such defects are difficult to detect. One aircraft
manufacturer recommends using a 4-power
magnifying glass with adequate lighting to inspect
each ring before it is installed.
By rolling the ring on an inspection cone or
dowel, the inner diameter surface can also be checked
for small cracks, particles of foreign material, and
other irregularities that will cause leakage or shorten
the life of an O-ring. The slight stretching of the ring
when it is rolled inside out will help to reveal some
defects not otherwise visible. A further check of each
O-ring should be made by stretching it between the
fingers, but you must take care not to exceed the
elastic limits of the rubber.
inspection practices will prove to be a maintenance
economy. It is far more desirable to take care
identifying and inspecting O-rings then to repeatedly
overhaul components with faulty seals.
After inspection and prior to installation, immerse
the O-ring in clean hydraulic fluid. During the
installation, avoid rolling and twisting the O-ring to
maneuver it into place. If possible, keep the position
of the O-rings mold line constant. When the O-ring
installation requires spanning or inserting through
sharp threaded areas, ridges, slots, and edges, use
protective measures, such as O-ring entering sleeves,
as shown in view A of figure 2-47. If the
recommended O-ring entering sleeve (soft thin-wall
metallic sleeve) is not available, paper sleeves and
covers may be fabricated by using the seal package
(gloss side out) or lint-free bond paper. See views B
and C of figure 2-47.
Adhesive tapes should not be used to cover
danger areas on components. Gummy substances left
by the adhesives are extremely detrimental to
After the O-ring is placed in the cavity provided,
gently roll the O-ring with the fingers to remove any
twist that might have occurred during installation.
Backup rings are used to support O-rings and to
prevent O-ring deformation and resultant leakage.
Two types of backup rings are used in naval
aircraftTeflon® single and double spiral.
Teflon® rings are made from a fluorocarbon-resin
material, which is tough, friction-resistant, and more