you must take care not to exceed the elastic limits of the
Notice in view A of figure 8-15 how the hook-type
rubber. Following these inspection practices will prove
removal tool is positioned under the O-ring, and
to be a maintenance economy. It is far more desirable to
then lifted to allow the extractor tool, as well as the
take care identifying and inspecting O-rings than to
removal tool, to pull the O-ring from its cavity. View B
repeatedly overhaul components with faulty seals.
of figure 8-15 shows the use of another type of extractor
tool in the removal of internally installed O-rings. In
After inspection and prior to installation, immerse
view C of figure 8-15, notice the exterior tool
the O-ring in clean hydraulic fluid. During the
positioned under both O-rings at the same time. This
installation, avoid rolling and twisting the O-ring to
method of manipulating the tool positions both O-rings,
maneuver it into place. If possible, keep the position of
which allows the hook-type removal tool to extract both
the O-ring's mold line constant. When the O-ring
O-rings with minimum effort. View D of figure 8-15
installation requires spanning or inserting through
shows practically the same removal as view C, except
sharp threaded areas, ridges, slots, and edges, use
for the use of a different type of extractor tool.
protective measures, such as O-ring entering sleeves, as
shown in view A of figure 8-16. If the recommended
The removal of external O-rings is less difficult
O-ring entering sleeve (soft thin-wall metallic sleeve) is
than the removal of internally installed O-rings. Views
not available, paper sleeves and covers may be
E and F of figure 8-15 shows two accepted removal
fabricated by using the seal package (gloss side out) or
methods. View E shows the use of a spoon-type
lint-free bond paper. See views B and C of figure 8-16.
extractor, which is positioned under the seal. After the
O-ring is dislodged from its cavity, the spoon is held
Adhesive tapes should not be used to cover danger
stationary while simultaneously rotating and
areas on components. Gummy substances left by the
withdrawing the piston. View F of figure 8-15 is similar
adhesives are extremely detrimental to hydraulic
to view E, except only one O-ring is installed, and a
systems.
different type of extractor tool is used. The wedge-type
After the O-ring is placed in the cavity provided,
extractor tool is inserted beneath the O-ring; the
gently roll the O-ring with the fingers to remove any
hook-type removal tool hooks the O-ring. A slight pull
twist that might have occurred during installation.
on the latter tool removes the O-ring from its cavity.
After the removal of all O-rings, it is mandatory
Backup Rings
that you clean the affected parts that will receive new
O-rings. Ensure that the area used for such installations
Backup rings are used to support O-rings and to
is clean and free from all contamination.
prevent O-ring deformation and resultant leakage.
Two types of backup rings are used in naval
Each replacement O-ring should be removed from
aircraft--Teflon single and double spiral.
its sealed package and inspected for defects such as
blemishes, abrasions, cuts, or punctures. Although an
Teflon rings are made from a fluorocarbon-resin
O-ring may appear perfect at first glance, slight surface
material, which is tough, friction-resistant, and more
flaws may exist. These are often capable of preventing
durable than leather. Precautions similar to those
satisfactory O-ring performance under the variable
applicable to O-rings must be taken to avert
operating pressures of aircraft systems. O-rings should
contamination of backup rings and damage to hydraulic
be rejected for flaws that will affect their performance.
components. Teflon backup rings may be stocked in
individual sealed packages similar to those in which
Such defects are difficult to detect. One air-
O-rings are packed, or several may be installed on a
craft manufacturer recommends using a 4-power
cardboard mandrel.
magnifying glass with adequate lighting to inspect each
ring before it is installed.
If unpackaged rings are stored for a long period of
time without the use of mandrels, a condition of overlap
By rolling the ring on an inspection cone or dowel,
may develop. To eliminate this condition, stack
the inner diameter surface can also be checked for small
Teflon rings in a mandrel of a diameter comparable to
cracks, particles of foreign material, and other
the desired diameter of the spiral ring. Stack and clamp
irregularities that will cause leakage or shorten the life
the rings with their coils flat and parallel. Then place
of an O-ring. The slight stretching of the ring when it is
the rings in an oven at a maximum temperature of
rolled inside out will help to reveal some defects not
350F for a period of approximately 10 minutes. The
otherwise visible. A further check of each O-ring
rings are then removed and water quenched.
should be made by stretching it between the fingers, but
8-27
