require that seals and gaskets be stored in a cool, dark, dry place;
they must be protected from dirt, heat, strong air currents,
dampness, petroleum products, and electric motors or equipment giving
Seals and gaskets are used in aircraft plumbing systems to prevent
leaks when two components are joined together.
The fluid being
conducted and the operating pressure of the system determine the type
of seal or gasket to be used and the material to be used in its
manufacture. Once a seal or gasket has been removed from service it
must never be reused, even if removal was only incidental to the
disassembly of a component.
In hydraulic systems, seals manufactured from rubber, leather, felt,
cork, paper, teflon, or metal are used.
The O-ring is the most
widely used type of hydraulic seal.
It is effective in controlling
pressures coming from any direction or for use where there is either
linear or rotative motion.
means of preventing O-ring extrusions, prolonging O-ring life, or
when system pressure exceeds 1,500 psi. Other types of seals used in
hydraulic systems are: V-rings, U-rings, cup seals, oil seals, and
These are special seals, used to contain fluid or
prevent leaks in the various components of the aircraft plumbing
All seals must be inspected for serviceability prior to installation,
and care must be taken not to damage them during assembly.
A seal placed between two components where there is no relative
movement is termed a gasket.
Its function is to compensate for any
irregularities on the surfaces of two mating parts and thus to
Crush washers and O-ring gaskets are the most common types of gaskets
used in aircraft hydraulic systems.
If a gasket is to be field
fabricated, ensure that the exact thickness of the original gasket is
Gaskets, like seals, must be examined prior to installation to ensure
their serviceability. During assembly, do not exceed the recommended
torque value of the components.
Overtightening is likely to crimp
the gasket or compress it into the threads of the component, and
hence, break the seal.
When stored, seals and gaskets must be protected from excessive heat,
dampness, air currents, dirt, petroleum products, and equipment