Grommets are made of rubber, and they are used on
small openings where single cables pass through the
walls of unpressurized compartments.
Pressure seals are used on cables or rods that must
move through pressurized bulkheads. They fit tightly
enough to prevent air pressure loss, but not so tightly as
Figure 3-36.--Turnbuckle tolerances.
to hinder movement of the unit.
Fairleads (rubstrips), grommets, pressure seals, and
pulleys are all types of cable guides. They are used to
Pulleys (or sheaves) are grooved wheels used to
protect control cables by preventing the cables from
change cable direction and to allow the cable to move
rubbing against nearby metal parts. They are also used
with a minimum of friction. Most pulleys used on
as supports to reduce cable vibration in long stretches
aircraft are made from layers of cloth impregnated with
(runs) of cable. Figure 3-37 shows some typical cable
phenolic resin and fused together under high
temperatures and pressures. Aircraft pulleys are
extremely strong and durable, and cause minimum
wear on the cable passing over them. Pulleys are
provided with grease-sealed bearings, and usually do
Fairleads may be made of a solid piece of material
not require further lubrication. However, pulley
to completely encircle cables when they pass through
bearings may be pressed out, cleaned, and relubricated
holes in bulkheads or other metal parts. Fairleads may
with special equipment. This is usually done only by
be used to reduce cable whipping and vibration in long
depot-level maintenance activities.
runs of cable. Split fairleads are made for easy
Pulley brackets made of sheet or cast aluminum
installation around single cables to protect them from
are required with each pulley installed in the aircraft.
rubbing on the edges of holes.
Figure 3-37.--Typical cable guides.