WAVEGUIDE PRESSURIZATION
SYSTEM
The F-18 aircraft waveguide pressurization
system (fig. l-16) provides regulated, filtered, dry
air to the radar and electronic countermeasures
waveguide cavities. The air is supplied by either
the ACS or ground air cooling through a
waveguide test port. The system is made up of
a filter, two pressure regulating valves, two air
desiccators, two ground test ports, and tubing to
contain and transport the regulated air.
Filter System
The filter assembly is made up of a filter
element and pressure relief valve. During
operation, air passes through the filter ele-
ment, which removes 98% of particles larger
than 10 microns and 100% of particles larger
than 25 microns. When the filter element is
contaminated, a pressure differential of 4 to 5 psi
will open a relief valve and bypass air around the
filter element without interrupting the system
operation.
Pressure Regulating Valves
The waveguide pressurization system contains
two pressure regulating valves, one for electronic
countermeasures and one for radar waveguide.
Each valve regulates air to 19 psia. The valves use
two aneroids to regulate air pressure. Primary
aneroid force is balanced against spring force
through an opening on which a ball is seated. An
auxiliary aneroid functions as an added adjust-
ment and as a trigger assembly to allow internal
pressure relief to atmosphere when regulated
pressure exceeds 19 psia. A resettable indicator
is visible when an overpressure condition has
occurred. A check valve next to the outlet port
of the regulating valve closes to maintain
Figure 1-16.—Waveguide pressurization system.
1-22
