On some aircraft, the radiator is a welded
Manual Shutoff Valves
aluminum assembly with two semicylindrical and
Manual shutoff valves may be used as fire wall
baffled hydraulic fluid chambers with multiple pencil
shutoff valves as well as subsystem shutoff valves.
diameter size tubes, which direct and contain fuel flow
Some aircraft have a manual fire wall shutoff valve
through the individual hydraulic chambers. The
operated by cable linkage.
radiator is so constructed to prevent mixing of engine
fuel with hydraulic fluid and one hydraulic system
Some aircraft use the needle-type shutoff valve in
fluid with the other. As fuel flows through the radiator
their landing gear and bomb bay systems. This
tubes, heat energy is transferred from the hydraulic
needle-type valve consists of a handle, stem and valve,
fluid to the engine fuel prior to hydraulic fluid entry
and body. Turning the handle in a clockwise direction
into the hydraulic reservoir.
places the valve on its seat within the body, stopping
the flow of fluid.
Figure 12-28 shows the cooling radiator used to
cool two hydraulic systems; moreover, it has a fuel
These shutoff valves are used during maintenance
filter incorporated that filters the fuel supplied to the
to shut off hydraulic fluid to the subsystems, thus
engine. The radiator unit consists of a cylindrical case
allowing maintenance personnel to work safely in the
containing two cooling coils of l/4-inch aluminum
wheelwell and bomb bay areas. Also, by closing the
alloy tubing and a replaceable fuel filter element. The
particular valve a desired amount, the speed of the
utility system cooling coil is installed in the right-hand
operating unit can be controlled to aid in observing the
end of the case; the flight control system cooling coil
sequence and full operation of the components being
and the filter element are installed in the left-hand end,
operated.
as shown in figure 12-28. The case ends contain
fittings for connecting fuel hoses. Two threaded
HYDRAULIC FLUID COOLERS
bosses, which are welded to the cooling coil ends,
Hydraulic fluid coolers are used in some hydraulic
serve to connect the hydraulic lines for each system.
systems for the purpose of lowering the temperature of
During normal operation, hydraulic fluid returning to
the fluid within the system lines, thus preventing
each reservoir is directed through its applicable system
inadvertent overboard dumping of fluid from the
cooling coil, where sufficient heat is transferred to the
reservoir due to thermal expansion. Fluid coolers are
engine fuel to maintain the hydraulic fluid at less than
200F.
installed in systems in which the temperature of the
fluid is likely to exceed the maximum allowable limit.
Should the cooling coils become clogged, each
According to the military specifications for
system is equipped with a bypass relief valve, which
aircraft hydraulic systems, 400F is the maximum
opens and bypasses fluid around the coil and directly to
the reservoir.
allowable temperature for any type of hydraulic
system. In some systems, this temperature might be
Fin Tubing Types
exceeded without some means of cooling the fluid.
Several types of fluid coolers are used on naval
Some aircraft use fin tubing for cooling hydraulic
aircraft. The most common is the radiator type, in
system fluid. Hydraulic fluid coolers are mounted
which both the hydraulic fluid and engine fuel flow
internally in the wing inboard fuel tanks. As shown in
separately through the cooling unit. Another radiator
figure 12-29, each cooler is an assembly of fin-walled
type uses ram air in flight and an electric blower while
tubing, two unions, and mounting supports. Fluid
on the ground to produce an air source as a cooling
enters the inlet coupling and is passed through the
medium.
fin-walled tubing, which acts as a heat exchanger, and
is directed to the outlet coupling for return to the
Radiator Types
system reservoir. The heat of the fluid passing through
the coolers is absorbed by both the fin-walled tubing
Radiator-type fluid coolers are also called heat
and the fuel.
exchangers and fluid coolers, as well as radiators.
Their principles of operation are the same; however,
NOTE: The fuel level in the inboard tanks must be
the manner in which they obtain their objective may
maintained at a specific level to ensure adequate
differ.
cooling of the fluid.
12-27
