Figure 9-3.--Model 310 fluid service cart.
the cart in its upright position, may be positioned
CHECKING AIRCRAFT HYDRAULIC
around and secured to a 10-gallon fluid drum without
FLUID LEVELS
lifting the drum. Once it is installed in the bridle, you
can move the drum using the dolly, or tilt it back 90
There are specific procedures for checking
degrees from vertical to the operating position.
hydraulic fluid levels in each model of aircraft. These
procedures must be followed to make sure the system
Hydraulic fluid is removed through a swivel fitting
operates at the required fluid level. Fluid level is
installed in a 2-inch hole. The swivel fitting is
generally determined by an indicating device at the
connected by a flexible hose to a single-action pump
system reservoir. The type of indicator used varies
that has a displacement of 2 fluid ounces per stroke at 0
with the aircraft model. Sight-glass, gauge, and
to 250 psi. A replaceable 3-micron (absolute)
piston-style indicators are commonly used.
disposable filter installed at the pump assembly base
removes particulate contamination from the fluid
There is close tolerance between the operating
being delivered to the suction side of the pump. A
parts of equipment used in aircraft hydraulic systems
check valve in the filter assembly prevents operation
and the level of hydraulic fluid contamination;
without an installed filter element.
therefore, do not introduce foreign matter into a
system being serviced. All servicing must be
Filtered fluid from the hand pump is routed to an
accomplished by qualified personnel using authorized
air trap assembly, which contains a special chamber
fluid-dispensing equipment.
that removes any free air present in the fluid. The air
trap assembly contains a manual bleed valve for
The information given here gives general guidance
venting collected air and a 0- to 300-psi pressure gauge
and requirements to follow when fluid servicing
for monitoring output pressure. Fluid is delivered to
hydraulic systems and components. Remember, you
the system or component being serviced by a 15-foot
need to follow the procedures contained in the
service hose. A 3-micron, in-line filter assembly is
applicable technical manuals when you actually
located near the discharge end of the service hose to
service hydraulic systems and components. When you
ensure against system contamination.
service these systems, use approved fluid-dispensing
9-4
