the brake system accumulator installation used on one
majority of the accumulators installed in naval aircraft
are equipped with air pressure gauges for this purpose.
type of aircraft. The air valve used in the accumulator
When the accumulator is not equipped with a
installations is usually the same type as that used on
high-pressure air gauge, you may install one at the air
shock struts.
preload fitting for this purpose. The required pressure
To service an accumulator, the hydraulic pressure
can be found in the MIM for each aircraft.
that is trapped in the accumulator must be relieved.
The preload pressure may be checked by another
This is accomplished by actuating the units involved.
method in case the accumulator is not equipped with an
For example, the hydraulic pressure in a brake
air pressure gauge. With the system pressure (as
a c c u m u l a t o r m a y b e r e l i eve d b y a p p l y i n g t h e
indicated by the cockpit gauge) at the normal operating
emergency brake several times. When the hydraulic
value, relieve system pressure by operating the wing
pressure is relieved, the accumulator gauge should
flaps or another unit slowly. The pressure gauge
indicate the air or nitrogen pressure specified for the
reading must be watched carefully. The last reading
particular accumulator installation. If the pressure
before the indicator needle drops suddenly to zero is
i n d i c a t e d i s b e l ow t h e s p e c i fi e d p r e s s u r e , t h e
accepted as the accumulator preload air pressure.
accumulator must be recharged with dry compressed
Before disassembly of any accumulator, ensure
air or nitrogen.
that the air preload has been completely exhausted.
This may be accomplished by loosening the swivel nut
PRESSURE INDICATORS
on the air filler valve until all air is out; then remove the
Pressure gauges installed in hydraulic and
valve.
pneumatic systems are used to indicate existing
Servicing
hydraulic and pneumatic pressures, and are calibrated
in pounds per square inch. Naval aircraft use both the
The purpose of the hydraulic system accumulator
direct reading gauges and the synchro (electric) type.
is to store an extra volume of fluid under pressure. The
energy stored in an accumulator is used for various
Direct Reading Type
purposes, such as the actuation of a unit in the event of
normal hydraulic system failure. For example,
Direct reading gauges are used in installations
sufficient energy can be stored in an accumulator for
such as accumulators, emergency air bottles, arresting
several applications of the wheel brakes.
gear snubbers, and brake systems. The gauge is
connected directly into units or lines leading from units
Most accumulators are installed with an air gauge
and become part of the container or system. At these
and a high-pressure air valve mounted on a panel of the
structure near the accumulator. Figure 12-35 shows
points, the gauge is able to sample existing pressure.
Figure 12-35.--Accumulator air charge valve and gauge installation.
12-36
