loss of hydraulic fluid, and prevent the induction of air
or contaminants into the system.
In many cases, air inspection procedures are
inadequate. Support equipment specifically designed
to detect and measure air is not presently available in
the fleet. You should use indirect methods to
determine the amount of air present in a system.
Operating the air bleed valve on the reservoir reveals
whether or not there is air present in the reservoir.
Large amounts of air might be present somewhere else
in the system and go undetected. An effective means
for measuring the air in your system is known as the
reservoir sink check. In this method, the fluid level in
the aircraft reservoir is checked with the system, both
pressurized and nonpressurized. The presence of air or
any compressible gas in the system causes the
pressurized reading to be lower (reservoir sink),
indicating the need for possible maintenance action
(fig. 9-11). This check is particularly effective when
performed after a long aircraft down period, in which
case dissolved air has had lots of time to come out of
solution.
Figure 9-11.--Reservoir level changes (reservoir sink)
presence of air in system.
All air bleed operations must be followed by a
check of the system hydraulic fluid level. Fluid
point drain) and analyzed for particulate level and
replenishment may be required, depending upon the
water content. If the fluid is unacceptable, it is
amount of air and fluid purged from the system.
recirculation cleaned, purified, flushed, or purged.
Hydraulic filter elements that can be cleaned are
OPERATIONAL USE
ultrasonically cleaned or replaced at the prescribed
m a i n t e n a n c e i n t e r va l . B e c a u s e o f t h e i r l a rg e
Operate test stands equipped with hydraulic
dirt-holding capacity, disposable 3-micron pressure
manifolds for self-recirculation cleaning before they
line filters are replaced only upon actuation of their
are connected to equipment or components under test.
differential pressure indicators. Disposable filters that
Recirculation clean the test stand for a sufficient period
do not have differential pressure indicators are
of time to let a minimum of one pass of its total
reservoir contents through the internal filtration.
replaced at the prescribed interval.
Closely monitor differential pressure of loaded filter
Age-controlled, deteriorative hoses used to carry
indicators during all SE operations after the fluid
hydraulic fluid in SE units are not to remain in service
reaches normal operating temperature (+85F
for more than 7 years beyond the manufacturer's cure
minimum). Equipment operation is terminated
date. Additionally, hoses of this type that are internally
i m m e d i a t e l y u p o n a p p e a r a n c e o f l o a d e d fi l t e r
located in the equipment are replaced at each
indications. Replace the loaded element. You should
prescribed major rework interval, not to exceed 4
stop using the SE if the reservoir or outlet fluid is, or is
years. The date of the required removal and serial
suspected to be, unacceptably contaminated. Inform
number of the equipment is etched or peened on the
the supporting maintenance activity immediately so
hose collar. Replace external deteriorative hoses used
that required remedial action can be taken.
to transfer fluid between SE and aircraft or
components under test that cannot be positively
PERIODIC MAINTENANCE
identified as having been in use for less than 2 years as
soon as possible, and at regular intervals thereafter, not
Supporting activities for hydraulic SE perform
to exceed 2 years. The date of required replacement
periodic maintenance at prescribed intervals, unless
and the SE serial number is etched or peened on the
otherwise directed. At this time, samples are taken
hose collars. Hoses should remain attached to the
from all hydraulic SE reservoirs (preferably at a low
9-18
