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|  MIL-H-8891A
element and the filter assembly shall be suitable for the pressure and
temperature specified in the detail specification. Filters incorporating
elements having absolute ratings lower (finer) than 15 microns may be
used subject to approval of the procuring activity. These filters shall
be used to filter all circulating fluid in the system. The acceptable
contamination level for aircraft delivery shall be specified by the procuring
activity.
Filter locations - Filters shall be provided in the
3.10.8.3
following locations as a minimum requirement. Other filter locations shall
be provided at the option of the procuring activity.
Pressure line installation - Anon-bypass-type filter(s)
3.10.8.3.1
-
shall be installed in" the system pressure line and shall be so located that
all fluid from the vehicle pump(s) and the ground test equipment pressure
connection will be filtered prior to entering any major equipment or com-
ponents of the system. In multi-pump systems, each pump shall have a sepa-
.
rate filter installation.
Return line installation - A bypass-type line filter
3.10.8.3.2
shall be installed in the return line. All fluid entering the return circuit
shall be circulated through the filter prior to entering the return line to
the reservoir and/or pump suction line.
Reservoir fill line installation - A non-bypass-type
3.10.8.3.3
line filter shall be installed to filter all fluid entering the system
through the reservoir fill connection. The-absolute filtration rating
shall be in agreement with paragraph 3.10.8.1 and 3.10.8.2 respectively.
Pump-case drain line installation - Each pump-case
3.10.8.3.4
drain (bypass) line shall have a bypass-type filter installed.
Sequencing valves - Where hydraulic sequencing is
3.10.8.4
critical, each sequence valve shall be protected from contamination in each
direction of flow by a suitable screen-type filter element. This element
may be included as a part of the sequence valve assembly.
Fittings - All tube fittings (other than connections
3.10.9
at production break points, to removable components, and where needed to
facilitate maintenance) shall be permanently joined employing no screw
threads or similar mechanical means and shall require approval by the pro-
curing activity prior to installation in the applicable vehicle. In addi-
tion, suitable repair and replacement methods involving failed tubing and
fittings shall be established for each vehicle model and shall be included
in the applicable vehicle publications. Separable fittings (e.g., a screw
thread design) shall be used on removable components where needed to facili-
tate maintenance and production. The tube fitting designs shall be selected
primarily on the basis of high-reliability and light weight, and shall be
qualified by a comprehensive test program. Consideration shall be given to
selection of fittings and installation equipment of types which are already
in the inventory of the using service. Suitable repair and replacement
methods involving failed tubing and fittings shall be established. NO
thread lubricant other than hydraulic fluid specified in 3.3 shall be used
on tube fittings, unless specifically authorized by the procuring activity.
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