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|  3.4.1 Metals.- All metals used in the construction of float switches that
are not of a corrosion-resi stant types shall be suitably protested to re sist corro-
sion during the normal sevice life of the switch. The use of di ssimilar metals,
e specially brass, copper, or steel, in contact with aluminum or alumimum alloy,
shall be avoided where practicable. Dissimilar metals are defined in MS33S86.
Magnesium shall not be used. Neither brass nor copper shall be used in contact
with fuel.
3.4.2 Selection of materials.- Specifications and standards for all mater-
ials, parts, and Government certification and approval of processes and equipment,
which are not specifically designated herein and which are necessary for the execu-
tion of this specification, shall be selected in accordance with MIL-STD-143,
except as provided in the following paragraph.
3.4.2.1 Standard parts.- Standard parts (MS or AN) shall be used wherever
they are suitable for the purpose, and shall be identified on the drawing by their
part numbers. Commerical utility parts such as screws, bolts, nuts, cotter pins,
posse as suitable properties and are replaceable
etc., may be used, provided
by the standard parts (MS or AN without alteration, and provided the correspond-
ing standard part numbers are referenced in the parts list and if practicable, on
the contractor' a drawings. In the event there is no suitable corresponding stand-
and part in ef feet on date of invitation for bids, commercial part a may be used,
provided they conform to all requirements of this specification.
3.5 Design.- Fuel float witches shall be designed in accordance with stand-
ard aircraft practices. The weight and sise of the unit shall be kept to a minimum.
Reliability, however, shall be the paramount consideration l Pockets, wells, or
traps, in which water or condensed moisture can collect shall be eliminated or
properly drained. Consideration shall be given to the nece ssity for sufficient
pretravel and overtravel of moving parts, and sufficient actuating force shall be
available that wear and other deterioration of such parts shall not induce failure
during the normal life of the component. A protective cover shall be provided to
prevent damage to vital part a during shipment storage, Installation, and subsequent
possible handling during maintenance and operation. Suffinient clearance shall be
provided between the switch mechnaism and the cover to minimize the possiblity of
malfunction in the event of damage to the protective cover. Consideration shall be
given to the effect of icing] of the switch and float mechanism, and the switch shall
be examined for icing effects during low temperature test.
3.5.1 Special tools.- When the float switch is a repairable item, disassembly
and replacement of parts shall be accompli shable without the use of special tools.
3.5.2 Lubrication Float switches shall not require added lubrication
between overhaul periods. Parts in contact with the fuel shall not require lubri-
cation.
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