01 March 2005
g. Relays. Deposits of varnish on the armature,
c. Sealing Compound, MIL-PRF-81733 (Volume IV
pivots, or similar components will cause the relays to
bind. The whole relay should be carefully masked until
faying surfaces with temperatures up to 250°F (121°C).
after spraying has been completed. A brush should be
This material is applied by brush.
used to coat the coils and leads after the masking has
been removed. Relays with palladium-tipped contacts
d. C o n f o r m a l Coating. For information on
should be removed before application of varnish.
procedures and equipment used to apply conformal
coatings, refer to NAVAIR 01-1A-23 (Navy) and TO
h. Meters. Since meters are easily damaged by a
00-25-234 (Air Force).
the varnish spray treatment, all meters must be checked
for accuracy before treatment. Some meters may be
affected by heat. In other instances, meter magnets
may be affected by magnetic fields that exist around
A large number of RTV silicone sealants
drying equipment. Refer to the applicable service
contain an acetic acid curing agent. These
directives for instructions on varnish spray treatment of
sealants, in contact with metal, result in rapid
meters. If guidance is not available, do not apply varnish.
corrosion. RTV sealants that contain acetic
acid are not authorized for use on electronic or
5-5. SEALANTS FOR AVIONICS. Sealants are
electrical circuit. They may be identified in
another type of protective film used in avionic
most cases by a vinegar odor while in a liquid
equipment. Sealants are usually liquid or paste, which
or curing state.
solidify after application. They form a flexible seal,
preventing moisture intrusion at mechanical joints,
5-5.2. SEALANT CONTAINING ACETIC ACIDS.
spot-welds, and threaded closures. In addition, sealants
Table 5-1 lists some of the RTV silicone sealants
prevent entry of corrosive environments to faying
considered corrosive. These sealants shall not be
surfaces, fastener areas, exposed landing gears
used in avionic equipment.
switches, and other metal-encased avionic equipment.
They function principally as waterproof barriers. It is
Corrosive Silicone Sealants,
therefore very important that damaged sealants be
Adhesives, and Coatings
repaired as soon as possible.
For application procedures of Sealing
Compound, MIL-PRF-81733, refer to Volume
II of this manual.
5-5.1. TYPES OF SEALANTS. The following sealants
shall be used on avionic equipment:
a. Sealing Compound, Low Temperature Curing,
cure sealant used for sealing gaps and depressions on
areas during extreme cold activities. Apply with Brush,
Typewriter, A-A-3077 Style T (Volume IV or V,
b. Adhesive-Sealant, Silicone, RTV, Noncorrosive,
sealing avionic equipment in areas where temperatures
are between 250°F (121°C) to 600°F (315°C). It is
used for encapsulating and sealing of electrical and
RTV 730 is a high temperature (550° to 600° F) corrosive sealant
electronic components. This material has good
connectors. RTV 730 shall be used only when specified by the
cognizant engineering authority.