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|  MIL-T-18847C(AS)
3.5.1 .8.2 External (vacuum) pressure.
The external vacuum pressure loads
are as follows:
Operating:
0 psig
Proof:
10 psig negative
Burst:
12 psig negative
3.5.1.9 Fuel transfer system. The fuel transfer system shall be designed
in accordance with MIL-F-17874 and allow for both ground and in-flight fueling
and defueling of the fuel tank. The fuel tank fuel lines and connections and
installation shall be in accordance with MIL-F-8615. Provisions shall be
incorporated to prevent fuel spillage from the fuel and air connectors during
jettison or disengagement from the aircraft.
3.5.1 .9.1 Pressure relief/vent valve. Unless otherwise specified, the
tank shall be equipped with a pressure relief/vent valve that conforms to
MIL-V-81356. If it is not practical to utilze a valve conforming to
MIL-V-81356, the tank shall be equipped with a pressure relief valve. The
valve shall be designed to remain closed when the pressure differential
between the tank and ambient atmospheric pressure is less than 2 0.5 psi
above normal, and to open and relieve the excess fuel pressure when the
differential is greater than 2 0.5 psi above normal. The pressure relief
valve shall incorporate a means to prevent leakage of fuel during catapult and
arrested landing.
3.5.1.9.1.1 External leakage. The pressure relief valve shall be capable
of containing any pressure less than the relief setting without external
leakage.
3.5.1.9.2 Vent fitting locations. When applicable, ram type vents shall
be located at the forward part of the tank with a minimum vent diameter of
1/2 inch for tanks of 100 gallons capacity but less than 350 gallons, and
1-1/4 inch for tanks with a capacity equal to or greater than 350 gallons.
The vent system shall be designed so that proper venting is obtained during
flight maneuvers likely to be performed by the particular aircraft to which
the tank is applied. Intercostals and annular frames attached to the top
inner profile of the tank shall be vented sufficiently to allow entrapped air
to pass freely to the external vent fitting. The design shall be such that
siphoning or spillage shall be prevented in flight or during catapulting or
arrested landings. The vents shall be designed to minimize entry of dirt,
oil, or other foreign matter into the tank.
3.5. 1.9.3 Drain valves. The tank shall contain sufficient drain valves in
accordance with MS29571-1. The drain valve shall be replaceable without
entering the tank.
3.5.1.9.3.1 Drain location. A drain opening shall be provided at the low
point resulting at the ground attitude of the aircraft for which the tank is
designed. Where the tank is intended to be used on more than one model of
aircraft, drain openings shall be provided at each low point resulting at the
ground attitude of each applicable aircraft.
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