When cell is completely drained, close drain valve and fill cell with lubricating oil, MIL-L-6081, grade 1010.
Allow oil to remain in fuel cell for at least eight to ten hours.
Drain lubricating oil from fuel cell and save to flush other cells.
After two or three hours, test fuel cells with a combustible gas indicator for presence of fuel vapors. If an
unsafe condition exists, discard drained lubricating oil. Reflush with fresh oil until a safe reading is obtained.
Attach a tag to the fuel filler cap with the following information printed on it: This fuel cell has been preserved
with lubricating oil, MIL-L-6081, grade 1010. No flushing is required during depreservation.
Alternate method. If the proper equipment is not available or the lubricating oil supply, MIL-L-6081,
is limited, use the following procedures to preserve the fuel system:
Drain and flush fuel cell in accordance with paragraph 4-5f(4)(a) 1 and 2.
Use only dehydrated air. Residual moisture may cause contamination of the fuel when the
cell is refilled.
With drains and vents open, and filler cap off, introduce into filler neck a reduced pressure air hose supplying
air through a one-quarter inch orifice at approximately fifty psi. Purge fuel tank for approximately one-half hour. Close
Purge fuel cells with CO2 or nitrogen gas.
· When using a fire extinguisher bottle as a source of CO
for purging fuel tanks, regardless
of the size of the bottle used, the fiber horn shall be removed, not only because it is too
large for insertion into the tank filler neck, but to avoid generating static electrical charges
which can build up by gas moving rapidly through the horn. The nozzle, as well as the
bottle itself, must be grounded to the aircraft.
· The CO
must be discharged into fuel tanks slowly, at a rate of one pound per minute. C02
must be released slowly, because the rapid passage of a gas through a hose can generate
A very rapid rate of discharge allows rapid expansion of the CO2 gas when it flows into a fuel
cell. The expanding gas can lower the temperature to the point that it will cause damage to
· The size of the C0
bottle used can be varied to meet existing conditions. The fifteen
pound size is handy.
· The total amount recommended is based on the quantity usually needed to purge a tank or
tanks of the size under discussion. However, more may be needed to obtain a safe reading
on the combustible gas indicator.
· It is permissible to use nitrogen or other inert gas in place of the C0
gas called out in any
of the purging procedures. The same precautionary measures stated above shall be
Introduce into fuel cell filler neck CO2 or nitrogen from a tank set to discharge at a rate of not more than one
pound of purging gas per minute.
Use not less than three pounds of C02 or nitrogen to purge fuel cells.