MIL-V-27296C
principles of pressure compenstion and damping. The inhalation-exhalation device of figure 2 shall be considered
as a typical method of design Any deviations in envelope or critical interface dimensions from figures 2,3,4 and
5 may, at the option of the procuring activity, require the contractor to install the valve in all sizes of the
appropriate type oxygen mask assembly as described in MIL-M-27274 and MIL-M-87163. The contractor will
then be required to demonstrate to the procuring activity, the ability of the valve to meet the requirements of the
following performance tests as per MIL-M-27274 and MIL-M-87163:
Mask Leakage
Combination Valve Installation Inlet Performance
Combination Valve Installation, Exhalation performance
Combination Valve Installation, Exhalation Resistance
3.4.1 Valve sticking. The exhalation valves may have a tendency to stick in the closed position if there is a
sufficient buildup of sticky residue on the exhalation valve seat, the valves shall be so designed that the valve seat
can be cleaned by first removing the valve cap and then swabbing the valve seat with a cotton-tipped swab
saturated with a warm diluted solution of a mild detergent and water followed by a rinse with distilled water.
3.4.2 Inadvertent oxygen regulator shut-off protection - The design of the valves shall include a feature which
shall provide protection during inadvertent oxygen regulator shut-off. This feature shall prevent the breathing of
ambient air through the valve.
* 3.4.3 Reliability. The valves shall have specified mean Cycles between failures (MCBF) of not less than
180,000 cycles at the 90 percent lower confidence limit (see 4.6.22). (This equivalent to a minimum acceptable
MCBF of 120,000 cycles and a reliability of 0.9775 for a 10-hour, 9,000 cycle mission.)
3.5 Construction. The valves shall withstand the strains, jars, vibration, and other conditions incident to
shipping,storage,installation, and service. There shall be no undue flutter or vibration of the valves under service
conditions. The valves shall be so constructed that they cannot be disassembled without visible evidence, since it is
intended to replace the entire valve instead of permitting repairs when failure occurs. If threads are used in the
assembly of the body of the valves, the threads shall be sealed by a method approved by the procuring activity.
3.6 Performance.
3.6.1 Dumping. The differential pressure shall not fall below 0.1 inch of water (gauge) with a regulator
pressure of 0.5 to 14 inches of water (gauge) and an increase of flow from 1.0 to 150 liters per minute (see 4.6.2).
3.6.2 Leakage - suction. Leakage of the valves shall not exceed 0.1 liter per minute when the valve is
subjected to the leakage-suction test (4.6.3).
3.6.3 Leakage - suction, low inlet valve. Back leakage through the inlet check valve shall be not more than
15 milliliters per minute with a suction of 0.1 inch of water (gauge) (see 4.6.4).
3.6.4 Inhalation resistance. The inhalation resistance of the valve shall not exceed 0.75 inch of water (gauge)
at a flow of 50 liters per minute and shall not exceed 1.50 inches of water (gauge) at a flow of 100 liters per minute
(see 4.6.5).
3.6.5 Leakage - pressure. Leakage shall not exceed 0.1 liter per minute with a flow of 1.0 to 50 liters per
minute at a pressure of 0.5 to 14 inches of water (gauge) (4.6.6).
l 3.6.6 Exhalation resistance. Differential pressure shall be between 0.1 and 1.5 inches of water (gauge) with
flows in the range of 0.1 to 50 liters per minute (see 4.6.7).
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