MIL-M-27274E(USAF)
4.5.2.2 Sampling plan B. One mask facepiece of each size specified in the contract or order shall be selected at random from each batch of silicone rubber compound received from the manufacturer. Test sheets fabricated (see 4.4.1) shall also be made from each batch. The test sample shall be subjected to the following tests as described (see 4.6):
a. Tear resistance. b. Hardness.
4.5.2.3 Sampling plan C. If hardshells are molded in an essentially continuous operation, three hardshells shall be selected at random from each day's production of each mold cavity and subjected to the test described (see 4.6.13). If hardshells are not molded in an essentially continuous operation, three mask hardshells of each size of mask specified in the contract or order (fabricated from each batch of material received from the manufacturer and molded under the same conditions and at substantially the same time) shall be selected at random and subjected to the test described (see 4.6.13).
4.5.3 Reject criteria. When one item selected from a production run fails to meet the specification, no items still on hand or later produced shall be accepted until the extent and cause of failure are determined and corrected. Individual tests may be continued pending the investigation of a sampling test failure. However, final acceptance of items on hand or later produced shall not be made until it is determined that the items meet all the requirements of this specification. The investigation of a test failure could indicate that defects may exist in items already accepted; if so, the contractor shall fully advise the procuring activity of all defects likely to be found and methods of correcting them.
4.6 Inspection methods.
4.6.1 Examination of product. Each oxygen mask shall be carefully examined to determine conformance to the requirements of this specification with respect to materials, construction, workmanship, dimensions, and marking.
4.6.2 Mask leakage. Each mask (with combination valve installed correctly and the microphone plug in place) shall be placed on a suitable test stand and adjusted so there is no leakage around the face seal. The inboard leakage shall not exceed 100 milliliters per minute when a suction of 13 millimeters of mercury is applied within the facepiece of the mask with the free end of the mask tubing plugged.
4.6.3 Combination valve installation, inlet performance (low suction). The inlet valve portion shall be completely dry throughout this test. The inlet valve shall be inspected for imperfect seating of the flapper on the seat and leaks around the valve seat by applying and maintaining a suction of 0.19 millimeters of mercury at the free end of the delivery tube. The total leakage through the combination valve inlet portion shall not be more than 15 milliliters per minute. If necessary, a suitable means shall be used to prevent collapse of the hose.
4.6.4 Combination valve installation, inlet performance (high suction). This test is the same as 4.6.3 except that a suction of 22.4 millimeters of mercury shall be used. The leakage through the combination valve inlet portion shall not exceed 150 milliliters at this suction.
4.6.5 Combination valve installation, exhalation performance. Each mask shall be placed on a suitable test stand and all suction and pressure from the previous test exhausted. A pressure of 20 millimeters of mercury shall be applied at the mask tubing. The pressure at the mask tubing shall then be gradually reduced, causing the inlet valve to close and causing a pressure differential to be applied
across the exhalation valve. The mask exhalation valve shall open with a pressure in the tube between 15
and 19.9 millimeters of mercury. If an extreme pressure is encountered, the inlet valve shall be rechecked for leakage. If the valve is properly seated and the mask still fails to function properly, the valve shall be replaced and the test repeated.
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