MIL-STD-202H.pdf - 第62页

MI L - S TD - 202 - 10 9 4.2 .2 Test ex ecution. T he f ol l ow i ng pr ov i de s t h e pr o c ed ur al s t ep s f or ex ec ut i on of t he ex p losive atmo sphere test; a. W ith the test i t e m i ns t al l ed, t he t e…

MIL-STD-202-109

FIGURE 1. Specific gravity of n-hexane

4.2. PROCEDURE

4.2.1 Test preparation.

4.2.1.1 Controls. Before each test, verify the critical parameters. Ensure spark devices function properly and the

fuel atomizing system is free from deposits that could inhibit its functioning. Adjust the empty test chamber to the

highest test altitude, shut off the vacuum system and measure the rate of any air leakage. Verify that any leakage will

not prevent the test from being performed as required; i.e., introduce the test fuel and wait three minutes for full

vaporization, yet still be at least 3300 feet (≈1000m) above the test altitude.

4.2.1.1.2 Mounting. The specimen to be tested shall be mounted in the test chamber in such a manner that

normal electrical operation is possible and so that the mechanical controls may be operated through the pressure

seals from the exterior of the chamber. All external covers of the test specimen shall be removed or opened to insure

adequate circulation of the explosive mixture. The test specimen shall then be operated to determine that it is

functioning properly and to observe the location of any sparking or high temperature spots that may constitute

potential explosion hazards.

4.2.1.2 Loading. Applicable mechanical and electrical loads applied to the specimen shall be as specified in the

individual specification. Proper precaution shall be taken to duplicate the normal load in respect to torque, voltage,

current, inductive reactance, etc. In all instances it shall be considered preferable to operate the specimen as it

normally functions during service use.

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MIL-STD-202-109

4.2.2 Test execution. The following provides the procedural steps for execution of the explosive atmosphere test;

a. With the test item installed, the test chamber shall be sealed and the test item and chamber inner walls stabilized to

71°C ±3°C (160°F ±5°F), or to a lower temperature as specified, if the specimen is designed to operate at a lower

temperature.

b. Adjust the chamber air pressure to simulate the desired test altitude (see 4.2.3) plus an additional

10,000 feet to allow for introducing, vaporizing, and mixing the fuel with the air as described in 4.1.3.

c. Slowly introduce the required volume of n-hexane into the test chamber.

d. Circulate the test atmosphere and continue to reduce the simulated chamber altitude for at least three

minutes to allow for complete vaporization of fuel and the development of a homogeneous mixture.

e. At a pressure equivalent to 5,000 feet (1525 meters) above the test altitude, verify the potential

explosiveness of the fuel-air vapor by attempting to ignite a sample of the mixture taken from the test

chamber by using a spark-gap device or glow plug ignition source with sufficient energy to ignite a 3.82

percent hexane mixture. If ignition does not occur, purge the chamber of the fuel vapor and repeat

steps a through e. (An alternative method of determining the explosive characteristics of the vapor is by

using a calibrated explosive gas meter that verifies the degree of explosiveness and the concentration

of the fuel-air mixture.)

f. Operate the test specimen and continue operation through step g. Make and break electrical contacts

as frequently and reasonably possible.

g. If no explosion occurs as a result of operation of the test specimen, slowly reduce the simulated

chamber altitude to 5,000 feet (1525 meters) below the test altitude (at a rate no faster than 330 feet

(100 meters) per minute by bleeding air into the chamber). Perform one last operational check and

switch off power to the test specimen.

h. If no explosion has occurred as the result of operation of the test specimen by the time the simulated

altitude has reached 5,000 feet (1525 meters) below the test altitude, verify the potential explosiveness

of the air-vapor mixture as in step e. If ignition does not occur with the sample, purge the chamber of

the fuel vapor, and repeat the test from step a.

i. Repeat steps b through h for the required test altitudes (see 4.2.3).

4.2.3 Test altitudes. Unless otherwise specified, the test shall be accomplished at simulated test altitudes of local

ground level to 5,000 feet, 20,000 feet, and 40,000 feet. However, if an explosion occurs at an altitude of less than

40,000 feet, further testing shall be discontinued.

5. DETAILED REQUIREMENTS

5.1 Summary. The following details are to be specified in the individual specification:

a. Fuel, if other than that specified and all specific details associated with the fuel (see 4.1.2).

b. Mechanical and electrical load (see 4.2.1.2).

c. Chamber temperature condition, if lower than 71°C ±3°C (160°F ±5°F) (see 4.2.2 a).

d. Test altitudes, if other than those specified (see 4.2.3).

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MIL-STD-202-109

6. NOTES

(This section contains information of a general or explanatory nature that may be helpful, but is not mandatory.)

6.1 Supersession data. The main body and 38 parts of this revision of MIL-STD-202 replace superseded MIL-STD-

202.

Custodians: Preparing activity:

Army - CR DLA – CC

Navy - EC

Air Force - 85 (Project 59GP-2015-013)

DLA - CC

Review activities:

Army - AR, AT, AV, CR4, MI, SM, TE

Navy - AS, OS, SH

Air Force - 19, 99

NSA - NS

NOTE: The activities listed above were interested in this document as of the date of this document. Since

organizations and responsibilities can change, you should verify the currency of the information above using the

ASSIST Online database at https://assist.dla.mil/

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联系方式：xuyj@beice-sh.com 13917165676