Downloaded from https://www.everyspec.com MIL-STD-81OD.. 19 July 1983. d.,,..,, Mind velocity. High rainfall intensities accompanied by winds of 18 &s (40 mph) are not unoommon during storms. Unless otherwise specified, this velocity ,is,recommended for procedure I tests. Winds of 33 m/s (75 mph) are the threshold for hurricane-force winda. e. -~. Wind-driven rain will usually have more of an effect on vertical surfacea than on horizontal surfacea, and vice versa for ‘verticalor near-vertical rain. All surfaces onto which the rain could fall or be driven must be exposed to the test.conditions. f. M&LWi&Q. Procedure III relies on pressurized water.
The pressure may be varied according to the requirements documents, but a minimum value of 377 kpa (40 psig) nozzle.pressure is given as a.guideline based on past experience. This value will produce water dropleta traveling at approximately 64 km/h (40 mph) when a nozzle as specified in paragraph II-1.1e ia used. .4. ~. Review the requirements documents for any additional guidelines., 1-! 1-4.1 ~ 1-811.1 reaumementa. . The failure of the test item to satisfy the re’qui”rements of the equipment specification must be analyzed carefully, and related information must be considered, such.as: a. Degradation allowed in the performance characteristic because cf rainfall exposure. b.
Necessity for special kits for special operating procedures. c. Safety of operation. 1-4.1.2 Mater Dene trati~. Based on the individual test item and the requirements for its nonexpcsure to water, determine if.one of the following ia applicable: a. ~1 fail=. Any evidence.of water perietraticninto the test item enclosure follcwing the rain test shall be considered a failure. ,. b. &&Dtab e water Dene 1 tratioq. Water penetration of not more than 4 ; cm3 per 28,000 cm3.(1 ft3) of test item enclosure z/ shall be acceptable, provided“the following conditions are met: . .
., ,.2 2/ This quantity of water,(4 cm3) is approximately the quantity required to raise the relative humidity of 1 cubic foot of air at standard ambient ccn- ditiona (5o% RH at 21° C (70° F) to saturation at 49° C (120° F)). zhe 49° C value is realistic for equipment exposed to higher temperature and.solar radiation effects. 19 July 1983 506.2-5 t.fSTHOD506.2