MIL-STD-810F Method 512.4 - Immersion

Experience has shown that a temperature differential between the test item and the water can affect the outcome (leakage) of an immersion test. Increasing the test item temperature above the water temperature for the immersion test usually includes heating of the test item to establish a pressure differential (while cooling) to determine if the seals or gaskets leak under relatively low-pressure differential, and to induce expansion/contraction of materials. Although desired, establishing a specific temperature differential for fording tests is often impractical due to the size of the materiel. Also, consider materiel adjacent to heat-producing equipment such as engines, and use temperatures indicative of actual exposure.

How TDS Tests for Immersion
The minimum requirements to pass the immersion test are heating a unit for an hour, till it reaches 120 degrees. Within a minute after the removal from the heat source, you must plunge the item into 72 degree water to a depth of 1 meter, and keep it there for 30 minutes. And, the unit must continue working the entire time, start to finish. We pulled two Recons off the shelf, and subjected them to this test. Except that we doubled the underwater time – to an hour.

So, how did the Recon immersion test come out? From our engineer test report, "The units continued to operate for the duration of the test. On removing the cap, some water droplets were noted around the seal but none was found inside the unit. The unit was then disassembled and further examined. No water was detected inside the main cavity of the unit. Both units produced the same results."