MIL-DTL-28788 Switches, Air And Liquid Flow, Sensing, General Specification ForThis specification covers the general requirements for flow switches intended primarily for use in equipment to sense velocity and flow of air or liquid.

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MIL-DTL-28788C

4.7.16 Dielectric withstanding voltage (see 3.20). Switches shall be tested in accordance with

4.7.16.2 and, when applicable (see 3.1 and 6.2), in accordance with 4.7.16.1. This test shall be

performed with the switch in normal position, and shall then be repeated for other operating positions.

4.7.16.1 At atmosepheric pressure. Switches shall be tested in accordance with method 301 of

MIL-STD-202. The following details shall apply

a. Magnitude of test voltage � 1,000 volts plus twice the working voltage.

b. Nature of potential � AC.

c. Duration of application of test voltage � 1 minute for qualification, 5 seconds for quality

conformance tests, at 20 percent higher voltage.

d. Points of application of test voltage � Between all terminals and ground.

e. Maximum leakage current � 500 microamperes.

f. Examination after test � Switches shall be examined for evidence of arcing and flashover.

4.7.16.2 At reduced barometric pressure. Switches designed for operation above 10,000 feet shall

be tested as specified in 4.7.16.1, and in accordance with method 105 of MIL-STD-202. The following

details and exception shall apply.

a. Method of mounting � Normal mounting means.

b. Test condition � C or D, as applicable.

c. Test voltage � 500 volts, unless otherwise specified (see 3.1 and 6.1).

4.7.17 Seal (as applicable, see 3.21). Switches shall be tested in accordance with 4.7.17.1, or

4.7.17.2, as applicable.

4.7.17.1 Watertight. Switches shall be immersed to a depth of 2 � 1 inches in a container of water

containing approximately � of 1 percent aerosol, and shall then be placed in a vacuum chamber. The

absolute pressure shall be 1.3 inches of mercury and this pressure shall be maintained for a period of 1

minute. The absolute pressure shall then be increased to 2.5 inches of mercury and this pressure

maintained for 2 minutes. During the 2-minute period, the switches shall be observed for evidence of a

continuous stream of bubbles. Any bubbles coming from within the switches shall be considered as

leakage. Bubbles which are the result of entrapped air on the exterior of the switches shall not be

considered as an indication of leakage.

Hermetic. Switches shall be tested in accordance with method 112 of MIL-STD-202.

4.7.17.2

The following details shall apply:

a. Test condition � C.

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1. Procedure III or IV, leakage-rate sensitivity � 1x10 atm cc/sec; for checking gross

leaks, test condition B.

2. For procedure IV.

a. Reduced pressure of the chamber and duration of pressurization � Determination

made in accordance with the type of equipment used.

b. Measurements after test � None.