MIL-DTL-28693A
4.7.1.4 Wall thickness (see 3.4.3.5). The wall thickness of all hoses in the sampling shall be
measured at both ends using a deep throat micrometer to determine conformance to 3.4.3.5. The
measurements shall be made at least every 90º around the circumference at points 2, 8, and 12 inches
(5.08, 20.3, and 30.5 cm) in from the ends of the hoses. The entire lot shall be rejected if the wall
thickness of any hose in the sampling is more than .016 inch (0.41 mm) above the maximum given in
3.5. The lot shall be accepted if the wall thickness of any hose in the sampling is above the maximum
tolerance providing that all of the following conditions are met:
a. The excess above the maximum tolerance is no more than .016 inch (0.41 mm).
b. The excess thickness prevails over not more than 25 percent of the applicable circumference.
c. An equal or greater proportion of the applicable circumference has a wall thickness at least
.016 inch (0.41 mm) under the maximum tolerance.
4.7.2 Unit weight (see 3.6.2). The unit weight of all hoses shall be determined by weighing the
hoses without couplings. The readings shall be accurate to the nearest pound. The weight of each hose
shall be divided by its length to determine conformance to 3.6.2.
4.7.3 Proof pressure (see 3.6.3). Each length of hose shall be equipped with couplings and
subjected to 300 psig proof pressure to determine conformance to 3.6.3. The following details shall
apply:
a. Before starting the tests, a 10 psig (0.69 bar) hydrostatic pressure shall be established in the
hose, and the length, the OD, and a zero index for the twist (see 4.7.4) determined.
b. The method shall be as described in ASTM D380, except that the hydrostatic pressure rate
shall not exceed 1,000 psig (6.9 MPa) per minute.
c. The proof pressure shall be held for 5 minutes and the hose and fittings examined for leakage
or other indication of weakness.
d. At the end of the 5-minute period and while the pressure is maintained, the length, OD, and
twist of the hose shall be measured for the determination of dimensional stability.
e Failure of any hose to meet the requirements of proof pressure shall be cause for rejection of
the entire lot.
4.7.4 Dimensional stability (see 3.6.4). The effect of the proof test pressure on the length, OD, and
twist of all hoses in the sampling shall be determined as specified in 4.7.3 and ASTM D380. The
following details shall apply:
a. The pressure shall then be reduced to "0" psig and the hose left in this condition for 5
minutes.
b. At the end of this period, the diameter and length of the hose shall be measured to determine
conformance to 3.6.4.
c. The entire lot shall be rejected if any hose sample fails to meet the requirement for
dimensional stability.
4.7.5 Air pressure test (see 3.6.5). Hoses when tested for air pressure shall meet the requirements
of 3.6.5. The following details shall apply:
a. Each of the hoses in the sampling shall be subjected to 125 ±5 psig (8.61 bar ±0.34 bar) air
or nitrogen pressure for not less than 10 minutes, followed by a complete release of pressure
within 15 seconds.
b. The outside and inside surfaces of the hose shall be examined within 5 minutes for blisters or
other evidence of disruption.
c. The inside of the hose shall be inspected by sighting from one end of the straight hose while
a light is held at the other end of the hose.
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