MIL-DTL-81716A
The humidified packings and the metal plates shall be immersed in MIL-PRF-6083 fluid and
drained to the drip point. The packings and plates shall then be laid together in a stack such that
at least two packings contact each specified metal. The stack shall be held together with a force
of 20 to 30 pounds and placed in a desiccator which is maintained at 90 to 92 percent relative
humidity at room temperature. A separate set of metallic plates shall also be prepared (buffed,
cleaned and dipped in MIL-PRF-6083 fluid and drained) and placed in the desiccator in such a
manner that the control plates shall not touch each other or any of the packings (dipotassium acid
phosphate, K2HPO4, when placed in distilled water in sufficient quantity to produce a saturated
solution, will maintain approximately 92 percent relative humidity in a sealed desiccator at 68F
(20C)).
Time of storage for this portion of test shall be 336 hours. No more than 15 minutes shall
elapse between the time the test samples are removed from the prehumidifying chamber and
placed in the stacked condition in the second humidity chamber.
At the termination of this test, the test samples shall be examined as follows:
(a) The surfaces of the plates that were in contact with the packings shall be inspected
for evidence of deposit formation or adhesion of packing material. If deposits or adhesion
are evidenced the surfaces of the plates shall be washed in precipitation naphtha.
Deposits determined as rubber compounds or elements therefrom, which can be
removed by this process and which do not occur on the separate control plates, shall be
construed as adhesion. There shall be no evidence of adhesion of the packing material
to the metal plates.
(b) If any other marks remain on the surfaces of the plates after step (a), the surfaces
shall be lightly polished with a non-abrasive buffing cloth. Any pits or eroded marks
remaining after this process shall be construed to be corrosion. Discoloration or staining
(marks which do not physically affect the surface of the plates and which easily wash or
buff off) shall not be considered detrimental. If any doubt should arise about the
presence of pitting, erosion or corrosion on the metal plates, a microscope of
approximately 10 to 15-power magnification shall be used to determine the actual
condition. There shall be no evidence of severe discoloration, corrosion (pitting), or
erosion.
4.5.2.9 Installation stretch.
4.5.2.9.1 Installation stretch at normal temperature. Twelve SAE AS33931, MS3393-3
packings shall be used in this test. Six packings shall be unaged and six shall be air aged (see
4.4.2) unless the result of the elongation test indicated that the material decreased in elongation
due to air aging by more than 30 percent, in which case all twelve packings shall be air aged.
The packings shall be stretched onto a smooth metallic mandrel of .390 ± .002 inch diameter and
allowed to remain in this condition on the .390 inch diameter section of the mandrel for 1 hour at
room temperature. There shall be no evidence of breakage or cracking of any of the packings.
4.5.2.9.2 Installation stretch at -20F (-29C). The test of 4.5.2.9.1 shall be duplicated at -20
± 2F (-29 ± 1C) except that three each of the unaged and air aged (see 4.4.2) packings shall be
used (regardless of change in elongation). The unaged and air aged packings and the threaded
mandrel (see Figure 2) shall be held at -20 ± 2F (-29 ± 1C) for 24 hours (packings unstretched)
prior to stretching on the mandrel. Each packing shall be rapidly pushed from the cone of the
mandrel over the threaded .390 inch diameter onto the smooth 0.320 inch diameter undercut.
There shall be no breakage of packings in this test and each packing shall decrease in inside
diameter to grip the .320 inch diameter undercut in a maximum of 10 seconds after being inserted
on the mandrel while still at the specified temperature.
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