FED-STD-791D
4.2.4.4.2 Metal specimens. Metal specimens are mounted within the test-oil sump in
order to provide information concerning possible metal attack by the lubricant. The specimen
holder is a 0.95-cm (3/8-in) rod mounted on the sump lid and extending 20.32 cm (8 in) into the
sump (or approximately 5.08 cm (2 in) below the cold oil level). The specimens are secured to
the rod by a 10-32 size screw, 3.81 cm (1-1/2 in) in length. The specimens are individually
placed on the screw and separated by spacers of 0.32-cm (1/8-in) thickness and 0.79-cm (5/16-
in) O.D. The mounting rod is tapped at the lower end to accept the screw such that the
specimens are mounted with their major axis in a vertical plane. The metal specimens are 0.081-
cm (0.032-in) thick, 1.905-cm (3/4-in) diameter disks with 0.635-cm (1/4-in) center holes. A
five-specimen set is used consisting of the following materials:
Aluminum
ASTM B 209, temper T-3 or T-4
Titanium
8Mn Annealed, 110 ksi (758 MPa)
yield strength-UNS R56080
Silver
99.9% purity
Steel
AMS 5040
Stainless Steel
SAE AMS 5518
A sketch of the metal specimen assembly, indicating the metal specimen order, is shown on
Figure 3.
4.2.5 Air system. Water saturated air is metered to the test-oil compartment in the
bearing head. The air supply for the test-bearing compartment is filtered shop air connected in
the following sequence: air supply to pressure regulator to flow control valve to rotameter to
water saturator to water separator column to end cover fitting on bearing head. The air directed
through the end cover (at 1 o'clock on the same diameter as the test-oil jet) into the bearing
compartment is used primarily to control the pressure drop across the seal so as to insure against
oil transfer from the support section into the test-oil section. A 0.64- to 0.32-cm (1/4- to 1/8-in)
tubing to pipe fitting, J of Figure 1, should be used for the metered air supply fitting at the end
cover. The water saturator consists of a 1-in-diameter spherical gas diffuser stone submerged in
distilled water within a 2 L filtering flask. The flask is initially charged with 1200 mL of water
and is refilled to this level at each shutdown period during the test. A water separator column is
connected downstream of the saturator to remove entrained droplets. The column consists of a
61-cm (24-in) length of 5.08-cm (2-in) borosilicate or equivalent, glass pipe flanged at both ends.
The flanges are constructed of suitable aluminum plate with a polytetrafluoroethylene gasket seal
between the glass pipe and flange, (see AMS 3652, 3656, 3660, 3667). The column is loosely,
but completely, packed with glass wool fiber, Corning Cat. No. 3950, or equivalent.
4.2.5.1 Air to the test head is metered through a rotameter. Prior to each run, the
rotameter is calibrated against a wet-test gas meter for a flow of 9.91 0.57 L/sec (0.35 0.02
cfm). The procedure is to disconnect the air supply line at the fitting where the air enters the
head and then connect the supply line to a wet-test gas meter which in turn discharges to
atmosphere. A mercury manometer is located immediately downstream from the rotameter. The
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