MIL-PRF-87257B
4.4
Method of inspection and test
4.4.1 Inspection
Inspection shall be in accordance with Method 9601b of FED-STD-791.
4.4.2 Tests
The hydraulic fluid properties shall be determined in accordance with the applicable methods
specified in tables I and III and sections 4.4.3 through 4.4.6. Physical and chemical values
apply to the average of the determinations made on the samples.
4.4.3 Compatibility
Samples of candidate fluid in amounts of 20-ml, 100-ml, and 180-ml shall be mixed with
samples from each of the fluids previously approved under this specification. Total volume of
each mixture shall be 200-ml. Mixtures shall be prepared in 250-ml stoppered flasks. The
flasks shall be thoroughly agitated and then stored in an oven at 200°C for 2 hours. At the end
of this time, none of the mixtures shall show any sign of sediment, turbidity, or crystallization.
The samples shall then be stored at -54°C for a period of 2 hours. Slight turbidity after this time,
which later disappears, will be permitted in the samples. Compatibility tests described herein
shall also be conducted with representative fluids qualified to MIL-PRF-5606 and MIL-PRF-
83282.
4.4.4
High-temperature stability
4.4.4.1 Apparatus
Thermal stability characteristics of the hydraulic fluid shall be determined using the following
test apparatus: a 50-ml, round-bottom flask or a test tube (25 mm x 50 cm) with standard taper
24/40 (Ace Glass Inc., Vineland, NJ 08360 or equivalent); a 75° angle adapter with standard
taper 24/40 (Ace Glass 5040-10 or equivalent); gas inlet tube, 6 mm OD (Ace Glass 8700-37 or
equivalent); and a high-temperature bath capable of maintaining a temperature of 200 ± 2°C.
4.4.4.2 Procedure
The following procedures shall be followed for determining high-temperature stability:
a. Place 25 ml of candidate fluid in a flask or test tube fitted with a 75° angle adapter and
gas inlet tube.
b. Adjust the height of the glass inlet tube to within 1.0 cm above the level of the fluid.
c. Place a 2.5-cm length of ¼-inch OD stainless steel tubing, type 304, into the fluid.
d. Heat the fluid for 100 hours at a temperature of 200 ± 2°C while maintaining a 1-liter-per-
hour flow of dry nitrogen (lamp grade) on the surface of the fluid via the gas inlet tube.
Upon completion of the test, the fluid shall meet the requirements of table I.
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