MIL-PRF-87257B
3.
REQUIREMENTS
3.1 Qualification
The hydraulic fluids furnished under this specification shall be products which are authorized by
the qualifying activity for listing on the applicable Qualified Products List (QPL) at the time of
approved product unless specific, written approval of the qualifying activity is obtained.
3.2 Materials
The materials used in formulating this hydraulic fluid shall consist of synthetic hydrocarbon base
and shall contain additives as specified in 3.2.1. A base oil mixture of 2 cSt and 4 cSt
polyalphaolefin is suggested but is not mandatory. The hydraulic fluid shall contain no
admixture of resins, soaps, gums, fatty oils, or oxidized hydrocarbons.
3.2.1 Additives
There shall be no restriction on the types of materials used as additives in the fluid except for
those listed and those imposed by technical requirements of this specification. No pour point
depressant materials or viscosity index improvers may be used.
3.2.1.1 Oxidation inhibitors
Oxidation inhibitors of the phenolic type shall not exceed a concentration of 2.0 percent by
weight.
3.2.1.2 Anti-wear agent
Anti-wear agents, such as tricresyl phosphate (TCP) conforming to TT-T-656, shall be blended
in sufficient quantity, not to exceed 3.0 weight percent, to permit the finished oil to meet four-ball
requirements specified in table I. If TCP is used, the finished fluid shall contain less than 0.03
weight percent of the ortho-isomer.
3.2.1.3 Blending fluid
Blending fluids, such as diesters, shall be blended in a concentration not to exceed 35 percent
by weight of the finished fluid but in sufficient quantity to meet the rubber swell, as specified in
3.2.1.4 Color
The fluid shall contain red dye in concentration not greater than 1 part of dye per 10,000 parts of
oil by weight.
3.3 Finished fluid
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