MIL-STD-419E
5.5.1.2.2 Long term (internal surfaces). For petroleum or PAO oil system components, which are expected to be in storage for considerably longer than 1 year, and are easily disassembled and cleaned, the internal surfaces shall be treated with preservative in accordance with MIL-STD-2073, Type P-2 (MIL-PRF-16173, Grade 2). A tag with the following information shall be attached to the assembly: "The interior of this item is coated with corrosion preventive compound, Grade 2 of MIL-PRF-16173. This compound shall be removed just prior to installation." Phosphate ester system components in long term storage will require annual treatments with fluid in accordance
with MIL-H-19457 with addition of vapor space inhibitor in accordance with MIL-I-22110. The assembly shall be tagged as specified in 5.5.1.2.1.
5.5.1.2.3 External surfaces. For external surfaces of petroleum or PAO oil and phosphate ester fluid system components requiring preservation, coatings in accordance with MIL-STD-2073, Type P-1 (MIL-PRF-16173, Grade
1) or Type P-19 (MIL-PRF-16173, Grade 4) shall be applied where the preservative will not have to be removed for system operation, or where preservative removal by scraping or solvent action would not damage the part or
equipment. Where removal of the preservative will be required, such as when the preservative would otherwise be in contact with the system fluid, a coating in accordance with MIL-STD-2073, Type P-2 or Type P-19 shall be
applied. A tag with the following information shall be attached to the assembly: "The exterior of this item has been coated with corrosion preventive compound to (specification), (coating type or grade). Removal of this compound
(is, is not) necessary prior to installation."
5.5.1.3 Preservative removal. The coatings in accordance with MIL-STD-2073, Type P-2 and P-19 and fluid films in accordance with MIL-PRF-6083 may be removed with dry cleaning solvent in accordance with
MIL-PRF-680, Type II. Surfaces cleaned with solvent will be left unprotected and shall be immediately wetted with the system fluid unless welding or brazing will be required to reassemble the system. For preserved petroleum or
PAO fluid system components which will not require degreasing, the system oil may be used to remove the preservative. When solvent in accordance with MIL-PRF-680 is used to remove protective coatings, complete
removal of the solvent is required to avoid subsequent contamination of the system operating fluid. (See 5.9 for
disposal instructions for these fluids.)
5.6 System flushing. Installed piping shall be flushed before being put into operation. It is important for designers of hydraulic systems to plan for system flushing in the design phase. Dead ends without circulation shall be avoided. If there is a risk of particulate contamination moving from the dead end to the rest of the system, then the dead end shall be capable of being outflushed or a flush path loop using temporary jumpers shall be established. Flushing fluid shall be the system operating fluid or a fluid compatible with system fluid as approved by the acquiring activity. The primary difference between flushing oils and the system fluid is viscosity; lower viscosity oils (such as MIL-PRF-5606 and MIL-PRF-17672, Sym 2075TH) require much lower flow rates to maintain the Reynolds number specified in 5.6.1 while having much lower pressure drops than the higher viscosity oils (such as
2135TH and 2190TEP). This means that by using low viscosity oils as the flushing fluid, longer pipe lengths for any given pipe size can be flushed with a given flushing plant or the same length of pipe can be flushed at higher flow rates than with high viscosity oils. Flushing shall be performed on the entire system, but may be accomplished piecemeal on those circuits which can be independently cleaned and isolated. Complex systems may be divided into parts in order to assure the required flow rate in every part of the system during flushing. Hydraulic pumps, motors, complex valves, and devices that restrict flow or could be damaged by contaminants dislodged during flushing shall be removed from the circuit; and temporary pipe, flushing blocks, tube or hose substituted in their place. See
figure 1 for an example of a typical flushing loop on a complex system, such as that on a submarine. System flushing shall be in accordance with the following:
a. A temporary filter, in accordance with SAE J2321, or equal, shall be installed in the circuit being flushed and clean filter elements installed as necessary to keep the pressure drop across the filter within specified limits. Care shall be taken to select a filter with the optimum filtration ratio, so as to achieve the desired cleanliness level within an acceptable period of time. Filter bypass valves shall not be used. The flushing fluid shall be filtered through a filter in accordance with SAE J2321, or equal, as the system is filled.
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