Patch testing is the primary contamination measurement method used at all levels of maintenance. The P/N57L414 contamination analysis kit (fig. 4-3) is used to perform patch testing. In the patch test method, a fluid sample of known volume is filtered through a filter membrane of known porosity. When the fluid passes through the filter, all particulate matter in excess of a size determined by the filter characteristics is retained on the surface of the membrane. The retention of particulate matter causes the membrane to discolor proportionally to the particulate level of the fluid sample. Free water will appear either as droplets during the fluid sample processing or as a stain on the test filter. The typical color of contamination in any given system is usually uniform. The degree of filter membrane discoloration correlates to a level of particulate contamination. By visually comparing the test filter with contamination standards that represent known contamination levels, the contaminant level of the system can be determined.

Figure 4-3.P/N57L414 contamination analysis kit.

Accurate determination of hydraulic contaminant levels requires proper sampling techniques, using equipment and materials that are known to be clean. If you allow any foreign matter to contaminate the sample fluid or testing equipment, the results will be wrong. The operational procedures discussed in the following paragraphs are general in nature. For specific information on the use of contamination analysis kits, you should refer to NAVAIR 01-1A-17 and NAVAIR 17-15E-52. Table 4-2 lists the materials required to perform the analysis.

Table 4-2.Materials Required for Contamination Analysis

The components of the contamination analysis kit are shown in figure 4-4. Look at this figure as you read about the procedure you should follow to prepare hydraulic fluid for contamination analysis. The Millex point-of-use filter unit consists of two threaded half-sections and an internal support screen. Use forceps to place one 25-mm solvent filter on the gridded plastic surface of the filter holder. 

NOTE: Packaged filter membranes are separated by blue separator discs. Remove separators before installing solvent filter in the filter holder. Position the perforated support screen on top of the solvent filter to provide support for both sides of the solvent filter. Reassemble the two halves of the filter holder fingertight Fill the wash bottle (with short spout) with an approved solvent. Trichloro-trifluoroethane Solvent MIL-C-81302A, Type II (Freon), is the preferred solvent because it evaporates rapidly and is compatible with materials used in the analysis kit. MIL-T-81533 (1,1,1-trichloroethane solvent) is an alternative solvent. However, when using this sol vent, sufficient drying time must be allowed. Dry-cleaning solvent, P-D-680, is also a suitable substitute. As with the 1,1,1 trichloroethane solvent, sufficient drying time must be allowed.

MIL-C-81302 evaporates rapidly and will displace oxygen. Use only in a well-ventilated area. MIL-C-81302 should not be used in large volumes, and all containers must be closed when not in use. A standby safety observer must be present during test to ensure the person performing the test is not overcome by fumes. Failure to observe proper safety precautions could result in personal injury or death to personnel.

When MI L-C-81302 is not available, MIL-T-81533 or P-D-680 may be used only when an immediate demand exists. However, if either solvent is used, appropriate precautions must be observed due to their toxicity and flammability. In the event that either MIL-T-81533 or P-D-680 must be used, use only in a well-ventilated area and avoid inhalation of vapor. P-D-680 is flammable. Keep it away from open flame. Failure to observe proper safety precautions could result in personal injury or death to personnel.

Fill the wash bottle (with long spout) with dry-cleaning solvent P-D-680 to flush sampling points. Replace their screw caps. Attach the filter holder to the wash bottle with the short spout. Make sure the tip of the wash bottle is not damaged by forcing the filter holder on too tightly. If damaged, the other wash bottle may be modified by carefully cutting off the tip so that the filter holder will fit. The damaged wash bottle may then be used for flushing fittings and sampling points.

Clean the required number of sample bottles before use by rinsing and flushing them with filtered solvent. Fill the bottle to be cleaned approximately half full. Replace the cap on the opening, shake the sample bottle several times, remove the cap, and dump the contents. Repeat this operation three or more times to remove residual hydraulic fluid. When the bottle is considered clean, flush down the external threads of the sample bottle and the internal threads of the bottle cap with filtered solvent. Replace the cap on the bottle.