additional analysis, but omit the solvent rinses. Water, if present, will still appear on the surface of the filter membrane, but will now tend to spread out rather than to appear in discrete droplet form. Examine closely. NOTE: If 1,1,1-trichloroethane or dry-cleaning solvent is used as the filtered solvent, the filter must be dried thoroughly prior to being placed in petri slide. Either these solvents, or their fumes, will craze and cloud the polystyrene petri slides. Test Filter Analysis After you process the fluid sample, visually compare the test filter or patch with the contamination standards. To determine the particulate contami- nation level, compare the shade and color of the test patch with the corresponding colors of the contamination standards. If the test patch displays a rust or tan color, use the tan standard patch. If the test patch is gray, use the gray standard patch. In any case, you should follow the operating instructions contained in the contamination standards. Tan patches occur when rust or iron chlorides are formed in the system, or the system contains abnormal amounts of silica (sand). Gray patches are typical of systems containing normal proportions of common wear materials and external contaminants. The maximum acceptable particulate level for naval aircraft is Navy Standard Class 5. For related SE, the maximum acceptable particulate level is Navy Standard Class 3. If visible free water is present in either the sample bottle or on the surface of the test filter (at completion of filtration), the system under test is rejected. A stain on the test filter membrane may be an indication of the presence of free water. When a stain is seen on the test filter, obtain a second fluid sample from the system under test and process it so that water content can be confirmed prior to system rejection. Make sure that observed water is not a result of atmospheric condensation during the sampling process. If the system under test fails to meet the Navy Standard Class 5 particulate requirement or if it exhibits free water, the system must be decon- taminated according to the procedures listed in the applicable MIM. Filter Bowl Contents Analysis Hydraulic fluid samples obtained from filter bowls and/or elements cannot be used to determine system contamination levels. The following combination of factors makes the filter bowl sample useless when determining the system’s level of contamination: sedimentation, functional location, and/or an inability to obtain the required 100 milliliters of fluid. Filter bowl residue analysis may be used to monitor hydraulic system degradation, monitor for suspected impending component failure, or isolate a cause for continued contaminant generation. Evaluate filter bowl patch residues by following the procedures in applicable manuals. As you gain experience about normal contaminates for specific aircraft systems and hours of operation, you will be able to evaluate filter bowl patch residue. Through experience, analysis of main pressure line and case drain filter bowl residues is useful in verifying failure of the upstream hydraulic pump, as large amounts of metal usually show up in these particular assemblies. Residue in other filter assemblies is affected by so many other components and factors that analysis is difficult. Filter bowl residues should be analyzed only as a means of identifying or verifying suspected component failure. Examine residue from those filter assemblies directly downstream from the component. ELECTRONIC PARTICLE COUNT ANALYSIS Electronic particle counters, such as the HIAC Contamination Test Center, Model C-600-1, or Royco Electronic Particle Counters, are used to determine counts of the number of particles in the various size ranges. The counts obtained are compared with the maximum allowable under Navy Standard Class 5. Counts that exceed the maximum allowable in any size range make the fluid unsuitable for use in Navy aircraft. The test results obtained by using automatic particle counters and the contamination analysis kit are not always precisely the same. Both are authorized for fleet use, and you may use either one. Automatic particle counters optically sense particles contained in the fluid sample and electronically size and count them. Most fleet equipments are calibrated so that the smallest particle counted has an effective diameter of 5 microns. Particles smaller than 5 microns, although always present, do not affect the 4-13