Samples taken from aircraft hydraulic systems and SE should be representative of the fluid in the system under test. Aircraft samples should be taken immediately after flight. If postflight samples cannot be obtained, the system is cycled according to directions in the applicable aircraft MIM or MRC before drawing a sample. Before sampling SE hydraulic systems, recirculate the fluid for a minimum of 5 minutes at full flow rate or for a proportionately longer time at a lower flow rate. Remove external contaminants from the sampling point by flushing it with solvent and wiping the sampling point with clean, disposable wiping cloths. When the sampling point is visibly free of external contaminants, subject it to a final solvent flush. Sampling points not adequately cleaned before use may produce test results that needlessly cause the rejection of the system under test. Begin the flow of fluid to be sampled, by appropriate means, allowing an initial quantity to flow into a waste receptacle. This procedure serves to flush away any contaminant in the sampling line and any contaminants generated by mechanical operation. Without interrupting the

Figure 4-4.Contamination analysis kit components.

flow of fluid, take the required sample by placing a clean sample bottle under the fluid stream. You should take two samples at this time. In the event the first sample is rejected, you will have another sample readily available. End the flow of sample fluid after the sample bottles are full, and it is removed from the stream. Install the caps on the bottle, and put a tag or label on the bottles that identifies the aircraft or equipment sampled and the specific sampling point that was used.

Sample aircraft filter assemblies by removing the filter bowl and transferring the fluid contents of both the bowl and the element to a clean sample bottle. The amount of fluid obtained varies, depending on the type of filter assembly.