Before the sample is processed, the fluid to be tested is examined visually for evidence of possible free water. Water can be found in hydraulic fluid samples as droplets that usually settle to the bottom of the sample bottle. Allowing the fluid sample to remain motionless for 10 minutes or longer may make it easier to see visible droplets, if water is present. If fluid samples are hazy or pink, water may be present. Another identical sample bottle filled with a standard of unused fluid can be used for comparison. If water is observed, take another sample from the system to verify the indication before rejecting the system under test.

Before you can process a sample, get the equipment ready. Remove the filter holder assembly from its storage position in the kit. The funnel and holder support are assembled and stored in an inverted position in the vacuum flask. To prepare the funnel and holder support for use, remove them from the vacuum flask, invert them, and reinstall them in the vacuum flask. If it is difficult to remove the holder support from the vacuum flask, insert the back end of forceps into the slot (present on some holder supports) and pry the holder support from the vacuum flask.

You should use the tube and adapter to connect the syringe to the small opening located on the side of the holder support. Wash down the inside wall of the funnel with filtered solvent to flush any surface contamination present. Make sure that the holder support screen, now located at bottom of funnel neck, is also cleaned with filtered solvent.

NOTE: Rapid evaporation of the filtered solvent may result in the condensation of atmospheric moisture on the funnel surface. The moisture can cause inaccurate indications of free water in the sample under test. Carefully inspect for condensation on the funnel surface. If condensation is present, move equipment to an air-conditioned workspace.

Remove the funnel from the holder support by rotating the outer knurled ring in a counterclockwise direction until it disengages, and lift it upwards. Use forceps to carefully remove a single 47-mm test filter, and place it on top of the screen of the holder support. Make sure that the blue separator discs are not installed with the test filter. Reinstall the funnel on the holder support, and secure it by rotating the outer knurled ring in a clockwise direction until it is fully seated. Use filtered solvent to repeatedly rinse the inside of the graduate to remove all possible contaminants. Pour out any residual solvent. Measure out approximately 15 milliliters of the filtered solvent, using the cleaned graduate, and pour the solvent into the funnel to "prewet" the filter membrane.

Shake the bottle of sample fluid. This action distributes the particulate content. Remove the cap from the sample bottle and pour exactly 100 milliliters of fluid into the graduate. Discard any remaining fluid. Pour the contents of the graduate into the funnel, on top of the previously introduced filtered solvent. Allow the contents of the graduate to drain completely into the funnel. Use the filtered solvent to wash down the inside surface of the graduate until it contains approximately 100 milliliters of solvent.

Operate the syringe by slowly pumping it, which draws a vacuum, until sustained filtration of the fluid is indicated by a steady drop of the fluid level in the funnel. When the fluid level in the funnel drops enough to allow addition of approximately 50 milliliters of solvent, pour half of the contents of the graduate into the funnel as filtration continues. If necessary, operate the syringe again to maintain sufficient vacuum for filtration. Carefully watch the filtration process in the funnel, and note the decreasing fluid level. When the fluid level drops to the narrow neck of the funnel, pour the remaining contents of the graduate into the funnel.

NOTE: Pour the contents so they flow down the inside of the funnel, making sure that the solvent is not poured directly onto the test filter.

When filtration is complete, inspect the test filter surface. If the central area shows a pinkish color, it indicates that the test filter still has a residue of hydraulic fluid. Direct a stream of filtered solvent against the walls of the funnel until fluid reaches the top of the tapered portion. Operate the syringe again to initiate filtration and allow all of this fluid to pass through the test filter. If free water is indicated, test to see if the water originated from the hydraulic fluid sample and not from the rinsing solvent. Perform an 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.