ASTM D7261 Standard Test Method for Determining Water Separation Characteristics of Diesel Fuels by Portable Separometer
13. Procedure
13.1 Select Mode D (Mark V Deluxe) or DIESEL (Mark X) operation.
13.1.1 Depress push button D or DIESEL for Mode D operation.

NOTE 13 - Sequential illumination of the push buttons will cease and the depressed push button will stay lit. The correct syringe drive speed is set automatically.

13.2 To remove any contaminants from the syringe barrel and stirrer, run two 50 mL portions of the fuel to be tested through the mixing system in clean cycles, as follows.
13.2.1 Remove the plunger from a new 50 mL syringe and wipe the tip using a clean, lintless wipe to remove any sheen caused by excess lubricant. Insert a plug into the exit hole of the syringe barrel, add 50 mL +/- 1 mL of fuel, and place the syringe barrel on the emulsifier mount, turning to lock in place.
13.2.1.1 To mitigate the buildup of static charge, only nitrile gloves are recommended for use while handling the syringe barrel.

13.2.2 Ensure that the syringe barrel is properly aligned concentrically with the mixer shaft and is not touching the propeller. Proper alignment can be verified by grasping the syringe barrel and moving the same until the propeller on the end of the mixer shaft is free and not touching.

NOTE 14 - Misalignment can cause plastic shavings to form and collect on the coalescer filter material resulting in erroneous test results. This applies to all instruments manufactured prior to July 1988 that have not been serviced by EMCEE Electronics, Inc. since that date. Since July 1988, with ASTM approval, all new instruments and those returned for service have had a standoff installed on the mixer shaft to prevent the syringe barrel from coming into contact with the mixer blades.

13.2.3 Initiate the clean cycle by depressing the START push button on the Mark V or the CLEAN 1 push button on the Mark X, as designated by the annunciator light. (Warning - Do not operate the mixer without having a syringe with fuel in place. The mixer bearings depend on the fuel for lubrication.)

13.2.4 At the end of the first clean cycle, when the mixer motor stops, remove the syringe barrel from the emulsifier, discard the fuel, and drain the syringe thoroughly.

13.2.5 Add 50 mL +/- 1 mL of fresh fuel into the syringe and place the syringe barrel on the emulsifier mount (turn to lock in place). Visually inspect that the syringe barrel is properly aligned concentrically with the mixer shaft and is not touching the propeller.

13.2.6 Add about 15 mL to 20 mL of the fuel to be tested into a new vial. Wipe the outside of the vial with a clean, lintless wiper, and insert the vial into the turbidimeter well, aligning the black mark on the vial at 90° from the white line on the front of the turbidimeter well. Rotate the vial until the black mark on the vial aligns with the white line on the front of the turbidimeter well (Fig. 1). (This vial of clean fuel is required for setting the meter reading to 100 in 13.8.)

13.2.7 Initiate the second clean cycle on the Mark V by pressing the RESET and START push buttons sequentially. Initiate the second clean cycle on the Mark X by pressing the CLEAN 2 push button, as designated by the annunciator light.

13.3 At the end of the second clean cycle, when the mixer motor stops, remove the syringe barrel from the emulsifier, discard the fuel, and drain the syringe thoroughly.

13.4 Add 50 mL +/- 1 mL of fresh fuel sample into the syringe.
13.4.1 Handle the syringe in such a manner as to minimize warming of the fuel sample by body heat.

13.5 Refer to 5.3 for guidance on whether to use the D Cell or DB Cell. Using a fresh plastic tip on the hand pipet, add 50 µL of double-distilled water (8.7) to the fuel sample as follows: Holding the pipet in hand, give a slight twist to the plastic tip to ensure a tight seal, push in the plunger, immerse the tip just below the water surface, release the plunger, and withdraw from the water slowly to avoid water drops adhering to the outside of the tip. Immerse the tip of the pipet just below the fuel surface in the center of the syringe (Fig. 5). To ensure the water drops break away cleanly and fall to the bottom, push and hold in the plunger, and release and push again. With plunger still down withdraw the pipet, and release the plunger. This ensures that all the water is in the sample.

13.6 Place the syringe barrel on the emulsifier mount, turning to lock in place.

13.7 With the syringe in place, initiate the automatic portion of Test Mode D on the Mark V by depressing the START push button (Fig. 6) or the RUN switch (Fig. 2) on the Mark X (see Table 6).

NOTE 15 - If for any reason it is desired to interrupt the sequence and start over, the reset push button will cancel the test in progress and reset the program to the beginning of the clean segment of the test cycle.

13.8 The automatic program for the Mark V starts with a read meter indication (four short tones) followed by a 10 s full-scale adjustment period. During this period, depress the illuminated arrow push buttons on the Mark V to adjust the meter to read 100 (Fig. 7). The 100 reading is automatically set on the Mark X and does not require any adjustment. After the full-scale adjustment period, the mixer motor activates and the emulsion process is initiated.

NOTE 16 - If the Mark V meter adjustment cannot be completed at this time, final adjustment may be accomplished during the second meter adjust period occurring later in the test sequence.

NOTE 17 - A few drops of fuel can seep from the hole in the emulsifier head during the high-speed mixing operation. This should not affect the test results.

NOTE 18 - If the emulsifier speed of the Mark X is outside of acceptable limits, the ERROR ALERT indicator on the Mark X will illuminate and ERR-05 will be displayed. The Mark V does not have an error alert.

13.9 When the mixer stops (after emulsification), remove the syringe barrel from the emulsifier and partially insert the plunger to seal the open end of the syringe. Invert the syringe (exit hole up), remove the plug, and exhaust the entrapped air in the syringe barrel without significant fuel loss by carefully inserting plunger to the 50 mL mark. (Use a clean wipe over the exit hole to capture the small amounts of fuel which may be extruded as foam.) Affix a new coalescer (8.3.4) to the end of the syringe barrel. Warning - Use of an incorrect coalescer, such as a jet fuel coalescer, will give erroneous results.
13.9.1 Place the entire syringe assembly into the syringe drive mechanism (Fig. 8). To minimize the effect of plunger resistance (drag) in the syringe barrel, align the syringe assembly vertically in the syringe drive mechanism with the end of the syringe plunger parallel with pushbar of the syringe drive mechanism. Position a waste container beneath the coalescer to collect the unwanted portion of the processed fuel sample during the coalescing period.

13.9.2 Electrically bond the coalescer to the Micro-Separometer to prevent buildup of an electrostatic charge that could result in ignition of flammable test fluids.
13.9.2.1 Fasten the alligator clip to the coalescer and insert the plug in the chassis ground jack (Fig. 8). Other suitable grounding methods may be used for previous models.

NOTE 19 - Each Micro–Separometer instrument is furnished with a ground lead that has an alligator clip on one end and a banana plug on the other.

13.10 The second meter adjust period for the Mark V will occur after four short tones. Adjust the meter reading to 100, if necessary. The Mark X does not require any adjustment. The syringe drive mechanism will start down at the end of the meter-adjust period forcing the water/fuel emulsion through the coalescer (Fig. 8). During this operation, remove the vial from the turbidimeter well and discard the fuel.

13.11 Collect the last 15 mL of fuel sample being processed from the coalescer (Fig. 9) when the collect sample annunciator lamp (marked C/S) illuminates and a pulsed tone of short duration sounds. To lessen the amount of air introduced into the fuel during this operation, position the vial at a slight angle and allow the fuel to flow down the inner surface. Remove the vial just prior to when the last amount of sample is expelled from the coalescer.

13.12 Wipe the outside of the vial with a clean, lintless wiper to remove any fingerprints and fuel. Place the sample vial into the turbidimeter well aligning the marks on the vial and on the control panel in front of the well.

NOTE 20 - At the end of the settling time (1 min), a steady (4 s duration) tone will alert the operator that the meter is about to activate. At the end of the tone, the meter will automatically activate for approximately 10 s.

13.13 Read the DSEP rating (displayed as a whole number) at the midpoint of the 10 s meter read cycle indicated by a short 1 s tone.

NOTE 21 - Numerical values obtained outside the measurement range from 50 to 100 are undefined and invalid (see 5.2 and Note 2).

14. Interpretation of Results
14.1 DSEP ratings are only valid within the range of 50 to 100. Ratings at the upper end of the range indicate a clean fuel with little or no contamination by surfactants. Thus a fuel with a high DSEP rating is expected to show good water-separating properties when passed through a filter-separator (coalescing-type filter) in actual service. Conversely, fuels that give low DSEP ratings likely contain strong surfactants that can disarm filter-separators and allow dispersed water droplets to pass through the filters.