ASTM D3240 Test Method for Undissolved Water In Aviation Turbine Fuels
5. Apparatus
5.1 Test Pad Rater - A device for comparing the fluorescence of the test pad to a known standard, while both are illuminated by the same source of UV light, shall be used. The amount of UV light striking the standard shall be modulated until the total fluorescence of the test pad and the standard are equal; this shall be determined using a photocellbridge circuit null indicator. The light modulating device for controlling the UV light striking the standard shall provide a direct reading in parts per million by volume of free water.
5.2 Test Pads - Absorbent filter disks of 25-mm diameter shall be coated on one side with uranine (sodium fluorescein) dye at a concentration of 0.23 to 0.29 mg per 25 mm pad. The test pads shall be individually packaged in hermetically sealed envelopes or other suitable containers. Fresh, unused test pads shall have an orange color over the dyed surface. Any discoloration, unevenness in dye content, or faded (to a yellow color) appearance shall be cause for rejection.
5.3 Test Pad Holder and Sampling Line - A test pad holder and sampling line shall be used to draw the fuel sample through the test pad at a rate of 600 to 800 mL/min. Means shall be provided to flush the test pad sampling line and holder immediately prior to use. The test pad holder shall include an orifice of 1-mm (0.040-in.) diameter upstream of the pad to disperse water droplets in the fuel.
5.4 Tweezers - Suitable clean, dry tweezers shall be used at all times when handling the test pad.
5.5 Blotting Paper - Clean, dry, absorbent paper towels, blotters, etc., shall be provided for blotting the test pad prior to rating to remove excess fuel. The blotterpaper shall neither impart color or stain nor leave any residue on the test pads.
5.6 Sampling Valve Connection, designed to meet the following requirements: (1) It shall be mounted in the sampling point and must incorporate a self-sealing quick action coupling designed to mate with a suitable connection leading to the selector valve of the sampling assembly. (2) It must be completely resistant to fuel and be leak proof up to the maximum working pressures to be encountered. (3) It must have a minimum of internal recesses which could cause the holdup of contaminant. (4) It must be provided with a dust cap.
5.7 Calibrating Standard, Calibration of the instrument should be performed using a calibrating standard of known values.
6. Sampling
6.1 The following procedure is applicable for dynamic line samples only; that is, taking the fuel sample directly from the test system and through the test pad without exposing the sample to the atmosphere or to a sample container. The use of sample containers such as bottles or cans for the temporary storage of the sample will result in large errors and is not recommended.
NOTE 1 - The amount of free water in a sample is very sensitive to the temperature of the sample. The use of sample containers such as bottles or cans can result in large errors due to changes in sample temperature, adsorption of water on container walls, etc.
6.2 Attach the test pad holder assembly to the sampling port on the system.
6.3 Flush the test pad holder assembly immediately prior to sampling, displacing the sampling line with at least two volumes of test fuel.
6.4 Remove the sampling assembly, open the pad holder, and insert the new test pad using tweezers making sure that the treated side of the test pad is facing upstream. Installation of a three-way valve immediately upstream of the test pad holder will permit flushing with the test pad in place.
NOTE 2 - Do not remove the test pad from the hermetically sealed package until ready for use. Do not allow any discrete water droplets to come into contact with the pad (from rain, sneezing, coughing, etc.). Exposure of the test pad to the atmosphere, especially on humid days, will also ruin the pad in a matter of minutes.
6.5 Pass 500 mL of fuel through the pad, accurately measuring the test sample quantity. Normal sample volume is 500 mL of test fuel, but if the reading is off scale (on high side), sample volumes down to 100 mL in volume may be used. In the latter case, a small graduated cylinder should be used to measure the sample volume.
