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D5191_8 (15) 07-2017 (1)

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The extreme sensitivity of vapor pressure measurements to losses through evaporation, and the resulting changes in composition, is such to require the utmost precaution and the most meticulous care in the drawing and handling of samples. Obtain samples and test specimens in accordance with practice D4057, except do not use the sampling by water displacement section for fuels containing oxygenates. Use either 250 milliliters or one liter, one quart-sized containers, filled with between 70% and 80% with sample. For best testing precision, reproducibility, it is recommended that one liter sized containers be used. The current precision statements were derived from the 2003 ILS using samples in 250 milliliter, and one liter, one quart clear glass containers. However, samples and containers of the other sizes-- as prescribed in practice D4057-- may be used with the same usage requirement, if it is recognized that the precision can be affected. The differences in precision results obtained from 250 milliliter and one liter containers are found to be statistically significant, whereas there was no statistically observable bias detected between 250 milliliter and one liter containers. See tables in section 16 of the written standard, as well as figures one and two of the written standard, for more specific details on precision differences as a function of DVPE value and container size. In general, numerically better repeatability values were determined at DVPE values less than 85 kilopascal, 12.3 PSI, for samples in one liter containers versus 250 milliliter containers. Secondly, numerically better reproducibility values were determined for samples in one liter containers versus 250 milliliter containers, for the entire DVPE range, covered in 16.1.2 of the written standard. To determine conformance with specifications or regulations, or both, it may be necessary to prepare laboratory hand-blends of gasoline blend stocks and denatured fuel ethanol for testing purposes, including vapor pressure. If necessary, then, a hand-blend assembly, prepared carefully in accordance with a procedure, such as that described in practice D7717, shall be considered suitable for the performance of this test. This hand-blend, once prepared, shall then be considered equivalent to the sample, or samples, referred to in 8.1.4 through 8.5 of the written standard of this sampling section, as well as in subsequent sections of this test method. Perform the vapor pressure determination on the first test specimen withdrawn from a sample container. Do not use the remaining sample in the container for a second vapor pressure determination. If a second determination is necessary, obtain a new sample. The effect of taking more than one test specimen from the same sample container was evaluated as part of the 2003 ILS. A precision effect was observed between the first and second replicates taken from both the one liter and 250 milliliter containers evaluated. The current precision statements were derived from the 2003 ILS, using the first test specimen withdrawn from 250 milliliter and one liter clear glass containers. Protect samples from excessive temperatures prior to testing. This can be accomplished by storage in an appropriate ice bath or refrigerator. Do not test samples stored in leaky containers. Discard and obtain a new sample if leaks are detected. Place the sample container and contents in an ice bath or refrigerator, to the zero degrees Celsius to one degree Celsius, 32 degrees Fahrenheit to 34 degrees Fahrenheit range, prior to opening the sample container. Allow sufficient time to reach this temperature. One way to verify the sample temperature is by direct measurement of the temperature of a similar liquid in a similar container placed in the cooling bath or refrigerator at the same time as the sample. Alternatively, temperature monitoring studies conducted by laboratories have determined the minimum amount of time necessary to achieve the required temperature requirements-- stated in 8.2 of the written standard-- based upon typical sample receipt temperatures and cooling capacities of the instrumentation employed by the laboratory on samples included in such studies. The results of such studies have subsequently been applied to additional samples submitted for analysis. Typical minimum time durations reported by laboratories have ranged between approximately 30 minutes and 45 minutes. However, laboratories choosing this option need to determine the minimum cooling time required for their specific operation by conducting their own temperature monitoring study. Verification of sample container filling. With a sample at a temperature of zero degrees Celsius to one degrees Celsius, take the container from the cooling bath or refrigerator and wipe dry with absorbent material. If the container is not transparent, unseal it, and using a suitable gauge, confirm that the sample volume equals 70% to 80% of the container capacity. See note 10 of the written standard. If the sample is contained in a transparent glass container, verify that the container is 70% to 80% full, by suitable means. See note 10 of the written standard, Discard the sample if the container is filled to less than 70% by volume of the container capacity. If the container is more than 80% by volume full, pour out enough sample to bring the container contents within the 70% to 80% by volume range. Do not return any sample to the container once it has been withdrawn. Reseal the container, if necessary, and return the sample container to the cooling bath or refrigerator. For non-transparent containers, one way to confirm that the sample volume equals 70% to 80% of the container capacity, is to use a dipstick that has been pre-marked to indicate the 70% and 80% container capacities. The dipstick should be of such material that it shows wetting after being immersed and withdrawn from the sample. To confirm the sample volume, insert the dipstick into the sample container so that it touches the bottom of the container at a perpendicular angle before removing the dipstick. For transparent containers, using a marked ruler or by comparing the sample container to a light container, which has the 70% to 80% levels clearly marked, has been found suitable. Since 8.3 of the written standard does not require that the sample container be opened to verify the sample capacity, it is necessary to unseal the cap momentarily, before re-sealing it, so that samples and transparent containers are treated the same as samples in nontransparent containers. With the sample, again, at a temperature of zero degrees Celsius to one degree Celsius, take the container from the cooling bath or refrigerator. Wipe it dry with an absorbent material. Remove the cap momentarily, taking care that no water enters. Reseal, and shake vigorously. Return it to the cooling bath or refrigerator for a minimum of two minutes. Repeat 8.4.2 of the written standard twice more. Return the sample to the cooling bath or refrigerator until the beginning of the procedure. After drawing a test specimen and introducing it into the instrument for analysis, check the remaining sample for phase separation. If the sample is contained in a transparent container, this observation can be made prior to sample transfer. If the sample is contained in a nontransparent container, mix the sample thoroughly, and immediately pour a portion of the remaining sample into a clear glass container and observe for evidence of phase separation. A hazy appearance is to be carefully distinguished from separation into two distinct phases. The hazy appearance shall not be considered grounds for rejection of the fuel. If a second phase is observed, discard the test and the sample. Hazy samples may be analyzed. See section 15, of the written standard.

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Posted by: abuckmaster on Aug 23, 2018

D5191_8 (15) 07-2017 (1)

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