ASTM D6378 Determination of Vapor Pressure of Petroleum Products
ASTM D6378 Standard Test Method for Determination of Vapor Pressure (VPX) of Petroleum Products, Hydrocarbons, and Hydrocarbon-Oxygenate Mixtures (Triple Expansion Method)
6. Apparatus
6.1 The apparatus suitable for this test method employs a small volume, cylindrically shaped measuring chamber with associated equipment to control the chamber temperature within the range from 0 to 100 °C. The measuring chamber shall contain a movable piston with a minimum dead volume of less than 1 % of the total volume at the lowest position to allow sample introduction into the measuring chamber and expansion to the desired vapor-liquid ratio. A static pressure transducer shall be incorporated in the piston. The measuring chamber shall contain an inlet/outlet valve combination for sample introduction and expulsion. The piston and the valve combination shall be at the same temperature as the measuring chamber to avoid any condensation or excessive evaporation.
6.1.1 The measuring chamber shall be designed to contain between 5 and 15 mL of liquid and vapor and be capable of maintaining a vapor-liquid ratio of 4:1 to 1:1. The accuracy of the adjusted vapor-liquid ratio shall be within 0.05.

NOTE 3 - The measuring chamber employed by the instruments used in generating the precision and bias statements were constructed of nickel plated aluminum and stainless steel with a total volume of 5 mL. Measuring chambers exceeding a 5-mL capacity can be used, but the precision and bias statements (see Section 15) are not known to apply.

6.1.2 The pressure transducer shall have a minimum operational range from 0 to 200 kPa (0 to 71 psi) with a minimum resolution of 0.1 kPa (0.01 psi) and a minimum accuracy of +/-0.2 kPa (+/-0.002 psi). The pressure measurement system shall include associated electronics and readout devices to display the resulting pressure reading.

6.1.3 Electronic temperature control shall be used to maintain the measuring chamber at the prescribed temperature within +/-0.1°C for the duration of the test.

6.1.4 A platinum resistance thermometer shall be used for measuring the temperature of the measuring chamber. The minimum temperature range of the measuring device shall be from 20 to 100°C with a resolution of 0.1°C and an accuracy of +/-0.1°C.

6.1.5 The vapor pressure apparatus shall have provisions from rinsing the measuring chamber with a solvent of low vapor pressure or with the next sample to be tested.

6.2 Vacuum Pump for Calibration, capable of reducing the pressure in the measuring chamber to less than 0.01 kPa (0.001 psi) absolute.

6.3 McLeod Vacuum Gage or Calibrated Electronic Vacuum Measuring Device for Calibration, to cover at least the range from 0.01 to 0.67 kPa (0 to 5 mm Hg). The calibration of the electronic measuring device shall be regularly verified in accordance with Annex A1 of Test Method D1160.

6.4 Pressure Measuring Device for Calibration, capable of measuring local station pressure with an accuracy and a resolution of 0.1 kPa (1 mm Hg), or better, at the same elevation relative to sea level as the apparatus in the laboratory.

NOTE 4 - This test method does not give full details of instruments suitable for carrying out this test. Details on the installation, operation, and maintenance of each instrument may be found in the manufacturer's manual.

7. Reagents and Materials
7.1 Purity of Reagents - Use chemicals of at least 99 % purity for quality control checks (see Section 10). Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee of Analytical Reagents of the American Chemical Society where such specifications are available. Lower purities can be used, provided it is first ascertained that the reagent is of sufficient purity to permit its use without lessening the accuracy of the determination.

NOTE 5 - The chemicals in this section are suggested for quality control procedures (see Section 11) and are not used for instrument calibration.
2,2-Dimethylbutane (Warning–See Note 6)
2,3-Dimethylbutane (Warning - See (Note 6)
Toluene (Warning - See Note 6)
Pentane (Warning - See Note 6)
Methanol (Warning - See Note 6)
Acetone (Warning - See Note 6)

NOTE 6 - Warning: 2,2–dimethylbutane, 2,3-dimethylbutane, toluene, pentane, methanol, and acetone are flammable and health hazards.