ASTM D6897 Standard Test Method for Vapor Pressure of Liquefied Petroleum Gases (LPG) (Expansion Method)
6. Apparatus
6.1 Vapor Pressure Apparatus - The type of 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 of 5 °C to 70 °C. The measuring chamber shall contain a movable piston with a maximum 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 absolute 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 test chamber shall be designed to contain a total of 5 mL of liquid and vapor and be capable of maintaining a vapor-liquid ratio of 0.5:1 with a maximum deviation of 0.02.

NOTE 3 - The test chamber employed by the instruments used in generating the precision and bias statements were constructed of nickel-plated aluminum and stainless steel.

NOTE 4 - Test 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 Electronic temperature control shall be used to maintain the measuring chamber at the prescribed temperature within +/- 0.1 °C for the duration of the vapor pressure measurement.

6.1.3 The pressure transducer shall have a range of 0 kPa to 3500 kPa with a minimum resolution of 1 kPa. The minimum accuracy shall be +/- 1 kPa for pressures up to 700 kPa, +/- 2 kPa for pressures up to 1750 kPa, and +/- 4 kPa for pressures up to 3500 kPa.

6.1.4 A platinum resistance thermometer, or equivalent, shall be used for measuring the temperature of the test chamber. The minimum temperature range of the measuring device shall be from 0 °C to 80 °C with a resolution of 0.1 °C and a minimum accuracy of +/- 0.1 °C.

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

6.3 McLeod Vacuum Gage or Calibrated Electronic Vacuum Measuring Device for Calibration, to cover at least the range from 0.01 kPa to 0.67 kPa (0.1 mm to 5 mm Hg). The calibration of the electronic vacuum measuring device shall be regularly verified in accordance with A6.3 of Test Method D2892.

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 5 - 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. Commonly used quality control check materials are propane, butane, and pentane (see Section 11). Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on 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 6 - The chemicals in this section are suggested for quality control procedures (see Section 11) and are not used for instrument calibration.

7.2 Cleaning Solvents - Use noncorrosive solvents capable of cleaning the measuring chamber, the valves, and the inlet and outlet tubes. A commonly used solvent is acetone. (Warning - Propane, butane, pentane, and acetone are flammable and health hazards.)