ASTM D323 for vapor pressure of petroleum products (Reid method)
3. Summary of Test Method
3.1 The liquid chamber of the vapor pressure apparatus is filled with the chilled sample and connected to the vapor chamber that has been heated to 37.8°C (100°F) in a bath. The assembled apparatus is immersed in a bath at 37.8°C (100°F) until a constant pressure is observed. The reading, suitably corrected, is reported as the Reid vapor pressure.
3.2 All four procedures utilize liquid and vapor chambers of the same internal volume. Procedure B utilizes a semi-automatic apparatus immersed in a horizontal bath and rotated while attaining equilibrium. Either a Bourdon gage or pressure transducer may be used with this procedure. Procedure C utilizes a liquid chamber with two valved openings. Procedure D requires more stringent limits on the ratio of the liquid and vapor chambers.
4. Significance and Use
4.1 Vapor pressure is an important physical property of volatile liquids. This test method is used to determine the vapor pressure at 37.8°C (100°F) of petroleum products and crude oils with initial boiling point above 0°C (32°F).
4.2 Vapor pressure is critically important for both automotive and aviation gasolines, affecting starting, warmup, and tendency to vapor lock with high operating temperatures or high altitudes. Maximum vapor pressure limits for gasoline are legally mandated in some areas as a measure of air pollution control.
4.3 Vapor pressure of crude oils is of importance to the crude producer and the refiner for general handling and initial refinery treatment.
4.4 Vapor pressure is also used as an indirect measure of the evaporation rate of volatile petroleum solvents.
