(Equivalent Test Methods: IP 69, ISO 3007, DIN 51754, JIS K 2258, and AFNOR M41-007)
EXPLANATION
Vapor pressure is an important physical property of liquid spark-ignition engine fuels. It provides an indication of how a fuel will perform under different operating conditions, such as whether it will cause vapor lock at high ambient temperature or at high altitude, or will provide easy starting at low ambient temperature. Petroleum product specifications generally include vapor pressure limits to ensure products of suitable volatility performance. Vapor pressure of fuels is regulated by various government agencies. This test method measures vapor pressure of gasoline, volatile crude oil, and other volatile petroleum products. Procedure A is applicable to samples with a vapor pressure of less than 180 kPa. Procedure B may also be applicable to these products, but only gasoline samples were included in the precision study. Neither procedure is applicable to LPG or fuels containing oxygenated compounds other than MTBE. Procedure C is for materials with a vapor pressure of greater than 180 kPa. Procedure D is for aviation gasoline with a vapor pressure of approximately 50 kPa.
Reid vapor pressure differs from the true vapor pressure of the sample due to some small sample vaporization and the presence of water vapor and air in the confined space.
TEST SUMMARY
This test method provides two procedures for determining vapor pressure. The liquid chamber of the vapor pressure apparatus is filled with chilled sample and connected to the vapor chamber at 100° F. The apparatus is immersed in a bath of 100° F until a constant pressure is observed. The pressure reading, suitably corrected, is reported as the vapor pressure. All four procedures utilize liquid and vapor chambers of the same internal volume. Procedure B utilizes a semiautomatic apparatus immersed in 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.
TEST PRECISION
