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'''Reid vapor pressure''' (RVP), as determined by the [[ASTM]] test method D323,<ref>Test method D323-08 of the [[American Society for Testing and Materials]] (ASTM). [http://www.astm.org/ABOUT/aboutASTM.html ASTM website]</ref>  is widely used in the petroleum industry as a measure of the volatility of [[petroleum crude oil]], [[gasoline]] and other volatile petroleum products. It is a quick and simple method of determining the [[vapor pressure]] at 37.8 °[[Celsius|C]] (100 °[[Fahrenheit and Rankine temperatures|F]]) of crude oil and petroleum products  having an initial [[boiling point]] above 0 °C (32 °F).


== Importance and uses ==
{{main|Gasoline}}
Vapor pressure is an important physical property of volatile liquids. It is of critical importance for automotive and aviation gasolines since it affect the starting and warm-up of spark-ignited [[internal combustion engine]]s as well as the tendency to cause "vapor lock" in the fuel [[pump]]s with high operational [[temperature]]s and/or high altitudes.
Air pollution regulatory authorities mandate maximum gasoline vapor pressures in many areas so as to limit the [[evaporation|evaporative]] emissions of [[smog]]-forming [[hydrocarbon]]s from gasoline.
Vapor pressure is also important as an indirect measure of the evaporation tendency of volatile petroleum [[solvent]]s.
== The difference between RVP and TVP ==
True vapor pressure is referred to in the petroleum industry as TVP. Both the Reid vapor pressure (RVP) and the true vapor pressure (TVP) are ''absolute'' pressures as distinguished from ''gauge'' pressures (see [[Pressure#Absolute pressure versus gauge pressure|Pressure]]).
Because of the presence air (and its of water vapor content) in the vapor space within the test method's sample container, as well as some small amount of sample vaporization during the warming of the sample to 37.8 °C (100 °F), the RVP differs by a small amount from the TVP of the sample.
RVP values may be converted to TVP values using the [[nomogram]]s or the equations provided in Chapter 7 of the [[AP 42 Compilation of Air Pollutant Emission Factors]] published by the [[U.S. Environmental Protection Agency]] and available online.<ref>[http://www.epa.gov/ttn/chief/ap42/ch07/final/c07s01.pdf AP42, Chapter 7, Section 7.1] On pdf pages 54-56 of 123 pdf pages. All units are [[U.S. customary units]].</ref>
== Other test methods for certain petroleum products ==
Test method ASTM D323 is not applicable for [[liquified petroleum  gas]]es (LPG). ASTM D1267 or D6897 should be used for LPG.
ASTM D323 is also not applicable for gasolines containing oxygenated compounds other than [[methyl tertiary-butyl ether]] (MTBE).<ref>For more information about MTBE, see [[Gasoline]].</ref> For gasolines containing other oxygenated compounds, refer to ASTM D4953.
== References ==
{{reflist}}

Revision as of 10:21, 28 October 2009

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