Reid Vapor Pressure
Encyclopedia
Reid vapor pressure is a common measure of the volatility of gasoline. It is defined as the
absolute vapor pressure
exerted by a liquid at 100 °F (37.8 °C) as determined by the test method ASTM-D-323. The test method applies to volatile crude oil and volatile nonviscous petroleum liquids, except liquified petroleum gas
es.
The matter of vapor pressure is important relating to the function and operation of gasoline powered, especially carbureted, vehicles. High levels of vaporization are desirable for winter starting and operation and lower levels are desirable in avoiding vapor lock during summer heat. Fuel cannot be pumped when there is vapor in the fuel line (summer) and winter starting will be more difficult when liquid gasoline in the combustion chambers has not vaporized. Thus, oil refineries manipulate the Reid Vapor Pressure seasonally specifically to maintain gasoline engine reliability.
The Reid vapor pressure (RVP) differs slightly from the true vapor pressure
(TVP) of a liquid due to small sample vaporization and the presence of water vapor and air in the confined space of the test equipment. That is, the RVP is the absolute vapor pressure and the TVP is the partial vapor pressure. Conversion between the two measures can be found here, from p. 7.1-54 onwards.
absolute vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
exerted by a liquid at 100 °F (37.8 °C) as determined by the test method ASTM-D-323. The test method applies to volatile crude oil and volatile nonviscous petroleum liquids, except liquified petroleum gas
Liquified petroleum gas
Liquefied petroleum gas is a flammable mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles. It is increasingly used as an aerosol propellant and a refrigerant, replacing chlorofluorocarbons in an effort to reduce damage to the ozone layer...
es.
The matter of vapor pressure is important relating to the function and operation of gasoline powered, especially carbureted, vehicles. High levels of vaporization are desirable for winter starting and operation and lower levels are desirable in avoiding vapor lock during summer heat. Fuel cannot be pumped when there is vapor in the fuel line (summer) and winter starting will be more difficult when liquid gasoline in the combustion chambers has not vaporized. Thus, oil refineries manipulate the Reid Vapor Pressure seasonally specifically to maintain gasoline engine reliability.
The Reid vapor pressure (RVP) differs slightly from the true vapor pressure
True vapor pressure
True vapor pressure is a common measure of the volatility of petroleum distillate fuels. It is defined as theequilibrium partial pressure exerted by a volatile organic liquid as a function of temperature as determined by the test method ASTM D 2879....
(TVP) of a liquid due to small sample vaporization and the presence of water vapor and air in the confined space of the test equipment. That is, the RVP is the absolute vapor pressure and the TVP is the partial vapor pressure. Conversion between the two measures can be found here, from p. 7.1-54 onwards.
See also
- Gasoline volatility
- True Vapor PressureTrue vapor pressureTrue vapor pressure is a common measure of the volatility of petroleum distillate fuels. It is defined as theequilibrium partial pressure exerted by a volatile organic liquid as a function of temperature as determined by the test method ASTM D 2879....
- Vapor pressureVapor pressureVapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
- Crude oil assayCrude oil assayA crude oil assay is essentially the chemical evaluation of crude oil feedstocks by petroleum testing laboratories. Each crude oil type has unique molecular, chemical characteristics. No crude oil type is identical and there are crucial differences in crude oil quality...
External links
- ASTM D323 - 06 Standard Test Method for Vapor Pressure of Petroleum Products (Reid Method)
- USA's Environmental Protection Agency (EPA) publication AP-42, Compilation of Air Pollutant Emissions. Chapter 7 (RVP is a parameter in the estimation of petroleum tank evaporative losses)