== EGR vacuum switching valve == Despite the rather lengthy name the EGR-VSV (exhaust gas recirculation vacuum switching valve) does little more than allow vacuum to flow through the system depending on engine coolant temperature.
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that is between two carbon atoms, can be found in alkenes. Many types of double bonds exist between two different elements. For example, in a carbonyl group with a carbon atom and an oxygen atom. Other common double bonds are found in azo compounds (N=N), imines (C=N) and sulfoxides (S=O).
Bond-line structure (bond-line formula, skeletal structure, skeletal formula): A representation of molecular structure in which covalent bonds are represented with one line for each level of bond order. single bond is represented with a single line, a double bond is shown by two parallel lines, and a triple bond by three parallel lines. The position of carbon atoms may be shown with letters, or may be implied (in certain circumstances).