== 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).
Unlike ionic bonding, covalent bonding may have single, double bonds or triple bonds between two atoms. These bonds are formed in such a way that the two atoms obey the octet rule. The bond occurs via the overlapping of atomic orbitals. A single bond is formed when two electrons are shared. A double bond is formed when four electrons are shared. Sharing of six electrons may result in a triple bond. The characteristics of compounds with covalent bonds include strong bonding between two atoms due to similar electronegativity values.