Glossary Of Water Treatment Industry Terms . . ."V"
vacuum breaker - A mechanical
device which automatically vents a water line to the atmosphere when
subjected to a partial vacuum, thus preventing back-flow. (See back-flow,
air gap, back-flow preventer.)
valence - A small positive
or negative whole number, also called oxidation number, which indicates
the net number of electrons gained or lost in the formation of an ion,
or the number of electrons the substance can donate or accept in a chemical
reaction, and thus the numbers of each kind of ion necessary for a balanced
chemical reaction. For example, two hydrogen ions (each with a valence
of +1) must be present for each ion of oxygen (-2) to form a molecule
of water (H2O).
viable - Alive and capable
of continued life.
virus - The smallest form
of life known to be capable of producing disease or infection, usually
considered to be of large molecular size. They multiply by assembly
of component fragments in living cells, rather than by cell division,
as do most bacteria.
viscosity - The resistance
of fluids to flow, due to internal forces and friction between molecules,
which increases as temperature decreases.
void volume - The volume
of the spaces between particles of ion exchanger, filter media, or other
granular material; often expressed as a percentage of the total volume
occupied by the material.
volatile - Capable of
vaporization at a relatively low temperature.
volatile solids - Matter
which remains as a residue after evaporation at 105 or 180oC,
but which is lost after ignition at 600oC. Includes most
forms of organic matter.
volumetric - Referring
to measurement by volume rather than weight. (See gravimetric.)