447VAPOR PRESSURE: Pressure of vapor over a liquid at equilibrium.
VAPOR: When a substance is below the critical temperature while in the gas phase.
VAPORIZATION: Phase change from liquid to gas.
VARIABLE DISPLACEMENT PUMP: A pump that will produce different volumes of water
dependent on the pressure head against it.
VELOCITY HEAD: The vertical distance a liquid must fall to acquire the velocity with which it
flows through the piping system. For a given quantity of flow, the velocity head will vary indirectly
as the pipe diameter varies.
VENTURI: If water flows through a pipeline at a high velocity, the pressure in the pipeline is
reduced. Velocities can be increased to a point that a partial vacuum is created.
VIRION: A complete viral particle, consisting of RNA or DNA surrounded by a protein shell and
constituting the infective form of a virus.
VIRUSES: Are very small disease-causing microorganisms that are too small to be seen even
with microscopes. Viruses cannot multiply or produce disease outside of a living cell.
VISCOSITY: The resistance of a liquid to flow (oil).
VITRIFICATION: Vitrification is a process of converting a material into a glass-like amorphous
solid that is free from any crystalline structure, either by the quick removal or addition of heat, or
by mixing with an additive. Solidification of a vitreous solid occurs at the glass transition
temperature (which is lower than melting temperature, Tm, due to supercooling). When the
starting material is solid, vitrification usually involves heating the substances to very high
temperatures. Many ceramics are produced in such a manner. Vitrification may also occur
naturally when lightning strikes sand, where the extreme and immediate heat can create hollow,
branching rootlike structures of glass, called fulgurite. When applied to whiteware ceramics,
vitreous means the material has an extremely low permeability to liquids, often but not always
water, when determined by a specified test regime. The microstructure of whiteware ceramics
frequently contain both amorphous and crystalline phases.
VOC WAIVER: The longest term VOC waiver that a public water system using groundwater could
receive is 9 years.
Void: An opening, gap, or space within rock or sedimentary formations formed at the time of
origin or deposition.
VOLATILE ORGANIC COMPOUNDS: (VOCs) Solvents used as degreasers or cleaning agents.
Improper disposal of VOCs can lead to contamination of natural waters. VOCs tend to evaporate
very easily. This characteristic gives VOCs very distinct chemical odors like gasoline, kerosene,
lighter fluid, or dry cleaning fluid. Some VOCs are suspected cancer-causing agents. Volatile
organic compounds (VOCs) are organic chemical compounds that have high enough vapor
pressures under normal conditions to significantly vaporize and enter the atmosphere. A wide
range of carbon-based molecules, such as aldehydes, ketones, and other light hydrocarbons are
VOCs. The term often is used in a legal or regulatory context and in such cases the precise
definition is a matter of law. These definitions can be contradictory and may contain "loopholes";
e.g. exceptions, exemptions, and exclusions. The United States Environmental Protection Agency
defines a VOC as any organic compound that participates in a photoreaction; others believe this
definition is very broad and vague as organics that are not volatile in the sense that they vaporize
under normal conditions can be considered volatile by this EPA definition. The term may refer
both to well characterized organic compounds and to mixtures of variable composition.
VOLATILE ORGANIC COMPOUNDS: (VOCs) Solvents used as degreasers or cleaning agents.
Improper disposal of VOCs can lead to contamination of natural waters. VOCs tend to evaporate
very easily. This characteristic gives VOCs very distinct chemical odors like gasoline, kerosene,
lighter fluid, or dry cleaning fluid. Some VOCs are suspected cancer-causing agents. Volatile
organic compounds (VOCs) are organic chemical compounds that have high enough vapor
pressures under normal conditions to significantly vaporize and enter the atmosphere. A wide
range of carbon-based molecules, such as aldehydes, ketones, and other light hydrocarbons are
VOCs. The term often is used in a legal or regulatory context and in such cases the precise
definition is a matter of law. These definitions can be contradictory and may contain "loopholes";
e.g. exceptions, exemptions, and exclusions. The United States Environmental Protection Agency
defines a VOC as any organic compound that participates in a photoreaction; others believe this
definition is very broad and vague as organics that are not volatile in the sense that they vaporize