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A pressure less than atmospheric pressure, measured either from the base of zero pressure or from the base of atmospheric pressure.
Vacuum-Relieving Device
A device to automatically admit air or gas into space at a pressure below atmospheric.
A property of ions or of radicals determining the number of ions with which they can combine in chemical reactions.
Valley Filling
The building of off-peak loads.
Value of Service
The concept that the value of a utility service to a consumer cannot be greater than the cost of an equally satisfactory substitute service or the consumer will switch to the substitute.
Value of Service Pricing
A method of apportioning costs among utility customers so that users who place a greater value on the service are charged higher rates than the more price sensitive customers.
A mechanical device for controlling the flow of fluids and gases; types such as gate, ball, globe, needle, and plug valves are used.
Valve Box
A housing around an underground valve to allow access to the valve and to protect the valve from mechanical damage or the effects of weather.
Valve Chamber
The space in a dry gas meter containing the slide valves and mechanism for their operation.
Valve Control
A fuel-air control system that operates by means of mechanical linkage of related valves, common in industrial combustion systems.
Valve Seat
The stationary portion of the valve which, when in contact with the movable portion, stops flow completely.
Valve, Automatic Input Flow Control
A device for controlling the gas supply to the main burner without manual attention.
Valve, Automatic Shut-Off
A device designed to shut off gas flow upon flame failure, pilot outage, control impulse, overpressure, or underpressure without manual attention.
Valve, Back Pressure
A valve built to maintain a given pressure in a piping system by remaining in a closed position until the given pressure is reached, at which time it opens to permit flow until the pressure falls below the specified pressure. Compare VALVE, CHECK.
Valve, Ball
A valve in which a pierced sphere rotates within the valve body to control the flow of fluids. The sphere may be trunnion mounted or free.
Valve, Butterfly
A throttling valve made up of a disc that rotates on an axis within the valve body, thereby varying the cross-section that is open to fluid or gas passage.
Valve, Check
A valve built to pass a fluid in one direction but to close automatically when the fluid tries to flow in the opposite direction. Compare VALVE, BACK PRESSURE.
Valve, Expansion
A valve for controlling the flow of refrigerant to the cooling element.
Valve, Firing
A lubricated plug-type variable position valve which is usually operated with an attached handle or, in the large sizes, by a loose fitting key or extended handle wrench. Compare VALVE, TEST FIRING.
Valve, Gate
A full-opening valve controlled by a vertical movement of a single or pair of solid discs perpendicular to the direction of flow. There are several other types such as wedge, slab, expanding gate, etc.
Valve, Globe
A valve equipped with an orifice and a stem attached to a plug and matching circular seat. Shut-off is obtained by direct contact of the plug and the seat. Body of valve is normally spherical.
Valve, Input Flow Ratio Control
Valve, Lubricated Plug
A valve of the pierced plug and barrel type provided with means for maintaining a lubricant between the bearing surfaces. It is designed so that the lapped bearing surfaces can be lubricated and the lubricant level maintained without removing the valve from service.
Valve, Main Burner Control
A valve which controls the gas supply to the main burner manifold.
Valve, Manual Input Flow Control
A manual valve, usually with stops, which can be set to limit the gas flow to the maximum required input to the burner or burners.
Valve, Manual Main Shut-Off
A manually operated valve or stop in the gas line for the purpose of completely turning on or shutting off the gas supply to the appliance except to pilot or pilots which are provided with independent shut-off valves.
Valve, Manual Rest
An automatic shut-off valve installed in the gas supply piping and set to shut off when unsafe conditions occur. The device remains closed until manually reopened.
Valve, Needle
A small valve that is opened and closed to permit or restrict fluid or gas flow by the movement of a pointed plug or needle in an orifice or tapered orifice in the valve body.
Valve, Plug
Metal valve in which a pierced plug rotates in a tapered or cylindrical body to control flow through the valve.
Valve, Relief
An automatic valve designed to discharge when a preset pressure and/or temperature condition is reached. 1. Pressure Relief Valve. An automatic valve which opens and closes a relief vent, depending on whether the pressure is above or below a predetermined value. 2.Temperature Relief Valve. a. Fusible Type. A valve which opens and keeps open a relief vent by the melting or softening of a fusible element at a predetermined temperature. b.Manual Reset Type. A valve which automatically opens a relief vent at a predetermined temperature and which must be manually returned to the closed position. c. Reseating or Self-Closing Type. An automatic valve which opens and closes a relief vent when the temperature reaches a predetermined value. d. Vacuum Relief Valve. An automatic valve which opens or closes a vent for relieving a vacuum, depending on whether the vacuum is above or below a predetermined value. Frequently used in a hot water supply system.
Valve, Safety Shut-Off (Cut-Off)
A valve which automatically shuts off the supply of fuel through the functioning of a flame safeguard control or limiting device. This device may interrupt the flow of fuel to the main burner(s) only or to the pilot(s) and main burner(s).
Valve, Shut-Off
Stops or valves readily accessible and operable by the consumer, located in the piping system (to shut off individual equipment) or between the meter and gas main to shut off the entire piping system. Compare SERVICE STOP.
Valve, Solenoid
An automatic valve that is opened or closed by an electromagnet.
Valve, Tamper-Proof
A shut-off valve designed and constructed to minimize the possibility of the removal of the core of the valve or stop accidentally or willfully with ordinary household tools.
Valve, Test Firing
A firing valve downstream of all other valves on the valve train.
Vanes, Straightening
Round, square, or other shape tubing installed inside the piping preceding an orifice to eliminate swirls and crosscurrents set up by the pipe fittings and valves.
The gaseous state of a substance as distinguished from permanent gases. A gaseous fluid may be classified as either a vapor or a gas. If it is near the region of condensation, it is called a vapor. If it is well above the region of condensation, it is called a gas. Vapors in general do not follow the ideal gas law, and engineers prefer to use tables and charts based on experimental data when working with vapors. Gases, however, may obey the ideal gas laws over a wide range of temperature and pressure.
Vapor Barrier
A moisture-impervious layer applied to the warm side for the purpose of preventing moisture travel.
A heat exchange used to return liquid natural gas to a gaseous form and then continue to heat the gas to a temperature at which it can be sent into the distribution system.
Variable Cost
Operating costs which, in the aggregate, vary either directly or indirectly in relation to any change in the volume of gas sold and/or transported; i.e., compressor station fuel and expenses. See FIXED COST.
An enclosed room or pit having an access opening in the top, side wall, or both. May be in a building, a separate above-ground structure, or underground.
Vegetation Survey
Leakage surveys made for the purpose of finding leaks in underground gas piping by observing vegetation.
Vehicle Accident Frequency Rate
The frequency rate of motor vehicle accidents is the number of motor vehicle accidents per 1,000,000 miles. It is derived by multiplying the number of accidents by one million and dividing by the mileage.
Velocity Pressure
An opening in a tank or other piece of equipment, sealed to prevent escape of material within the equipment at normal pressures but so arranged that it automatically opens to relieve excessive pressure in the equipment. Can be arranged for manual opening to depressure equipment as desired. Also, the relief opening in a pressure regulator, normally open to the atmosphere.
Vent Connector
That portion of the venting system which connects the gas appliance to the gas vent or chimney.
Vent Damper
A device installed in the vent pipe that connects the furnace to the chimney. When the burner goes off, the damper closes automatically, restricting the amount of heated air that can be lost through the chimney.
Vent Gas
Vent, Flue Gas
A conduit or passageway for conveying flue gases to the outer air.
The process of supplying or removing air by natural or mechanical means to or from any space. Such air may or may not have been conditioned.
Ventilation Air
That portion of supply air which comes from outside, plus any recirculated air that has been treated to maintain the desired quality of air within a designated place.
Venting System Categorizations
For gas-fired, central furnaces, the venting systems are classified and furnaces marked as follows: Category I - A central furnace that operates with a non-positive vent pressure and with a vent gas temperature at least 140 degrees F (60 degrees C) above its dew point. Category II - A central furnace that operates with a non-positive vent pressure and with a vent gas temperature less than 140 degrees F (60 degrees C) above its dew point. Category III - A central furnace that operates with a positive vent pressure and with a vent gas temperature at least 140 degrees F (60 degrees C) above its dew point. Category IV - A central furnace that operates with a positive vent pressure and with a vent gas temperature less than 140 degrees F (60 degrees C) above its dew point.
Venturi Meter
Venturi Throat or Tube
A tube tapered down to a lesser diameter and then expanding gradually to its original diameter. Pressure-measuring taps are provided at the entrance and at the constricted throat for determining pressure differential through the tube used for metering.
Verified Nomination
A nomination that has been validated against the conditions specified in the service contract and with any upstream/downstream or third parties involved in the transaction.
The term used by FPC and FERC to indicate the period in which a gas sales contract was made and/or the date drilling was started on a well.
The tendency of plastics to respond to stress as if they were a combination of viscous liquids and elastic solids.
In general, resistance to flow; that property of semi-fluids and gases by virtue of which they resist an instantaneous change of shape or arrangement of molecules.
Volatile Matter
Matter which is readily vaporizable at a relatively low temperature.
Volume Imbalance
Volume, Specific
The volume of a unit weight of a substance at specific temperature and pressure conditions.
Volumetric Rates
A classification method which assigns 100% of fixed costs to the commodity rate.
VOM--Volt Ohmmeter
A device for measuring the voltage or the resistance of an electrical circuit. Some models also measure current flow through components in electrical circuits.


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