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V

VACUUM Reduction in pressure below atmospheric pressure.

VACUUM FILTRATION Using a vacuum to remove water from a sludge and leave solid matter behind on a filter surface.

VALENCE The number of positive or negative charges on an ion.

VALVE, EXPANSION Type of refrigerant controls which maintains pressure difference between high side and low side pressure in refrigerating mechanism. Valve is caused to operate by pressure in low suction side. Often referred to as an automatic expansion valve or AEV.

VALVE, KING Stop valve between receiver and liquid main.

VAN DER WAALS ATTRACTIVE FORCES The innate attractive force between two identical particles such as calcium carbonate-calcium carbonate or iron-iron.

VAPOR A gas, particularly one near to equilibrium with the liquid phase of the substance and which does not follow the gas laws. Usually used instead of gas for a refrigerant, and in general for any gas below the critical temperature.

VAPOR DENSITY The weight of a vapor or gas compared to the weight of an equal volume of air; an expression of the density of the vapor or gas. Material lighter than air have vapor densities less than 1.0 (examples: acetylene, methane, hydrogen). Materials heavier than air (examples: propane, hydrogen sulfide, ethane, butane, chlorine, sulfur dioxide) have vapor densities greater than 1.0. All vapors and gases will mix with air, but the lighter the material will tend to rise and dissipate (unless confined). Heavier vapors and gasses are likely to concentrate in low places-along or under floors, in sumps, sewers, and manholes, in trenches, and ditches-where they may create fire or health hazards.

VAPOR PRESSURE The pressure exerted by a saturated vapor above its own liquid in a close container. When quality control tests are performed on products, the test temperature is usually 100° F (38° C), and the vapor pressure is expressed as pounds per square inch (psig or psia)-but vapor pressures reported on MSDS are in millimeters of mercury (mm/Hg) at 68° F (20° C), unless stated otherwise. Three facts are important to remember.

1. Vapor pressure of a substance at 100° F (38° C) will always be higher than the vapor pressure of the substance at 68° F (20° C).
2. Vapor pressure reported on MSDS’s in mmHg are usually very low pressures; 760 mmHg is equivalent to 14.7 pounds per square inch.
3. The lower the boiling point of substance, the higher its vapor pressure.

VAPOR, SUPERHEATED Vapor at a temperature which is higher than the saturation temperature (i.e., boiling point) at the existing pressure.

VELOCIMETER Instrument used to measure air velocities using a direct reading air speed indicating dial.

VELOCITY REGAIN STACK A venturi shaped fan cylinder. The increase in performance obtained on this type of cylinder is due to the reduction in total head above the fan. The attendant decrease in total head differential across the fan results in an increase in air rate at constant horse power or a decrease in horse power at constant air rate.

VENTILATION See "general exhaust," "local exhaust," and "mechanical ventilation."

VENTURI A device for measuring fluid flow, including a short converging cone succeeded on the same axis by a long diverging cone. This device is also used in gas scrubbing.

VERSENATE A chemical reagent which reacts with hardness and which is widely used to measure hardness quantity colormetrically.

VIBRATION Safety switch used to de-energize the driver circuit should the mechanical equipment assembly vibrate excessively.

VISCOSITY The viscosity of a fluid is a measure of how easily a fluid will flow.

VISCOSITY RATIO The viscosity ratio is the ratio of the viscosity of the bulk fluid to the viscosity of the fluid at the tube wall.

VISCOUS Thick liquid, like syrup.

VITON® Copolymer of vinylidene fluoride and perfluoropropylene. Used for pump diaphragms, seals and seats. Trade name of DuPont.

VOID VOLUME The open volume between the resin beads in a given volume of resin bead. Expressed as a Percent of resin bed volume. Usually varies between 35-40% of the resin bed.

VOIDS The space between the resinous particles in a ion exchange bed.

VOLATILE LIQUID One which evaporates readily at atmospheric pressure and room temperatures.

VOLATILE MATTER That matter that is changed under conditions of the test from a solid or a liquid state to the gaseous state.

VOLUME RESISTIVITY The electrical resistance beneath the surface of the fly ash particle.

VOM Volt-Ohm Milliamp Meter.

W

WALK-IN COOLER Large commercial refrigerated space kept below room temperature. Often found in large supermarkets or wholesale meat distribution centers.

WASTAGE The sum of blowdown, drift, and leakage.

WATER ANALYSIS Chemical analysis of dissolved materials in water. Also includes determination of pH and the amount of suspended solids.

WATER COOLING TOWER An enclosed, steady flow device for cooling water by evaporation and sensible heat exchange through direct contact with air.

WATER COLUMN A boiler control equipment package consisting of boiler water level controls, feed water flow controls, and a sight glass for visual inspection of boiler water level.

WATER FLOODING A process of displacing oil from underground formations with water and returning it to the surface for recovery.

WATER GAUGE (See Gauge or Sight Glass)

WATER LOAD Circulation rate of water over the tower, irrespective of temperature range.

WATER LOADING Circulating water flow expressed in gallons per minute (GPM) per square foot of effective horizontal wetted area of the tower. Unit:GPM/ft.^2..

WATER QUALITY CRITERIA The levels of pollutants that affect the suitability of water for a given use. Generally, water use classification includes: public water supply; recreation; propagation of fish and other aquatic life; agricultural use and industrial use.

WATER-FORMED DEPOSITS Any accumulation of insoluble material derived from water or formed by the reaction of water upon surfaces in contact with water. Note: Deposits formed from or by water in all its phases may be further classified as scale, sludge, corrosion products or biological deposits. The over-all composition of a deposit or some part of a deposit may be determined by chemical or spectrographic analysis; the constituents actually present as chemical substances may be identified by microscope or X-ray diffraction studies. Organisms may be identified by microscopical or biological methods.

WATERTUBE BOILER Boiler design with water/steam in the tubes and hot gases outside the tubes on the shell side.

WATERWALLS In a watertube boiler, tubes through which water is circulated to maximize heat absorption.

WATT Unit of electrical power.

WAX Ingredient in many lubricating oils which may separate out if cooled sufficiently.

WEAKLY BASIC ANION RESIN These resins are employed in deionizers when silica removal is not required. When regenerated with soda ash, ammonia or caustic soda, the resin will adsorb strong acids such as hydrochloric and sulfuric. The resin usually receives its exchange capacity from tertiary amino groupings.

WEIR A spillover device used to measure or control water flow.

WET BULB The temperature of saturated air. At 100% humidity the wet bulb temperature equals the dry bulb reading. The lower the humidity, the drier the air and the greater the difference in reading. The lower the wet bulb, the more work a cooling tower can do. A cooling tower cannot cool the water below the wet bulb temperature of the inlet air.

WET BULB TEMPERATURE The temperature of saturated air, or the dew point of air, which is also the coolest temperature water can be cooled by passing through air.

WET BULB TEMPERATURE (WBT) Temperature indicated by a psychrometer. Also known as the thermodynamic wet bulb temperature or the temperature of adiabatic saturation. Unit:§ F.

WET/DRY TOWER When two dissimilar metals are in contact in the same electrolyte, a difference of potential results, causing corrosion of the less noble member of the couple.

WET-SALT TANK So called because the saturated brine is always above the undissolved salt level at all times. This type of equipment is normally used with manually regenerated softeners.

WHITE LIQUOR Cooking liquor from the draft pulping process produced by recausticizing green liquor with lime.

WHITE ROT The type of decay which results in almost complete removal of lignin with a minimum attack of the cellulose - the advanced areas of this type of decay will be pitted and the remaining fiber will be white to cream in color. This type of decay does not occur in redwood, but is common in oak, fir, cypress, etc.

WHITE WATER The filtrate from a paper- or board-forming machine, usually recycled for density control.

WIND LOAD The load applied to a structure by a wind blowing against its surface. Wind load is expressed in pounds per square foot. Unit:lbs./ft².

WINDAGE Water loss out of the side of a cooling tower usually effected by wind direction and velocity.

WINDAGE LOSS Loss of fine droplets of water entrained by circulating air. The amount varies with different types of equipment and is replaced by make-up water. Windage loss tends to limit the cycles of concentration, and is usually expressed as a percentage of the rate of circulation.

WINTERIZATION Modification of one or more cells to operate under freezing ambient temperatures.

WOOD DETERIORATION Degradation of cooling tower wood through chemical or biological action.

Y

YIELD The rate of production of cake from a dewatering device.

YIELD POINT In low- and medium-carbon steel, the stress at which a marked increase in deformation occurs without increase in load.

Z

ZEOLITE Naturally occurring hydrous silicates exhibiting limited base exchange.

ZERO DISCHARGE The discharge of no pollutants in the wastewater stream of a plant that is discharging into a receiving body of water.

ZETA POTENTIAL The difference in voltage between the surface of the diffuse layer surrounding a colloidal particle and the bulk liquid beyond.

ZINC ION Cathodic inhibitor commonly used in conjunction with chromate, polyphosphate, organics, or combinations of these.

ZONE OF INHIBITION The area in which the growth and development of the organism has been completely inhibited. This, however, does not necessarily mean that the organism is killed in this area since the toxic agent in the area may be present only in sublethal concentrations.

ZONE SETTLING Settling particles sink as one mass at the same velocity.

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