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ABSORPTION REFRIGERATION SYSTEM – a type of refrigeration system that uses lithium bromide salt as the absorbent, water as the refrigerant and heat as the means to pressurize the refrigerant.
ACID – a substance that releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with alkaline substances (base) to form a neutral salt and water.
ACID CLEANING – procedure for removal of waterside deposits in which an acid-based material is used as the primary cleaning agent.
AERATION – process of introducing air into water.
AEROBIC – with or in the presence of oxygen.
AIRBORNE CONTAMINANT – solids or gases brought into open cooling system water in the air flowing through the tower.
AIR-TO-FUEL RATIO – ratio of air to fuel supplied to the boiler burner.
AIR WASHER – system for removal of airborne contaminants or foulants from air in a plant by flowing it through a water spray chamber, often chilled, that also regulates temperature or humidity.
ALGAE – simple plants. Under conditions favorable for their growth, they mature into colonies and produce mats or similar masses. A simple form of plant life that generally requires sunlight and air for existence. Causes plugging of heat exchanger tubes and cooling tower distribution systems.
ALGAECIDE – chemical treatment used to control growth of microorganisms in water systems. A toxic material that will retard or prevent the growth of algae and slimes. Some of the more commonly used algaecides are chlorine, copper sulfate, and phenolic compounds.
ALKALINITY – the quantitative capacity of a water or water solution to neutralize an acid. It is usually measured by titration with a standard solution of sulfuric acid and expressed in terms of its calcium carbonate equivalent. Alkalinity is related to the amount of carbonate (CO32-), bicarbonate (HCO3-), and hydroxide (OH-) ions dissolved in the water.
AMBIENT TEMPERATURE – (1) Outdoor temperature as reported by periodic readings.
(2) Also known as the dry bulb temperature, measured in the regular manner with conventional instruments.
AMINE – a class of chemical used to control the rate of corrosion in condensate return piping and related components. See FILMING AMINE, NEUTRALIZING AMINE (CYCLOHEXYLAMINE, DIETHYLAMINOETHANOL, MORPHOLINE)
ANAEROBIC – in the absence of oxygen.
ANION – a negatively charged ion in solution, such as bicarbonate, chloride, or sulfate.
ANODE – the electrode of an electrolyte cell at which oxidation occurs. Electrons flow away from the anode in the external circuit. It is usually at the electrode that corrosion occurs and metal ions enter solution. Contrast with cathode.
ANODIC CORROSION INHIBITOR – corrosion inhibitor that interferes with the anodic reaction in a corrosion cell (ex: molybdenum, nitrite, silicates, chromate).
ANTIFOAM – class of chemical treatment used in water treatment to limit foaming of system water.
AQUEOUS – using water as a solvent.
AQUIFER – a layer or zone below the surface of the earth capable of yielding a significant volume of water.
ATMOSPHERIC COOLING TOWER – Cooling tower in which air movement is dependent upon atmospheric conditions, not on mechanical fans, to force or induce air through the tower. The hot moist air rises in the chimney, pulling colder outside air through the intake louvers.
ATOM – the smallest unit of matter retaining the characteristics of an element. The smallest particle of an element that can exist either alone or in combination with similar particles of the same element or of a different element.
ATOMIC WEIGHT – method of comparing the weight of an atom with that of an oxygen atom. Oxygen has an atomic weight of 16; hydrogen has an atomic weight of one.
AUTOCLAVE – a chamber for sterilizing with steam under pressure.

BACK PRESSURE – pressure opposed to the desired flow of a fluid in a confined place such as a pipe. It is often caused by obstructions or tight bends in the confinement vessel.
BACKWASH – upward flow of water though a media (ion exchange resin, sand, etc) bed to clean, expand, and classify the media.
BACTERIA – single cell microorganisms that typically reproduce by cell division. Although usually classified as plants, bacteria contain no chlorophyll.
BASE – a substance that releases hydroxyl ions when dissolved in water. Bases react with acids to form a neutral salt and water.
BASIN – lower area of a recirculating water system, in which system water collects (ex: the bottom area of a cooling tower).
BED – the area in an ion exchanger or filter containing the media.
BICARBONATE ALKALINITY – the alkalinity of water due to the presence of bicarbonate ions (HCO3-).
BIOCIDE – group of chemical treatments used to control growth of microorganisms (algae, bacteria, fungi) in water systems including cooling towers and closed loops.
BIOFILM - complex communities of surface attached bacteria growing inside a protective microbial secretion often called slime. Although biofilms start out microscopic in size, they can grow into visible biofouling deposits in just a matter of days. A wide range of problem causing microorganisms can grow to high levels protected within biofilms and associated microorganisms, especially amoebae. Once established, biofilms are difficult to remove and kill.
BIOLOGICAL DEPOSIT – deposits of microorganisms, or byproducts of their life processes, on waterside surfaces.
BLEED or BLEEDOFF – Discharge of water from an evaporative cooling water system such as cooling tower. Bleed helps prevent problem-causing impurities in the system water from over-concentrating by replacing a portion of the system water with unconcentrated makeup water. Bleed can be intentional or unintentional. Bleed is the term usually associated with evaporative cooling systems, while blowdown is the term usually associated with steam boilers. The terms are used interchangeably.
BLEED RATE – rate at which water is bled from a cooling tower recirculating system.
BLISTER – A bump on a boiler tube that swells into the fire side that can lead to partial or complete failure due to overheating and expansion of the boiler tube metal.
BLOWDOWN – Discharge of water from an evaporative heating or cooling water system such as steam boiler or cooling tower system. Blowdown helps prevent problem-causing impurities in the system water from over-concentrating by replacing a portion of the system water with unconcentrated makeup water. Blowdown can be intentional or unintentional. Bleed is the term usually associated with evaporative cooling systems, while blowdown is the term usually associated with steam boilers. The terms are used interchangeably. The Value of Good Boiler Blowdown
BOD – abbreviation for Biological Oxygen Demand.
BOILER EFFICIENCY – the ratio of the net energy output of the boiler fluid divided by the input of the primary energy source(s) (ex: 800,000 Btu output to 1,000,000 Btu input = 80% boiler efficiency).
BOILER HORSEPOWER – a measure of steam boiler output. One boiler horsepower equals to the generation of 34.5 lbs steam/hour at 212°F.
BRASS – a metal alloy consisting mainly of copper (over 50%) and zinc to which smaller amounts of other elements may be added.
BRINE – a salt solution, generally sodium chloride or calcium chloride.
BRONZE – a copper-tin metal alloy with or without small proportions of other elements such as zinc and phosphorus. Also, certain other essentially copper-based alloys containing no tin, such as aluminum bronze, silicon bronze, and beryllium bronze.
BTU – stands for British Thermal Unit. The quantity of heat required to raise the temperature of one pound of water one degree F.
BUFFER – a solution that resists change in pH.

Ca – chemical symbol for the element calcium.
CaCO3 – chemical symbol for the chemical compound calcium carbonate.
CALCIUM – one of the principle elements making up the earth’s crust. Calcium is a major cause of scale deposits in all types of heat exchange equipment. It forms several compounds with a relatively low solubility including calcium carbonate, calcium phosphate, calcium silicate, and calcium sulfate. The presence of calcium and magnesium in water makes it hard to wash with because more soap is required. Consequently, water that contains high levels of these minerals is often termed “hard.”
CALCIUM CARBONATE – the precipitant resulting from heating of water that contains calcium bicarbonate.
CARBONATE – the CO3- ion.
CARBONATE ALKALINITY – alkalinity due to the presence of the carbonate ion.
CARBONATE CYCLE – a method of internal boiler water treatment. Calcium carbonate is precipitated in the presence of an organic polymer dispersing agent.
CARBON DIOXIDE – corrosive gas found in most surface and ground water supplies. Released in the chemical reactions that occur in boiler system water.
CARBONIC ACID – acid produced from the mixture of carbon dioxide and water.
CARRYOVER – condition that develops in boiler water resulting in liquid water, dissolved solids and/or chemical treatment being carried out of the system as part of the steam. What You Need to Know About Boiler Water Carryover
CATHODE – the area in a corrosion cell where the reduction reaction (electron loss) occurs. Metal is generally not lost from the cathode.
CATHODIC INHIBITOR – corrosion inhibitor that reduces corrosion by interfering with the cathode surface of a corrosion cell (ex: zinc, polyphosphates, phosphonates).
CATION – an ion with a positive electric charge, such as calcium, magnesium, and sodium.
CAUSTIC – any substance capable of burning or destroying animal flesh or tissue. The term is usually applied to strong bases such as sodium hydroxide or potassium hydroxide.
CAVITATION – the formation and then immediate implosion of bubbles in a liquid that occurs when a liquid is subjected to rapid changes of pressure. This can cause the formation of cavities where the pressure is relatively low. Cavitation can cause intense metal attack (corrosion) characterized by deep, circular pits.
CELL – smallest unit of a living organism.
CENTRIFUGAL PUMP – water pump with an impeller that moves water by centrifugal force as the impeller spins in a housing.
CENTRIFUGAL CHILLER – turbine or rotating compressor in a vapor compression type chiller for a cooling system, as compared to a reciprocating type of compressor.
CHANNELING – the flow of water taking the “line of least resistance” through a resin bed.
CHELANT – a chemical sequestrant that prevents an ion from exhibiting its normal properties by complexing (bonding) with it.
CHEMICAL OXYGEN DEMAND – amount of oxygen, expressed in parts per million, consumed under specified conditions in the oxidation of organic matter contained in water.
CHLORIDE – acid radial contained in both surface and ground water supplies.
CHLORIDE TEST – test performed on a water sample to determine the total amount of chlorides present. Results are expressed in ppm. Recommended upper limits to which chlorides can build in system water provides a method for controlling waterside deposits. Amount of chloride in system water compared to chloride content of makeup or feedwater provides means of determining cycles of concentration at which a system is operating provided that no chlorine based products have been added to the system water.
CHLORINATOR – a device used to meter chlorine into cooling water at a pre-selected rate.
CHLORINE – oxidizing-type biocide. Used to control growth of microorganisms in cooling tower system water.
CHLORINE REQUIREMENT – amount of chlorine, expressed in parts per million, required to achieve chlorination.
CHLORINE RESIDUAL – amount of available chlorine present in system water at any specific time.
CHROMATE – anodic type corrosion inhibitor that forms a highly passive film of ferric and chromate oxide on the anode of a corrosion cell. Chromate is a known carcinogen.
CIRCULATING HOT WATER SYSTEM – system in which water is heated and circulated through a system of piping, or to a heat exchanger. In circulating through the system, heat in water is transferred and utilized for space heating or heating of potable water.
CLARIFICATION – external treatment process that removes suspended solids, turbidity, color, and colloidal matter from makeup water.
CLOSED SYSTEM – system in which water is continuously re-circulated and loss of water from the system is minimal.
COAGULATION – to bring together small particles into a single larger mass that can be filtered or settled out of solution.
COD – abbreviation for Chemical Oxygen Demand.
COGENERATION – the production of both steam and electricity in the same plant.
COLLOIDAL – composed of extremely small-size particles that are not removed by normal filtration.
CONDENSATE – water condensed from steam.
CONDENSATE POLISHER – special high temperature cation exchange equipment used to remove soluble and insoluble contaminants from condensate returned from steam boiler systems. Primarily used to remove hardness and iron.
CONDENSATE TANK – tank or reservoir in a steam boiler system to which condensate flows and collects.
CONDUCTANCE – a measure of the ability of water to conduct an electric current.
CONDUCTIVITY – the ability of electrical current to flow through water as a measure of its ion content expressed in micromhos/cm or micromhos/cm measured by a meter.
CONDUCTIVITY TEST – test made on any water sample with a conductivity meter to determine the amount of total dissolved solids present. Results expressed in micromhos, µmhos, or conductivity. Test results are utilized to control dissolved solids in system water within limits that prevent deposition.
CONTAMINANT – any solid, gas, or liquid in system water that is foreign and not normally found under the conditions of operation.
CONDENSER – heat exchanger in a cooling system in which a gas condenses into a liquid as it gives up heat.  
CONTINUOUS BLOWDOWN – intentional, controlled continuous flow of boiler system water taken from the top or upper section of the boiler to the drain. Also called skimmer blowdown or surface blowdown.
CONVECTION – transference of heat by the circulation of the heated parts of gas or liquid whereby heated portions are lighter and rise vertically.
COOLING POND – large body of water (pond or small lake) to which cooling water is pumped and heat contained in the water is released to the atmosphere by natural evaporation.
COOLING RANGE – numerical difference between the temperature of the water entering the top of the cooling tower and the temperature of water leaving the basin or sump of the tower. Also called delta T (∆T).
COOLING TOWER – device for the evaporative cooling of water by contact with air. Achieved partially by an exchange of latent heat resulting from evaporation of a portion of the circulating water and partially by transfer of sensible heat to the air.
COPOLYMER – polymerization of different monomers on the backbone of a polymer or on its branch chains. A type of dispersant used in boiler water and cooling water scale inhibitors.
CORROSION – electrochemical process in which a difference in electrical potential develops between metals or between different sites of the same metal. The difference in potential results in metal being removed at the anode site.
CORROSION CELL – two points on different metals, or different sites of the same metal, consisting of an anode and cathode. Difference in electrical potential between the two points results in metal being removed at the anode site.
CORROSION COUPON – test metal strip used to measure the rate of corrosion.
CORROSION PRODUCTS – oxides of metal that have been removed as a result of the corrosion process.
COUNTER FLOW COOLING TOWER – cooling tower where air flows straight up vertically through tower fill packing while water flows down counter, or opposite, to the airflow.
CREVICE CORROSION – corrosion taking place where a specific area is isolated from the bulk solution (ex: a flange area).
CROSS FLOW COOLING TOWER – cooling tower in which air moves horizontally through the fill packing while falling water flows down across the moving air.
Cu – chemical symbol for copper.
CUPRONICKEL – a copper-based alloy containing 5-30% nickel.
CUPROUS METAL – metal containing copper.
CUPROUS OXIDE – passivated oxide state of copper.
CYCLES OF CONCENTRATION – ratio between the amount of dissolved solids in makeup water and the amount of dissolved solids in system water.
CYCLOHEXYLAMINE – neutralizing type amine. Used to help control the rate of corrosion in the condensate return system of a steam boiler.

DEAERATOR – external treatment equipment in which boiler feedwater is heated to 212°F+ for the purpose of releasing dissolved gases, primarily oxygen and carbon dioxide, from the water.
DEALKALIZATION – external treatment process by which natural alkalinity of raw makeup water is lowered.
DECK-FILLED COOLING TOWER – cooling tower that contains baffling inside the tower housing to increase the break-up of water falling through the tower and also to provide additional wetted surface.
DEIONIZATION – general term that embraces the removal of all charge ionizable salts (both organic and inorganic) from solution.
DEIONIZE – to remove ions from solution.
DELIGNIFICATION – loosening of surface fibers in cooling tower wood members causing weakening of the timber.
DEMINERALIZE – removal from solution of inorganic salts by means of absorption by ion exchange.
DENITRIFYING BACTERIA – bacteria that cause the microbial breakdown of nitrates and nitrites to ammonia and nitrogen.
DEPOSITION – general term describing accumulation of matter on the waterside surface of heating or cooling equipment. Can be hard scale, sludge, iron oxide, foulants, biological deposits.
DESICCANT – moisture-absorbing material (ex: quicklime, silica gel, activated alumina). Used to control condensation in a boiler during dry lay-up.
DEW POINT – temperature at which a given mixture of air and water will have a relative humidity of 100% saturation.
DEZINCIFICATION – leaching of zinc from brass.
DIETHYLAMINOETHANOL – a type of neutralizing amine, abbreviated DEAE.
DISPERSANT – chemical that causes particulates in water to remain in suspension.
DISSOLVED MATTER – matter, exclusive of gases, present in water.
DISSOLVED OXYGEN – the amount of gaseous oxygen (O2) dissolved in an aqueous solution.
DISSOLVED SOLIDS – minerals in surface and ground water supplies that have been dissolved in water from contact with the earth’s surface.
DISTRIBUTION DECK – area on top of a cooling tower into which cooling water returning from the heat source is dumped.
DISTRIBUTION SYSTEM – mechanical method of uniformly distributing returned cooling water over the fill area inside the tower preparatory to cooling. Low-pressure spray through piping and nozzles is normally used in a counter-flow tower and gravity drop in cross-flow tower.
DOWNCOMER – tube or pipe in a water tube boiler that connects the drums. Water flows downward in downcomer tubes.
DRIFT – water droplets that are entrained in the air-stream as it passes through the tower. Water entrained is carried out of the tower and lost to the atmosphere. Also called windage.
DRIFT ELIMINATOR – baffling in a cooling tower that causes hot air, with entrained water droplets, to change direction a number of times causing the droplets to hit eliminator surfaces and fall back into the tower water.
DRY BULB TEMPERATURE – (DBT) ambient temperature of air measured in the standard manner with conventional instruments.
DRY LAY-UP – period during which equipment or system is non-operational, all water is drained, and the system left dry.
DRY ROT – a term loosely applied to wood that has dry, crumbly rot, but especially to that which, when in an advanced stage, permits the wood to be crushed easily into a dry powder.
DRY STEAM – steam containing no moisture. Commercially dry steam contains not more than 0.5% moisture.

ECONOMIZER – heat exchanger placed in the gas passage between a boiler and stack. Designed to recover heat from exhaust gases and transfer this heat to the boiler feedwater flowing through it as it goes to the boiler.
EDR – abbreviation for equivalent direct radiation. The rate of heat transfer from a radiator or convector.
It is equivalent to the square feet of surface area necessary to transfer heat at the same rate at which it is produced by the generator. A single boiler horsepower equals 140 ft2 EDR.
EDTA – abbreviation for ethylene diaminetetraacetic acid. A type of chelating agent.
EFFLUENT – flow of water out of a tank or from a system.
ELECTRIC BOILER – unit for production of steam by heating water with electrical resistance elements, or by passing AC current through the water between electrodes.
ELECTRODES – conductive materials placed in water solutions that have a positive or negative charge.
ELECTRON – a subatomic particle with a negative electrical charge.
EMULSION – a colloidal dispersion of one liquid in another.
ENTHALPY – total heat content, which is the sum of the sensible heat of the air and water vapor, plus the latent heat of vaporization of the water.
ENTRAIN – to carry or draw along. The transport of water in a gas or vapor stream or the transport of air in a liquid stream.
EQUILIBRIUM – the stage in a reversible reaction when there is no driving force in either direction.
EROSION – form of corrosive attack associated with metal removal due to high water velocity or the presence of abrasive suspended solids in the fluid.
EVAPORATIVE CONDENSER – cooling system in which the condenser or heat exchanger is located within the body of the cooling tower. Water is sprayed from nozzles above the condenser tube bundle while air is blown across the condenser tubes or coil. Refrigerant inside the condenser tubes is cooled due to the extraction of heat from the refrigerant gas caused by the evaporation of water on the outside of the condenser tubes.
EVAPORATION – portion of the tower re-circulating water that is lost to the atmosphere through evaporation in the process of rejecting heat from tower re-circulating water. The amount lost varies depending on the level of heat contained in tower water. Each pound of water evaporated releases 1,000 BTU of heat.
EVAPORATIVE COOLING – heat transfer where a liquid evaporates into its gaseous state, thereby giving up latent heat. The simplest example of this basic premise of cooling tower operation: wet the back of your hand then blow on the wetted surface. The drop in temperature on your skin is due to evaporative cooling.
EVAPORATOR – heat exchanger in which chilled water or air is cooled by giving up the heat it contains to refrigerant gas, which causes the refrigerant gas to evaporate.
EXOTHERMIC – giving off heat in reaction or solution of a substance.
EXTERNAL TREATMENT – any process or procedure which reduces solids or gases from water before it enters the boiler or cooling tower system water.

FAN – an air foil rotating to move air through a cooling tower. Mounted on the top of the tower (induced draft) or the side of the tower (forced draft).
Fe – chemical symbol for iron.
FEEDWATER – water fed to boiler. Can be a mixture of condensate and softened makeup, all condensate, or all softened makeup depending on operating conditions.
FEEDWATER HEATER – a heat exchanger used to preheat boiler feedwater with steam.
FERRIC OXIDE – metal removed in corrosion of iron bearing metal.
FERROUS METAL – metal constructed from iron (ex: cast iron, nickel iron, galvanized steel, silicon steel, stainless steel).
FILL – structural material within a cooling tower that facilitates contact between water and air. See FILL PACKING, SLATS, SPLASH PACKING, DECK-FILLED TOWER.
FILL PACKING – fill material such as cross-fluting designed to distribute water in a thin film in a cooling tower.
FILMING AMINE – class of inhibitor used to control corrosion in the condensate return portion of steam boiler system. Forms an adherent non-wettable organic film on metal surfaces, thereby preventing contact between a metal system and water.
FILTER – porous media through which liquid may be passed to effect removal of suspended matter.
FILTRATE – liquid that passes through a filter.
FILTRATION – external treatment process in which water passes through a filter bed or granular material to effect removal of suspended matter.
FIRETUBE BOILER – term used to describe a boiler in which tubes are surrounded by water while fire and gases pass through inside of boiler tube.
FIRING RATE – the rate at which a fuel is supplied to a burner.
FLASH TANK – tank into which blowdown from a boiler is introduced. Part of the water flashes into steam while the remainder is removed from the tank as a liquid.
FLOC – clump of solids formed in water.
FLOCCULANT – long chain polymeric material of varying charges and molecular weights that form physical bridges to agglomerate the suspended solids so that they can be removed by precipitation or floatation.
FLOW CONTROL – a device designed to limit the flow of water to a predetermined value over a broad range of inlet water pressures.
FLUID COOLER – similar to evaporative condenser except coils in the tower are filled with fluid (typically water) instead of refrigerant. Commonly used to cool the closed loop water in a heat pump air conditioning system.
FOAMING – small, stable, non-coalescing bubbles formed on the water surface of a boiler. Extreme foaming can cause carryover.
FOG – fats, oils, and grease.
FORCED-DRAFT COOLING TOWER – type of cooling tower in which the air intake is at the bottom or side of the tower with fans that force the air up and through the tower.
FOULANT – term loosely used to define any type of deposit composed of silt, organics, particulates scrubbed from the atmosphere, microbiological deposition, dirt, etc.
FOULING – a general term for deposits on surfaces.
FREE AVAILABLE CHLORINE – refers to the portion of the total chlorine level in chlorinated water that is not combined with ammonia or nitrogen compounds. More chemically reactive than total chlorine.  
FREE CO2 – dissolved carbon dioxide gas in water.
FUNGICIDE – chemical that kills fungi.
FUNGUS – a simple plant, containing no chlorophyll and not differentiated into roots, stems, or leaves.

GALVANIC CORROSION – corrosion that occurs when two dissimilar metals are in contact in a solution.
GALVANIC SERIES – table listing metals according to their ability to experience galvanic corrosion when electrically connected when submerged in an electrolyte such as seawater. The less noble metal will serve as the anode and be corroded when connected to more noble metal. The rate of corrosion is determined by the electrolyte and the difference in nobility.
GENERAL CORROSION – metal attack uniformly distributed over a surface.
GPD – symbol for gallons per day.
GPG – symbol for grains per gallon.
GPH – symbol for gallons per hour.
GRAIN – (gr.) a unit of weight equal to 1/7,000th of a pound or 0.0648 grams.
GRAIN PER GALLON – (gpg) a common basis for reporting water analysis in the United States and Canada; one grain per U.S. gallon equals 17.1 milligrams per liter (mg/L) or parts per million (ppm).
GRAM – (g) the basic unit of weight (mass) of the metric system originally intended to be the weight of one cubic centimeter of water at 4°C.
GROOVING – term describing corrosion of condensate piping due to carbonic acid attack. Characterized by development of a groove or flat area in the bottom portion of condensate piping.
GROUND WATER – portion of water that percolates into the earth’s crust and collects in subterranean pools and underground rivers. Source of well and spring water.

H – symbol for hardness.
HANDHOLE – an opening in a boiler drum or water leg that permits limited visual inspection of internal water-side surfaces of the boiler.
HARDNESS – a characteristic of water generally accepted to represent the total concentration of calcium and magnesium ions.
HARDNESS TEST – test performed on a water sample to determine the presence or absence of the elements of calcium or magnesium. Results expressed in ppm. Calcium and magnesium minerals are the principle cause of scale deposits.
HEAT EXCHANGER – equipment in which heat is transferred from one medium to another.
HEAT LOAD – amount of heat dissipated in a cooling tower measured in BTUs.
HEAT PUMP – closed loop system used to extract lower-level heat from one medium, normally air or water, boost its temperature, and release it into another medium.
HIGH HEAD – term used loosely to indicate pressure or refrigerant gas in compressor higher than it should be at a specific load condition.
HOLDING TIME INDEX – (HTI) also called the half-life, a measure of how much time it takes to dilute a chemical that has been added to an evaporative system to 50% of its original concentration.  
HOT WELL – closed or open tank in which condensate water is stored.
HP – stands for horsepower.
HUMIDITY, ABSOLUTE – amount of water vapor contained in the air at a given condition, usually expressed in pounds of water per pound of dry air.
HUMIDITY, RELATIVE – ratio of water vapor pressure in the air to the saturated vapor pressure at the same temperature, usually expressed as a percentage.
HYDRATED FERRIC OXIDE – (ferric hydroxide) a flaky, red to brown corrosion product of iron or steel that forms upon exposure to subterranean, atmospheric, or aqueous environments. Fe2O3.3H2O.
HYDRAULICS – movement or action resulting from liquid flow.
HYDRAZINE – a nitrogen compound, N2H4, used to remove oxygen.
HYDROGEN EMBRITTLEMENT – a loss of ductility in metal caused by the absorption of hydrogen.
HYDROGEN ION CONCENTRATION – the concentration of hydrogen ions in moles per liter of solution; often expressed as pH.
HYDROLOGIC CYCLE – the water cycle, including precipitation of water over or through the earth, and evaporation to water vapor in the atmosphere.
HYDROMETER – a device to measure specific gravity of fluids.
HYDROPHILIC – term that means to attract water.
HYDROUS FERROUS OXIDE – a hydrated form of ferrous oxide, FeO, a jet black corrosion product. It is readily oxidized by air.
HYDROXYAPATITE – a hydrated calcium phosphate; the type of phosphate deposit or sludge usually present in boilers.
HYDROXYL – term used to describe the OH radical.
HYPERBOLIC COOLING TOWER – chimney or natural draft type cooling tower, commonly seen at nuclear power plants.

IMPINGEMENT – metal attack usually due to turbulent flow of water high in dissolved or suspended solids or entrained gases. Results in horseshoe shaped pits on the surface of the metal.
INDICATOR – substance that gives visible change, usually of color, at a desired point in a chemical reaction.
INDUCED-DRAFT COOLING TOWER – cooling tower with an air mover or fan on top of the tower pulling air through the tower fill and out through the top.
INFLUENT – a liquid flow into a system.
INORGANIC MATTER – matter other than plant or animal matter.
INTERNAL TREATMENT – chemical treatment added to system water to aid in controlling corrosion, prevention of waterside deposits, or control of microbiological growth.
ION – an atom or radical in solution carrying an integral electrical charge either positive (cation) or negative
ION EXCHANGE – the interchange of one ion in solution with another ion on an insoluble material that is commonly called resin.
IONIZATION – dissociation of molecules into either positively charged particles called cations or negatively charged particles called anions.
IRON FOULING – plugging of piping, nozzles, etc with iron oxide or rust.
IRON – an element often found dissolved in ground water in concentrations usually ranging from zero to 10 ppm. It is objectionable in water supplies because of the staining caused after oxidation and precipitation (as ferric hydroxide) and because of unsightly colors produced when iron reacts with tannins in beverages such as coffee and tea.
IRON BACTERIA – organisms capable of utilizing ferrous iron, either from water or steel pipes, in their metabolism, and precipitating ferric hydroxide in their sheaths and gelatinous deposits. These organisms tend to collect in pipe lines and tanks, such as softeners, during periods of low flow and break loose in slugs or turbid water to create staining, taste, and odor problems.
IRON OXIDE – metal removed in the corrosion of iron-bearing materials.

JAR TESTING – a test done on wastewater to determine the appropriate flocculating agents needed to clarify the water.

LAMINAR FLOW – straight line flow of a fluid in a pipe, as opposed to turbulent flow where the fluid tumbles as it flows in a pipe. Typically occurs when flow rate is less than 3 feet per second.
LANGELIER SATURATION INDEX – (LSI) an index used to determine the scaling or corrosive tendencies of water, based on the conductivity, calcium, total alkalinity, pH and temperature of the water.
LATENT HEAT – heat required to change a liquid into a vapor without change of temperature or pressure.
LATENT HEAT OF VAPORIZATION – heat given off by a vapor condensing or gained by a liquid evaporating without a change in temperature.
LAYERED OR STRATIFIED BED – resins with sufficient difference in density and hydraulic characteristics to be layered in the same tank in place of two separate tanks.
LIGNIN – major non-cellulose constituent of wood. Sometime used as a dispersant in boiler water treatment.
LIME SCALE – hard water scale containing a high percentage of calcium carbonate.
LIMESTONE – a sedimentary rock, largely primarily composed of calcium carbonate. May also contain significant amounts of magnesium carbonate which would be more correctly called dolomitic limestone or simply dolomite.
LIME SODA SOFTENER – water softener employing calcium hydrate and sodium carbonate as the reacting chemicals to precipitate calcium and magnesium from incoming water.
LOAD – term used to express the amount of steam produced by a boiler or heat being rejected by a cooling tower when compared to amount for which system was designed. If producing or rejecting half of its designed or rated capacity, system is said to be operating at 50% load.
LOUVER – baffle used for the purpose of changing the direction of air flow in a cooling tower. Also, to prevent water droplets from splashing out of a cooling tower on descent through the structure.
LOW-PRESSURE BOILER – relative term used to indicate boilers operating below 30 psig.

M-ALKALINITY – Also known as Total Alkalinity. Measures the amount of carbonate, bicarbonate and hydroxide present in water as ppm of calcium carbonate. M-Alkalinity measurement is based on a sulfuric acid titration using a Methyl orange indicator that goes from yellow at a pH of 4.5 to orange at pH of 4.4 at the endpoint.
MAGNESIUM – one of the elements making up the earth’s crust, the compounds of which, when dissolved in water, make the water hard. The presence of magnesium in water is a factor contributing to the formation of scale and insoluble soap curds.
MAGNETITE – the black, magnetic, protective film of Fe3O4 normally present on surfaces of steel.
MAKEUP – treated or untreated water introduced into a system to replace any water losses, whether from evaporation, bleed or blowdown, or leaks.
MANHOLE – opening in a boiler or tank that permits a person to crawl through for internal inspection.
MECHANICAL DRAFT COOLING TOWER – cooling tower in which air is constantly being moved over water falling through the tower by fans located on the tower that either induce or force a draft through the tower.
MEMBRANE – a barrier, usually thin, that only permits passage of particulates up to a certain size or of specific nature.
METABOLIC – undergoing or pertaining to a change in state.
METABOLIZE – to convert food, such as organic matter, to cellular matter and gaseous byproducts by a biological process.
MICROBIOCIDE – a chemical toxic to microorganisms.
MICROORGANISM – organisms whose cells cannot be seen with the naked eye. In water treatment, it usually refers to organisms that grow in a cooling tower environment (ex: algae, bacteria, fungi).
MICROMHO – basic unit of electrical conductance (µmho). Equivalent to a microSieman (uS).
MIL – measure of thickness or depth equal to 1/1,000 of an inch. Term used in water treatment to express degree of metal loss due to corrosion per unit of time, in mils per year.
MILD STEEL – carbon steel having a maximum carbon content of approximately 0.25%.
MILL SCALE – matter formed on iron or steel in the process of production. Consists mainly of magnetic iron oxide.
MINERAL – a term applied to inorganic substances, such as rocks and similar matter found in the earth’s strata, as opposed to organic substances, such as plant and animal matter. Minerals normally have a definite chemical composition and crystal structure. The term is also applied to matter derived from minerals, such as the inorganic ions found in water.
Mn – chemical symbol for manganese.
MOLECULE – the smallest unit of matter retaining properties of a compound.
MOLYBDATE – (MoO4) often used synonymously with molybdenum (Mo+6).
MOLYBDENUM – (Mo+6) filming type of corrosion inhibitor that forms a passivating film on the anode of a corrosion cell.
MONOMER – a single reactive molecule capable of combining with another like itself or another different monomer to form a polymer.
MONOMOLECULAR – a film that is one molecule thick.
MORPHOLINE – chemical treatment utilized to neutralize carbonic acid in a condensate return portion of steam boiler system.
MPY – abbreviation for mils per year. Used to express the rate of corrosion.
MUD DRUM – lower drum on a water tube boiler where insoluble sludge collects.

NATURAL DRAFT COOLING TOWER – tower in which the air movement through the tower is dependent only upon atmospheric conditions.
NEGATIVE CHARGE – the electrical charge of an electrode or ion in solution, due to the presence of an excess of electrons.
NEUTRAL – in electrical systems, the term used to indicate neither an excess nor a lack of electrons; a condition of balance between positive and negative charges. In chemistry, the term used to indicate a balance between acids and bases; the neutral point of the pH scale is 7.0 indicating the presence of equal numbers of free hydrogen (acidic) and hydroxyl (basic) ions.
NEUTRALIZATION – in general, the addition of either an acid or a base to a solution. The use of alkaline or basic materials to neutralize the acidity of some waters is a common practice in water conditioning.
NEUTRALIZING AMINE – a class of inhibitors that neutralizes carbonic acid by elevating the pH of condensate water from an acid to an alkaline state.
NITRATE – a nitrogen compound with the formula NO3-.
NITRIFYING BACTERIA – bacteria that oxidize ammonia and nitrites to nitrates.
NITRITE – a nitrogen compound with the formula NO22-. Also an anodic inhibitor that induces metal to form its own impervious film at the anode site in a corrosion cell.
NITROGEN BLANKET – a covering of nitrogen gas over water usually in a closed environment such as a tank or boiler. Used to prevent contact of oxygen with water.
NON-FERROUS – metal that does not contain any iron (Fe), such as copper, brass, zinc, aluminum.
NON-OXIDIZING BIOCIDE – class of biocide that functions to kill microorganisms by absorbing into the microorganisms.
NOZZLES – water spouts in the distribution decking of a cooling tower that break up the returning water into droplets and distribute them uniformly over the top of the fill.
NTA – abbreviation for nitrilotriacetic acid, a chelating agent.

O2 – chemical symbol for oxygen.
OFF LINE – term used to denote a system that is in short or long-term lay-up.
OHM – a unit of resistance to the passage of electric current.
OH-ALKALINITY – a measurement of hydroxide anions present in water. See P-ALKALINITY.
ONCE THROUGH COOLING SYSTEM – any system in which water is only used once and then put to drain.
OPEN FEEDWATER HEATER – tank in which feedwater is heated by steam, but where the pressure does not go above atmospheric pressure.
OPERATING PRESSURE – the range of pressure, usually expressed in pounds per square inch, over which a water conditioning device or water system is designed to function.
ORGANICS – carbon containing compounds, generally from vegetation or non-mineral origin.
ORGANO-TIN – non-oxidizing “heavy metal” inorganic biocide used for the control of microorganisms in system water.
ORTHOPHOSPHATE – (1) Internal chemical treatment that functions as an anodic inhibitor or antiscalant; (2) A form of phosphate resulting from reversion of polyphosphate.
OSMOSIS – process where water on one side of a membrane tries to pass through the membrane to dilute a salt solution on the other side in an attempt to equalize the concentration of salt on both sides.
OXIDATION – a chemical process in which electrons are removed from an atom, ion, or compound. The addition of oxygen is a specific form of oxidation. Combustion is an extremely rapid form of oxidation, while the rusting of iron is a slow form.
OXIDE – a compound composed of metal and oxygen.
OXIDIZING AGENT – substance that can take electrons from an atom or metal.
OXYGEN – an element occurring free as a colorless, tasteless, odorless gas.
OXYGEN ATTACK – corrosion caused by oxygen.

P-ALKALINITY – water in which hydroxyl ions (alkaline) predominate, causing the pH of system water to be above 8.2. Also referred to as caustic, OH, or carbonate alkalinity.
P-ALKALINITY TEST – reveals all OH-Alkalinity ions and half of the carbonate ions in a water sample.
PACKAGED BOILER – a shop-assembled steam boiler generator with necessary auxiliary equipment, complete and ready to use.
PACKING – slats, baffling, or corrugated fill found inside the casing of a cooling tower.
PARAMETERS – two figures indicating an upper and lower limit.
PARTICULATE MATTER – any matter, exclusive of gases, existing in a non-liquid state in water.
PARTITION – an interior wall subdividing the tower into cells or into separate fan plenum areas.
PARTS PER MILLION – (ppm) a common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of a dissolved or suspended constituent, per million parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit.
PASSIVATION – the transformation of a metallic surface to a state in which it does not readily oxidize. Usually accomplished by forming a protective film on the metal surface.
PEARLITE – product that results when slowly cooled steel transforms at about 1,328°F. It consists of alternate layers of iron and iron carbide.
pH – a logarithmic measurement of the concentration of hydrogen ions in water. pH is a number between 0 and 14, denoting various degrees of acidity and alkalinity. Neutral water has a pH of 7. Values below 7 and approaching 0 are increasingly acid while values of 7 to 14 are increasingly alkaline.
PHASE – one of the states of matter: liquid, gas, or solid.
PHOSPHATE – chemical used in treatment of boilers that aids in the prevention of scale type deposits by precipitating calcium hardness as a soft sludge when in an alkaline environment.
PHOSPHONATE – an organic phosphate compound that serves as: (1) A cathodic corrosion inhibitor for ferrous metal, (2) A deposit control agent used in cooling and boiler waters
PITTING – term that describes localized attack on metal surface. Results in crater-like indentations in metal.
PITTING FACTOR – ratio of a pit to the average depth of metal penetration.
PLAIN CARBON STEEL – (ordinary steel) steel containing carbon up to about 2% and only residual quantities of other elements except those added for deoxidation.
PLANKTON – minute animal and plant life found in water.
PLANKTONIC – floating or swimming in water.
PLATE-AND-FRAME HEAT EXCHANGER – an exchanger that consists of a stack of thin plates supported in a frame. The plates are typically corrugated and made of stainless steel. The two fluids flow along opposite sides on each plate.
PO4 – chemical symbol for phosphate.
POLARIZATION – extent of potential change in volts, caused by net flow of current to or from an electrode. When there is no difference in potential between the anode and cathode, corrosion ceases and the metal is said to be in a passive state.
POLYACRYLATE – synthetic polymer formed from monomers. Used as a boiler and cooling water dispersing agent.
POLYELECTROLYTE – a high molecular weight water soluble polymer with high charge density or multi-charged ions.
POLYMER – synthetic chemicals with long-chain molecules or repeating units.
POLYMERIZATION – the act of reacting monomers to form a long chain polymer.
POROSITY – the degree of openness or a sponge-like quality.
POSITIVE CHARGE – the electrical potential acquired by an atom that has lost one or more electrons.
POTABLE WATER – water that meets drinking water quality standards.
PPB – stands for parts per billion.
PPM – stands for parts per million.
PRECIPITATE – matter that has separated out of solution as a result of chemical reaction or physical change.
PRECIPITATING PROGRAM – a treatment program that results in precipitation from solution of scale-forming contaminants in the form of non-adhering sludge.
PRESSURE DIFFERENTIAL – the difference in pressure between two points in a system due to the differences in elevation and/or pressure drop due to flow.
PRESSURE DROP – static pressure or amount of resistance in air or liquid caused by system piping or obstructions in system fabrication.
PRESSURE GAUGE – measurement of pressure above atmospheric.
PRESSURE VESSEL – a closed vessel or container designed to confine a fluid at a pressure above atmospheric.
PRETREATMENT – any process or procedure that removes or reduces solids or gases from water before it enters the system.
PRIMING – spasmodic action resulting in spouting or surging of boiler water into a steam header or outlet. Most often caused by a sudden increase in load or drop in pressure.
PROCESS STEAM – steam used to heat or operate some manufacturing process.
PROCESS WATER – water used in a product or in the manufacture of a product.
PUMPING HEAD – energy required to raise water and overcome friction losses inherent in fabrication of the system.

RADIANT HEAT – heat supplied by radiation without the necessity of some medium for transmission (ex: heat from the sun or fire).
RANGE – numerical difference between the water temperature entering the cooling tower at the top and the cold water leaving the basin or sump at the bottom of the tower, also called the temperature differential or ∆T.
RATED TONNAGE – thermal parameters for which a cooling tower was designed.
RAW WATER – natural water as it comes from the environment or municipal water treatment plant.
REAGENT – any substance that, from its capacity for certain reactions, is used in detecting, examining, or measuring other substances.
RECEIVER – tank or reservoir into which steam condensate flows and makeup water are introduced in a boiler system.
RECIRCULATING RATE – (RR) flow rate of cooling water in gallons per minute (GPM) maintained by the recirculating pumps.
RECIRCULATION – a phenomenon where hot, humid exhaust air is forced downward and back into the cooling tower, mixing with the cool fresh inlet air and lowering its ability to provide cooling through evaporation, usually due to design or placement problems. This raises the wet bulb temperature of the entering air above that of the ambient air and greatly reduces tower performance.
REFRACTORY – brickwork or castable material used on boilers to protect metal surfaces against heat.
REFRIGERATION TON – a common measure of cooling capacity used to rate heat rejection equipment, such as cooling towers and chillers. One refrigeration ton is the amount of heat absorbed by one ton (2,000 lbs) of ice causing it to melt completely by the end of one day (24 hrs) which is 12,000 BTUs.
REGENERANT – a chemical used to restore the ion exchange resin back to its desired form.
REGENERATION – process by which an ion exchanger is restored to its operative form. Water softener regeneration involves four steps: backwash, brining, slow rinse, and fast rinse.
REHEAT – returning partially expanded steam to a boiler so additional heat is added before the steam passes through the final stages of a turbine.
RELATIVE HUMIDITY – (RH) ratio of water vapor pressure in the air to the saturated vapor pressure at the same temperature, usually expressed as a percentage. Also the number of pounds of water carried by one pound of dry air.
RESIDUAL – the amount of a specific material remaining in the water following a water treatment process. May refer to material remaining as a result of incomplete removal or to material meant to remain in the treated water.
RESISTANCE – the property of opposing the flow of electric current.
RETURN – the warm water returned to the top of a cooling tower.
REVERSE OSMOSIS – an external treatment process in which raw makeup water, under pressure, passes through a membrane and in the process dissolved solids are removed. In reverse osmosis systems, a small portion of the water flowing into the system is wasted to drain as the mineral content becomes concentrated while a larger portion of the water passes through the membrane and is free of almost all dissolved solids.
RINSE – step in regeneration of an ion exchanger.
RISER – (1) The vertical section of piping that carries hot water to the top of the cooling tower; (2) The tubes in a water tube boiler in which steam is generated which makes the steam and water flow upward, or rise, in the tube.
RO – abbreviation for reverse osmosis.
RUST – a corrosion product consisting of hydrated oxides of iron.
RYZNAR STABILITY INDEX – an index to determine the scaling and corrosion tendencies of a water, based on the conductivity, calcium, total alkalinity, pH, and temperature of the water.

SATURATED – the maximum amount of a substance that can be put into a solution.
SATURATED STEAM – steam that is saturated with heat at a particular temperature and pressure.
SCALE – a hard, adherent, crystalline layer or layers. By analysis, usually contains well over 50% calcium and magnesium. May also contain significant amounts of silica compounds.
SCALE INHIBITOR – term broadly used when referring to any treatment that reacts with calcium or magnesium ions, preventing them from depositing as scale.
SEDIMENTATION – gravitational settling of solid particles in a liquid.
SENSIBLE HEAT – the heat you can feel. The heat required to change the temperature of the air or water. Hot water gives up a portion of its heat to the colder air by the heat flowing downhill from hot to cold.
SETTLEABLE MATTER – matter that will settle out of solution by gravity under low-flow conditions.
SEQUESTRANT – term that describes any chemical that forms a stable, water-soluble complex.
SHELL-AND-TUBE HEAT EXCHANGERS – the most widely used form of heat exchanger, in which a bundle of hollow tubes is held within a cylindrical shell. One fluid passes through the inside of the tubes housed in the shell, while the second fluid passes through the inside of the shell on the outside of the tubes.
SHOCK FEED – introduction of a large quantity of chemical treatment into system water within a very short period of time. Usually used to describe feeding of biocide into tower cooling system.
SHOT FEED – chemical feed system in which water flow, from high to low pressure side, forces chemicals from a feed tank, called a shot feeder or pot feeder, into the system.
SIGHT GLASS – glass tube mounted on the outside of a boiler or water tank indicating the water level within the boiler or tank.
SILICA – element found in water that is dissolved sand. It can form a highly insulating scale on heat exchange surfaces.
SiO2 – chemical symbol for silica.
SLATS – thin strips of wood or plastic suspended from frames inside a cooling tower that help break up the falling water into fine droplets for better release of heat.
SLIME – a soft, sticky, mucus-like substance originating from bacterial growth. On heat exchange surfaces, slime is four times more insulating than calcium carbonate scale of equal thickness.
SLIMICIDE – another term for biocide.
SLUDGE – matter in solution or matter that collects at the bottom of the boiler drum, typically as the result of precipitation of dissolved solids in the water.
SLUDGE CONDITIONER – natural or synthetic treatment that aids in preventing coagulation of system water particulates into a large floc or mass.
SLUG DOSE – adding a treatment product to achieve a target concentration based on the entire system volume, typically used when adding non-oxidizing biocides.
SO3 – chemical symbol for sulfite, a common boiler water oxygen scavenger.
SODIUM SILICATE – anodic corrosion inhibitor that hydrolyzes in water to form negatively charged colloidal particles, which migrate to the anodic site of a corrosion cell.
SODIUM SULFATE – byproduct of reaction between sodium sulfite and dissolved oxygen.
SODIUM SULFITE – compound used to aid in reducing dissolved oxygen in steam boiler system by combining with dissolved oxygen to form sodium sulfate.
SOFTENER – external treatment process in which calcium and magnesium (hardness) are removed and replaced with sodium through the process of cation exchange.
SOFT WATER – water that contains little or no calcium or magnesium.
SOFT ROT – decay developing under very wet conditions in the outer wood layers, caused by cellulose-destroying microfungi that attack the secondary cell walls and not the inter-cellular layer.
SOLUBILIZING PROGRAM – a deposit control program in which deposit forming cations are complexed (tied up), held in solution, and dispersed in colloidal form in system water.
SOOT – fine deposits, consisting primarily of carbon, that are a result of incomplete combustion. Soot insulates the boiler tubes, resulting in high stack temperatures.
SPRAY NOZZLE – device used in a distribution system to break up the flow of circulating water into droplets and effect uniform spreading of water over the wetted area of the tower.
SPECIFIC GRAVITY – ratio of the weight of a given volume of a substance to the weight of an equal volume of water at a fixed temperature.
SPLASH PACKING – type of cooling tower fill consisting of slats arranged so water falling through the tower is broken up into small droplets, thus achieving better contact with air.
SPORE – a cell in a resistant envelope, capable of developing into a normal organism.
SPRAY POND – system in which hot water in a cooling system is pumped to a large pond or small lake, sprayed into the atmosphere through nozzles, and cooled by natural evaporation.
SS – chemical symbol for suspended solids.
STABLE WATER – water that is neither scale forming nor corrosive.
STAINLESS STEEL – any of several steels containing 12-30% chromium as the principal alloying element; the steels usually exhibit passivity in aqueous environments.
STANDARD AIR – has a density of 0.075 lbs/cu. ft., which is air at 68°F DBT, 50% RH, and a barometric pressure of 29.92 inches mercury (Hg) (and substantially equivalent to 70°F dry air).
STANDBY – period during which system or equipment serves as a back-up.
STATIC – an ion exchange reaction occurring with a volume of liquid in contact with a volume of resin.
STEAM BLANKET – a covering of steam over water.
STEAM BOILER – any device designed for the production of steam under pressure.
STEAM DRUM – the upper drum of a water tube boiler where steam is produced and withdrawn.
STEAM, DRY SATURATED – steam at the saturation temperature corresponding to the pressure and containing no water is suspension.
STEAM GENERATOR – any device designed for the rapid production of steam under pressure - see STEAM BOILER.
STEAM HEADER – large pipe, usually located on top of the boiler, through which steam exits a boiler. May also refer to a large manifold where steam headers from several boilers dump steam in and one or more steam lines leave and go out to the equipment being heated by the steam.
STEAM TRAP – a device for bleeding condensate out of a steam line without allowing the steam to escape.
STEAM PURITY – measurement that expresses the amount of contamination, either organic or inorganic, contained in steam.
STEAM QUALITY – the ratio of the weight of vapor to total weight of the steam water mixture.
STEAM, WET SATURATED – steam containing particles.
STRAINER – a screen to remove matter that would otherwise cause plugging or deposits.
STRESS-CORROSION CRACKING – failure by cracking under the combined action of a specific corrosive and stress, either external (applied) stress or internal (residual) stress. Cracking may be either intergranular or transgranular, depending on the metal and the corrosive medium.
SUCTION SCREEN – screen over the water sump or the pump suction pit on a tower cold water basin; prevents debris from entering the pump and piping system.
SULFATE-REDUCING BACTERIA – bacteria that assimilate oxygen from sulfate compounds, reducing them to sulfide.
SULFITE TEST – test performed on boiler system water to determine the amount of sodium sulfite present. Results expressed in ppm. When sulfite residual is within the prescribed rate, usually 30-60 ppm, it is assumed no dissolved oxygen is present and therefore pitting corrosion is under control.
SUMP – depressed section of the cold water collecting basin where the cooled water is returned to the heat source, such as condensers, compressors, or process water equipment.
SUPER CRITICAL BOILER – boiler operating at a pressure higher than the critical pressure, 3,203.6 psig. You do not want to treat boilers that are above 300 psig.
SUPER HEAT – the number of degrees Fahrenheit of steam above the temperature of saturated steam at some specified pressure.
SUPER HEATER – tubes within a boiler that saturated steam passes through after leaving a boiler and where steam absorbs additional heat.
SUPER SATURATED – to contain more in solution than normal for a given temperature.
SUPPLY HEADER – portion of the water supply system from which the riser or inlet connection receives the circulating water flow.
SUPPORT MEDIA – a graded particle size, high-density material, such as gravel, anthracite, quartz, etc, used to support the resin bed.
SURFACE TENSION – the resultant attractive forces on molecules at the surface of a liquid, exerted by molecules within the liquid, that tends to make the surface contract to the smallest possible area.
SURFACE WATER – water that has a short contact with the earth’s surface, collecting in streams, rivers, lakes, and reservoirs.
SURFACTANT – chemical that alters surface and interfacial tension.
SUSPENDED MATTER – (1) Finely dispersed particles of impurities in water, including industrial waste, silt, and organic substances; (2) Mineral salts (hardness) that have precipitated out of solution due to heat or other influences.
SUSPENDED SOLIDS – undissolved solid particles that are suspended in water.
SYMBIOSIS – relationship between a microorganism and a host that is beneficial to both.
SYNERGISM – (1) A cooperative effort between two or more species of bacteria resulting in something the individual species could not accomplish alone; (2) Blending together of two or more chemicals so the total effect is greater than the sum of the single effects taken separately.

TDS – chemical symbol for total dissolved solids.
TEMPERATURE DROP – (∆T) (1) The difference between the temperature of hot return water to a cooling tower and the cooled supply water from the basin; (2) The temperature difference between the inlet and outlet of a heat exchanger. Also called Temperature Differential.
THERMAL SHOCK – a stress strain condition set up by a sudden change in temperature.
THRESHOLD TREATMENT – control of scale-type deposits by feeding of a sub-stoichiometric dosage of treatment to system water.
TITRATE – determining the amount of a substance in solution by adding a measured amount of another substance to produce a desired reaction or end point.
TON – term used to express capacity of size of a cooling system. Equal to 12,000 Btu per hour of heat rejection capacity.
TONNAGE – term used to indicate rated capacity of a cooling system.
TOTAL CHLORINE RESIDUAL – total amount of chlorine present, without regard to type.
TOTAL DISSOLVED SOLIDS – term indicating the total amount of dissolved solids present in a water sample. Usually expressed as TDS in parts per million. The weight of solids per unit volume of water that are in true solution, usually determined by the evaporation of a measured volume of filtered water and the determination of the residual weight. A term used to describe the conductivity as related to the concentration of ions capable of carrying electrical current.
TOWER CELL – one complete unit of a cooling tower consisting of one distribution system, normally one set of mechanical equipment, and partition walls. Each cell can be designed to operate independently of its neighbors and receive an equal share of the total water volume if required for the flexibility of the system.
TOWER CIRCULATING PUMP – pump that recirculates water to and from the cooling tower.
TSS - chemical symbol for total suspended solids.
TUBERCULATION – a hard, dense, scab-like deposit of metal oxide on a metal surface.
TUBE RE-ROLLING – required to stop a leak when one occurs at the tube-to-tube sheet or drum attachment.
TUBE SHEET – area in a boiler or heat exchanger to which tubes are affixed or fabricated.
TURBIDITY – a suspension of very fine colloidal size particulates that obscures light rays, but requires many days for sedimentation due to the small particulate size.
TURBINE – rotary device powered by boiler steam that drives some other rotating piece of equipment.

µMHO – abbreviation of micromho, the unit of measurement for conductivity.
UNDER DEPOSIT CORROSION – corrosion that takes place under any type of deposit due to the differential aeration or temperature differential.
UNIFORM THINNING – type of corrosion in which metal is uniformly removed and thinned. Generally associated with metal exposed to low pH or acid solution.
USDA – abbreviation for United States Department of Agriculture.

VALENCE – the number of positive or negative charges on an ion.
VOLATILE AMINE – treatment used to aid in control of corrosion in the condensate system of a boiler.

WATER COLUMN – a metal vessel installed on the outside of a boiler shell or drum at the normal operating water level to help an operator determine the water level in the boiler.
WATER-FORMED DEPOSIT – any accumulation of insoluble material derived from water or formed by the reaction of water upon surfaces in contact with water (ex: scale, sludge, corrosion, byproducts, or biological deposits).
WATER HAMMER – banging caused by steam and water mixing in the steam line.
WATER TUBE BOILER – boiler in which water is on the inside of the boiler tubes and flame and gases are on the outside.
WET BULB – the temperature of saturated air. At 100% humidity the wet bulb temperature equals the dry bulb reading.
WET BULB TEMPERATURE – (WBT) temperature indicated by a psychrometer. Also known as the thermodynamic wet bulb temperature or the temperature of adiabatic saturation. Measured in °F.
WET/DRY TOWER – a wet (evaporative) cooling tower in combination with a dry (non-evaporative) heat exchanger system, used to reduce or abate cooling tower fog during cold weather by modifying the tower exhaust air condition.
WET LAY-UP – period when system or equipment is non-operational and left full or partially full of water.
WET STEAM – steam containing moisture or water.
WINDAGE – water droplets that are entrained in the air-stream as it passes through the tower. Water entrained is carried out of the tower and lost to the atmosphere. Also called drift.
WINTERIZATION – modification of one or more cells to operate under freezing ambient temperatures. Consists of installing steam or electrical heating coils in the basin, an additional water distribution system below the fill packing to by-pass going through the decks, together with necessary valving, and a fan reversal switch, if required, to keep heat in the tower if water cannot by-pass fill to help melt ice formation.

ZEOLITE – a mineral composed of hydrated silicates of aluminum and sodium or calcium. A naturally occurring ion exchange media that can be used to remove hardness, iron, and other dissolved contaiminants from water.
ZEOLITE SOFTENER – a term loosely used to designate a sodium regenerated ion exchange softener.
ZINC – a non-ferrous metal.