Glossary of Terms


TermDefinition
AAAtomic Absorption spectroscopy
AAMI Grade WaterWater meeting quality standards established by the Association for the Advancement of Medical Instrumentation and used mainly for hemodialysis systems
ABSalkylbenzene sulfonate
Absolute Filter RatingFilter rating meaning that 99.9 percent of the particles larger than a specified micron rating will be trapped on or within the filter. Standard test procedures are listed in the ANSI/NSF standards for particulate and cysts reduction by drinking water treatment units, should be used to determine and substantiate absolute filter ratings.
Absolute PressureThe pressure above a perfect vacuum. It is expressed as psia (pounds per square inch absolute)
Absorbed DoseThe amount of a chemical that enters the body of exposed organism.
AbsorptionThe process of one substance actually penetrating into the structure of another substance. This is different from adsorption in which one substance adheres to the surface of another.
Absorption FactorThe fraction of a chemical making contact with an organism that is absorbed by the organism.
Acceptable Daily Intake (ADI)Estimate of the largest amount of chemical to which a person can be exposed on a daily basis that is not anticipated to result in adverse effects.
Accessible EquipmentWater treatment equipment that when installed and operating is exposable and available for proper and thorough cleaning and inspection using only simple tools such as a screwdriver, pliers, or an open-end wrench. Equipment which is easily available for cleaning and inspection without having to use any tools at all is often referred to as readily accessible equipment
Accumulation TestA pressure test used to ensure that the safety valve has sufficient relieving capacity to vent all of the excess steam that the boiler can produce.
Acid DewpointThe temperature at which acidic vapors begin to condense out of the flue gases.
ActuatorA device that receives a control signal from a controller and converts the signal into a proportional movement of the valve.
AdsorptionAdsorption is the binding of a molecule to a surface (solid or liquid) by non-specific physical forces. For example, the removal of free chlorine and chloramines by activated carbon is through the mechanism of adsorption.
After-Treatment:The water treatment processes that occur during or after steam generation.
Air Pollutant:An airborne substance that produces an adverse effect on humans, animals, vegetation, or materials.
Air-To-Fuel RatioThe ratio of combustion air to fuel. Though not typically expressed as a ratio, it is a reference to the need for proper balance between the relative amounts of combustion air and fuel being delivered to the furnace at any given firing rate.
AlgaeA group of single-celled plants which includes both seawater and freshwater varieties.
AlkalinityA measurement of the quantity of chemicals present in water, which can neutralize acids. These include carbon dioxide, bicarbonate, carbonate, and hydroxides.
Aluminum SulfateAn aluminum salt commonly used as a flocculent by municipal water treatment facilities.
AmineA chemical that prevents corrosion in a condensate and steam piping.
AmphotericA substance, such as aluminum, capable of acting as either an acid or base.
Analog SignalA continuous signal used in the ongoing control of a continuous process. For example analog signals are used to continuously control the liquid level in a tank, the temperature of material flowing from a heat exchanger etc.
AnionsA negatively charged ion
AnnunciatorAn audible alarm that is created electrically or electronically.
Ash Fusion TemperatureThe temperature at which ash begins to become molten.
Anthracite CoalA geologically older coal that contains a high precentage of fixed carbon and a low precentage of volatiles. Anthracite is also known as hard coal.
Ash HopperLarge receptacle used to store ashes until they can be disposed of.
ASMECode written by ASME International (American Society of Mechanical Engineers) that governs and controls the types of material, methods of construction and procedures used in the installation of boilers.
“A” Style Watertube BoilerA watertube boiler design with a top steam and water drum and two smaller bottom mud drums.
Atmospheric Pressure:The force exerted by the weight of the atmosphere bearing on the Earth’s surface.
AtomizationThe process of breaking a liquid fuel stream into a mist of tiny droplets.
Back-SeatingThe situation where a slow-opening valve such as a gate or globe valve is fully opened until it stops.
BacteriaBacteria are single cell micro-organisms capable of replicating on their own. They can be divided into two broad categories, aerobic (requiring oxygen) and anaerobic (not requiring oxygen). Bacteria can live in a very broad range of habitats. Some, for example pseudomonads, can thrive in environments containing a very low level of nutrients. These bacteria are frequently slime producers and are a major problem in water treatment systems. Other bacteria, which adhere to surfaces, secrete a gelatinous material that serves to protect the bacteria from chemical disinfectants. This combination of bacteria and their protective coating is sometimes referred to as biofilm. The concentration of bacteria in water is commonly given in terms of colony forming units (cfu) per mL. A colony forming unit is viable bacterium able to replicate to form a whole colony when incubated in each environment.
Badge PlateA data plate attached to a boiler.
BaffleA metal or refractory-covered panel that directs the flow of gases of combustion for maximum boiler heating surface contact.
BagA protruding bubble or bulge in the steel plate of a boiler.
Ball Check ValveAn automatic self-closing gauge glass valve.
Ball ValveA quick-acting, two position shutoff valve.
Banking A FireThe process of greatly slowing the burning of coal or some other solid fuel.
Barometric DamperA free swinging adjustable balanced damper used on smaller boilers to automatically limit the amount of air pulled through the combustion chamber.
BatteryA group of boilers that feed steam into the same steam header.
BellowsA flexible device that expands and contracts with changes in pressure.
Bent-Tube Watertube BoilerA boiler design in which the tubes are bent to some degree.
Bituminous CoalA geologically younger coal that contains a high precentage of volatiles and a low precentage of fixed carbon. Bituminous coal is also known as soft coal.
Bended Fuel OilA mixture of distillate oils and residual oils that may contain some crude oil.
BlisterA lamination of steel plate or tube surfaces or where the steel plate splits into layers.
BlowbackThe drop in pressure in the boiler that occurs after the safety valve has opened.
BlowdownThe amount of pressure in a pressure vessel that must be reduced before a safety valve reseats. Removal of impurities from the boiler water by draining some of the water.
Boiler Heating SurfaceAny part of the boiler metal that has hot gases of combustion on one side and water on the other.
Boiler Horsepower (BHP)The energy required for the evaporation of 34.5 lb of water at 212°F into steam at atmospheric pressure and at 212°F in 1 hr.
Boiler LoadThe amount of steam being produced by a boiler.
Boiler MasterA controller that determines the appropriate quantities of fuel and air that need to be provided to a boiler’s combustion equipment in order to produce the required quantity of steam.
Boilers in BatteryTwo or more boilers connected to a common steam header.
Boiler Thermal EfficiencyThe percentage of the heat liberated that is transferred into the boiler water.
Boiler VentA section of steel pipe about 1/2″ to 1″ ID connected to the top of a boiler. The boiler vent allows air to be removed from the boiler when filling and when heating. It also allows air to be drawn in when steam in the boiler collapses into vacuum conditions during cool-down, or when draining the boiler.
Boil-Out ProcedureThe process of removing oily residues from a boiler by adding chemicals to the boiler water and boiling the mixture for a period of time.
Bottom BlowdownThe process of periodically draining part of the boiler water to remove heavy sludge that settles to the bottom of the boiler.
Bourdon TubeThe tube inside a mechanical pressure gauge. It is bronze or stainless steel tube bent into a question mark shape and flattened into an elliptical shape.
Branch LineThe piping that takes steam from the steam mains to individual pieces of steam using equipment.
BreechingThe ductwork that carries cooled flue gases from the exit of the boiler to the stack.
Bridge WallA firebrick wall built across a boiler furnace.
BrineA Solution of salt and water.
Bristish Thermal Unit (BTU)The amount of heat necessary to raise the temperature of 1lb of water by 1°F.
Bubbler ControlA set of components that use a small flow of compressed air or another gas to detect the level of liquid in a vessel such as a storage tank.
BuckstayA metal brace used to attach a wall to steel framework that supports the wall.
Bunker OilOne of the heavy oils formed as crude oil is stabilized after the lighter components have been distilled off.
Butterfly Valvea valve that consists of a circular disc that is rotated by the valve stem so that the disc is parallel to the flow through the valve, perpendicular to the flow or somewhere in between.
Bypass DamperControls the air temperature in air heaters to prevent corrosion.
Bypass LineA pipeline that passes around a control, heater or steam trap. Used so that a plant can operate while equipment is serviced or repaired.
CationsA positively charged ion
CalibrateAdjusting an instrument to optimize its accuracy.
CalorieThe amount of heat necessary to raise the temperature of 1 g of water by 1°c
CalorimeterA laboratory instrument used to measure the heat content of a substance, such as a sample of a fuel to be used for a boiler.
CapacityThe maximum performance of a devise i.e., condensate flow through a steam trap, steam generation of a boiler or liquid delivery by a pump.
Capillary TubeA long, small-diameter tube, usually of stainless steel or a copper alloy.
CarryoverThe entrainment of small water droplets with steam leaving the boiler.
Cascading ControlA Control scheme in which one process variable is measured and used to set the setpoint of another controller.
CationAn ion that has a postive electrical charge.
Caustic EmbrittlementA problem in which boiler metal becomes brittle and weak because of cracks in the crystalline structure of the metal.
CavitationThe condition caused when a portion of the water or other liquid entering the eye of a pump impeller flashes into steam bubbles.
CellulaseAn enzyme which causes the decomposition of cellulose.
Cellulose AcetateA synthetic polymer derived from naturally occurring cellulose and widely used in the fabrication of membranes. The polymers used for water purification membranes may be diacetate, triacetate or blends of these materials.
Centrifugal PumpA pump in which a rotating impeller throws liquid from its vanes through centrifugal force.
Chain-Grate StokerA stoker in which the grates are composed of thousands of small staggered segments that are interlaced by support bars or rods, forming a heavy chain conveyor.
Check ValveA One-way flow valve for fluids.
CharacterizationThe relationship between the amount a valve is open and the amount of flow through the valve.
ChelantA chemical that helps keep the hardness in the water dissolved so that it does not crystallize on heating surfaces.
Chemical ConcentrationThe amount of a specific chemical found in a solution, i.e. boiler water, condensate etc.
Chemical EnergyEnergy in the fuel that converts to heat energy during the combustion process.
ChimneyUsed to create draft. Also an outlet to the atmosphere for the gases of combustion.
ChloraminesChemicals used to disinfect municipal water. They are formed by reacting ammonia and free chlorine and may occur naturally when free chlorine combines with ammonia arising from the breakdown of vegetation. Chloramines are strong oxidants that are highly toxic in hemodialysis applications.
Chlorinated HydrocarbonsA group of organic chemicals formed by reacting petroleum derived chemicals with chlorine. Such chemicals include pesticides and herbicides and are frequently potent carcinogens.
ClassifierA spinning set of vanes located at the coal and air outlet from the pulverizer that separates very fine coal dust from larger coal particles.
Class Of FireThe five classes of fires are Class A, started from wood, paper or other combustible materials containing carbon; Class B, started from oil, grease, or flammable liquids; Class C started from electrical devices; Class D started from combustible metals; and Class K, started from grease in commercial cooking equipment.
ClinkerA mass of coal and ash that has fused together during burning.
Clinker GrinderLarge set of steel rollers with heavy teeth that grind ash and clinkers to reduce their size before they enter the ash hoppers.
Closed Feedwater HeaterFeedwater heater in which steam and feedwater do not come into direct contact. Steam is in the shell of the heater while water passes through tubes.
Closed Heat ExchangerA heating unit in which the heating medium and the fluid being heated do not mix but are separated by tube walls or other heating surfaces.
Closed ImpellerAn impeller that has shrouds on both sides of the vanes.
Closed SystemA steam system in which the condensate is recovered and returned to the boiler.
CoagulantA chemical that causes dispersed colloidal particles to become destabilized thereby aiding in their removal during municipal water treatment. Aluminum and iron salts are commonly used for this purpose.
CoagulationA practice common in municipal water treatment in which a chemical (coagulant), most commonly alum, is added to water to destabilize colloidal particles by neutralization of their electrical charges. Coagulation is used, together with flocculation, as a process for colloid removal.
Coal BunkerAn overhead bin where large quantities of coal are stored.
Coal FeederControls the flow of coal entering the pulverizer
Coal GateUsed to control the depth of coal entering the boiler furnace on chain grate stokers.
Coal RamDistributes coal evenly into the center retort on underfeed stokers and forces the coal up to the top where it is burned.
Coal ScaleMeasures and records the amount of coal fed to stoker-fired or pulverized coal-fired boilers.
CodeA regulation or law.
Coefficient of ExpansionThe property of a given material that expresses how much a standard unit of length of the material expands or contracts under a specific change in temperature.
CogenerationThe process of generating electricity and then using the leftover heat from the generating process for heating buildings, providing process heat, or for further electrical generation
Coil Watertube BoilerA boiler design in which the tubes are formed into a continuous coil, with the combustion gases passing through the interior of the coil.
CokingThe separation of heavy carbon-based fractions from the oil, resulting in precipitation of solids that may plug the piping.
ColloidUndissolved, submicron-sized suspended particles that are well dispersed in a solution and will not readily settle out on standing.
Color Wheel Comparator TestA relatively simple test used to determine the quantity of iron in the condensate or makeup water.
Column of WaterWater of some specified depth or height.
Combined-Cycle BoilerAn electric power generating system that uses both a gas turbine-driven generator and a steam turbine-driven generator.
Combustion Air PreheaterA piece of equipment provided to preheat the combustion air to some degree before the combustion air enters the furnace.
Combustion ChamberThe area of a boiler where the burning of fuel occurs.
Combustion EfficiencyThe percentage of the British Thermal Unit (BTU) content of fuel that is liberated as heat by a boiler’s fuel-burning equipment.
CommissioningThe process of inspecting, preparing, and testing each major component of a system prior to operation.
CompactionThe undesirable physical compression of a reverse osmosis or ultrafiltration membrane that results in reduced flux rates. The phenomenon is accelerated at higher temperatures, pressures, and fouling.
Complete CombustionA fire where the fuel is burned with a slight excess of oxygen so that the fuel is completely consumed without forming any smoke, and only a minimal amount of oxygen is left over.
CompressionThe exertion of equal forces from opposite sides of an object that push toward the middle.
ConcentrateIn crossflow filtration, the portion of a feed stream which does not permeate the medium but retains and is increased in the amounts of ions, organics, and suspended particles which are rejected by the medium.
CondensateThe water formed when steam condenses to water.
Condensate PolisherAn ion-exchange water softener similar to a sodium zeolite water softener but with resin that can withstand the high temperatures encountered with condensate.
Condensate PumpUsed to return condensed steam to the open feedwater heater.
Condensate ReceiverA tank or other collection point where condensate is accumulated and saved for reuse.
Condensate Return LineA pipe that carries the condensate and air discharged by the steam traps.
Condensate TankWhere condensed steam (water) is stored before it is delivered back to the open feedwater heater by the condensate pump.
CondensationThe process of a vapor reverting to liquid when the heat is removed.
ConductanceThe quantitive measure of the ability of an electric circuit to allow current flow.
ConductionA method of heat transfer in which heat moves from molecule to molecule.
ConductivityThe ability of an aqueous solution to carry electric current depends on the presence of ions in the solution. Conductivity is a quantitative measure, in which describes this ability. Solutions of inorganic ions are relatively good conductors, whereas solutions of organic molecules are rather poor conductors. Highly purified water is also a poor conductor. Conductivity is expressed in units of Siemen/cm (also known as µs/cm). Conductivity measurements are frequently encountered in monitoring the performance of reverse osmosis equipment. Conductivity is temperature-dependent and should be measured with a temperature-compensated meter. The usual reference temperature is 25°C. Conductivity measurements are sometimes used to estimate total dissolved solids (TDS) in water. While convenient, this practice is imprecise.
Confined SpaceA space that has limited or restricted means for entry and exit has unfavorable natural ventilation such that a dangerous atmosphere could exist inside that does not naturally vent out, and is not intended for continuous employee occupancy.
Continuous BlowdownThe process of continuously draining water from a boiler to control the number of impurities in the remaining water.
ControllerA device that takes an input signal, compares the signal to a setpoint, performs computation, and sends an output signal to a final control element.
Control LoopThe collection of control devices and other components necessary for automatic control of a process or sub-process.
Control ValveA valve used to modulate the flow of fluid.
ConvectionA method of heat transfer that occurs as heat is conveyed by a fluid.
Corresponding PressureThe pressure associated with steam at a given specific temperature.
CorrosionThe loss of metal that occurs in boilers, ductwork, etc. as a result of a chemical or electrochemical attack.
CounterflowThe principle used in heat exchangers where the medium being heated flows in one direction and the medium supplying the heat flows in the opposite direction.
Critical PressureThe pressure at which the density of the water and the density of the steam are the same.
Cross-LimitingThe configuration of boiler combustion controls such that, with an increase or decrease in the firing rate, the combustion conditions never become oxygen deficient.
Cross “T”used on connections on a water column for inspection of steam and water lines to ensure they are clean and clear.
Cycles of ConcentrationThe measure of the concentration of a specific impurity in the boiler water divided by the concentration of the same impurity in the feedwater.
Cyclone SeparatorA Cylindrical device that separates water droplets from steam through centrifugal force.
DamperA device that partially or totally inhibits the flow of air or combustion gases through ductwork.
Data PlateA plate attached to a piece of equipment such as a motor or safety valve that provides important information about the equipment.
DeaeratorAn open heat exchanger that removes dissolved gases from the feedwater going to a boiler.
Decatherm10 Therms or 1,000,000 Btu
DeionizationRemoval of ions from water by exchange with other ions associated with fixed charges on a resin.
DemineralizerA highly efficient ion-exchange process generally used for high-pressure boilers.
DesiccantA drying agent
DesuperheatingRemoving heat from superheated steam to make it suitable for process water.
Diagonal StaysBraces that are installed in a firetube boiler to keep the upper portions of the tube sheets above the tubes from bulging outward due to internal pressure.
Diaphragm ValveA valve that uses a flexible diaphragm as the movable sealing surface.
Differential PressureThe difference between to pressures measured at different points within the same process.
Differential TemperatureThe difference between two temperatures measured at different points within the same process.
Diffusion RingA stationary vane in the pump casing.
Digital SignalAn instantaneous signal used to implement a one-time action. For example, digital signals are used to shift the position of solenoid-operated valves, to detect the position of a level switch.
Dirt PocketThe pipe nipple installed on the bottom of the drip leg that catches rust and weld slag.
Discharge PipingThe piping attached to the outlet side of a component, that carries the outlet flow.
Disc Steam TrapA comparatively small steam trap that uses a flat, round disc as the means of opening and losing the outlet orifice.
DisinfectionDisinfection is the process of killing microorganisms, usually by one of a variety of chemical agents, such as formaldehyde and sodium hypochlorite. Disinfection lowers the number of microorganisms without necessarily killing all those present. Although the total killing of all organisms is virtually impossible, sterilization will reduce the number of organisms to a safe predetermined level. Sterilization can generally only be achieved routinely by heat, gamma irradiation, ethylene oxide, and in certain cases, special filtration. Of these methods, the only filtration is suitable for mass sterilization of water and none is suitable for sterilization of water treatment equipment used in hemodialysis facilities. However, a proprietary chemical disinfectant incorporating peracetic acid as the active ingredient has been qualified as a sterilant, and this agent may be suitable for sterilization of certain water system components.
DisplacementThe volume of fluid forced out of a full container when another body is forced into the container.
DisplacerA long, fairly heavy cylindrical float of small diameter used to measure liquid level in a tank or vessel.
Dissolved GasesGases that have gone into solution in water.
Dissolved SolidsSolid impurities that have gone into solution.
Distillate Fuel OilA fuel produced by distilling crude oil.
Double-Acting PumpA reciprocating pump that moves fluid in both directions of stroke.
Double Block and BleedA valve configuration that consists of two automatic shutoff valves arranged in series, with a vent or bleed valve between them that vents outdoors.
Double-Seated ValveA control valve that has two discs on one stem and two seats in the body.
Double-Suction PumpA Pump with a casing and impeller designed to allow a liquid to flow into both sides (eyes) of the impeller at once.
Downcomer TubesTubes that contain the cooler, descending water.
DraftThe movement of air and/or gases of combustion from a point of higher pressure to a point of lower pressure.
Draft LossThe loss of available draft due to friction and other pressure losses as the flue gases flow through the combustion gas passageways.
Draft SystemConsists of the equipment, controls, and ductwork that deliver air to the boiler furnace area for combustion of the fuel, and then conduct the spent combustion gases to the atmosphere.
Drainable SuperheaterA superheater configured so that condensate in the superheater tubes migrates to a low point from which it can be drained.
Drip LegA downward extension from a steam distribution line or piece of heat exchange equipment where condensate is allowed to drain.
Drum DesuperheaterAn attemperator that diverts part of the super-heated steam through a heat exchanger in the boiler mud drum.
Drum Pressure Control ValveA control valve that is configured so as to maintain constant pressure on the steam drum of a water-tube boiler or the shell of a firetube boiler at all times.
Dryback Scotch Marine BoilerA firetube boiler with a refractory-lined chamber at the rear of the boiler that is used to direct the combustion gases from the flue furnace to the first pass of tubes.
Dry PipeAn upside-down T-shaped pipe connected to the main steam outlet from either a firetube or water-tube boiler that removes entrained droplets of boiler water from the steam.
Dry SheetThe metal that is an extension of the cylindrical shell of a firetube boiler, past the tube sheet. The dry sheet forms the smokebox.
“D” Style Water-Tube BoilerA water-tube boiler with top steam and water drum and a bottom mud drum that are interconnected by banks of tubes that form a “D” shape. The open area of the “D” is for the combustion of the fuel.
D-slide ValveA valve that controls the movement of steam into and out of the steam cylinder in a duplex pump.
DuctilityThe plasticity exhibited by a material under tension loading.
Duplex PumpA steam-driven, reciprocating, positive-displacement, double-acting pump with two steam cylinders and two liquid cylinders.
Duplex StrainersRemove solid particles from the fuel oil in fuel oil systems.
EconomizerA series, or bank, of tubes used to recover heat from the boiler flue gas by using it to heat the boiler feedwater.
EfficiencyThe comparison of energy output to energy input in a piece of equipment or in a system.
Electric BoilerA boiler that has heat produced by electric resistance coils or electrodes.
Electronic Flue Gas AnalyzerA device used to analyze flue gas for temperature, gases, draft, and smoke.
Electrostatic PrecipitatorA device used to separate fly ash particles from the flue gas stream before it goes out the stack.
Emergency PlanA document that details procedures, exit routes, and assembly areas for facility personnel in the event of an emergency.
Emission FactorAn expression of the rate of pollutant production per unit of fuel input.
Empty Bed Contact TimeThe empty bed contact time (EBCT) is used as a measure of how much contact occurs between particles, such as activated carbon, and water as the water flows through a bed of the particles. As the EBCT increases, the time available for the particles to absorb solutes from the water also increases, as does the amount of solute removed from the water during its transit through the bed. EBCT is calculated from EBCT = Vm/Q where Vm is the column of particles in the bed the Q is the volumetric flow rate. A consistent set of units must be used when calculating EBCT with this equation. For example, if Vm is given in ft³ then Q must be expressed in ft³/min for the EBCT to have units of minutes. Values of Q can be converted from other units, such as GPM, to ft/min using the conversion factor.
EndotoxinBacterial lipopolysaccharide, a substance released from the cell walls of gram-negative bacteria when the organism is broken down.
EnthalpyTotal heat in the steam.
EntrainmentThe process where solid or liquid particles are carried along with steam flow.
Equalizing LineA small line used to equalize the temperatures and/or pressures on both sides of a large valve before opening it. This is sometimes called a bypass line.
ErrorThe amount of deviation of a measurement from the setpoint.
Evaporation TestA test that allows a low water condition to occur in the boiler in order to test the low water fuel cutoff switch.
EvaporatorA set of heat exchangers that produces water suitable for boiler use from water that contains large quantities of impurities.
Excess AirThe amount of air added to the combustion process over and above that which is theoretically necessary.
Expansion BendA section of piping, commonly formed in a “U” shape, that provides flexibility for expansion and contraction of the piping with changes in temperature.
Exposed-Tube (Dry-Top) Vertical Boiler:A firetube boiler with fire tubes extending several inches through the steam space at the top before ending at the tube sheet.
External Header Cast Iron SectionalContains cast iron sections individually connected to external manifolds with screwed nipples.
Externally-Fired Firetube BoilerA boiler with a separate furnace area that is usually built of refractory brick.
External TreatmentBoiler water treated before it enters the boiler to remove scale-forming salts, oxygen, and noncondensable gases.
Extractive CEMSA monitoring system that withdraws a sample of the flue gas stream, conditions the sample, analyzes the conditioned sample and then provides a readout of the flue gas condition.
Factor Of EvaporationThe heat added to the water in an actual boiler in Btu/lb and divided by 970.3
FeatheringThe point when a safety valve is about to lift.
Feedback TransmitterA transmitter used to provide confirmation that a valve or damper actuator has made a change as commanded.
FeedwaterA mixture of condensate and makeup water that is provided to the boiler to make steam.
FeedwaterWater entering a purification system or an individual piece of purification equipment, such as an ultrafilter or reverse osmosis system.
Feedwater LineThe piping that carries the feedwater from the feedwater pump to the boilers.
Feedwater PumpA pump that sends the returned condensate and any makeup water into the boiler.
Feedwater SystemConsists of all equipment, controls, and piping that prepare and treat the water for use in the boiler, put the water into the boiler, and maintain a normal, safe amount of water in the boiler.
Field-Assembled BoilerA boiler of large size that cannot be shipped as a completed unit by the manufacturer to the site where it will be placed in service.
Field-Erected BoilerA boiler that must be erected in the field because of its size and complexity.
Filming AmineA chemical that prevents corrosion of condensate piping by providing a protective barrier.
Final ElementThe device that actually causes a change in the process.
FireboxThe part of the boiler where the combustion of fuel takes place.
Firebox BoilerA firetube boiler In which an arch-shaped furnace is surrounded on both sides by a water leg area.
Fired VesselA pressure vessel that includes a burner or combustion equipment of some kind.
Fire ExtinguisherA portable unit used to put out small fires or contain larger fires until the company fire brigade or the fire department arrives.
Fire PointThe lowest temperature at which the vapor given off by a substance will ignite and burn for at least 5 sec when exposed to an open flame.
Firetube BoilerHas heat and gases of combustion passing through tubes that are surrounded by water.
Firing RateThe rate at which fuel is being burned by a burner at any particular time.
First Law Of ThermodynamicsEnergy cannot be created or destroyed but can be changed from one form to another.
FittingsTrim found on the boiler that is used for safety, and/or efficiency.
Fit-upThe process of fitting and rolling the tubes into the drums of a new water-tube boiler.
Fixed CarbonThe burnable remainder of coal left when coal is heated and the volatile matter is driven off.
Flame Failure:A situation where the flame in a furnace fails to light properly or goes out during operation as a result of a problem with the burner-related equipment.
Flame ImpingementA condition where the flame from burning fuel continually strikes the boiler surfaces or refractory brick.
Flame Propagation RateThe rate at which the flame can ignite the incoming air-fuel mixture, in feet per second.
Flame Safeguard SystemThe collection of automatic control devices that ensure safe operation of the combustion equipment.
Flame ScannerA device that proves that the pilot and main burner flames have been established and remain in service.
Flame SensorA device in a flame scanner used to sense the pilot and the main flame in the burner.
FlarebackFlames discharging from the boiler through access doors or ports. Caused by delayed ignition or furnace pressure buildup
FlashbackThe condition where a flame travels upwind and into the burner assembly
Flash EconomizerA heat recovery system used to reclaim the heat from the boiler blowdown water and used in conjunction with the continuous blowdown system.
Flash PointThe lowest temperature at which the vapor given off by a substance will make a flash of flame, but not continue to burn when an open flame is passed over it.
Flash SteamSteam that is instantly produced when very hot water is released to lower pressure and, thus a lower boiling temperature.
Flash TankA pressure vessel in which condensate or other very hot water under high temperature and pressure is allowed to partially flash into steam.
Flat Gauge GlassType of gauge glass used for pressures over 250 PSI.
Flexible JointUsed to allow for expansion and contraction of steam or water lines.
Flexible Tube Watertuber BoilerA boiler design in which the tubes exposed to the combustion gases are sharply bent to provide the maximum possible flexibility.
Float & Thermostatic Steam TrapContains thermostatic bellows or other thermostatic element and also contains a steel ball float connected to a discharge valve by a linkage.
FlocculationA practice common in municipal water treatment in which destabilized colloidal particles are formed into larger particles (flocs), usually by stirring. The floc is removed from the water by settling or filtration. The process may also incorporate the addition of such compounds as synthetic poly-electrolytes, which increases the size of the flocs, thereby making them more easily removed by settling or filtration. The removal of colloids by flocculation is done in combination with coagulation.
FlocculentA substance, used in combination with coagulants, which causes submicroscopic suspended matter (colloids) to aggregate into larger particles that can be removed by settling or filtration.
Flow VelocityThe flow of fluid at any point in a water treatment system may be expressed quantitatively in two ways, either in terms of the volume of fluid passing the point in a given timer or in terms of the velocity with which fluid passed the point. The flow velocity depends on the geometry of the conduit through which the fluid flows and is related to the volumetric flow by V=Q/A Where A is the cross-sectional area of the conduit. As an example, the table below shows the volumetric flow rate as a function of flow velocity in PVC Schedule 80 pipe of different diameters.
Flue Gas RecirculationThe process of reintroducing a stream of the spent flue gases from the breeching or stack back into the combustion air stream.
FluidAny material that can flow from one point to another. Fluids can be liquids or gases.
FluidizationA flowing liquid impinging on a bed of particles imparts some of its momentum to each particle. The imparted momentum is in the direction of the fluid flow. The particles are held to the floor of their container by gravity and to each other by adhesive forces. If the fluid flow is upward through the bed of particles, and if the transfer of momentum from the fluid to the particles is sufficient to overcome both the gravitational and the adhesive forces, the particles become suspended, or fluidized, in the fluid stream.
Fluidized Bed BoilerA boiler in which fuels are burned in a bed of inert materials such as limestone pellets or sand.
FluorideAn ion of hydrofluoric acid which may occur naturally in water supplies or be added by municipal processes for the prevention of dental cavities. Fluoride is considered toxic in the hemodialysis setting and has been implicated with renal bone disease.
Flux RateThe rate per unit of area at which water passes through a semi-permeable membrane, such as those used for ultrafiltration or reverse osmosis.
Fly AshAsh from the combustion of coal or other solid fuels that is carried along with the draft through a boiler furnace and ductwork.
FoamingThe development of froth on the surface of the boiler water.
Foot-PoundA unit of work equal to the movement of a 1-lb object over a distance of 1 ft.
Foot ValveA check valve installed at the bottom of the suction line on a negative suction pump that keeps the suction line primed when the pump shuts down.
Forced CirculationA variation in water-tube boiler design in which boiler water circulation through the tubes is enhanced by a pump.
Forced DraftThe discharge of combustion air from a fan into a furnace to combine with the fuel for combustion.
FoulingThe deposition of insoluble materials, such as bacteria, colloids, oxides, and water-borne debris, on to the surface of a reverse osmosis or ultrafiltration membrane. Fouling is associated with decreased flux rates and may also reduce the rejection rates of reverse osmosis membranes.
FrequencyThe number of cycles of the AC sine wave in one second. Frequency is measured in hertz (Hz) or cycles per second.
Friction HeadThe pressure loss associated with friction in the pump piping and fittings. Converted into the equivalent feed of static head.
Fuel NoxN0x that is formed as a result of the oxidation of nitrogen in the fuel.
Fuel SystemConsists of all the equipment, controls, and piping that deliver the fuel to the boiler combustion equipment and control the combustion process.
Fuel-To-Steam EfficiencyThe percentage of the heat content of the fuel that is transferred into the boiler water.
Fulvic AcidsAcidic substances which are found in humic soils and which may become suspended in water.
Furnace Volume:Amount of space available in a furnace to complete combustion.
Fusible PlugA temperature-sensitive device that causes an audible alarm when exposed to excessive temperature.
Fyrite AnalyzerAn instrument used to measure the percentage of carbon dioxide in the gases of combustion.
GaggingApplication of a clamp-on a safety valve spindle to keep the valve in the full closed position during a hydrostatic test.
GalvanometerUsed to measure small electric currents.
Gas AnalyzerUsed to analyze the gases of combustion to determine combustion efficiency.
Gas CalorimeterUsed to determine the BTU content of natural gas.
Gas CockA manual quick-closing shutoff valve.
Gases Of CombustionGases produced by the combustion process.
Gas Leak DetectorA device used to locate gas leaks in a boiler room.
Gas Mixing ChamberWhere air and gas mix before they enter the furnace in low-pressure gas burners.
Gas Pressure RegulatorUsed to supply gas to the burner at the pressure needed for the combustion of the gas.
Gas Tungsten Arc WeldingA welding process in which a virtually non-consumable tungsten electrode is used to provide the arc for welding.
Gas TurbineA rotating machine used to generate electricity from the flow of hot gases of combustion.
Gate ValveA valve used to stop or start the flow. It has a wedge-like disc that is lowered into or raised out of the path of the fluid that flows through the valve.
Gauge GlassA tubular or flat glass connected to a water column that allows an operator to see the water level in the water column, and thus in the boiler, at a glance.
Gauge Glass Blowdown ValveA valve used to remove any sludge and sediment from gauge glass lines.
Gauge PressureThe pressure above atmospheric pressure. It is expressed as psig.
Gear PumpA rotary positive-displacement pump in which the liquid being pumped fills the open spaces between the teeth of rotating cylindrical gears and the pump housing.
Glauconite SandA mineral which is frequently used in depth filters.
Globe ValveA valve that has a tapered, rounded, or flat disc held horizontally on the stem.
GradeThe size of the pieces of coal
Grains of HardnessAlthough the theoretical hardness of water is the sum of the concentrations of all metallic ions, other than alkali metals, it is commonly expressed as the equivalent concentration of calcium carbonate in grains. Ionic concentrations can be expressed in terms of their combining potential, the number of moles, or their masses in any of several conventions. In the English system, masses are expressed in terms of pounds which contain 7000 grains each. Although considered outdated in most of the world, the US water purification industry continues to express hardness in units of grains/gal expressed as calcium carbonate. Grains/gal expressed as calcium carbonate can be converted to metric units by multiplying the former by 17.1 grains/gal expressed as calcium carbonate can also be converted into mEq/L of a univalent ion, such as sodium (Na+) by multiplying by 0.342. Care must be taken in using these conversion factors to size equipment based on ion exchange principles since the ionic content of the water will depend on the type of ions present as well as their total mass.
GratesThe collection of horizontal or semi-horizontal cast iron or steel components that support a burning mass of solid fuel and allow combustion air to pass through the fuel.
GreensandA dark, coarse, sandy material sometimes used in iron removal.
Gunning MaterialsPlastic refractory materials that are gunned, or sprayed, under pressure onto a surface.
Hammer TestA test performed on the stays inside the boiler to check the integrity of each, relative to the others.
HandholeA small access hole used for looking and reaching into the boiler shell during inspections.
HardnessHardness was originally defined as a measure of the ability of water to precipitate soaps made from fatty carboxylic acids. These soaps precipitated in the presence of calcium and/or magnesium ions. Today hardness is used to describe the total concentration of calcium and magnesium, expressed as mg/L or calcium carbonate. It is generally calculated from the measurement of calcium and magnesium ion present as well as their total mass.
Hazardous MaterialA substance that could cause injury to personnel or damage to the environment.
HeadA vertical column of liquid that, due to its weight, exerts pressure on the bottom and sides of its container.
Heat EnergyKinetic energy caused by molecular motion within a substance.
Heat ExchangerAny piece of equipment that transfers the heat from a heating medium into some other material.
Heating SurfaceThe part of the boiler that has heat and gases of combustion on one side and water on the other.
Heating ValueExpressed in BTU per gallon or per pound. Heating value varies with the type of fuel used.
Heat TransferMovement of heat from one substance to another that can be accomplished by radiation conduction or convection.
Higher Heating ValueThe total heat obtained from the combustion of a specified amount of fuel under perfect combustion conditions, and before subtracting the heat required to evaporate the water vapor formed during the combustion process. Also known as gross heating value.
High-Pressure Steam BoilerA boiler that operates at a steam pressure over 15 psi and over 6 BHP.
High-Temperature Water BoilerA boiler in which the maximum operating temperature of the water may reach temperatures in excess of 250°F and the operating pressure may exceed 160 psig.
Horizontal Return Tubular Boiler (HRT)A firetube boiler consisting of a horizontal shell set above a refractory brick-lined furnace.
Horiztonal Split-Case PumpA pump that has a horizontally split pump casing where the top half of the pump casing can be lifted off for inspection and maintenance without disturbing the shaft, impeller, or bearings.
Horizontal Through StaysBraces that are installed in a firetube boiler to keep the upper portions of the tube sheets above the tubes from bulging outward due to the internal pressure.
Horsepower (HP)A unit of power equal to 33,000 foot-pounds of work done in 1 minute.
Hot Process Water SoftenerA pressure vessel that uses steam to heat makeup water by direct contact and uses a chemical injection to precipitate the hardness out of the water.
Hot Water BoilerA boiler that generates hot water, not steam. The heated water produced by a hot water boiler is usually between approximately 170°F and 190°F
Hot WellA reservoir located at the bottom of a condenser where condensate collects.
Huddling ChamberThe part on a safety valve that increases the area of the safety valve disc, thus increasing the total upward force, causing the valve to pop open.
Huddling RingAn adjustment in a safety valve that controls the degree to which the escaping steam is directed against the safety valve disc.
HydrolysisA Chemical process resulting from reactions with water; frequently used in reference to the breakdown of polymers.
HydrophilicPertaining to a substance which readily absorbs water
HydrophobicPertaining to a substance that does not readily absorb water.
Hydrostatic TestA test in which the boiler is filled with approximately 70°F water and then pressurized to 1 1/2 times its MAWP. Any leaks are exposed by observing water drips.
IgnitionThe initiation of the combustion process.
Ignition ArchThe curved refractory brick arch directly above the location where green coal enters the furnace in a chain-grate stoker-fired boiler.
ImpellerThe rotating element found in a centrifugal pump that converts centrifugal force into pressure:
ImpingementThe condition in which flame continually strikes brickwork or boiler heating surfaces, causing localized overheating and soot deposits. The condition in which steam from a soot blower element directly strikes the tube surfaces in a boiler, causing erosion of the tube metal.
ImplosionAn inward collapse from external pressure.
Incomplete CombustionA fire where the fuel is burned without the proper amount of oxygen, without enough mixing of fuel and oxygen, or at a temperature too low to allow satisfactory reaction of the fuel and oxygen.
Induced DraftThe use of a fan to simulate the effect of a stack by drawing the combustion gases from the furnace and through the flue gas passages.
InjectorA motive fluid pump that uses the velocity of steam to draw water and pump into a boiler.
Inleakage AirAir that leaks into a furnace.
In-line Steam SeparatorA cylindrically shaped vessel that is installed in a steam pipe to remove moisture droplets after the steam has left the boiler.
Input SignalThe flow of control information provided to a control device.
In Situ CEMSA monitoring system that directly measures the concentration of a specific constituent in the stack, without conditioning, and provides a readout of that concentration for the boiler operator.
InstrumentA device that measures, indicates, records, or controls a specific variable condition such as pressure, temperature, level, flow, or pH.
InsulationThe material used to cover hot piping or other hot surfaces to reduce heat losses and prevent thermal burns. Also, the material used to cover cold piping and other cold surfaces to prevent external corrosion due to condensation of moisture from the surrounding air.
IntegratorA calculating device that totalizes the amount of flow over a specified time period.
InterlockThe configuration of control devices such that two or more pieces of equipment cannot be operated independently of each other.
Intermittent PilotA pilot that is lit at the appropriate time to light the main burner and then stays on during the entire period that the burner is on.
Internally Fired Firetube BoilerA boiler with a furnace area surrounded by the pressure vessel.
Internal TreatmentThe addition of chemicals directly into the boiler water to control pitting, scale, and caustic embrittlement.
Interrupted PilotA pilot that is lit at the appropriate time to light the main burner and then extinguished as soon as the main burner is lit.
Inverse SolubilityThe tendency of certain impurities in the water to crystallize and precipitate as the temperature of the boiler water increases.
Inverted Bucket Steam TrapContains an upside-down steel cup, called a bucket, that is attached to a linkage that opens and closes a discharge valve as the cup rises and falls inside the trap.
IonAn atom or molecule with an electrical charge.
Ion ExchangeIon exchange is based on the principle of electroneutrality, that is, charged species are stable only when they exist as balanced pairs of positive and negative charges. Ion exchange resins, the materials used to carry out the process of ion exchange, are particles that contain fixed charges on their surface. To maintain electroneutrality, each of these charges has an ion of equal and opposite charge held to it; these ions are called counter ions. The counterions are mobile and can leave the fixed charge if some other counter ion is available to replace it. The replacement ion must be of the same charge as the initial counter ion in order to maintain electroneutrality. The initial counter ion is established by washing the resin with a concentrated solution of the desired counter ion. For example, the softener resins are cation exchangers containing carboxylic acids on their surfaces. If these resins are washed with strong NaCL solutions, the predominant cation in solution is Na+ and it will become the counter ion. In use, the perfusing water will provide competing  counter ions, such as Ca2+, because of the preference of carboxylic acids for Ca2+ over Na+ in dilute solutions, the water will be depleted of Ca2+ in exchange for Na+ initially present.
IonAn atom or molecule having either a positive or negative electrical charge. Positively charged ions are referred to as cations and ions having a negative charge are termed anions.
Iron FilterA pressure vessel used to remove iron from the raw water supply so that the iron will not interfere with the operation of other water treatment equipment or contribute to water-related problems in boilers.
Langelier Saturation Index (LSI)The precipitation of calcium and magnesium carbonates in water purification systems is a serious cause of system failure. The insolubility of these compounds is a complex function of the pH of the water, the dissolved carbon dioxide content, the carbonate content, the presence of other salts, and the temperature. The Langelier Saturation Index is a method of predicting whether or not carbonate deposits will form under given conditions. Reverse osmosis vendors may use the index in determining the maximum recovery and rejection rates that can be obtained from a reverse osmosis system before carbonate deposits will seriously reduce water quality and recovery. It should be noted that the utility of such determinations is limited to those situations in which a softener is not used as part of the pre-treatment scheme for reverse osmosis.
Latern RingA spacer installed between the rings of packing in a pump to allow cooling water to cool the packing and the pump shaft.
Lap JointA riveted joint with tow overlapping plates that are drilled through and riveted together at the edges.
Latent HeatThe Btu content of a substance that represents the heat absorbed or given up as it changes state between solid, liquid, and gas.
Laying UpThe procedure used to protect a boiler from internal corrosion if it is to be taken out of service for a longer than normal period.
LiftThe condition where the level of the liquid to be pumped is below the elevation of the pump.
LigamentThe portion of the drum wall between the tube holes.
Lighting OffThe initial ignition of the fuel.
LigniteVery young and very soft coal that has a high moisture content.
Lime-Soda ProcessA process that uses lime and soda ash to soften water.
Limulus amebocyte lysate (LAL)An extract from horseshoe crabs which forms a gel or clot in the presence of bacterial endotoxin and is widely used for quantitive measurements of these substances.
Line DesuperheaterA device that automatically removes superheat from superheated steam so that the steam becomes saturated steam.
Live SteamSteam in its pure, invisible form.
Lobe PumpA rotary positive-displacement pump in which liquid being pumped fills the open spaces between the lobes of matched rotors and the pump housing.
Local ControlA control device that is installed directly on or very near the equipment on which it is being used.
LockoutThe use of locks, chains, and other physical restraints to prevent the operation of specific equipment.
Lower Heating ValueThe quantity of heat remaining after subtracting the latent heat used in evaporating the water formed in the combustion of the hydrogen. Also known as net heating value.
Low-Pressure BoilerBoilers that operate at a steam pressure of no more than 15 psi
Low Water Fuel CutoffA device located slightly below the NOWL that turns off the boiler burner in the vent of low water.
Lug & Roller MethodA support method where steel lugs are welded or riveted to the front and rear of the boiler shell.
Main Steam Outlet LinesConsists of the piping and valves that direct the steam from the boilers to the steam header.
Main Steam Stop Valve:A gate valve in the main steam line between the boiler and the steam header used for isolating the steam side of a boiler that is to be out of service.
Main Trial For IgnitionA period of about 5 sec to 10 sec for the flame scanner to sense the presence of flame from the main flame.
Makeup WaterWater used to replace condensate that is not returned to the boiler.
Makeup Water FeederAn automatic float-operated valve that feeds makeup water to a low-pressure heating boiler to replace condensate that has been lost from the system or water that has been lost in the form of steam leaks.
Makeup Water LineA city water pipe or well water pipe through which makeup water is added to a boiler.
MalleabilityThe ability of a material to deform permanently under compression without rupture.
ManholeOpening found on the steam and waterside of a boiler that is used for cleaning and inspection of the boiler.
ManometerAn instrument that measures draft by comparing pressure at two locations.
Manual Reset ValveA safety shutoff valve that automatically closes by spring action when it’s hold-open mechanism is electrically or pneumatically tripped by a connected interlock sensing a dangerous condition. It must be reopened by hand after the dangerous condition is rectified and the hold-open mechanism re-energized.
Master ControlA unit that receives the primary signal and relays signals to individual control units.
Material Safety Data SheetMSDS Printed material used to relay chemical hazard information from the manufacture importer or distributor to the user.
MAWP (Maximum Allowable Working Pressure)The highest pressure at which a boiler or pressure vessel may be safely operated.
Maximum CapacityThe maximum rating in pounds of steam that a boiler is designed to produce in 1 hour at a given pressure and temperature.
Mechanical DraftDraft created by fans and blowers.
Mechanical SealAn assembly installed around a pump shaft that prevents leakage of the pumped liquid along the shaft.
MembranesMembranes are thin films made with structures designed to provide selective transport of solutes. In general, the selectivity of a membrane is based on its ability to pass or exclude species according to their size. Membrane structures may become homogeneous or asymmetric. Homogeneous membranes have structures which are uniform in cross-section, at least to a magnification of 100x. Most homogeneous membranes have been developed for micro-filtration and hemodialysis. Membranes reduce not only the flow of undesirable solutes but also the flow of solvent. In order to minimize the reduction in solvent flow, asymmetric membranes have been developed. These membranes are made with asymmetric cross-sections, that is they consist of two parallel layers. The resistance to the flow of the skin layer, which gives the membrane its filtration selectivity, is minimized by reducing its thickness. The resistance to the flow of the thicker support layer, which provides structural strength, is minimized because of its open pore structure. These different layers may be made from the same material as in asymmetric cellulose acetate membranes or from different materials as in thin-film composite membranes. Membranes used in water treatment equipment are fabricated in two forms as flat sheets or as hollow fibers.
Membrane Watertube BoilerA boiler design in which rows of tubes are formed into solid panels through the use of welded steel strips that fill the spaces between each of the water wall tubes.
Membrane WaterwallsWaterwalls that are formed into a solid airtight panel by welding a strip of steel between each of the waterwall tubes.
Mercury SwitchA switch that uses the movement of mercury in a glass tube to start or stop electrical current flow in a circuit.
Metering ControlAn approach to control where the flows of fuel and air are precisely measured by flow-measuring devices and then adjusted by the control system so as to always be in the correct proportions.
Metering Feedwater Regulating SystemA control that continually measures the boiler condition and adjusts the feedwater control valve.
Metering PumpA small-capacity pump used to pump a closely measured amount of a liquid.
MicroporousIn the context of water purification, membranes having an average pore size, which is between 0.1 and 1.0 microns in diameter.
Miniature BoilerA small boiler that meets several criteria for dimensions and capacity.
Modulating Feedwater Regulating SystemContinually adjusts the position of feedwater regulating valve as needed in an effort to maintain a constant boiler water level by matching the position of the valve to the change in the boiler water level.
Modulating MotorA small electric motor and reduction gear assembly enclosed in a metal box, used for positioning a valve and/or damper.
Modulating Pressure ControlA control device that regulates the burner for a higher or lower fuel-burning rate, depending on the steam pressure in the boiler.
Monovalent IonA cation or anion having a single deficit or extra electron.
Motive Fluid PumpA pump that uses the force of a secondary fluid to pump the primary fluid.
Multiple-Pass BoilerA boiler equipped with one or more baffles that direct the flow of combustion gases such that the gases pass over two or more successive sections of heating surfaces.
Natural DraftDraft that occurs without mechanical aid.
Needle ValveA valve that is very similar to a globe valve, except that the opening/closing mechanism on the end of the valve stem is usually a sharply tapered cone that seats in a matching cone-shaped seat.
Negative-Suction Pump InstallationAny installation where the pump must draw (lift) liquid up from a source below the pump.
Neutralizing AmineA chemical that neutralizes the pH of the condensate.
NitrateAn anion comprised of one nitrogen atom and three oxygen atoms. Nitrates are considered toxic in hemodialysis water and are also harmful to infants when consumed orally.
Noncondensable GasA gas that does not change into a liquid when its temperature is reduced to room temperature.
Nondestructive Testing (NDT)A method of determining the condition of components without causing damage and impairing their future usefulness.
Nondrainable Superheatera superheater that does not have condensate drain connections.
Non-Permit Confined SpaceA confined space that does not contain or, with respect to atmospheric hazards, has the potential to contain any hazards capable of causing death or serious physical harm.
Non-Return ValveA combination shutoff valve and check valve that allows steam to pass out of the boiler, but not return into the boiler.
Nonrising Stem ValveA valve that has a disc in the valve that threads up onto the stem as the stem is turned, and the stem does not back out of the valve.
Normal Operating Water Level (NOWL)The water level carried in the boiler gauge glass during normal operation.
N0xAn abbreviation used to represent a group of gases that are produced as a result of the chemical reaction between nitrogen and oxygen at high temperatures.
Off/Low/High ControlAn approach to steam pressure control in which a burner is either OFF or it is operating with a lower firing rate or with a high firing rate.
ON/Off ControlAn approach to steam pressure control in which a burner is either ON or OFF.
ON/OFF Feedwater Regulating SystemA Level Control system that uses a water level-detecting device to turn the feedwater pump ON when the boiler water level drops to a preset point, and turn the pump OFF when the water level has risen to an upper setting.
ON/OFF/ with modulation controlAn approach to steam pressure control in which the amount of flame is changed to a degree that is proportional to the need and includes the function of automatically shutting down or starting the burner when necessary.
OpacimeterAn automatic indicator that measures the amount of light blocked by the smoke and ash going up the stack.
Open Heat ExchangerA heating unit in which steam or another heating medium and the fluid being heated come into direct contact.
Open ImpellerAn impeller that has vanes that are not enclosed or supported by a shroud on either side.
Operating RangeThe range within which a controlled variable is maintained by a control device.
Orifice PlateA plate having a concentric circular hole of precise size that is installed in a pipeline. The pressure difference that occurs across the hole is used for measuring the flow of fluid through the pipeline.
Orsat AnalyzerA flue gas analyzer that measures the percentages of carbon dioxide, carbon monoxide, and oxygen in the gases.
OSHAThe occupational Safety and Health Administration.
Osmotic PressureWhen a solution, such as saltwater, is separated from pure water by a membrane which is impermeable to the salt, a flow of water will occur from the pure water to the salt solution. The driving force for this flow is called the osmotic pressure and its magnitude depends on the number of salt particles in the solution. Note that the osmotic pressure depends on the number of particles and not on the total mass on particles. For example, 1 g/L of a small solute such as sodium chloride will exert greater osmotic pressure than 1 g/L of a large solute, such as protein. For water to flow from the salt solution to the pure water, the solution must be exposed to a hydrostatic pressure greater than its osmotic pressure. This is the principle of reverse osmosis.
“O” Style Watertube BoilerA water-tube boiler design with top steam and water drum and a bottom mud drum that are interconnected by banks of symmetrical tubes in an “O” shape.
Output SignalThe flow of control information leaving a control device and traveling to another device.
Outside Stem & Yoke Valve (OS&Y)A valve containing a stem that screws out from the center of the valve handwheel when the valve is opened.
Overfire AirThe high-velocity secondary air creates turbulence in the flue gases above the top of the fuel bed. This helps mix oxygen with the combustibles in the flue gases for greater efficiency.
OverfiringForcing a boiler beyond its designed steam-producing capacity.
Overhead Suspension MethodA support method where the boiler is suspended from an overhead steel beam structure by sling members.
OxidantsChemicals that provide oxygen and accept an electron in an oxidation-reduction reaction. Free chlorine and chloramines are oxidants that are widely used for disinfection.
Oxyacetylene WeldingA welding process that uses acetylene which is combined with oxygen to produce a flame with a temperature over 6,000°F.
Oxygen Trim SystemAn automation Control System that makes fine adjustments in the amount of combustion air used in order to minimize excess air.
Oxygen ScavengerA chemical that reacts with any oxygen remaining in the boiler feedwater and changes it into a form that does not cause corrosion.
OzoneAn extremely active oxidizing agent who consists of three oxygen atoms. It can be formed by the action of a high voltage electrical field on oxygen gas or ambient air with oxygen content.
Package BoilerA boiler that is supplied from the manufacture complete with controls, burner(s), and appliances attached.
Packing GlandHolds packing or seals in place on valves and pumps to minimize leakage.
ParallelIn water purification, an arrangement of equipment in a side-by-side configuration such that water flow is divided and passes through one or both of these branches.
Parallel Positioning ControlAn approach to steam pressure control in which a master device or controller sense the steam header pressure and modulates the fuel feed and combustion airflow independently to vary the boilers firing rate while maintaining a correct air-fuel ratio.
ParticulateFine ash particles from a burner that ultimately settle back to earth.
Part Per Billion (ppb)The concentration of a solution equal to one part of a chemical in one billion parts of the solution.
Part Per Million (ppm)The concentration of a solution equal to one part of a chemical in one million parts of the solution.
Passes:The number of times the gases of combustion flow the length of the boiler as they transfer heat to the water.
Perfect CombustionA fire where the fuel is burned with precisely the right quantity of oxygen so that no fuel or oxygen remains and the maximum possible heat results.
Permanent HardnessA type of hardness can be reduced only by the use of chemicals or distillation.
PermissiveA process condition that must be met before a certain action may be taken.
Permit-Required Confined SpaceA confined space that has specific health and safety hazards associated with it.
Personal Protective EquipmentAny device worn by a boiler operator to prevent injury.
pHWater can dissociate into two ions: hydrogen (H+) and hydroxyl (OH). These ions can also be added to water in combination with other oppositely charged ions. Thus, a solution of hydrochloric acid added to water provides both H+ and chloride anion, Cl-. The concentration of H+ in the water is a measure of the water’s acidity and the concentration of OH- a measure of its alkalinity. pH values range from 1 to 14. A pH of 7 is considered neutral. Lower values of pH indicate acidic conditions and higher pH values indicate alkaline conditions.
PhosphateA chemical that causes hardness in boiler water to precipitate and settle out as a heavy sludge.
PhosphonateAn organic phosphate that provides multiple functions in water treatment.
pi (π)The ratio of the circumference of a circle to its diameter. The circumference of a circle is always equal to the diameter multiplied by pi.
PilotUsed to ignite the fuel at the proper time in a firing cycle.
Pilot Trial For Ignition or PTFIA period of about 5 sec to 10 sec for the flame scanner to sense the presence of flame from the pilot.
Piston ValveA valve that contains a finely machined piston that moves up or down in the interior of a cylindrical steel cage.
Plant MasterThe master controller that calculates and distributes the steam production requirements to two or more boiler when they are used to maintain the pressure in a common steam header, such as when the boilers are installed in the battery.
Plug ValveA valve that is similar to a ball valve, except that a plug valve contains a semi-conical plug through which the flow passes.
PneumercatorAn air-actuated liquid level measuring device.
Polymer DispersantA synthetic compound that prevents scale deposits on boiler surfaces.
PolyamideA synthetic polymer of nylon family used in the fabrication of reverse osmosis and ultrafiltration membranes.
PolysulfoneA synthetic polymer used in the fabrication of reverse osmosis and ultrafiltration membranes which are characterized by extreme thermal stability and chemical resistance.
Polyvalent IonA cation or anion having multiple electrical charges.
Polyvinyl Chloride (PVC)A thermoplastic material produced by the polymerization of vinyl chloride. Used extensively in the U.S. for piping, food packaging, and injection-molded plastic parts. PVC is the most common pipe material used in the U.S. for dialysis applications.
Popping PressureA predetermined pressure at which a safety valve opens and remains open until the pressure drops.
Pop-Type Safety ValveA spring-loaded valve that opens fully and instantly and causes a definite, measured drop in pressure before closing.
Positioning ControlsAn approach to control in which a master device, or controller, senses the pressure in the steam header and uses compressed air to modulate power units, or actuators which in turn position control linkages.
Positive-Displacement PumpA pump that moves the same amount of liquid with every stroke or rotation.
Positive DraftThe condition wherein the pressure inside the boiler furnace becomes greater than the pressure outside the furnace.
Positive-Suction Pump InstallationAny installation where the pump receives liquid on the suction side from a source above the pump-that is under the head.
Potassium PermanganateAn oxidizing agent commonly used for the regeneration of manganese greensand iron filters and occasionally used as a disinfectant. This material can cause significant damage to membrane elements.
Pour PointThe lowest temperature at which a liquid will flow from one container to another.
PowerThe rate at which work is done.
Predictive MaintenanceA study of the history of the plant components and determination of the expected service life of critical components.
Pressure DropExpenditure of a certain amount of energy is required for fluid flow through any channel such as pipe, particle bed, or membrane. The pressure at any point is a measure of the energy content of the fluid at that point. Since some of this energy is expended in flowing to a second point downstream, the pressure at the downstream point is less than at the original point. The amount of energy expended and hence the decrease in pressure (or pressure drop), is dependent on the flow rate and viscosity of the fluid and or PSI or in the SI system kPa (kilopascals) or Kg/cm2. Pressure drop is sometimes referred to colloquially as “delta-P”.
Pressure Reducing Valve (PRV)A valve that is designed to reduce the pressure of a fluid flowing through a pipe to a desired lower pressure, and constantly maintains this desired pressure downstream of the valve.
PretreatmentThe water treatment process that occurs before the water enters the boiler.
Preventive MaintenanceThe practice of performing maintenance activities on a piece of equipment to prevent breakdowns from normal or predictable causes.
Primary AirThe initial volume of air enters the furnace with the fuel for most of the combustion process.
Primary ControlA flame safeguard control that consists of the relays and electronics required to safely start, run, and stop the burner under orders from an external control device such as a pressure switch.
Primary Element or SensorA device that measures the process variable and produces a usable output in the form of a mechanical movement, electrical output, or instrument air pressure output.
PrimingA severe form of carryover in which large slugs of water leave the boiler with the steam.
Priming PumpA vacuum pump that ejects air from the suction line of larger negative-suction pump installation.
Private OrganizationAn organization that develops standards from an accumulation of knowledge and experience with materials, methods, and practices.
ProcessThe collection of equipment and actions required to accomplish the desired objective.
Process VariableThe condition that is being controlled. It is the condition that may vary within the process.
Product WaterThe purified water stream from purification equipment, such as reverse osmosis units and ultrafilters.
Programmable Logic Controller (PLC)A small computer that may be configured, or programmed, to control a wide variety of processes.
Programming ControlA flame safeguard control that consists of all the components needed to safely perform a desired sequence of operations for a larger commercial or industrial burner.
Proof Of Closure Switch (POC)A sensor that detects the position of a valve to ensure that the valve closes properly.
Proximate AnalysisThe percentages of moisture, volatiles, fixed carbon, ash, and often the percentage of sulfur and the British Thermal Unit (BTU) content of a coal sample.
Pulverized CoalCoal that has been ground to the consistency of talcum powder.
PulverizerA mill that grinds the coal to a very fine powder.
Pump ControllerStarts and stops a feedwater pump, depending on the water level in the boiler.
Purge PeriodA short period of time, typically 30 sec to about 2 min, when air is blown through the furnace area to ensure that no volatile fuel vapors are present prior to the pilot being lit.
Push-Nipple Cast Iron Sectional BoilerContains hollow cast-iron sections joined with tapered nipples and pulled tightly together with tie rods or bolts.
PyriteA common mineral consisting of iron disulfide.
Pyrite TrapA compartment or box in the pulverizer that catches nuggets of pyrite as they are separated from coal.
Pyrogenic ReactionsA physical response to the presence of endotoxin in the bloodstream, which is characterized by fever and occasionally, chills or shaking rigors.
PyrometerAn instrument that measures temperatures above the temperature range of mercury thermometers.
Quality Of SteamThe dryness of the steam.
Quick-Closing ValveA valve that requires a one-quarter turn to be fully open or closed.
Quick-Drain TestA test that empties the float chamber or electric probe chamber while that burner is firing in order to test the low water fuel cutoff switch.
QuicklimeLimestone that has been thoroughly dried.
Quick-Opening ValveA valve that requires only a 90° change in the position of a lever arm to move the valve from fully closed to fully open.
Radiant SuperheaterA superheater that is directly exposed to the radiant heat of the furnace.
Ramming MaterialsPlastic refractory materials that are rammed into place using heavy bars and other tools.
RankThe hardness of the coal.
Rate Of CombustionThe amount of fuel that is being burned in the furnace per unit of time.
ReagentA chemical used in a water treatment test to show the presence of a specific substance, such as hardness.
Rear HeaderFound on straight-tube water-tube boilers. Connected to the front header by water tubes.
Reciprocating PumpA displacement pump that uses a reciprocating piston or diaphragm to repeatedly displace fluid from a cylinder or chamber.
Recirculation LineA line that provides a minimum flow through a pump to prevent overheating.
RecorderAn instrument that records data such as pressures and temperatures over a period of time.
Recovery (Percent Recovery)A measurement applied to reverse osmosis and ultrafiltration equipment, which characterizes the ratio of product water to feedwater flow rates. The measurement is descriptive of reverse osmosis or ultrafiltration equipment as a system and not of individual membrane elements.
RectifierAn electrical device that converts alternating current (AC) into direct current (DC).
RefractoryBrickwork used in boiler furnaces and for boiler baffles.
Regenerative Air PreheaterA combustion air preheater that consists of a rotating segmented wheel containing corrugated metal in each segment. As the rotating wheel passes through the hot flue gases, the corrugated metal is heated. As the rotating wheel passes through the combustion air, the combustion air is heated by the hot corrugated metal.
ReinsuranceThe insurance purchased by insurance companies for large-loss contingencies.
Rejection (Percent Rejection)A measure of the ability of a reverse osmosis membrane to remove salts.
Relative HumidityThe ratio of the actual amount of water vapor in the air to the greatest amount possible at the same temperature.
Relief ValveA valve that opens in the proportion to the excess pressure, rather than popping open fully.
Remote ControlA control device that is installed a considerable distance from the equipment on which it is being used.
Representative SampleA sample that is exactly the same as the item being tested.
ResetThe act of restoring a switch or other control device or system to service-ready condition after it has been tripped by an unsafe or otherwise prohibited condition.
Residual Fuel OilFuel oil that remains after the lighter, more volatile hydrocarbons have been distilled off.
ResiliencyThe ability of a material to return to its original shape after being deformed.
ResistanceThe measure of the ability of an electric circuit to oppose current flow.
ResistivityResistivity is a measure of the current-resisting characteristics of a substance when an electrical charge is applied. The standard unit of resistance is the Ohm. Because of the variable nature of water, a distance between measuring probes must be maintained if accurate measurements are desired. The almost universal standard distance for this is the centimeter, hence the “Ohm-cm”. Resistivity measurements, like conductivity measurements, can be used in many ways to improve the management of a water purification system, and are commonly used to assess the quality of water produced by deionizers. Because temperature affects the resistivity of water, temperature-compensating devices are frequently used. These adjust the resistance meter to indicate what the water-resistance would be at one temperature, usually 25°c.
RetortA V-shaped trough, usually about 5′ to 12′ long, with a backplate enclosing the rear end of the trough opposite the feeding mechanism. Solid fuel is fed by the feeding mechanism into the bottom of the trough and slowly overflows onto grate bars.
Retort ChamberA V-shaped trough, usually about 5′ to 12′ long, with a backplate enclosing the rear end of the retort opposite the feed ram.
Retort StokerA stoker in which both the fuel and the combustion air are fed from below the combustion zone.
Reverse OsmosisA water-purification process in which the water to be treated is pressurized and applied against the surface of a semipermeable membrane.
Ringelmann ChartA comparison chart used to measure opacity.
Riser TubesTubes exposed to the highest temperatures in the furnace area and contain rising water.
Rising Stem ValveA valve that has a handwheel and stem that move outward from the body of the valve as the valve is opened.
RotameterA variable-area instrument used for measuring the rate of flow.
Rotary Cup BurnerA fuel oil burner that has a spinning cone-shaped cup, usually made of brass or stainless steel. Fuel oil is mixed with air as the oil is sprayed from the rim of the spinning cup.
Rotary PumpA pump with a rotating shaft. A rotary pump may be either a dynamic pump or a displacement pump.
RTDAn acronym for resistance temperature device.
Safety Relief ValveA valve specially designed to serve as either a safety valve or relief valve, depending on the application for which it is used.
Safety ValveA valve that opens fully and instantly and causes a definite, measured drop in pressure before closing.
Salt Passage RateA measurement of the passage of salts through a reverse osmosis membrane. The salt passage is related to rejection.
Sample CoolerA small, closed heat exchanger that cools condensate or other hot water to a temperature below about 130°F to 140°F before the water emerges from the cooler and into a sample container.
Sample CouponA small, flat strip of steel that is inserted into an elbow or tee fitting in a piping network.
SaturatedThis means that a substance has absorbed as much of another substance as it can absorb.
Saturated SteamA type of steam that contains no liquid water and is at the temperature of the boiling water that formed the steam.
ScaleDeposits caused by improper boiler water treatment. Learn more about scale HERE.
ScalingIn reference to reverse osmosis equipment, scaling is the precipitation of sparingly soluble salts such as calcium carbonate onto the surface of the membrane. Scaling is associated with decreased flux and reduced reverse osmosis rejection.
ScannerA device that monitors the pilot and main flame of the furnace. The scanner is used to prove the pilot and main flame.
Scotch Marine BoilerA firetube boiler that has a flue furnace and horizontal shell.
ScrubberA device that removes undesirable gaseous elements from flue gas.
Secondary AirAir mixed with the fuel to ensure that enough oxygen is available to complete the burning.
Second Law Of ThermodynamicsHeat always flows from a body having a higher temperature toward a body having a lower temperature.
SedimentParticles of solid foreign matter that settle out from a body of liquid.
SedimentationThe process by which solids are separated from water by gravity and deposited on the bottom of a container or basin.
Semiclosed ImpellerAn impeller that has a shroud on one side of the vanes.
Semi-PermeableDescriptive of a material such as a reverse osmosis or ultrafiltration membrane, which allows the passage of some molecules and ions and prevents the passage of others.
Sensible HeatThe BTU content of a substance that represents the heat absorbed or given up as it changes temperature.
SeriesIn water purification an arrangement of equipment in a successive or end to end configuration.
SetpointThe desired point at which an automatic controller maintains a variable condition within a process.
ShakeoutThe process of operating a new system as needed to expose and correct the major impediments to reliable operation.
Shaft SleeveA replaceable sacrificial part covering a pump shaft.
ShearThe exertion of equal forces in opposite direction in the same plane.
Shear PinA link used in a mechanical drive that is designed to break under a specific amount of shear stress.
Shielded Metal Arc WeldingA welding process that uses an electric arc to heat the metal in the weld area; metal from te electrode is added to the weld pool.
SignalThe language that the control devices use to communicate with each other.
Silt Density Index (SDI)The silt density index is a measure of the ability of water to foul a membrane element or plug a filter. SDI is measured using an apparatus which typically consists of an inlet pressure regulator and pressure gauge followed by a filter holder containing a 0.45-micron microporous membrane filter. Commercial test kits, complete with instructions on how to calculate the index are available.
Simplex PumpA steam-driven, reciprocating, positive-displacement, double-acting pump with one steam cylinder and one liquid cylinder.
Single-Acting PumpA reciprocating pump that moves the fluid in only one direction of the stroke.
Single-Loop ControlThe use of a controller to control a single process variable without any influence from any other controller or process variable.
SiphonA device used between the source of steam and the Bourdon tube in a steam pressure gauge to prevent the heat of the steam from damaging the Bourdon tube.
SlagThe solid deposits that accumulate on furnace walls and boiler tubes.
Slag ScreenA loosely spaced bank, or several rows of water tubes placed between the superheater and the combustion area of the furnace.
SlakerA conveyor in which lime is mixed with water to make a soluble paste.
Slinger RingA metallic ring that hands on the rotating shaft of a machine and delivers oil from an oil sump to a bearing.
SlipThe difference between the calculated and actual displacement of a pump.
Slow-Opening ValveA valve that requires five or more full turns of a handwheel to move the valve from fully closed to fully open.
SludgeAccumulated residue produced from impurities in water.
SluiceA trench through which water flows rapidly to carry away solid materials.
Smoke BoxThe area at the end of a firetube boiler where the flue gases are allowed to reverse direction for the subsequent pass.
Smoke IndicatorAn indicating or recording device that shows the density of the smoke leaving the chimney.
Sodium Zeolite Water SoftenerAn ion-exchange water softener that uses resin beads and a brine solution to soften water.
SolenoidAn electric actuator that consists of an iron plunger surrounded by an encased coil of wire.
Solenoid ValveA valve that is snapped open or closed by an electric actuator.
SootCarbon deposits caused by incomplete combustion.
Soot BlowersUsed to remove soot from around tubes to increase boiler efficiency. Mostly found on water-tube boilers.
SpallingHairline cracks in boiler brickwork (refractory) due to changes in furnace temperature.
Specific GravityThe weight of a given volume of a material divided by the weight of an equal volume of water when both are measured at the same temperature.
Specific VolumeThe space occupied by a fluid or gas of a particular unit of weight under the specified condition of pressure and temperature.
SpectrophotometerAn instrument that measures the ability of different frequencies of light to pass through a sample of liquid.
Spontaneous CombustionThe process where material can self-generate heat until the ignition point is reached.
Staged CombustionThe introduction of the combustion air at sequential points over the length of the burner housing to control the quantity of oxygen available at any given point.
StagingThe placement of more than one impeller on the same shaft in a centrifugal pump.
StandardAn accepted reference, practice, or method.
Standing PilotA gas pilot that is always lit.
Static Discharge HeadThe vertical distance from the centerline of the pump up to the surface of the liquid in the tank or vessel into which the piping discharges.
Static Suction HeadThe vertical distance from the centerline of the pump up to the level of the liquid in the supply tank.
Static Suction LiftThe vertical distance from the centerline of the pump down to the level of liquid in the supply source below.
StayboltA short bolt brace that passes through the water leg of a boiler.
SteamThe gaseous form of water.
Steam and Water DrumThe pressure vessel in a steam boiler that contains both steam and water.
Steam BlanketingA condition that occurs when steam bubbles are generated so quickly from a boiler heating surface that a layer of steam is formed between the water and the heating surface.
Steam BlowingThe process of cleaning impurities from new piping by blowing steam through the pipe.
Steam BoilerA closed vessel in which water is transformed into steam under pressure through the application of heat.
SteamboundA condition that occurs when the temperature in the open feedwater heater gets too high and the feedwater pump cannot deliver water to the boiler.
Steam HeaderA manifold that receives steam from two or more boilers and provides a single location from which steam may be routed through the steam mains and branch lines to various points of use.
Steam MainThe piping that carries steam to a section of a building or plant.
Steam RateThe combination of combustion efficiency and the thermal efficiency at the full range of loads and conditions that the boiler encounters over a typical period of time. The steam rate is expressed as average pounds of steam generated per unit of fuel.
Steam SeparatorDevice sued to increase the quality of steam. Found in the steam and water drum.
Steam SpaceThe space above the water line in the steam and water drum.
Steam SystemConsists of the equipment, controls, and piping that carry the steam generated by the boiler to its point of use.
Steam System EfficiencyMeasurement of steam usage that takes into account both the equipment supplying the steam and the equipment demanding the steam.
Steam TracingA small copper or steel tube which is supplied with steam and is usually run alongside a process pipe to keep the fluid within the pipe warm.
Steam TrapA mechanical device used for removing condensate and/or air from steam piping and heat exchange equipment.
Steam Trap SurveyThe process of identifying, testing, and documenting the condition of all steam traps in a facility.
Steam TurbineA rotary steam engine used to drive rotating equipment such as pumps, blowers, compressors, or electric generators.
Steam Working Pressure (SWP)The maximum steam working pressure of the valve.
StelliteAn alloy of chromium, cobalt, and tungsten.
SterilizationA physical or chemical process that reduces the number of organisms to a safe predetermined level.
Stirling BoilerA water-tube boiler design with three steam and water drums on the top and mud drum beneath, interconnected by a large number of water tubes.
StokerA device that automatically feeds green, unburned coal and other solid fuel to a furnace.
Stoichiometric CombustionThe process of burning fuel with precisely the amount of air required so that no unburned fuel or unused oxygen remains.
StopcockA quick-opening or closing valve usually found on gas lines.
Straight-Tube Watertube BoilerA boiler design in which the steam-generating tubes are straight rather than bent or curved.
StrainerA pipeline fitting containing a mesh or perforated metal screen used to capture impurities that could damage or interfere with the operation of another component, such as a steam trap, pressure-reducing valve, or turbine throttle valve.
Submerged Arc Welding (SAW)A welding process in which an electric arc is submerged or hidden beneath a granular material (flux).
Submerged ConveyorA heavy steel pan conveyor or apron conveyor immersed in a water trough.
Submerged-Tube Vertical BoilerA firetube boiler with fire tubes completely covered with water all the way to the upper tube sheet.
Suction PressurePressure on the liquid at the suction side of a pump.
Superficial VelocityThe velocity of a fluid flowing through a tank containing a bed of particles is described in terms of the superficial velocity. The superficial velocity is defined as the velocity that would be achieved by the fluid if it flowed at the same volumetric flow rate through the tank when it was empty of particles.
Superheated SteamA type of steam that has been heated above the saturation temperature.
SuperheaterA bank of tubes through which steam passes after leaving the boiler, in which additional heat is added to the steam. This causes the steam temperature to rise significantly above the saturated prior to boiler startup.
Superheater DrainA valve and line installed at the low point of drainable superheaters that allows condensate to be removed from the superheater prior to boiler startup.
Superheater HeaderMain inlet and outlet line to and from the superheater tubes in the superheater.
Superheater VentA vent to the atmosphere provided at the superheater outlet so that a flow of steam may pass through the superheater and out the roof of the plant while a boiler in the battery is being heated before being put on-line.
Surface BlowdownThe process of intermittently removing water from a boiler to control the number of impurities in the remaining water or to remove a film of impurities on the water.
Surge TankA type of pressurized water storage vessel also known as a bladder tank. Used almost exclusively on residential well water systems, they provide a small amount of pressurized water downstream valves or equipment without requiring a pump. When installed on a piston-type pump, they reduce violent pressure spikes. Surge tanks typically have large areas of stagnation that offer opportunistic bacteria a favorable environment for multiplication.
Suspended SolidsSolid impurities that are suspended in water.
Suspension SlingUsed to support the drum of an HRT boiler.
SwellThe rise in the boiler water level that occurs when the steam load on the boiler is increased or when the steam pressure drops.
SynchronizeThe process of bringing the process variable condition very near the setpoint of an automatic control before switching between manual mode and automatic mode.
TagoutThe use of a danger tag at the source of the hazardous energy to indicate to other personnel that the device is not to be operated until personnel working on the equipment have removed their lockout devices and the equipment is safe to operate.
Tandem ValveA blowdown valve configuration with two valves in series machined into a common valve body.
Technical SocietyAn organization made up of personnel having expertise in a particular subject and a common professional interest.
Temporary HardnessA type of hardness that can be reduced by heating the water.
Tensile StrengthThe amount of force required to pull an object apart.
TensionThe exertion of equal forces pulling in opposite directions that can stretch an object.
Tertiary AirCombustion air added to a burner in addition to and downstream of the secondary air.
ThermA unit of measure indicating 100,000 BTU
Thermal EfficiencyThe ratio of the heat absorbed by the boiler to the heat available in the fuel per unit of time.
Thermal Fluid BoilerA firetube or water-tube boiler that uses a chemical solution instead of water.
Thermal N0xN0x that is formed as a result of the combustion air when the molecules of nitrogen and oxygen in the air separate under high-temperature conditions and then bond together again as the temperature is reduced.
Thermal ShockThe stress imposed on boiler metal by a sudden and drastic change in temperature.
ThermocoupleA device used to measure temperature consisting of two dissimilar metals joined together.
Thermohydraulic Feedwater RegulatorA modulating control that controls feedwater flow in direct response to changes in the boiler water level. This regulator utilizes changes in temperature to create changes in hydraulic pressure and this hydraulic pressure is used to operate the feedwater regulating valve.
ThermometerAn instrument used to measure temperature. Calibrated in degrees Celsius or Degrees Fahrenheit.
Thermostatic Expansion Tube Feedwater RegulatorA modulating control that controls feedwater flow in direct response to changes in the boiler water level. This regulator utilizes the expansion and contraction of a long, slightly tilted expansion tube to create a proportional movement of the feedwater regulating valve.
Thermostatic Steam TrapA steam trap that contains a temperature-operated device, such as corrugated bellows, that controls a small discharge valve.
ThermowellA receptacle into which a temperature sensing instrument is inserted.
Three-Element Feedwater Regulating SystemA water level control system that measures the steam flow from the boiler and the feedwater flow into the boiler in addition to the water level.
ThrottlingControlling the amount of flow that passes through a valve by partially closing it.
Titration TestA test that determines the concentration of a specific substance dissolved in water.
Titratable AlkalinityWhen certain anions, such as carbonate (CO3-), are dissolved in water, they bind hydrogen ions (H+) and thus shift the water equilibrium to produce free hydroxyl ions (OH-). This excess concentration of OH- is termed alkalinity. Titratable alkalinity can be measured by determining the amount of H+ which must be added to water to restore the pH to 7.0 the condition of neutrality.
Total Dissolved Solids (TDS)The sum of all organic, inorganic, and ionic contents in a solution (excluding all dissolved gasses). Since a TDS meter cannot measure the non-ionic content of water, most TDS readings are an approximation. TDS measurements are widely used in the water and wastewater industries monitor final water quality. The TDS meter derives its value from resistivity and conductivity measurements of the product water.
Total Dissolved Solids (TDS)A measurement of the concentration of impurities in the boiler water.
Total Dynamic HeatThe total amount of heat produced by the pump and available to perform useful work, after losses have been subtracted.
Total ForceThe pressure (in psi) being exerted on a surface multiplied by the area of the surface.
Total HeatThe sum of sensible heat and latent heat.
Total Organic CarbonOrganic compounds dissolved in water are characterized by their carbon content. Total organic carbon is the mass of carbon present in a water sample excluding the carbon present as CO2 and/or carbonates.
Totalizing FlowmeterA flow measuring device that not only measures on an instantaneous basis, but also measures total flow over time.
Trade AssociationAn organization that represents the producers of specific products.
TransducerA device that converts one type of control signal into another type of control signal.
TransmitterAn instrument used to send information about the condition of a process to a control device. A device that conditions a low-energy signal from the primary element and produces a suitable signal for transmission to other components and devices.
TricockA valve used as a secondary water level indicator.
TubercleA bump on a steel boiler surface made up of corrosion products.
Tubular Air PreheaterConsists of tubes enclosed in a shell where flue gases heat up incoming combustion air.
TurbidityTurbidity is a measure of the presence of colloidal matter in the water that remains suspended. Suspended matter in a water sample, such as clay, silt or finely divided organic and/or inorganic material will scatter the light from an incident light beam. The extent of scattering is expressed in Jackson or Nephelometric turbidity units (JTU and NTU, respectively).
Turbine PumpA rotary positive-displacement pump that uses a flat impeller with small flat perpendicular fins machined into the impeller rim.
Turbine StagesThat part of the turbine where steam gives up its energy to the turbine blades. As the steam pressure drops, the stages (blades) become larger.
Turbine Tube CleanerA motorized mechanical cutter or knocker that removes scale from boiler tubes.
TurbulatorA device that swirls the hot gases of combustion as the gases pass through the center of the tube so that the gases come into more efficient contact with tube walls where heat transfer occurs.
Turbulence1.) Agitation at the water level inside a boiler. 2.) Agitation of a flame for the purpose of thoroughly mixing the combustion air and fuel.
Turndown RatioThe ratio of the maximum firing rate of the burner to the minimum firing rate.
Tuyere (Tweer)A special air-admitting grate designed to start combustion of the entering fuel.
Two-Element Feedwater Regulating SystemA water level control system that measures the steam flow from the boiler in addition to the water level.
Ultimate AnalysisThe percentages of nitrogen, oxygen, carbon, ash, sulfur, and hydrogen in the coal. (NOCASH)
Ultra FiltersA membrane-based filtration system in which the pore size ranges from .001 to .1 microns
Unfired VesselA pressure vessel without combustion equipment, such as compressed air tanks, feedwater heating tanks, steam piping, steam jacketed heat exchangers, and similar vessels.
Utility Watertube BoilerAn extremely large water-tube boiler that generates steam at very high pressure and temperature.
U-Tube ManometerA manometer configured in the shape of a long U and calibrated in inches. When filled with mercury, it is used to measure vacuum in inches of mercury. When filled with water, it is used to measure draft conditions in inches of water.
VacuumPressure lower than atmospheric pressure.
Vacuum BreakerA check valve that prevents the formation of a vacuum in a tank, pressure vessel, or piping system.
Vacuum GaugePressure gauge used to measure the pressure below atmospheric pressure that is calibrated in inches of mercury.
Vacuum PumpA pump that withdraws gases or vapors from a closed container and creates a vacuum in the container.
Vane PumpA rotary positive displacement pump that uses a rotating drum located eccentrically inside a cylindrical pump casing.
Vapor PressureThe equilibrium pressure where the number of molecules evaporating from a liquid surface equals the number of molecules condensing back to the liquid.
VaporstatControl with a large diaphragm that makes it highly sensitive to low pressure.
Variable-Area Flow MeterMeasures the flow of a substance by how much resistance is created by a float or piston that changes the area (size) of the flow path.
Variable Frequency Drive (VFD)An electronic system for controlling the speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor.
Vent CondenserAn in-line heat exchanger installed in the vent from a deaerator to the atmosphere.
VenturiA nozzle with a slight hourglass-shaped taper.
Vertical Firetube BoilerA firetube boiler in which the tubes are oriented vertically.
Vibrating Grate StokerInclined grates that vibrate, causing the fuel bed to move slowly toward the lower end.
VirusThe smallest infectious microorganism, made of RNA or DNA in a protein shell and which grows only in other living cells.
ViscosityA measurement of a liquid’s resistance to flow.
Viscous LiquidA liquid that is thick and resists flow.
Volatile MatterThe gas given off when coal burns.
VoluteA spiral-shaped form.
WarpingThe bending or distortion of metallic components such as boiler tubes, structural framework, etc. usually caused by overheating.
Waste Heat Recovery BoilerA firetube or water-tube boiler in which heat that would otherwise be discarded is used to make steam.
Water ColumnA metal vessel installed on the outside of the boiler shell or drum at the normal operating water level (NOWL) for the purpose of determining the location of the water level.
Water Column Blowdown ValveThe valve on the bottom of the water column used to remove sludge and sediment that might collect at the bottom of the water column.
Water HammerThe hydraulic shock in piping caused by the presence of liquids in the steam flow.
Water, Oil, Gas (WOG)The maximum pressure under which the valve may be used with these fluids.
Water SofteningThe removal of scale-forming salts from water.
Watertube Steam BoilerA boiler that has water in the tubes with heat and gases of combustion around the tubes.
WaterwallMany tubes placed side by side to create a large, flat surface against the furnace walls in a water-tube boiler.
Waterwall Blowdown ValveThe approved valve used to remove sludge and sediment from waterwalls and waterwall header.
Weight-type Alarm WhistleAlarm whistle that signals high or low water by the gain or loss of buoyancy of weights in water within the water column.
Wetback Scotch Marine BoilerA firetube boiler with a water-cooled reversing chamber used to direct the combustion gases from the flue furnace to the first pass of tubes.
WindboxThe plenum to which the forced draft fan (primary air fan) supplies air in order to maintain enough pressure to provide proper airflow through the furnace.
Window WeldA weld made through an opening, or window, in the tube.
Wire DrawingThe erosion that occurs as steam or another high-velocity fluid flows through a small opening like a throttled valve.
Working PressureA shortened term for maximum allowable working pressure, but it may also be used to mean the pressure at which the boiler is normally operated.
ZeoliteA synthetic sodium aluminosilicate cation-exchange material based on a naturally-occurring class called zeolites.

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