Glossary

January 7, 2020 - Nathan Olszak

Glossary of Terms

Term	Definition
AA	Atomic Absorption spectroscopy
AAMI Grade Water	Water meeting quality standards established by the Association for the Advancement of Medical Instrumentation and used mainly for hemodialysis systems
ABS	alkylbenzene sulfonate
Absolute Filter Rating	Filter 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 Pressure	The pressure above a perfect vacuum. It is expressed as psia (pounds per square inch absolute)
Absorbed Dose	The amount of a chemical that enters the body of exposed organism.
Absorption	The 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 Factor	The 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 Equipment	Water 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 Test	A 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 Dewpoint	The temperature at which acidic vapors begin to condense out of the flue gases.
Actuator	A device that receives a control signal from a controller and converts the signal into a proportional movement of the valve.
Adsorption	Adsorption 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 Ratio	The 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.
Algae	A group of single-celled plants which includes both seawater and freshwater varieties.
Alkalinity	A measurement of the quantity of chemicals present in water, which can neutralize acids. These include carbon dioxide, bicarbonate, carbonate, and hydroxides.
Aluminum Sulfate	An aluminum salt commonly used as a flocculent by municipal water treatment facilities.
Amine	A chemical that prevents corrosion in a condensate and steam piping.
Amphoteric	A substance, such as aluminum, capable of acting as either an acid or base.
Analog Signal	A 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.
Anions	A negatively charged ion
Annunciator	An audible alarm that is created electrically or electronically.
Ash Fusion Temperature	The temperature at which ash begins to become molten.
Anthracite Coal	A 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 Hopper	Large receptacle used to store ashes until they can be disposed of.
ASME	Code 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 Boiler	A 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.
Atomization	The process of breaking a liquid fuel stream into a mist of tiny droplets.
Back-Seating	The situation where a slow-opening valve such as a gate or globe valve is fully opened until it stops.
Bacteria	Bacteria 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 Plate	A data plate attached to a boiler.
Baffle	A metal or refractory-covered panel that directs the flow of gases of combustion for maximum boiler heating surface contact.
Bag	A protruding bubble or bulge in the steel plate of a boiler.
Ball Check Valve	An automatic self-closing gauge glass valve.
Ball Valve	A quick-acting, two position shutoff valve.
Banking A Fire	The process of greatly slowing the burning of coal or some other solid fuel.
Barometric Damper	A free swinging adjustable balanced damper used on smaller boilers to automatically limit the amount of air pulled through the combustion chamber.
Battery	A group of boilers that feed steam into the same steam header.
Bellows	A flexible device that expands and contracts with changes in pressure.
Bent-Tube Watertube Boiler	A boiler design in which the tubes are bent to some degree.
Bituminous Coal	A 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 Oil	A mixture of distillate oils and residual oils that may contain some crude oil.
Blister	A lamination of steel plate or tube surfaces or where the steel plate splits into layers.
Blowback	The drop in pressure in the boiler that occurs after the safety valve has opened.
Blowdown	The 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 Surface	Any 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 Load	The amount of steam being produced by a boiler.
Boiler Master	A 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 Battery	Two or more boilers connected to a common steam header.
Boiler Thermal Efficiency	The percentage of the heat liberated that is transferred into the boiler water.
Boiler Vent	A 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 Procedure	The 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 Blowdown	The process of periodically draining part of the boiler water to remove heavy sludge that settles to the bottom of the boiler.
Bourdon Tube	The 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 Line	The piping that takes steam from the steam mains to individual pieces of steam using equipment.
Breeching	The ductwork that carries cooled flue gases from the exit of the boiler to the stack.
Bridge Wall	A firebrick wall built across a boiler furnace.
Brine	A 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 Control	A 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.
Buckstay	A metal brace used to attach a wall to steel framework that supports the wall.
Bunker Oil	One of the heavy oils formed as crude oil is stabilized after the lighter components have been distilled off.
Butterfly Valve	a 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 Damper	Controls the air temperature in air heaters to prevent corrosion.
Bypass Line	A pipeline that passes around a control, heater or steam trap. Used so that a plant can operate while equipment is serviced or repaired.
Cations	A positively charged ion
Calibrate	Adjusting an instrument to optimize its accuracy.
Calorie	The amount of heat necessary to raise the temperature of 1 g of water by 1°c
Calorimeter	A laboratory instrument used to measure the heat content of a substance, such as a sample of a fuel to be used for a boiler.
Capacity	The 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 Tube	A long, small-diameter tube, usually of stainless steel or a copper alloy.
Carryover	The entrainment of small water droplets with steam leaving the boiler.
Cascading Control	A Control scheme in which one process variable is measured and used to set the setpoint of another controller.
Cation	An ion that has a postive electrical charge.
Caustic Embrittlement	A problem in which boiler metal becomes brittle and weak because of cracks in the crystalline structure of the metal.
Cavitation	The condition caused when a portion of the water or other liquid entering the eye of a pump impeller flashes into steam bubbles.
Cellulase	An enzyme which causes the decomposition of cellulose.
Cellulose Acetate	A 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 Pump	A pump in which a rotating impeller throws liquid from its vanes through centrifugal force.
Chain-Grate Stoker	A 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 Valve	A One-way flow valve for fluids.
Characterization	The relationship between the amount a valve is open and the amount of flow through the valve.
Chelant	A chemical that helps keep the hardness in the water dissolved so that it does not crystallize on heating surfaces.
Chemical Concentration	The amount of a specific chemical found in a solution, i.e. boiler water, condensate etc.
Chemical Energy	Energy in the fuel that converts to heat energy during the combustion process.
Chimney	Used to create draft. Also an outlet to the atmosphere for the gases of combustion.
Chloramines	Chemicals 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 Hydrocarbons	A group of organic chemicals formed by reacting petroleum derived chemicals with chlorine. Such chemicals include pesticides and herbicides and are frequently potent carcinogens.
Classifier	A 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 Fire	The 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.
Clinker	A mass of coal and ash that has fused together during burning.
Clinker Grinder	Large set of steel rollers with heavy teeth that grind ash and clinkers to reduce their size before they enter the ash hoppers.
Closed Feedwater Heater	Feedwater 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 Exchanger	A 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 Impeller	An impeller that has shrouds on both sides of the vanes.
Closed System	A steam system in which the condensate is recovered and returned to the boiler.
Coagulant	A 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.
Coagulation	A 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 Bunker	An overhead bin where large quantities of coal are stored.
Coal Feeder	Controls the flow of coal entering the pulverizer
Coal Gate	Used to control the depth of coal entering the boiler furnace on chain grate stokers.
Coal Ram	Distributes coal evenly into the center retort on underfeed stokers and forces the coal up to the top where it is burned.
Coal Scale	Measures and records the amount of coal fed to stoker-fired or pulverized coal-fired boilers.
Code	A regulation or law.
Coefficient of Expansion	The 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.
Cogeneration	The 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 Boiler	A boiler design in which the tubes are formed into a continuous coil, with the combustion gases passing through the interior of the coil.
Coking	The separation of heavy carbon-based fractions from the oil, resulting in precipitation of solids that may plug the piping.
Colloid	Undissolved, submicron-sized suspended particles that are well dispersed in a solution and will not readily settle out on standing.
Color Wheel Comparator Test	A relatively simple test used to determine the quantity of iron in the condensate or makeup water.
Column of Water	Water of some specified depth or height.
Combined-Cycle Boiler	An electric power generating system that uses both a gas turbine-driven generator and a steam turbine-driven generator.
Combustion Air Preheater	A piece of equipment provided to preheat the combustion air to some degree before the combustion air enters the furnace.
Combustion Chamber	The area of a boiler where the burning of fuel occurs.
Combustion Efficiency	The percentage of the British Thermal Unit (BTU) content of fuel that is liberated as heat by a boiler’s fuel-burning equipment.
Commissioning	The process of inspecting, preparing, and testing each major component of a system prior to operation.
Compaction	The 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 Combustion	A 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.
Compression	The exertion of equal forces from opposite sides of an object that push toward the middle.
Concentrate	In 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.
Condensate	The water formed when steam condenses to water.
Condensate Polisher	An ion-exchange water softener similar to a sodium zeolite water softener but with resin that can withstand the high temperatures encountered with condensate.
Condensate Pump	Used to return condensed steam to the open feedwater heater.
Condensate Receiver	A tank or other collection point where condensate is accumulated and saved for reuse.
Condensate Return Line	A pipe that carries the condensate and air discharged by the steam traps.
Condensate Tank	Where condensed steam (water) is stored before it is delivered back to the open feedwater heater by the condensate pump.
Condensation	The process of a vapor reverting to liquid when the heat is removed.
Conductance	The quantitive measure of the ability of an electric circuit to allow current flow.
Conduction	A method of heat transfer in which heat moves from molecule to molecule.
Conductivity	The 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 Space	A 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 Blowdown	The process of continuously draining water from a boiler to control the number of impurities in the remaining water.
Controller	A 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 Loop	The collection of control devices and other components necessary for automatic control of a process or sub-process.
Control Valve	A valve used to modulate the flow of fluid.
Convection	A method of heat transfer that occurs as heat is conveyed by a fluid.
Corresponding Pressure	The pressure associated with steam at a given specific temperature.
Corrosion	The loss of metal that occurs in boilers, ductwork, etc. as a result of a chemical or electrochemical attack.
Counterflow	The 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 Pressure	The pressure at which the density of the water and the density of the steam are the same.
Cross-Limiting	The 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 Concentration	The measure of the concentration of a specific impurity in the boiler water divided by the concentration of the same impurity in the feedwater.
Cyclone Separator	A Cylindrical device that separates water droplets from steam through centrifugal force.
Damper	A device that partially or totally inhibits the flow of air or combustion gases through ductwork.
Data Plate	A plate attached to a piece of equipment such as a motor or safety valve that provides important information about the equipment.
Deaerator	An open heat exchanger that removes dissolved gases from the feedwater going to a boiler.
Decatherm	10 Therms or 1,000,000 Btu
Deionization	Removal of ions from water by exchange with other ions associated with fixed charges on a resin.
Demineralizer	A highly efficient ion-exchange process generally used for high-pressure boilers.
Desiccant	A drying agent
Desuperheating	Removing heat from superheated steam to make it suitable for process water.
Diagonal Stays	Braces 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 Valve	A valve that uses a flexible diaphragm as the movable sealing surface.
Differential Pressure	The difference between to pressures measured at different points within the same process.
Differential Temperature	The difference between two temperatures measured at different points within the same process.
Diffusion Ring	A stationary vane in the pump casing.
Digital Signal	An 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 Pocket	The pipe nipple installed on the bottom of the drip leg that catches rust and weld slag.
Discharge Piping	The piping attached to the outlet side of a component, that carries the outlet flow.
Disc Steam Trap	A comparatively small steam trap that uses a flat, round disc as the means of opening and losing the outlet orifice.
Disinfection	Disinfection 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.
Displacement	The volume of fluid forced out of a full container when another body is forced into the container.
Displacer	A long, fairly heavy cylindrical float of small diameter used to measure liquid level in a tank or vessel.
Dissolved Gases	Gases that have gone into solution in water.
Dissolved Solids	Solid impurities that have gone into solution.
Distillate Fuel Oil	A fuel produced by distilling crude oil.
Double-Acting Pump	A reciprocating pump that moves fluid in both directions of stroke.
Double Block and Bleed	A 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 Valve	A control valve that has two discs on one stem and two seats in the body.
Double-Suction Pump	A Pump with a casing and impeller designed to allow a liquid to flow into both sides (eyes) of the impeller at once.
Downcomer Tubes	Tubes that contain the cooler, descending water.
Draft	The movement of air and/or gases of combustion from a point of higher pressure to a point of lower pressure.
Draft Loss	The loss of available draft due to friction and other pressure losses as the flue gases flow through the combustion gas passageways.
Draft System	Consists 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 Superheater	A superheater configured so that condensate in the superheater tubes migrates to a low point from which it can be drained.
Drip Leg	A downward extension from a steam distribution line or piece of heat exchange equipment where condensate is allowed to drain.
Drum Desuperheater	An attemperator that diverts part of the super-heated steam through a heat exchanger in the boiler mud drum.
Drum Pressure Control Valve	A 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 Boiler	A 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 Pipe	An 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 Sheet	The 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 Boiler	A 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 Valve	A valve that controls the movement of steam into and out of the steam cylinder in a duplex pump.
Ductility	The plasticity exhibited by a material under tension loading.
Duplex Pump	A steam-driven, reciprocating, positive-displacement, double-acting pump with two steam cylinders and two liquid cylinders.
Duplex Strainers	Remove solid particles from the fuel oil in fuel oil systems.
Economizer	A series, or bank, of tubes used to recover heat from the boiler flue gas by using it to heat the boiler feedwater.
Efficiency	The comparison of energy output to energy input in a piece of equipment or in a system.
Electric Boiler	A boiler that has heat produced by electric resistance coils or electrodes.
Electronic Flue Gas Analyzer	A device used to analyze flue gas for temperature, gases, draft, and smoke.
Electrostatic Precipitator	A device used to separate fly ash particles from the flue gas stream before it goes out the stack.
Emergency Plan	A document that details procedures, exit routes, and assembly areas for facility personnel in the event of an emergency.
Emission Factor	An expression of the rate of pollutant production per unit of fuel input.
Empty Bed Contact Time	The 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.
Endotoxin	Bacterial lipopolysaccharide, a substance released from the cell walls of gram-negative bacteria when the organism is broken down.
Enthalpy	Total heat in the steam.
Entrainment	The process where solid or liquid particles are carried along with steam flow.
Equalizing Line	A 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.
Error	The amount of deviation of a measurement from the setpoint.
Evaporation Test	A test that allows a low water condition to occur in the boiler in order to test the low water fuel cutoff switch.
Evaporator	A set of heat exchangers that produces water suitable for boiler use from water that contains large quantities of impurities.
Excess Air	The amount of air added to the combustion process over and above that which is theoretically necessary.
Expansion Bend	A 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 Sectional	Contains cast iron sections individually connected to external manifolds with screwed nipples.
Externally-Fired Firetube Boiler	A boiler with a separate furnace area that is usually built of refractory brick.
External Treatment	Boiler water treated before it enters the boiler to remove scale-forming salts, oxygen, and noncondensable gases.
Extractive CEMS	A 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 Evaporation	The heat added to the water in an actual boiler in Btu/lb and divided by 970.3
Feathering	The point when a safety valve is about to lift.
Feedback Transmitter	A transmitter used to provide confirmation that a valve or damper actuator has made a change as commanded.
Feedwater	A mixture of condensate and makeup water that is provided to the boiler to make steam.
Feedwater	Water entering a purification system or an individual piece of purification equipment, such as an ultrafilter or reverse osmosis system.
Feedwater Line	The piping that carries the feedwater from the feedwater pump to the boilers.
Feedwater Pump	A pump that sends the returned condensate and any makeup water into the boiler.
Feedwater System	Consists 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 Boiler	A 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 Boiler	A boiler that must be erected in the field because of its size and complexity.
Filming Amine	A chemical that prevents corrosion of condensate piping by providing a protective barrier.
Final Element	The device that actually causes a change in the process.
Firebox	The part of the boiler where the combustion of fuel takes place.
Firebox Boiler	A firetube boiler In which an arch-shaped furnace is surrounded on both sides by a water leg area.
Fired Vessel	A pressure vessel that includes a burner or combustion equipment of some kind.
Fire Extinguisher	A portable unit used to put out small fires or contain larger fires until the company fire brigade or the fire department arrives.
Fire Point	The 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 Boiler	Has heat and gases of combustion passing through tubes that are surrounded by water.
Firing Rate	The rate at which fuel is being burned by a burner at any particular time.
First Law Of Thermodynamics	Energy cannot be created or destroyed but can be changed from one form to another.
Fittings	Trim found on the boiler that is used for safety, and/or efficiency.
Fit-up	The process of fitting and rolling the tubes into the drums of a new water-tube boiler.
Fixed Carbon	The 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 Impingement	A condition where the flame from burning fuel continually strikes the boiler surfaces or refractory brick.
Flame Propagation Rate	The rate at which the flame can ignite the incoming air-fuel mixture, in feet per second.
Flame Safeguard System	The collection of automatic control devices that ensure safe operation of the combustion equipment.
Flame Scanner	A device that proves that the pilot and main burner flames have been established and remain in service.
Flame Sensor	A device in a flame scanner used to sense the pilot and the main flame in the burner.
Flareback	Flames discharging from the boiler through access doors or ports. Caused by delayed ignition or furnace pressure buildup
Flashback	The condition where a flame travels upwind and into the burner assembly
Flash Economizer	A heat recovery system used to reclaim the heat from the boiler blowdown water and used in conjunction with the continuous blowdown system.
Flash Point	The 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 Steam	Steam that is instantly produced when very hot water is released to lower pressure and, thus a lower boiling temperature.
Flash Tank	A pressure vessel in which condensate or other very hot water under high temperature and pressure is allowed to partially flash into steam.
Flat Gauge Glass	Type of gauge glass used for pressures over 250 PSI.
Flexible Joint	Used to allow for expansion and contraction of steam or water lines.
Flexible Tube Watertuber Boiler	A boiler design in which the tubes exposed to the combustion gases are sharply bent to provide the maximum possible flexibility.
Float & Thermostatic Steam Trap	Contains thermostatic bellows or other thermostatic element and also contains a steel ball float connected to a discharge valve by a linkage.
Flocculation	A 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.
Flocculent	A 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 Velocity	The 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 Recirculation	The process of reintroducing a stream of the spent flue gases from the breeching or stack back into the combustion air stream.
Fluid	Any material that can flow from one point to another. Fluids can be liquids or gases.
Fluidization	A 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 Boiler	A boiler in which fuels are burned in a bed of inert materials such as limestone pellets or sand.
Fluoride	An 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 Rate	The rate per unit of area at which water passes through a semi-permeable membrane, such as those used for ultrafiltration or reverse osmosis.
Fly Ash	Ash from the combustion of coal or other solid fuels that is carried along with the draft through a boiler furnace and ductwork.
Foaming	The development of froth on the surface of the boiler water.
Foot-Pound	A unit of work equal to the movement of a 1-lb object over a distance of 1 ft.
Foot Valve	A 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 Circulation	A variation in water-tube boiler design in which boiler water circulation through the tubes is enhanced by a pump.
Forced Draft	The discharge of combustion air from a fan into a furnace to combine with the fuel for combustion.
Fouling	The 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.
Frequency	The number of cycles of the AC sine wave in one second. Frequency is measured in hertz (Hz) or cycles per second.
Friction Head	The pressure loss associated with friction in the pump piping and fittings. Converted into the equivalent feed of static head.
Fuel Nox	N0x that is formed as a result of the oxidation of nitrogen in the fuel.
Fuel System	Consists of all the equipment, controls, and piping that deliver the fuel to the boiler combustion equipment and control the combustion process.
Fuel-To-Steam Efficiency	The percentage of the heat content of the fuel that is transferred into the boiler water.
Fulvic Acids	Acidic 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 Plug	A temperature-sensitive device that causes an audible alarm when exposed to excessive temperature.
Fyrite Analyzer	An instrument used to measure the percentage of carbon dioxide in the gases of combustion.
Gagging	Application of a clamp-on a safety valve spindle to keep the valve in the full closed position during a hydrostatic test.
Galvanometer	Used to measure small electric currents.
Gas Analyzer	Used to analyze the gases of combustion to determine combustion efficiency.
Gas Calorimeter	Used to determine the BTU content of natural gas.
Gas Cock	A manual quick-closing shutoff valve.
Gases Of Combustion	Gases produced by the combustion process.
Gas Leak Detector	A device used to locate gas leaks in a boiler room.
Gas Mixing Chamber	Where air and gas mix before they enter the furnace in low-pressure gas burners.
Gas Pressure Regulator	Used to supply gas to the burner at the pressure needed for the combustion of the gas.
Gas Tungsten Arc Welding	A welding process in which a virtually non-consumable tungsten electrode is used to provide the arc for welding.
Gas Turbine	A rotating machine used to generate electricity from the flow of hot gases of combustion.
Gate Valve	A 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 Glass	A 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 Valve	A valve used to remove any sludge and sediment from gauge glass lines.
Gauge Pressure	The pressure above atmospheric pressure. It is expressed as psig.
Gear Pump	A 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 Sand	A mineral which is frequently used in depth filters.
Globe Valve	A valve that has a tapered, rounded, or flat disc held horizontally on the stem.
Grade	The size of the pieces of coal
Grains of Hardness	Although 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.
Grates	The 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.
Greensand	A dark, coarse, sandy material sometimes used in iron removal.
Gunning Materials	Plastic refractory materials that are gunned, or sprayed, under pressure onto a surface.
Hammer Test	A test performed on the stays inside the boiler to check the integrity of each, relative to the others.
Handhole	A small access hole used for looking and reaching into the boiler shell during inspections.
Hardness	Hardness 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 Material	A substance that could cause injury to personnel or damage to the environment.
Head	A vertical column of liquid that, due to its weight, exerts pressure on the bottom and sides of its container.
Heat Energy	Kinetic energy caused by molecular motion within a substance.
Heat Exchanger	Any piece of equipment that transfers the heat from a heating medium into some other material.
Heating Surface	The part of the boiler that has heat and gases of combustion on one side and water on the other.
Heating Value	Expressed in BTU per gallon or per pound. Heating value varies with the type of fuel used.
Heat Transfer	Movement of heat from one substance to another that can be accomplished by radiation conduction or convection.
Higher Heating Value	The 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 Boiler	A boiler that operates at a steam pressure over 15 psi and over 6 BHP.
High-Temperature Water Boiler	A 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 Pump	A 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 Stays	Braces 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 Softener	A 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 Boiler	A 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 Well	A reservoir located at the bottom of a condenser where condensate collects.
Huddling Chamber	The 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 Ring	An adjustment in a safety valve that controls the degree to which the escaping steam is directed against the safety valve disc.
Hydrolysis	A Chemical process resulting from reactions with water; frequently used in reference to the breakdown of polymers.
Hydrophilic	Pertaining to a substance which readily absorbs water
Hydrophobic	Pertaining to a substance that does not readily absorb water.
Hydrostatic Test	A 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.
Ignition	The initiation of the combustion process.
Ignition Arch	The curved refractory brick arch directly above the location where green coal enters the furnace in a chain-grate stoker-fired boiler.
Impeller	The rotating element found in a centrifugal pump that converts centrifugal force into pressure:
Impingement	The 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.
Implosion	An inward collapse from external pressure.
Incomplete Combustion	A 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 Draft	The 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.
Injector	A motive fluid pump that uses the velocity of steam to draw water and pump into a boiler.
Inleakage Air	Air that leaks into a furnace.
In-line Steam Separator	A cylindrically shaped vessel that is installed in a steam pipe to remove moisture droplets after the steam has left the boiler.
Input Signal	The flow of control information provided to a control device.
In Situ CEMS	A 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.
Instrument	A device that measures, indicates, records, or controls a specific variable condition such as pressure, temperature, level, flow, or pH.
Insulation	The 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.
Integrator	A calculating device that totalizes the amount of flow over a specified time period.
Interlock	The configuration of control devices such that two or more pieces of equipment cannot be operated independently of each other.
Intermittent Pilot	A 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 Boiler	A boiler with a furnace area surrounded by the pressure vessel.
Internal Treatment	The addition of chemicals directly into the boiler water to control pitting, scale, and caustic embrittlement.
Interrupted Pilot	A 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 Solubility	The tendency of certain impurities in the water to crystallize and precipitate as the temperature of the boiler water increases.
Inverted Bucket Steam Trap	Contains 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.
Ion	An atom or molecule with an electrical charge.
Ion Exchange	Ion 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.
Ion	An 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 Filter	A 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 Ring	A spacer installed between the rings of packing in a pump to allow cooling water to cool the packing and the pump shaft.
Lap Joint	A riveted joint with tow overlapping plates that are drilled through and riveted together at the edges.
Latent Heat	The Btu content of a substance that represents the heat absorbed or given up as it changes state between solid, liquid, and gas.
Laying Up	The procedure used to protect a boiler from internal corrosion if it is to be taken out of service for a longer than normal period.
Lift	The condition where the level of the liquid to be pumped is below the elevation of the pump.
Ligament	The portion of the drum wall between the tube holes.
Lighting Off	The initial ignition of the fuel.
Lignite	Very young and very soft coal that has a high moisture content.
Lime-Soda Process	A 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 Desuperheater	A device that automatically removes superheat from superheated steam so that the steam becomes saturated steam.
Live Steam	Steam in its pure, invisible form.
Lobe Pump	A rotary positive-displacement pump in which liquid being pumped fills the open spaces between the lobes of matched rotors and the pump housing.
Local Control	A control device that is installed directly on or very near the equipment on which it is being used.
Lockout	The use of locks, chains, and other physical restraints to prevent the operation of specific equipment.
Lower Heating Value	The 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 Boiler	Boilers that operate at a steam pressure of no more than 15 psi
Low Water Fuel Cutoff	A device located slightly below the NOWL that turns off the boiler burner in the vent of low water.
Lug & Roller Method	A support method where steel lugs are welded or riveted to the front and rear of the boiler shell.
Main Steam Outlet Lines	Consists 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 Ignition	A period of about 5 sec to 10 sec for the flame scanner to sense the presence of flame from the main flame.
Makeup Water	Water used to replace condensate that is not returned to the boiler.
Makeup Water Feeder	An 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 Line	A city water pipe or well water pipe through which makeup water is added to a boiler.
Malleability	The ability of a material to deform permanently under compression without rupture.
Manhole	Opening found on the steam and waterside of a boiler that is used for cleaning and inspection of the boiler.
Manometer	An instrument that measures draft by comparing pressure at two locations.
Manual Reset Valve	A 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 Control	A unit that receives the primary signal and relays signals to individual control units.
Material Safety Data Sheet	MSDS 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 Capacity	The maximum rating in pounds of steam that a boiler is designed to produce in 1 hour at a given pressure and temperature.
Mechanical Draft	Draft created by fans and blowers.
Mechanical Seal	An assembly installed around a pump shaft that prevents leakage of the pumped liquid along the shaft.
Membranes	Membranes 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 Boiler	A 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 Waterwalls	Waterwalls that are formed into a solid airtight panel by welding a strip of steel between each of the waterwall tubes.
Mercury Switch	A switch that uses the movement of mercury in a glass tube to start or stop electrical current flow in a circuit.
Metering Control	An 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 System	A control that continually measures the boiler condition and adjusts the feedwater control valve.
Metering Pump	A small-capacity pump used to pump a closely measured amount of a liquid.
Microporous	In the context of water purification, membranes having an average pore size, which is between 0.1 and 1.0 microns in diameter.
Miniature Boiler	A small boiler that meets several criteria for dimensions and capacity.
Modulating Feedwater Regulating System	Continually 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 Motor	A small electric motor and reduction gear assembly enclosed in a metal box, used for positioning a valve and/or damper.
Modulating Pressure Control	A control device that regulates the burner for a higher or lower fuel-burning rate, depending on the steam pressure in the boiler.
Monovalent Ion	A cation or anion having a single deficit or extra electron.
Motive Fluid Pump	A pump that uses the force of a secondary fluid to pump the primary fluid.
Multiple-Pass Boiler	A 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 Draft	Draft that occurs without mechanical aid.
Needle Valve	A 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 Installation	Any installation where the pump must draw (lift) liquid up from a source below the pump.
Neutralizing Amine	A chemical that neutralizes the pH of the condensate.
Nitrate	An 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 Gas	A 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 Superheater	a superheater that does not have condensate drain connections.
Non-Permit Confined Space	A 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 Valve	A combination shutoff valve and check valve that allows steam to pass out of the boiler, but not return into the boiler.
Nonrising Stem Valve	A 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.
N0x	An 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 Control	An 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 Control	An approach to steam pressure control in which a burner is either ON or OFF.
ON/OFF Feedwater Regulating System	A 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 control	An 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.
Opacimeter	An automatic indicator that measures the amount of light blocked by the smoke and ash going up the stack.
Open Heat Exchanger	A heating unit in which steam or another heating medium and the fluid being heated come into direct contact.
Open Impeller	An impeller that has vanes that are not enclosed or supported by a shroud on either side.
Operating Range	The range within which a controlled variable is maintained by a control device.
Orifice Plate	A 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 Analyzer	A flue gas analyzer that measures the percentages of carbon dioxide, carbon monoxide, and oxygen in the gases.
OSHA	The occupational Safety and Health Administration.
Osmotic Pressure	When 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 Boiler	A 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 Signal	The 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 Air	The 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.
Overfiring	Forcing a boiler beyond its designed steam-producing capacity.
Overhead Suspension Method	A support method where the boiler is suspended from an overhead steel beam structure by sling members.
Oxidants	Chemicals 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 Welding	A welding process that uses acetylene which is combined with oxygen to produce a flame with a temperature over 6,000°F.
Oxygen Trim System	An automation Control System that makes fine adjustments in the amount of combustion air used in order to minimize excess air.
Oxygen Scavenger	A chemical that reacts with any oxygen remaining in the boiler feedwater and changes it into a form that does not cause corrosion.
Ozone	An 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 Boiler	A boiler that is supplied from the manufacture complete with controls, burner(s), and appliances attached.
Packing Gland	Holds packing or seals in place on valves and pumps to minimize leakage.
Parallel	In 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 Control	An 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.
Particulate	Fine 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 Combustion	A 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 Hardness	A type of hardness can be reduced only by the use of chemicals or distillation.
Permissive	A process condition that must be met before a certain action may be taken.
Permit-Required Confined Space	A confined space that has specific health and safety hazards associated with it.
Personal Protective Equipment	Any device worn by a boiler operator to prevent injury.
pH	Water 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.
Phosphate	A chemical that causes hardness in boiler water to precipitate and settle out as a heavy sludge.
Phosphonate	An 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.
Pilot	Used to ignite the fuel at the proper time in a firing cycle.
Pilot Trial For Ignition or PTFI	A period of about 5 sec to 10 sec for the flame scanner to sense the presence of flame from the pilot.
Piston Valve	A valve that contains a finely machined piston that moves up or down in the interior of a cylindrical steel cage.
Plant Master	The 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 Valve	A valve that is similar to a ball valve, except that a plug valve contains a semi-conical plug through which the flow passes.
Pneumercator	An air-actuated liquid level measuring device.
Polymer Dispersant	A synthetic compound that prevents scale deposits on boiler surfaces.
Polyamide	A synthetic polymer of nylon family used in the fabrication of reverse osmosis and ultrafiltration membranes.
Polysulfone	A synthetic polymer used in the fabrication of reverse osmosis and ultrafiltration membranes which are characterized by extreme thermal stability and chemical resistance.
Polyvalent Ion	A 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 Pressure	A predetermined pressure at which a safety valve opens and remains open until the pressure drops.
Pop-Type Safety Valve	A spring-loaded valve that opens fully and instantly and causes a definite, measured drop in pressure before closing.
Positioning Controls	An 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 Pump	A pump that moves the same amount of liquid with every stroke or rotation.
Positive Draft	The condition wherein the pressure inside the boiler furnace becomes greater than the pressure outside the furnace.
Positive-Suction Pump Installation	Any installation where the pump receives liquid on the suction side from a source above the pump-that is under the head.
Potassium Permanganate	An 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 Point	The lowest temperature at which a liquid will flow from one container to another.
Power	The rate at which work is done.
Predictive Maintenance	A study of the history of the plant components and determination of the expected service life of critical components.
Pressure Drop	Expenditure 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.
Pretreatment	The water treatment process that occurs before the water enters the boiler.
Preventive Maintenance	The practice of performing maintenance activities on a piece of equipment to prevent breakdowns from normal or predictable causes.
Primary Air	The initial volume of air enters the furnace with the fuel for most of the combustion process.
Primary Control	A 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 Sensor	A 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.
Priming	A severe form of carryover in which large slugs of water leave the boiler with the steam.
Priming Pump	A vacuum pump that ejects air from the suction line of larger negative-suction pump installation.
Private Organization	An organization that develops standards from an accumulation of knowledge and experience with materials, methods, and practices.
Process	The collection of equipment and actions required to accomplish the desired objective.
Process Variable	The condition that is being controlled. It is the condition that may vary within the process.
Product Water	The 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 Control	A 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 Analysis	The 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 Coal	Coal that has been ground to the consistency of talcum powder.
Pulverizer	A mill that grinds the coal to a very fine powder.
Pump Controller	Starts and stops a feedwater pump, depending on the water level in the boiler.
Purge Period	A 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 Boiler	Contains hollow cast-iron sections joined with tapered nipples and pulled tightly together with tie rods or bolts.
Pyrite	A common mineral consisting of iron disulfide.
Pyrite Trap	A compartment or box in the pulverizer that catches nuggets of pyrite as they are separated from coal.
Pyrogenic Reactions	A physical response to the presence of endotoxin in the bloodstream, which is characterized by fever and occasionally, chills or shaking rigors.
Pyrometer	An instrument that measures temperatures above the temperature range of mercury thermometers.
Quality Of Steam	The dryness of the steam.
Quick-Closing Valve	A valve that requires a one-quarter turn to be fully open or closed.
Quick-Drain Test	A 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.
Quicklime	Limestone that has been thoroughly dried.
Quick-Opening Valve	A 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 Superheater	A superheater that is directly exposed to the radiant heat of the furnace.
Ramming Materials	Plastic refractory materials that are rammed into place using heavy bars and other tools.
Rank	The hardness of the coal.
Rate Of Combustion	The amount of fuel that is being burned in the furnace per unit of time.
Reagent	A chemical used in a water treatment test to show the presence of a specific substance, such as hardness.
Rear Header	Found on straight-tube water-tube boilers. Connected to the front header by water tubes.
Reciprocating Pump	A displacement pump that uses a reciprocating piston or diaphragm to repeatedly displace fluid from a cylinder or chamber.
Recirculation Line	A line that provides a minimum flow through a pump to prevent overheating.
Recorder	An 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.
Rectifier	An electrical device that converts alternating current (AC) into direct current (DC).
Refractory	Brickwork used in boiler furnaces and for boiler baffles.
Regenerative Air Preheater	A 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.
Reinsurance	The 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 Humidity	The ratio of the actual amount of water vapor in the air to the greatest amount possible at the same temperature.
Relief Valve	A valve that opens in the proportion to the excess pressure, rather than popping open fully.
Remote Control	A control device that is installed a considerable distance from the equipment on which it is being used.
Representative Sample	A sample that is exactly the same as the item being tested.
Reset	The 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 Oil	Fuel oil that remains after the lighter, more volatile hydrocarbons have been distilled off.
Resiliency	The ability of a material to return to its original shape after being deformed.
Resistance	The measure of the ability of an electric circuit to oppose current flow.
Resistivity	Resistivity 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.
Retort	A 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 Chamber	A V-shaped trough, usually about 5′ to 12′ long, with a backplate enclosing the rear end of the retort opposite the feed ram.
Retort Stoker	A stoker in which both the fuel and the combustion air are fed from below the combustion zone.
Reverse Osmosis	A water-purification process in which the water to be treated is pressurized and applied against the surface of a semipermeable membrane.
Ringelmann Chart	A comparison chart used to measure opacity.
Riser Tubes	Tubes exposed to the highest temperatures in the furnace area and contain rising water.
Rising Stem Valve	A valve that has a handwheel and stem that move outward from the body of the valve as the valve is opened.
Rotameter	A variable-area instrument used for measuring the rate of flow.
Rotary Cup Burner	A 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 Pump	A pump with a rotating shaft. A rotary pump may be either a dynamic pump or a displacement pump.
RTD	An acronym for resistance temperature device.
Safety Relief Valve	A valve specially designed to serve as either a safety valve or relief valve, depending on the application for which it is used.
Safety Valve	A valve that opens fully and instantly and causes a definite, measured drop in pressure before closing.
Salt Passage Rate	A measurement of the passage of salts through a reverse osmosis membrane. The salt passage is related to rejection.
Sample Cooler	A 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 Coupon	A small, flat strip of steel that is inserted into an elbow or tee fitting in a piping network.
Saturated	This means that a substance has absorbed as much of another substance as it can absorb.
Saturated Steam	A type of steam that contains no liquid water and is at the temperature of the boiling water that formed the steam.
Scale	Deposits caused by improper boiler water treatment. Learn more about scale HERE.
Scaling	In 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.
Scanner	A device that monitors the pilot and main flame of the furnace. The scanner is used to prove the pilot and main flame.
Scotch Marine Boiler	A firetube boiler that has a flue furnace and horizontal shell.
Scrubber	A device that removes undesirable gaseous elements from flue gas.
Secondary Air	Air mixed with the fuel to ensure that enough oxygen is available to complete the burning.
Second Law Of Thermodynamics	Heat always flows from a body having a higher temperature toward a body having a lower temperature.
Sediment	Particles of solid foreign matter that settle out from a body of liquid.
Sedimentation	The process by which solids are separated from water by gravity and deposited on the bottom of a container or basin.
Semiclosed Impeller	An impeller that has a shroud on one side of the vanes.
Semi-Permeable	Descriptive 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 Heat	The BTU content of a substance that represents the heat absorbed or given up as it changes temperature.
Series	In water purification an arrangement of equipment in a successive or end to end configuration.
Setpoint	The desired point at which an automatic controller maintains a variable condition within a process.
Shakeout	The process of operating a new system as needed to expose and correct the major impediments to reliable operation.
Shaft Sleeve	A replaceable sacrificial part covering a pump shaft.
Shear	The exertion of equal forces in opposite direction in the same plane.
Shear Pin	A link used in a mechanical drive that is designed to break under a specific amount of shear stress.
Shielded Metal Arc Welding	A 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.
Signal	The 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 Pump	A steam-driven, reciprocating, positive-displacement, double-acting pump with one steam cylinder and one liquid cylinder.
Single-Acting Pump	A reciprocating pump that moves the fluid in only one direction of the stroke.
Single-Loop Control	The use of a controller to control a single process variable without any influence from any other controller or process variable.
Siphon	A 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.
Slag	The solid deposits that accumulate on furnace walls and boiler tubes.
Slag Screen	A loosely spaced bank, or several rows of water tubes placed between the superheater and the combustion area of the furnace.
Slaker	A conveyor in which lime is mixed with water to make a soluble paste.
Slinger Ring	A metallic ring that hands on the rotating shaft of a machine and delivers oil from an oil sump to a bearing.
Slip	The difference between the calculated and actual displacement of a pump.
Slow-Opening Valve	A valve that requires five or more full turns of a handwheel to move the valve from fully closed to fully open.
Sludge	Accumulated residue produced from impurities in water.
Sluice	A trench through which water flows rapidly to carry away solid materials.
Smoke Box	The area at the end of a firetube boiler where the flue gases are allowed to reverse direction for the subsequent pass.
Smoke Indicator	An indicating or recording device that shows the density of the smoke leaving the chimney.
Sodium Zeolite Water Softener	An ion-exchange water softener that uses resin beads and a brine solution to soften water.
Solenoid	An electric actuator that consists of an iron plunger surrounded by an encased coil of wire.
Solenoid Valve	A valve that is snapped open or closed by an electric actuator.
Soot	Carbon deposits caused by incomplete combustion.
Soot Blowers	Used to remove soot from around tubes to increase boiler efficiency. Mostly found on water-tube boilers.
Spalling	Hairline cracks in boiler brickwork (refractory) due to changes in furnace temperature.
Specific Gravity	The 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 Volume	The space occupied by a fluid or gas of a particular unit of weight under the specified condition of pressure and temperature.
Spectrophotometer	An instrument that measures the ability of different frequencies of light to pass through a sample of liquid.
Spontaneous Combustion	The process where material can self-generate heat until the ignition point is reached.
Staged Combustion	The 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.
Staging	The placement of more than one impeller on the same shaft in a centrifugal pump.
Standard	An accepted reference, practice, or method.
Standing Pilot	A gas pilot that is always lit.
Static Discharge Head	The 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 Head	The vertical distance from the centerline of the pump up to the level of the liquid in the supply tank.
Static Suction Lift	The vertical distance from the centerline of the pump down to the level of liquid in the supply source below.
Staybolt	A short bolt brace that passes through the water leg of a boiler.
Steam	The gaseous form of water.
Steam and Water Drum	The pressure vessel in a steam boiler that contains both steam and water.
Steam Blanketing	A 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 Blowing	The process of cleaning impurities from new piping by blowing steam through the pipe.
Steam Boiler	A closed vessel in which water is transformed into steam under pressure through the application of heat.
Steambound	A 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 Header	A 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 Main	The piping that carries steam to a section of a building or plant.
Steam Rate	The 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 Separator	Device sued to increase the quality of steam. Found in the steam and water drum.
Steam Space	The space above the water line in the steam and water drum.
Steam System	Consists of the equipment, controls, and piping that carry the steam generated by the boiler to its point of use.
Steam System Efficiency	Measurement of steam usage that takes into account both the equipment supplying the steam and the equipment demanding the steam.
Steam Tracing	A 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 Trap	A mechanical device used for removing condensate and/or air from steam piping and heat exchange equipment.
Steam Trap Survey	The process of identifying, testing, and documenting the condition of all steam traps in a facility.
Steam Turbine	A 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.
Stellite	An alloy of chromium, cobalt, and tungsten.
Sterilization	A physical or chemical process that reduces the number of organisms to a safe predetermined level.
Stirling Boiler	A 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.
Stoker	A device that automatically feeds green, unburned coal and other solid fuel to a furnace.
Stoichiometric Combustion	The process of burning fuel with precisely the amount of air required so that no unburned fuel or unused oxygen remains.
Stopcock	A quick-opening or closing valve usually found on gas lines.
Straight-Tube Watertube Boiler	A boiler design in which the steam-generating tubes are straight rather than bent or curved.
Strainer	A 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 Conveyor	A heavy steel pan conveyor or apron conveyor immersed in a water trough.
Submerged-Tube Vertical Boiler	A firetube boiler with fire tubes completely covered with water all the way to the upper tube sheet.
Suction Pressure	Pressure on the liquid at the suction side of a pump.
Superficial Velocity	The 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 Steam	A type of steam that has been heated above the saturation temperature.
Superheater	A 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 Drain	A 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 Header	Main inlet and outlet line to and from the superheater tubes in the superheater.
Superheater Vent	A 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 Blowdown	The 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 Tank	A 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 Solids	Solid impurities that are suspended in water.
Suspension Sling	Used to support the drum of an HRT boiler.
Swell	The rise in the boiler water level that occurs when the steam load on the boiler is increased or when the steam pressure drops.
Synchronize	The process of bringing the process variable condition very near the setpoint of an automatic control before switching between manual mode and automatic mode.
Tagout	The 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 Valve	A blowdown valve configuration with two valves in series machined into a common valve body.
Technical Society	An organization made up of personnel having expertise in a particular subject and a common professional interest.
Temporary Hardness	A type of hardness that can be reduced by heating the water.
Tensile Strength	The amount of force required to pull an object apart.
Tension	The exertion of equal forces pulling in opposite directions that can stretch an object.
Tertiary Air	Combustion air added to a burner in addition to and downstream of the secondary air.
Therm	A unit of measure indicating 100,000 BTU
Thermal Efficiency	The ratio of the heat absorbed by the boiler to the heat available in the fuel per unit of time.
Thermal Fluid Boiler	A firetube or water-tube boiler that uses a chemical solution instead of water.
Thermal N0x	N0x 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 Shock	The stress imposed on boiler metal by a sudden and drastic change in temperature.
Thermocouple	A device used to measure temperature consisting of two dissimilar metals joined together.
Thermohydraulic Feedwater Regulator	A 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.
Thermometer	An instrument used to measure temperature. Calibrated in degrees Celsius or Degrees Fahrenheit.
Thermostatic Expansion Tube Feedwater Regulator	A 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 Trap	A steam trap that contains a temperature-operated device, such as corrugated bellows, that controls a small discharge valve.
Thermowell	A receptacle into which a temperature sensing instrument is inserted.
Three-Element Feedwater Regulating System	A 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.
Throttling	Controlling the amount of flow that passes through a valve by partially closing it.
Titration Test	A test that determines the concentration of a specific substance dissolved in water.
Titratable Alkalinity	When 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 Heat	The total amount of heat produced by the pump and available to perform useful work, after losses have been subtracted.
Total Force	The pressure (in psi) being exerted on a surface multiplied by the area of the surface.
Total Heat	The sum of sensible heat and latent heat.
Total Organic Carbon	Organic 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 Flowmeter	A flow measuring device that not only measures on an instantaneous basis, but also measures total flow over time.
Trade Association	An organization that represents the producers of specific products.
Transducer	A device that converts one type of control signal into another type of control signal.
Transmitter	An 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.
Tricock	A valve used as a secondary water level indicator.
Tubercle	A bump on a steel boiler surface made up of corrosion products.
Tubular Air Preheater	Consists of tubes enclosed in a shell where flue gases heat up incoming combustion air.
Turbidity	Turbidity 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 Pump	A rotary positive-displacement pump that uses a flat impeller with small flat perpendicular fins machined into the impeller rim.
Turbine Stages	That 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 Cleaner	A motorized mechanical cutter or knocker that removes scale from boiler tubes.
Turbulator	A 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.
Turbulence	1.) 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 Ratio	The 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 System	A water level control system that measures the steam flow from the boiler in addition to the water level.
Ultimate Analysis	The percentages of nitrogen, oxygen, carbon, ash, sulfur, and hydrogen in the coal. (NOCASH)
Ultra Filters	A membrane-based filtration system in which the pore size ranges from .001 to .1 microns
Unfired Vessel	A pressure vessel without combustion equipment, such as compressed air tanks, feedwater heating tanks, steam piping, steam jacketed heat exchangers, and similar vessels.
Utility Watertube Boiler	An extremely large water-tube boiler that generates steam at very high pressure and temperature.
U-Tube Manometer	A 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.
Vacuum	Pressure lower than atmospheric pressure.
Vacuum Breaker	A check valve that prevents the formation of a vacuum in a tank, pressure vessel, or piping system.
Vacuum Gauge	Pressure gauge used to measure the pressure below atmospheric pressure that is calibrated in inches of mercury.
Vacuum Pump	A pump that withdraws gases or vapors from a closed container and creates a vacuum in the container.
Vane Pump	A rotary positive displacement pump that uses a rotating drum located eccentrically inside a cylindrical pump casing.
Vapor Pressure	The equilibrium pressure where the number of molecules evaporating from a liquid surface equals the number of molecules condensing back to the liquid.
Vaporstat	Control with a large diaphragm that makes it highly sensitive to low pressure.
Variable-Area Flow Meter	Measures 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 Condenser	An in-line heat exchanger installed in the vent from a deaerator to the atmosphere.
Venturi	A nozzle with a slight hourglass-shaped taper.
Vertical Firetube Boiler	A firetube boiler in which the tubes are oriented vertically.
Vibrating Grate Stoker	Inclined grates that vibrate, causing the fuel bed to move slowly toward the lower end.
Virus	The smallest infectious microorganism, made of RNA or DNA in a protein shell and which grows only in other living cells.
Viscosity	A measurement of a liquid’s resistance to flow.
Viscous Liquid	A liquid that is thick and resists flow.
Volatile Matter	The gas given off when coal burns.
Volute	A spiral-shaped form.
Warping	The bending or distortion of metallic components such as boiler tubes, structural framework, etc. usually caused by overheating.
Waste Heat Recovery Boiler	A firetube or water-tube boiler in which heat that would otherwise be discarded is used to make steam.
Water Column	A 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 Valve	The 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 Hammer	The 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 Softening	The removal of scale-forming salts from water.
Watertube Steam Boiler	A boiler that has water in the tubes with heat and gases of combustion around the tubes.
Waterwall	Many tubes placed side by side to create a large, flat surface against the furnace walls in a water-tube boiler.
Waterwall Blowdown Valve	The approved valve used to remove sludge and sediment from waterwalls and waterwall header.
Weight-type Alarm Whistle	Alarm 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 Boiler	A firetube boiler with a water-cooled reversing chamber used to direct the combustion gases from the flue furnace to the first pass of tubes.
Windbox	The 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 Weld	A weld made through an opening, or window, in the tube.
Wire Drawing	The erosion that occurs as steam or another high-velocity fluid flows through a small opening like a throttled valve.
Working Pressure	A shortened term for maximum allowable working pressure, but it may also be used to mean the pressure at which the boiler is normally operated.
Zeolite	A synthetic sodium aluminosilicate cation-exchange material based on a naturally-occurring class called zeolites.

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