Article Index



Absolute Pressure- The sum of gauge pressure and atmospheric pressure.

Accumulator- A pressure vessel containing water and/or steam, used for storing the heat of steam to be used at a later time at a decreased pressure.

Acid Cleaning- The method of washing the interior surfaces of steam generating systems by filling the unit with diluted acid followed by an determent to defend against corrosion, and afterward draining, washing and neutralizing the acid by a another wash of alkaline water.

Acidity- Amount of free carbon dioxide, mineral acids and salts such as sulfates of iron and aluminum, that undergo hydrolyzation giving hydrogen ions in water; and is reported as mill equivalents per liter of acid, or ppm acidity as calcium carbonate, or pH, the measure of hydrogen ions concentration.

Air- The mixture of oxygen, nitrogen, and other gases, that have varying amounts of water vapor, and forms the earth’s atmosphere.

Air atomizing oil burner- A burner used in firing oil where the oil is reduced (atomized) by restricted air, and forced into and through one or more currents by breaking the oil into the form of a fine spray.

Air deficiency- Mixture of air and fuel, that’s deficient in its air to supply the oxygen needed for full oxidation of the fuel.

Air free- A substance which air has been removed from.

Air fuel ratio- Ratio of weight and volume, of air to fuel.

Air infiltration- Air leak in a setting or duct.

Air vent- Opening at the top, highest drum of a boilers and pressure vessels to vent air.

Alkalinity- Is determined by analizing the water in the boiler water. Boiler water with a pH of 7 is considered alkaline.

Allowable working pressure- The pressure used in the construction of a boiler for the intendment of calculating minimum passable thickness or natural characteristics of the different parts of the boiler. See design pressure.

Ambient air- The air in the earths atmoshphere (outdoor air), that  surrounds the equipment.

Ambient temperature- Temperature of the air surrounding the equipment.

Aquastat- A device used in hydronic heating systems for controlling water temperature. To prevent the boiler from firing too often, aquastats have a high limit and a low limit.

Atomize- The breaking up of liquid into a fine mist.

ASME Code- The Code that is written by The American Society of Mechanical Engineers, that controls construction, repairs and the operation of steam boilers and associated equipment.

Aspirating burner- A burner in which the fuel in a vaporous or cautiously split form is burned in suspension, the air for combustion being furnished by bringing into contact with the fuel, air drawn through one or more openings by the lower static pressure created by the velocity of the fuel stream.

Atmospheric air- Air under the prevailing atmospheric conditions.

Atmospheric pressure- Pressure from the weight of air pressing down on earth.

Atomization- Method through which an amount of liquid is transformed into a fine mist or spray.

Atomizer- A device that converts a stream of liquid into a fine spray.

Baffle- A wall, barrier or panel used to change the direction of flow of liquid or gas.

Barometric pressure- The weight of the overlying air pressing down on the earth. It is also known as atmospheric pressure.

Barrel- Cylinder portion of a firetube boiler shell surrounding the tubes.

Base load- Is the term applied to that portion of a station or boiler load that is practically constant for long periods.

Beaded tube end- Rounded exposed end of a rolled tube when the tube metal is formed over against the sheet in which the tube is rolled and helps hold on a hose.

Blind nipple- A nipple, or a short piece of pipe or tube, closed at one end.

Boiler blowdown- Boiler blowdown is water intentionally wasted from a boiler to avoid concentration of impurities during continuing evaporation of steam. The water is blown out of the boiler with some force by steam pressure within the boiler. Occurs when water is removed from a steam boiler while the boiler is operating.

Boiler Blowdown safety valve- Boiler blowdown safety valve gets rid of excess pressure building in a boiler. A boiler safety measure.

Boiler blowdown valve- Blowdown Valves are designed for continuous use to control the concentration of dissolved solids in boiler water. (This is not a drain valve)

Boiler blow off valve- Blow off valves are designed for applications requiring intermittent operation in order to remove accumulated sediment from equipment, piping or to lower boiler water level in a rapid manner.

Blower- The blower provides a forced draught on the fire, encouraging combustion.

Boiler- Is "a closed vessel” in which water or other liquid is heated, steam or vapor is produced, steam is superheated, or any blend therefrom, under pressure or vacuum, for use outer to itself, by the direct usage of energy from the combustion of fuels, from electricity or nuclear energy."

Boiler design steam pressure- The temperature of steam for which a boiler is designed.

Boiler drain- A valved connection at the lowest point for the removal of all water from the pressure parts.

Boiler drum- A cylindrical shell closed at both ends designed to withstand internal pressure.

Boiler capacity- The ratio of the average load carried to the maximum boiler design capacity.

Boiler Chemical feed pipe- A boiler chemical feed pipe is a pipe inside a boiler drum through which chemicals for treating the boiler water are introduced.

Boiler Chemical feed pump- A boiler chemical feed pump automatically delivers the proper dose of chemicals to treat your water.

Boiler efficiency- Boiler efficiency is the term boiler efficiency is often substituted for combustion or thermal efficiency. True boiler efficiency is the measure of fuel-to-steam efficiency.

Boiler feedpump- A pump that supplies water to a boiler.

Boiler feedwater- Water introduced into a boiler during operation. It includes make-up and return condensate.

Boiler feedwater regulator- A device for admitting feedwater to a boiler automatically on demand. Practically a constant water level should result.

Boiler feedwater treatment- The treatment of boiler feed water by the addition of chemicals to control alkalinity, prevent scaling, correct pH, and to control conductivity or to eliminate other objectionable characteristics.

Boiler horsepower- Boiler Horsepower is a unit of measurement for measuring the evaporation of 34-1/2 lbs. of water per hour from a temperature of 212 °F into dry saturated steam at the same temperature. Equivalent to 33,475 Btu/hr.

Boiler rating- Heat capacity of a boiler expressed in boiler horsepower, Btu/hour, or pounds of steam/hour.

Boiler shell- The boiler shell the outer cylinder of a pressure vessel.

Boiler water- Boiler water is a relative sample of the circulating boiler water, after generated steam has been separated, before incoming feed water or added chemicals mix with it so that its composition is affected.

Boiling- The rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point and bubbles are formed.

Boiling out- Boiling high alkaline water in boiler pressure parts for the removal of oils, greases, etc.

Booster Fan- Device to increase the pressure or gas flow.

Breeching- Duct which transports the combustion products between parts of a steam generating unit or to the stack.

Bridgewall- A transverse baffle that serves to deflect products of combustion.

Brine- Concentration solution of salt added to pretreat hard water.

British thermal unit (Btu)- The amount of heat required to raise the temperature of 1 pound (0.4 kg) of water 1°F.

Buckstay- Beam held by stays to the exterior of a masonry wall, as that of a furnace or boiler, to keep the adjacent areas of the wall from being forced outward. Keeps the wall from moving.

Bunker C oil-/Fuel Oil No. 6. /Residual Heavy Fuel Oil/ Bunker C Fuel Oil/ -of high viscosity commonly used in marine and stationary steam power plants.

Burner- A device which combines fuel and air in proper proportions for combustion and which enables the fuel-air mixture to burn stably to give a specified flame size and shape.

Burner assembly- Burner assemblies are factory built as single and two or more assemblies which include all parts necessary for its normal function when installed as intended.

Burner block- The specifically fabricated intractable pieces mounted around the burner opening inside the furnace. The burner block forms the burner's airflow opening and helps stabilize the flame.

Burner capacity- Amount of fuel that can be completely burned through a burner at a given set of operating conditions.

Bypass- A passage for a fluid, allowing a percentage of the fluid to pass around its normal course flow channel.

Bypass temperature control- Controlling vapor or air temperature, diverting part of or all heating medium from passing over the heat absorbing surfaces, usually by means of a bypass damper.

C- Carbon element, the principal combustible components of all fuels.

CaCO3 - Calcium Carbonate.

Calorie- A calorie is the amount of energy required to raise one gram of water by one degree Celsius. The kilocalorie (kcal) is a unit used to measure process in industry, 1 kcal = 1000 calories.

Carbon- Element. The principal combustible constituent of all fuels.

Carryover- The chemical solids and liquid entrained with the film of steam bubbles, which is a result of foaming in a boiler. The carryover is a result of poor water condition in the boiler.

Casing- A covering of sheets of metal with fire resistant composition board or other material used to enclose all such portions of a steam generating unit.

Caustic cracking- Usually occurring in carbon steels or iron-chromium nickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 400 to 480 deg. F., Also called caustic embrittlement cracking.

Central station- A power plant or steam heating plant that generates power or steam.

Check valve- A valve designed to prevent reverse flow. One direction flow is only permitted.

Chemical analysis  Determination of the principal chemical constituents.

Chimney- A brick, metal or concrete stack.

Circulation- The movement of water and steam within a steam generating unit.

Circulation ratio- The ratio of water entering a circuit to the steam generated by that passes that circuit in a unit of time.

Circulating tube- A Boiler tube used to connect water spaces of two drums or the pressure parts of a boiler.

Circulator- Pipe or tube for steam or water to pass between upper boiler drums usually located where the heat absorption is low. Circulator is also used to apply tubes connecting headers of horizontal water tube boilers to drums.

Closing-in-line- The sealing with plastic refractory between boiler shell or head and firebrick wall; is used to prevent hot gases from making contact to the boiler above the lowest waterline.

CO- Carbon monoxide.

CO2- Carbon dioxide.

Collector- Device used in the removal of gas solids from flue gas.

Colloid- Organic substance divided fine which tends to inhibit the formation of dense scale and results in deposition of sludge, can cause it to remain in suspension, then it may be blown from the boiler.

Combined feedwater cutoff- Regulating device for makeup boiler water combined with the low water fuel cut off.

Combustion loss- Loss representing the unliberated thermal energy caused by complete oxidation failure to some of the combustible matter in the fuel.

Combustibles- Constituents of a fuel that produce heat.

Combustion- When oxygen is combined with the combustible elements of a fuel and results in a rapid chemical combination that releases heat.

Combustion air- Out door fresh air that is brought in through a furnace duct and/or hot water heater.

Combustion chamber- See Furnace.

Combustion efficiency- The burner’s ability to completely burn the fuel effectively.

Complete combustion- The complete oxidation of all the combustible materials of a fuel.

Concentration- Abundance of a constituent that’s divided by the total volume of a mixture.

Condensate- The liquid phase produced by the condensation of steam or any other gas.

Conduction- Heat transmission through and by means of matter unaccompanied by any obvious motion of the matter.

Conductivity- Is the measure of the ease at which an electric charge or heat can pass through a material.

Continuous blowdown- Uninterrupted removal of concentrated water from a boiler in to control an amount of suspended solid concentration in the remaining water. Blowdown amount depends on the rate of evaporation and the amount of sludge that’s forming material in the feedwater.

Control- Any manual or automatic device that regulates a machine to keep it in normal operation. Automatic devices are driven by changes in temperature, pressure, water level, time, light, or other forces.

Control- A valve used to control air, gas, water, steam or other substance flows.

Control limit- Automatic safety control responding to changes in pressure, liquids or temperature levels that are set normally beyond the operating ranges to limit the operation of controlled equipment.

Control operate- A control that starts or regulates input according to demand and to stop or regulate input on satisfaction of demand. This is not an interlock or safety control.

Convection- The circulatory transfer motion of heat or mass by large fluid movements.

Convection section- Part of a furnace between the radiant and the stack, filled with tubes or pipes that carry process steam that absorb heat by convection heat transfer from the hot gases passing through the area on the way out of the stack.

Corrosion- It is the gradual destruction of metal materials by chemical reaction with their environment. Usually caused by the presence of O2, CO2, or an acid inside a boiler.

Corrosion fatigue- Fatigue in a corrosive environment. It is the mechanical degradation of a material under the joint action of corrosion and cyclic loading. Cracks can be produced by the combined action of repeated or fluctuating stress and a corrosive environment.

Crimping- Reducing the diameter of the end of a boiler tube to remove it to from a boiler.

Crown sheet- The upper sheet of the inner firebox boiler, the plate forming the top of the furnace.

CSD-1- Abbreviation for the ASME standard for Controls and Safety Devices.

Damper- Device controlling the amount of air entering a system used to regulate the volume flow of a gas, such as air.

Davit- The structure or hinges on a firetube boiler which the front and rear doors are suspended when opened.

Deaerator- A device in which oxygen, carbon dioxide, or other noncondensable gases are removed from boiler feedwater, steam condensate, or a process stream. It heats the water to drive off oxygen.

Deaeration- Removing air and gases from boiler feedwater before putting into a boiler.

Delayed combustion- A continuation of combustion beyond the furnace.

Design load- The load for which a steam generating unit is designed, considered the maximum load to be carried.

Design pressure- The pressure used in the design of a boiler for the intendment of calculating minimum passable thickness or natural characteristics of the different parts of the boiler.

Dew point- The temperature at which condensation starts.

Disengaging surface- The surface of the boiler water from which steam is released.

Disassociation- The process by which a chemical compound breaks down into simpler constituents, as do CO2 and H2O at high temperature.

Dissolved solids- Those solids in water which are in solution.

Distillation- The evaporation and consequent collection of a liquid as a means of purification.

Distilled water- Water produced by vaporization and condensation with a resulting higher purity.

Dome- A raised location on the top of the main boiler drum, providing a high point from which to collect dry steam, reduces the risk of priming.

Downcomer- A tube or pipe in a boiler or waterwall circulating system through which fluid flows downward.

Downtime- Amount of time a piece of equipment is not operational.

Draft-The difference in pressure which will produce a flow of air. Drafts in boilers are used to supply combustion air to the boiler furnace.

Draft pressure differential- The difference in static pressure between two locations of gas flow in a system.

Draft gauge- A device for measuring draft air flow.

Drip leg- A bin used for removing condensate collected from steam transmission and distribution lines which it may be removed.

Drowned tube- Either a firetube or watertube that is entirely below the water-level of the operating boiler.

Drum- Cylindrical shell closed at both ends that is designed to withstand internal pressure.

Dryback boiler- Firetube boiler with a refractory lined back door, opens to allow maintenance and/or inspection.

Dry gas- Gas containing no water vapor.

Dry gas loss- The loss representing the difference between the heat content of the dry exhaust gases and their heat content at the temperature of ambient air.

Dry steam  Steam that is at the temperature of saturation, but does not contain any moisture. Commercially dry steam containing not more than one half of one percent moisture.

Duct- Passage for air or gas to flow.

Economizer- Utilizes waste heat by transferring heat from flue gases to warm incoming feedwater.

EDR- Equivalent Direct Radiation is the standard comparison method of heat transfer from a radiator or convector. It is equivalent to the square feet of a surface area necessary to transfer heat at the same rate at which it is produced by a generator. A single boiler horsepower equals 140 ft2 EDR.

Efficiency- The ratio of output to input.

Ejector- A device which utilizes the kinetic energy in a jet of water or other fluid.

Entrainment- The movement of sediment in a stream from the boiler water by the steam.

Equalizer- Creates equal pressure on the supply and return of the boiler.

Equivalent evaporation- Evaporation expressed in pounds per hour at which water would be vaporized in a given steam boiler if supplied and evaporated at the normal boiling point and normal atmospheric pressure.

Evaporation- The change of state from a liquid to a vapor.

Evaporation rate- The number of pounds of water that is evaporated in a unit of time.

Evaporator- Pressure vessel used to evaporate raw water by means of a steam coil. The steam is condensed b means of cooling water coils, and this distilled water is used as make up for boiler feed.

Excess air- Air supplied in optimum amount will minimize heat loss up the stack and improve combustion efficiency. Some amount of excess air, depending on the available fuel/air mixing energy, is required to assure thorough mixing of the fuel and air for complete combustion.

Expansion joint- Permits movement without causing high stresses in penetration pipe and boiler wall.

Explosion door- A door in a boiler or furnace that is designed to function like a pressure relief valve calibrated by a predetermined gas pressure and protect the boiler against major damages caused by combustion gas explosions.

External treatment- Boiler feed water that is treated prior to its addition to the boiler.

Fan- A motor made up of a propeller and housing used to move air or gases at a considerable lower pressure.

Fan performance- Measuring fan performance in specifications of volume, total pressures, static pressures, speed, power input, mechanical and static efficiency, at a certain air density.

Fan performance curves– Representation in a graph for total pressure, static pressure, power input, mechanical and static efficiency and the range of amounts as abscissa, at constant speed and air density.

Feed pump- A pump that supplies water to a boiler.

Feedwater- Water introduced into a boiler during operation. It includes make-up and return condensate.

Feedwater regulator- A device for admitting feedwater to a boiler automatically on demand. Practically a constant water level should result

Feedwater treatment– Chemicals used in Boiler feedwater treatment is used to control alkalinity, prevent scaling, correct pH, and to control conductivity.

FGR- Flue Gas Recirculation is highly effective technique used for lowering Nitrogen Oxide (NOx) emissions from burners.

Filter- A porous device for removing impurities or solid particles from a liquid or gas passed through it.

Fired pressure vessel- Is a pressure vessel which is completely or partially exposed to fire from burners or combustion gases or otherwise heated from the combustion of fuel.

Firetube boiler- A type of boiler design in which combustion gases flow inside the tubes and water flows outside the tubes.

Firing rate control- Controls the firing rate of the burner according to fluctuations from pressure or temperature set points. This system can be set up to operate the burner on-off, high-low or in capacity to load demand.

Fixed carbon- Is the solid combustible residue that remains after a coal particle is heated and the volatile matter is expelled.

Flame- A hot glowing body of ignited gas that is generated by something on fire.

Flame detector- Is a sensor designed to detect and respond to the presence of a flame or fire and if it’s been lost, may send a signal to a control system.

Flame Propagation rate- The velocity of a flame spread in a combustible environment outward from the point at which the combustion started.

Flame safeguard- A control that completely runs a burner through many steps of operation to produce proper air purge, ignition, normal operation, and shutdown for operation safety.

Flame speed- Is the measured rate of expansion of the flame front in a combustion mixture. Flame propagation is the result of strong coupling between chemical reaction, transport processes of mass diffusion & heat conduction and fluid flow.

Flammability- Is the ability of a substance to burn or ignite, causing fire or combustion.

Flammability limits- Refer to the range of compositions, for fixed temperature and pressure, within which an explosive reaction is possible when an external ignition source is introduced. The upper and lower bounds of the fuel/air mixture which will support combustion. The upper flammability limit indicates the maximum fuel concentration in air that will support combustion. The lower flammability limit indicates the minimum fuel concentration in the air that will support combustion. Outside of these bounds the mixture does not burn.

Flareback- A burst of flame back or out from a furnace or similar space in opposition to the normal direction of the draft.

Flashback- Is the unwanted intrusion of flame behind the burner nozzle resulting in uncontrolled fire within the premix supply conduit, occurring only in pre-mix gas burners when the flame speed overcomes the gas-air mixture flow velocity exiting the gas tip.

Flashing- The process of producing steam by discharging water into a region of pressure lower than the saturation pressure that corresponds to the water temperature

Flash point- The lowest temperature at which a liquid can form an ignitable mixture in air near the surface of the liquid.

Flue- Is a chamber through which smoke, hot gases, and combustion byproducts are vented.

Flue gas- A pipe or channel for conveying exhaust gases to the stack.

Foaming- The continuous formation of bubbles which have sufficiently high surface tension to remain as bubbles beyond the disengaging surface.

Forced circulation- An extra pump is used to increase the circulation rate as compared to that of natural circulation boiler.

Forced draft fan- Fan providing positive air pressure to fuel burning equipment.

Fouling- The buildup of unwanted solid deposits to gas passages or on heat transfer surfaces which results in restriction to the flow of gas or heat.

Fuel- A substance that can be burned to produce energy in the form of heat or power.

Fuel air mixture-The ideal mix of gas to air.

Fuel air ration- Is the mass ratio of air to fuel present in a combustion process.

Fuel Nox- Generic term for the mono-nitrogen oxides NO and NO2, are produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures.

Fuel oil- Is a general term for a number of burnable liquids made from crude oil.

Fuel to steam efficiency- This is the ratio of BTU output divided by BTU input on a particular boiler.

Furnace- Is a device used for high-temperature heating.

Furnace pressure- Pressure inside the combustion chamber.

Furnace volume- The heat release rate of the furnace or combustion chamber.

Furnace arch- Is one which spans the fire-chamber and supports; or it may form the ceiling and roof of a metal furnace, uppermost part (bridgewall) of a radiant furnace.

Furnace Draft- The difference between atmospheric pressure and the pressure existing in the furnace or flue gas passage of a boiler.

Furnace explosion- The violent combustion of refuse or fume build in a furnace or combustion chamber.

Fusible plug- A threaded metal cylinder usually of bronze, brass or gunmetal, with a tapered hole drilled completely through its length. This hole is sealed with a metal of low melting point that flows away if a pre-determined, high temperature is reached.

Gas analysis- Determination of ingredients of a gaseous blend.

Gas burner- Is a device to generate a flame to heat up products using a gaseous.

Gas pressure regulator- Gas pressure regulator is a valve that automatically cuts off the flow of a liquid or gas at a certain pressure to the burner supply line.

Gauge cock- A valve attached to a water column or drum used to ascertain the water level.

Gauge glass- The gauge glass or sight glass is a transparent tube through which the operator of a boiler can observe the level of water contained within.

Gauge pressure- Is the additional pressure in a system relative to atmospheric pressure.

Grade- Oil classification according to quality, generally based on ASTM specifications.

Grain- Unit of measure used in water analysis measuring impurities in water (17.1 grains = 1 part per million - ppm).

Handhole- Access opening in a boiler usually not larger than 6inches.

Handhole cover- A handhole closure.

Hardness- Is the amount of dissolved calcium and magnesium in the water. Usually expressed as grains per gallon or ppm as CaCO3.

Hard water-Is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of calcium and magnesium-containing minerals such as limestone, chalk and dolomite.

Header- A distribution pipe or manifolds that tie multiple steam mains to one boiler or multiple boilers to one or more steam mains supplying a number of smaller lines tapped off of it. .

Heat exchanger- A vessel in which heat is transferred from one medium to another.

Heating surface- Surface exposed to fire or to the heated products of combustion on one side and water on the other for absorption and transfer of heat to the heat medium per American Boiler Manufacturers Association (ABMA)

Heat release rate- Heat release rate is a measurement of heat energy released over a specific unit of time, expressed in Btu per hour per cubic foot of furnace volume or square foot of heating surface.

Heating value- Is the amount of heat produced by the complete combustion of a unit quantity of fuel. It is commonly expressed in Btu per lb., per gallon, or cu-ft.

High fire- The input amount of a burner at or near maximum.

High gas pressure control- A control to stop the burner if the gas pressure is too high.

High gas pressure switch- A switch to stop the burner if gas pressure is too high.

High oil presser control- A control to stop the burner if the oil temperature is too high.

Hot well- A tank used to receive condensate from various sources on its passage back to a boiler through the feedwater system. It usually is vented to the atmosphere.

Hydrocarbon- A chemical compound of hydrogen and carbon.

Hydrostatic test- strength and tightness test of a closed pressure vessel by water pressure.

Igniter- A device for igniting a fuel mixture that provides proven ignition energy required to immediately light off the main burner

Ignition- The initiation of combustion.

Ignition temperature- The lowest temperature at which a combustible substance when heated takes fire in air and continues to burn.

Incomplete combustion- Will occur when there is not enough oxygen to allow the fuel to react completely to produce carbon dioxide and water.

Induced draft fan- Is used on the exhaust side of boiler pulling air through the boiler to exhaust hot gases from the heat absorbing equipment.

Inhibitor- A substance that slows down or prevents a particular chemical reaction or other process, or that reduces the activity of a particular reactant, catalyst, or enzyme. An example in boiler work is the use of an inhibitor, when using acid to remove scale, to prevent the acid from attacking the boiler metal.

Injector- Utilizes a steam jet to deliver feed water into a boiler.

Input rating- The fuel burning capacity of a burner at sea level in Btu per hour as specified by the manufacturer.

Insulation- Material used to insulate something to reduce heat losses.

Interlock- A device to prove the physical state of a required condition, and to furnish that proof to the primary safety control circuit.

Intermittent blowdown- Intermittent Blowdown valves are designed to operate at predetermined intervals by releasing water & accumulated sludge periodically through a blowdown tap near the bottom of the boiler.

Intermittent firing- Cyclic firing whereby fuel and air are burned in a furnace for frequent short periods.

Internal treatment- The treatment of boiler water by introducing chemicals directly into the boiler.

Intermittent ignition- An igniter which burns during light off and while the main burner is firing and which is shut off with the main burner.

Internally fired boiler- A firetube boiler whose fire box or furnace is inside the boiler and surrounded by water.

Ion- An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Ion exchange-The exchange of ions of the same charge between an insoluble solid and a solution in contact with it, used in water-softening and other purification and separation processes.

Lagging- Material providing heat insulation for a boiler, pipes, etc.

Leakage- Gradual loss of fluid from which enters or leaves through the enclosure of air or gas passages.

Limit control- A device that has electrical settings to switch off at predetermined pressures or temperatures. Also known as an interlock. See interlock.

Lining- High temperature insulation known as refractory; this material insulates the area in furnace that is exposed to the burner flame.

Live steam- Is steam under pressure, obtained by heating water in a boiler. The steam is used to operate stationary or moving equipment.

Load- Amount of output required and weight carried.

Load factor- Load Factor is defined as the ratio of average demand to maximum demand during a given period.

Low draft switch- A control to limit the burner action if the draft is too low. Generally used with mechanical draft.

Low fire start- Used to prove the firing rate of burner controls in the low fire position. To provide safe operating position during light off.

Low gas pressure switch- A control to prevent the burner operation if gas pressure is too low.

Low gas pressure control- A control to prevent the burner operation if gas pressure is too low.

Low oil temperature control- A control to prevent burner operation if the temperature of the oil is too low. (cold oil switch)

Low water cutoff- A safety device used to cut fuel to the boiler when the water level falls below a safe level.

Lug- A bracket applied to boiler suspension, a steel eyepiece fitted and riveted or welded to the curved area of a boiler drum or shell and is connected by a steel U-bolt or sling rod to steel structures overhead.

Make up water- The water added to boiler feed to compensate for that lost through exhaust, blowdown, leakage, etc.

Manhole- The opening in a pressure vessel of sufficient size to permit a man to enter.

Manifold- A pipe or header that collects fluid or distributes fluid to multiple pipes and tubes.

Manual gas shut off valve- A valve in a gas line to be manually turned for completely turning on or shutting off the supply.

Manual reset device- A control that requires resetting by hand to restart the burner once safe operating conditions are restored.

Manufactured gas- Fuel gas manufactured from coal, oil, etc., as differentiated from natural gas.

Maximum allowable working pressure- Is the maximum pressure a pressurized vessel can be exposed to. The MAWP of the completed boiler shall be less than or equal to the lowest design pressure determined for any of its parts.

Maximum continuous load- The period of time the maximum load which can be maintained.

Maximum instantaneous demand- Is a sudden peak load demand and is usually for a short period of time.

Mechanical atomizing oil burner- A burner for firing oil that uses mechanical pressure for atomization in which fuel oil flow is broken down into tiny particles (spray).

Mechanical draft- A forced created by mechanical means.

Micron- A micron is a unit of length equivalent to a millionth of a meter, or 0.000039 in. or 1/25400 in. The diameter of dust particles is often expressed in microns.

MMBtu- Millions of Btus (British Thermal Units).

Moisture- Refers to the presence of a liquid, especially water, often in trace amounts, water in the liquid or vapor phase.

Moisture in steam- Is the amount of water particles carried by the steam, expressed as a percentage by weight.

Moisture loss- The difference in heat content between the moisture in the boiler exit gases and that of moisture at ambient air temperature.

Mud- Particles, precipitates and general impurities that builds up in the lower parts of a boiler. Mud reduces water circulation and so a local buildup may lead to localized overheating.

Mud drum- A water drum, particularly one mounted low on the boiler whose function is primarily to trap mud from circulation.

Mudhole- A small hole near the bottom, through which the sediment is withdrawn.

Multifuel burner- A burner that can use multiply fuels.

Natural circulation- Is the ability of a fluid in a system to circulate continuously, with the difference in density being the only driving force.

Natural gas- Gaseous fuel occurring in nature.

NOx- Produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures. Abbreviation for all of the family of oxides of nitrogen.

Nozzle- Is a short flanged or welded neck connection on a drum or shell to control direction of fluids into or out of.

Oil burner- Is a mechanical device that combines fuel oil with proper amounts of air before delivering the mixture to the point of ignition in a combustion chamber.

Oil gun- Part of a burner’s assembly that atomizes oil into a fine spray so it can be blown into the combustion chamber.

Oil tip- The part of the oil gun that blows the atomized oil fuel mixture into the furnace.

Oil heat and pumping set- Parts of a heater for warming fuel oil to yield the desired viscosity, and a pump for delivering the oil at the desired pressure.

Operating control- Is a burner management control to start and stop the burner and must be set below the high limit control.

Operating pressure- The pressure registered on a gauge when a system is in normal operation.

Orsat- Is a gas analyzer which is a piece of laboratory equipment used to analyze a gas sample (typically fossil fuel flue gas) for its oxygen, carbon monoxide and carbon dioxide content.

Overpressure- Excessive pressure applied and is dangerous to operate above the safe operating pressure.

Oxidation- Is the interaction between oxygen molecules and other substances.

Oxidizing atmosphere- Refers to a gaseous atmosphere in which an oxidation reaction occurs.

Oxygen attack- Oxygen in water produces pitting and corrosion.

Packaged boiler- A boiler supplied with all needed components including; burner, controls and auxiliary equipment, designed as a single engineered package, and ready for on-site installation.

Pass- Confined passage that contains a heating surface which fluid flows through in one direction typically.

Perfect combustion- The complete oxidation of all the combustible constituents of a fuel, utilizing all the oxygen supplied.

pH- Is a measure of the hydrogen ion concentration of a solution. Solutions with a high concentration of hydrogen ions have a low pH and solutions with a low concentration of H+ ions have a high pH.

Pilot (Ignitor)- A flame utilized to ignite the fuel at the main burner or burners.

Pitot tube- Is a pressure measurement instrument used to measure gas flow stream velocity.

Pitting- Is a form of extremely localized corrosion from an oxygen attack that leads to the creation of small holes in the metal of a boiler.

Port- An opening allowing the oils, slime and other floatable debris to pass through.

Postpurge- A method of scavenging the furnace and boiler passes to remove all combustible gases after flame failure controls have sensed pilot and main burner shutdown and safety shut-off valves are closed.

Power burner- A forced air burner controls the mixture of gas and air that is injected into the boiler's combustion chamber overcoming any resistance to deliver the quantity of air required for combustion.

ppm- Abbreviation for parts per million.

Precipitate- Is an insoluble solid that emerges from a liquid solution. To separate materials from a solution by the formation of insoluble matter by chemical reaction. The material which is removed.

Precipitation- Is the creation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid the removal of solid or liquid particles from a fluid.

Preheated air- Air at a temperature exceeding that of the ambient air, increases efficiency.

Pressure- Is the force applied by a liquid or gas on the surface of an object per unit area over which that force is distributed.

Pressure drop- The difference in pressure between two points in a system, caused by resistance to flow.

Pressure vessel- Pressure vessel is a closed container designed to confine a fluid at a pressure substantially different from the atmospheric pressure.

Primary air- The portion of the combustion air introduced with the fuel at the burner.

Primary safety control- Safety switch to provide safety shutdown, directly controlling the response to flame properties, sensing the presence of flame and in the event of ignition failure or unintentional flame extinguishments will cause a safety shutdown.

Priming- Is a condition in the boiler of which water is carried over into the steam delivery containing high concentrations of any solids.

Process steam- Steam used for heat and industrial processes other than producing power.

Products of combustion- Gases, vapors, and solids resulting from the combustion of fuel.

Pulsation- Recurring alternate increase and decrease of pressure.

Purge- To introduce air into the furnace and the boiler flue passages in such volume and manner as to completely replace the air or gas-air mixture contained therein.

Radiant- Emitting heat or having the property transfer heat by rays similar to rays of light.

Radiation– A form of heat transfer. Radiation is the process of continuous interchange of energy by means of electromagnetic waves without a change in the temperature of the medium between two bodies involved.

Radiation loss- A term used in boiler heat balance accounting for the conduction, radiation, and convection heat losses to the ambient air.

Rated capacity- The manufacturers stated intended full-load sustained capacity rating for boiler.

Rate of blowdown- A rate normally expressed as a percentage of the water fed.

Raw water- Water that is taken directly from its source without treatment.

Reaction- Chemical transformation or change, often accompanied by a release of energy, that occurs naturally over time, or is purposefully induced by the interaction of two substances.

Recirculation- Re-adding part of the flowing fluid to repeat the cycle of circulation.

Recycle- The operation of normal burner start up after a shutdown.

Reducing atmosphere- An atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapors, and which may contain actively reducing gases such as hydrogen, carbon monoxide and gases that would oxidize in the presence of oxygen, such as hydrogen sulfide.        

Refractory- Material that retains its strength at high temperatures and is used in boilers to protect metal surfaces and for boiler baffles.

Reheater- Steam boiler component in which heat is added to intermediate-pressure steam, which has given up some of its energy in expansion through the exhaust. Reheaters and superheaters are one of the most important accessories of boiler that improves the thermal efficiency.

Relay- An electrical device, typically incorporating an electromagnet, that is activated by a current or signal in one circuit to open or close another circuit

Relative humidity- he amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.

Relief valve(Safety Relief Valve)- A type of valve used to automatically relieve the pressure in a system or vessel actuated by the pressure upstream of the valve and characterized by opening pop action with further increase in lift with an increase in pressure.

Residual fuels- Bunker C oil -/Fuel Oil No. 6. /Residual Heavy Fuel Oil/ Bunker C Fuel Oil/ -of high viscosity commonly used in marine and stationary steam power plants Products remaining from crude petroleum by removal of some of the water and an appreciable percentage of the more volatile hydrocarbons.

Resin- A sticky bead like flammable hydrocarbon organic substance, insoluble in water, used in chemical exchange for softeners and dealkalizers.

Return flow oil burner- Atomizing oil burner that withdraws part of the oil supplied to the atomizer and returns it to be stored or to the line supplying it.

Ringelmann chart- Grid series for determining smoke density in stack gas streams. The series of rectangular grids consists of 4 grids of black lines; varying widths printed on a white background and is used as a method for measuring of blackness.

Rotary oil burner- Atomization is accomplished in a burner by feeding oil to the inside of a rapidly rotating cup.

Saddle- A support casting.

Safe working pressure- See "Design Pressure." The pressure used in the design of a boiler for safe operations.

Safety valve- Prevents boiler pressure from rising above the setting of the valve by relieving excessive steam pressure, guarding against hazards of over pressure.

Safety valve drain-  A hole required through the body below the valve-seat level in the safety valves that are larger than 2 in., used to prevent condensate from collecting.

Safety valve escape- A pipe that discharges steam from a safety valve to a safe area.

Safety valve lifting lever- A lever for lifting a safey valve from it's seat.

Safety relief valve- Is used for the purpose of relieving the boiler pressure when it exceeds the MAWP (maximum allowable working pressure) and thereby prevent an explosion

Safety shut off valve- Features a springing action that shuts off the valve automatically when a problem has been detected and opens the electric current to shut off the valve until it is fixed.

Sampling- The removal of a portion of a material for examination or analysis.

Saturated air- Air that contains the maximum amount of water vapor it can hold at its temperature and pressure. 100% humidity.

Saturated steam- Steam at the same temperature as the water from which it was formed.

Saturated temperature(Boiling point)-The temperature at which evaporation occurs at a particular pressure.

Saturated water- A mixture of dry air and water vapor at its maximum concentration for the prevailing temperature and pressure. Water at its boiling point.

Scale- Hard water deposits caused by improper boiler water treatment.

Secondary treatment- Treating the water after the initial treatment of the boiler feedwater.

Sediment- Solid material that settles in water at the bottom of the boiler.

Self-supporting steel stacks- A steel stack of strong enough to support itself without using lateral support.

Service water- Is water that has been chemically treated for use in boiler or other industrial processes.

Shell- The cylindrical exterior of a steam boiler forming a case.

Sludge- Accumulation residue produced from impurities.

Smoke- Tiny particles of carbon or soot resulted from incomplete combustion.

Softening- Is the removal of calcium, magnesium, and certain other metal atoms in hard water.

Soft water- Is water which has relatively low concentration of calcium carbonate and other ions.

Solenoid valve- An electromagnetic valve positioned open or closed.

Solution- Is a mixture of one substance dissolved in another so the properties are the same throughout such as boiler water.

Soot- Impure carbon particles resulting from the incomplete combustion of hydrocarbons.

Soot blower- A mechanical device for removing the soot that is deposited on the furnace tubes of a boiler during combustion.

Spalling- Hairline cracks in boiler brickwork (refractory) due to changes in furnace temperature.

Spark Arrester- Any device which prevents the emission of flammable debris to protect large dust particles flow or sparks from a stack, usually screening at the top.

Specific heat- The quantity of heat, expressed in Btu, required to raise the temperature of 1 lb. of a substance 1°F.

Specific humidity- The weight of water vapor in a gas water-vapor mixture per unit weight of dry gas.

Spontaneous combustion- Occurs when combustible materials self-ignite.

Spray nozzle- A nozzle from which a liquid fuel is discharged in the form of a spray.

Stack- A vertical conduit, which due to the difference in density between internal and external gases, creates a draft at its base.

Stack draft- The magnitude of the draft measured at the inlet to the stack.

Stack effect- That portion of a pressure differential resulting from difference in elevation of the points of measurement.

Stagnation- The condition of being free from movement or lacking circulation.

Standard air- Dry air weighing 0.075 lb. per cu ft. at sea level (29.92 in. Barometric Pressure) and 70 °F.

Standard flue gas- Gas weighing 0.078 lb. per cu ft. at sea level (29.92 in. Barometric Pressure) and 70 °F.

Static pressure- The measure of potential energy of a fluid.

Steam- The vapor phase of water, unmixed with other gases.

Steam boiler- A closed pressure vessel in which water is converted to steam by the application

Steam bound- Condition that occurs when the temperature in the open feedwater heater gets too high and the feedwater pump cannot deliver water to the boiler of heat.

Stem gauge- A gauge for indicating the pressure of steam.

Steam generating unit- A unit to which water, fuel, and air are supplied and in which steam is generated. It consists of a boiler furnace, and fuel burning equipment, and may include as component parts water walls, superheater, reheater, economizer, air heater, or any combination thereof.

Steam pressure gauge- Indicates the steam pressure in the boiler in pound per square inch.

Steam purity- The degree of contamination. Contamination is expressed in ppm.

Steam quality- The percent by weight of vapor in a steam and water mixture.

Steam separator- Device used 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 strainer- Used before steam traps and turbine throttle valves to remove solid impurities.

Steam supply stop valve- The valve installed at the steam outlet of the boiler to shut off the flow of steam

Steam trap- An automatic device that removes gases and condensate from steam lines and heat

exchangers without the loss of steam.

Steam turbine - Used to drive boiler auxiliaries or generators in large plants.

Stopcock- A quick-opening or closing valve usually found on gas lines.

Stud- A projecting pin serving as a support or means of attachment.

Suction pressure- Pressure on the liquid at the suction side of a pump

Sulfur- A combustible element found in coal and fuel oil.

Superheated steam- Steam at a temperature above it’s correspond pressure.

Superheater- Used to increase the amount of heat in the steam.

Superheater drain- Valve found on the superheater header outlet. Used to maintain flow throughout the superheater during start-up and shutdown.

Surface blowdown valve- Used to remove impurities from the surface of the water in a steam and water drum.

Surface blowoff- Removal of water, foam, etc. from the surface at the water level in a boiler. The equipment for such removal.

Surface condenser- A shell-and-tube vessel used to reduce the exhaust pressure on the outlet end of turbines or engines.

Surface tension- Caused by impurities on the top of the water in the steam and water drum.

Surge- The sudden displacement or movement of water in a closed vessel or drum.

Suspended solids- Undissolved solids in boiler water.

Swinging load- A load that changes at relatively short intervals.

Tertiary air- Air for combustion supplied to the furnace to supplement the primary and secondary air.

Theoretical air- The quantity of air required for perfect combustion.

Theoretical draft- The draft which would be available at the base of a stack if there were no friction or acceleration losses in the stack.

Therm- Unit used to measure BTU content of natural gas. One Therm = 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.    

Thermocouple- Used to measure temperatures in the system and send them back to a recording chart.

Thermometer- Instrument used to measure temperature (degree of heat). Calibrated in degrees Celsius or degrees Fahrenheit.

Thermal shock- A cycle of temperature swings that result in failure of metal due to expansion and contraction.

Through stay- A brace used in fire-tube boilers between the heads or tube sheets.

Tile- A preformed refractory, usually applied to shapes other than standard brick.

Total air- The total quantity of air supplied to the fuel and products of combustion. Percent total air is the ratio of total air to theoretical air, expressed as percent.

Total pressure- The sum of the static and velocity pressures.

Total solid concentration- The weight of dissolved and suspended impurities in a unit weight of boiler water, usually expressed in ppm.

Trap- A receptacle for the collection of undesirable material.

Treated water- Water which has been chemically treated to make it suitable for boiler feed.

Trim- Ancillary boiler components, like water level controls, pressure controls, and temperature controls.

Tube- A hollow cylinder for conveying fluids.

Tube brushes- Used in fire tube boilers to remove soot from inside of tubes.

Tube hole- A hole in a drum, heater, or tube sheet to accommodate a tube.

Tube sheets- Tubes are rolled, expanded and beaded into front and rear tube sheets of HRT and scotch marine boilers and upper and lower tube sheets of vertical fire tube boilers.

Tubular gauge glass- Round gauge glass used for pressures up to and including 250 psi.

Turbulence- Movement of water in the steam and water drum.

Turbulent burner- A burner in which fuel and air are mixed and discharged into the furnace in such a manner as to produce turbulent flow from the burner.

Turndown ratio- Ratio of maximum to minimum fuel or steam input or boiler output.

UL LISTED- Product certification that indicates the product meets safety standards determined by Underwriters Laboratories. (ULC and cUL indicate Canadian requirements.

Unfired pressure vessel- A vessel designed to withstand internal pressure, neither subjected to heat from products of combustion nor an integral part of a fired pressure vessel system.

Use factor- The ratio of hours in operation to the total hours in that period.

VA- Volt amperes.

Vapor- The gaseous product of evaporation.

Vaporization- The change from liquid or solid phase to the vapor phase.

Velocity pressure- The measure of the kinetic energy of a fluid.

Vent- An opening in a vessel or other enclosed space for the removal of gas or vapor.

Vent condenser- Removes oxygen and other non-condensable gases in a deaerating feedwater heater.

Vertical firing- An arrangement of a burner such that air and fuel are discharged into the furnace in practically a vertical direction.

Viscosity- Measure of the internal friction of a fluid or its resistance to flow.

Volume of air- The number of cu ft. of air per min expressed at fan outlet conditions.

Waste heat- Sensible heat in non-combustible gases discharged to the environment.

Water alkalinity- amount of carbonates, bicarbonates, hydroxides and silicates or phosphates in the water and is reported as grains per gallon, or ppm as calcium carbonate.

Warping- Bending or distortion of boiler or superheater tubes, usually caused by overheating.

Water column- A vertical tubular member connected at its top and bottom to the steam and water space respectively of a boiler, to which the water gauge, water level controls, and fuel cutoff may be connected.

Water column blowdown valve- 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 gauge- The gauge glass and its fittings for attachment.

Water hammer- A banging condition that is caused by steam and water mixing in a steam line.

Water level- The elevation of the surface of the water in a boiler

Water softening- The removal of scale-forming salts from water.

Watertube boiler- Boiler that has water in the tubes with heat and gases of combustion around the tubes.

Waterwall- Vertical or horizontal tubes found in the furnace area of water tube boilers that lengthen the life of the refractory.

Waterwall blowdown valve- Approved valve used to remove sludge and sediment from waterwalls and waterwall headers.

Water tube- A tube in a boiler having the water and steam on the inside and heat applied to the outside.

Water vapor- A synonym for steam, usually used to denote steam of low absolute pressure.

Waterwall- The side of the boiler consisting of water-carrying tubes which absorb radiant heat that prevent excessively high furnace temperatures.

Weep- a small leak (opening) that allows water to drain from within a boiler joint which forms droplets (or tears) of water very slowly.

Wetback boiler- Firetube boiler design with the back portion of the boiler has a water jacket.

Wetness- A term used to designate the percentage of water in steam. Also used to describe the presence of a water film on heating surface interiors.

Wet steam- Steam containing moisture.

Windbox (plenum chamber)- Pressurized air chamber that supplies air to a furnace.