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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

ABMA:
American Boiler Manufacturers Association.
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Absolute Pressure:
( 1 ) Total pressure measured from an absolute vacuum. It equals the sum of the gauge
pressure and the atmospheric pressure corresponding to the barometer.
( 2 ) Air at standard conditions (70°F air at sea level with a barometric pressure of 29.92
in Hg) exerts a pressure of 14.696 psi. This is the pressure in a system when the
pressure gauge reads zero. So the absolute pressure of a system is the gauge
pressure in pounds per square inch added to the atmospheric pressure of
14.696 psi (use 14.7 psi in environmental system work) and the symbol is "psia".
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Accumlator - Steam:
A pressure vessel containing water and/or steam, which is used to store the heat of
steam for use at a later period and at some lower pressure.
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Acid Cleaning:
The process of cleaning the interior surfaces of steam generating units by filling the unit
with dilute acid accompanied by an inhibitor to prevent corrosion and by subsequently
draining, washing, and neutralizing the acid by a further wash of alkaline water.
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Acid Soak:
A method of acid cleaning, in which the acid is pumped into the boiler and rests there for
a period of time.
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Acidity:
Represents the amount of free carbon dioxide, mineral acids, and salts (especially
sulfates of iron and aluminum) which hydrolyze to give hydrogen ions in the water. The
acidity is reported as millie equivalents per liter of acid, or ppm acidity as calcium
carbonate, or pH, the measure of hydrogen ion concentration.
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Active Storage Pile:
A method of stockpiling coal, sometimes called live storage. The pile is located outside
the plant but adjacent to it, and usually contains four or five days of operating supply.
The pile is not compacted, as it is not stored long enough to be exposed to the hazard of
spontaneous combustion.
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Actuator:
The portion of a regulating valve which converts mechanical, fluid, thermal, or electrical
energy into mechanical motion to open or close the valve seats or other such devices.
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Adiabatic Flame Temperature:
The theoretical temperature that would be attained by the products of combustion
provided the entire chemical energy of the fuel, the sensible heat content of the fuel and
combustion above the datum temperature were transferred to the products of
combustion. This assumes: No heat loss to surroundings and no dissociation.
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Air:
A substance containing by volume approximately 78 - 79% nitrogen, 20.95% oxygen,
.94% argon, traces of carbon dioxide, helium, etc.
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Air Atomizing Oil Burner:
A burner for firing oil in which the oil is atomized by compressed air, which is forced into
and through one or more streams of oil which results in the breaking of the oil into a fine
spray.
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Air Deficiency:
Insufficient air, in an air-fuel mixture, to supply the oxygen required for complete
oxidation of the fuel.
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Air-Fuel Ratio:
The ratio of the weight, or volume, of air to fuel.
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Air Purge:
The removal of undesired matter by replacement with air.
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Air, Ambient:
( 1 ) Generally the air surrounding the object. The air that surrounds the equipment.
( 2 ) The standard ambient air for performance calculations is air at 80°F, 60% relative
humidity, and a barometric pressure of 29.921 in. Hg, giving a specific humidity of
0.013 LB of water vapour per LB of dry air.
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Alkali:
A substance having marked basic properties applying to hydroxides of potassium,
sodium, lithium, and ammonium. They turn red litmus to blue. Includes hydroxides of the
alkaline earth metals of barium, strontium, and calcium.
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Alkaline:
Having a pH greater than 7.
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Alkalinity:
An expression of the total basic anions (hydroxyl groups) present in a solution. It also
represents, particularly in water analysis, the bi-carbonate, carbonate, and occasionally,
the borate, silicate, and phosphate salts that will react with water to produce the hydroxyl
groups.
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Ambient Air Temperature:
Temperature of fluid (usually air) which surrounds object on all sides.
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Amine:
A chemical used in water treatment as a filming or neutralizing agent to protect the metal
parts.
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Angle Valve:
A type of globe valve design having pipe openings at right angles to each other. Usually
one opening on the horizontal plane and one on the vertical plane.
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Anticipating Control:
One that, by artificial means, is activated sooner than it would be without such means, to
produce a smaller differential of the controlled property. Heat and cool anticipators are
commonly used in thermostats.
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Anti-Foam Additive (Foam Inhibitor):
An additive used to reduce or prevent foaming.
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Antifoam Agents:
The reduction of carryover by the addition of polymerized esters, alcohols, and amides.
The antifoam agent is absorbed on the steam generating surface resulting in a
hydrophobic condition, causing fewer but larger steam bubbles, which readily coalesce.
These agents also weaken the wall of the bubble formed, causing them to quickly burst
on the water surface.
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Antifoulants:
Materials that prevent fouling from depositing on heat transfer equipment. Materials
that prevent deposits from forming include anti-oxidants, metal coordinators, and
corrosion inhibitors. Compounds that prevent deposition are surfactants. They act as
detergents or dispersants.
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Antioxidant:
( 1 ) A substance which when added in small amounts to petroleum products will delay
or inhibit undesirable changes such as the formation of gum, sludge, and acidity,
which are brought about by oxidation.
( 2 ) An additive for the purpose of reducing the rate of oxidation and subsequent
deterioration of the material.
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Aquastat:
Water limit temperature control, a safety device often used on boilers.
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Ash:
The incombustible inorganic matter in the fuel.
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Ash-Free Basis:
The method of reporting fuel analysis, whereby ash is deducted and other constituents
are recalculated to total 100%.
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Ash Pit:
A pit or hopper located below a furnace where refuse is accumulated and from which
refuse is removed at intervals.
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ASHRAE
The American Society of Heating, Refrigeration, and Air Conditioning Engineers.
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ASME
American Society of Mechanical Engineers.
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ASME Boiler Code:
The boiler code listing standards, specified by the American Society of Mechanical
Engineers, for the construction of boilers.
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Aspirating Burner:
A burner in which the fuel in a gaseous or finely divided form is burned in suspension.
The air for combustion is supplied by bringing air, drawn through one or more openings
by the lower static pressure created by the velocity of the fuel stream, into contact with
the fuel.
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Atmospheric Pressure:
( 1 ) Pressure exerted by the weight of the atmosphere; standard atmospheric pressure
is 101.325 kPa or 1.01325 bars or 14.696 psia or 29.921 inches of mercury at sea
level.
( 2 ) The weight of a column of air, one square inch in cross section and extending from
the earth to the upper level of the blanket of air surrounding the earth. This air
exerts a pressure of 14.7 pounds per square inch at sea level, where water will boil
at 212°F. High altitudes have lower atmospheric pressure with correspondingly
lower boiling point temperatures.
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Atomize:
Process of changing a liquid to minute particles or a fine spray.
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Atomizer:
A device by means of which a liquid is reduced to a very fine spray.
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Attenuation:
The sound reduction process in which sound energy is absorbed or diminished in
intensity as the result of energy conversion from sound to motion or heat.
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Automatic Control:
The process of using the differences between the actual value and desired value of
any variable to take corrective action without human intervention.
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Automatic Controller:
A device that measures the value of a variable that operates to correct or limit the
deviation from a selected reference.
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Automatic Governing System:
A system that correlates steam flow, pressure, shaft speed, and shaft output for any
one-turbine unit.
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Available Draft:
The draft that may be utilized to cause the flow of air for combustion or the flow of
products of combustion.
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Azeotrope:
Having constant maximum and minimum boiling points.
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Background Noise:
Sound other than the wanted signal. In room acoustics, the irreducible noise level
measured in the absence of any building occupants.
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Baghouse:
A chamber containing bags for filtering solids out of gases.
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Base Metal:
( 1 ) The metal present in the largest proportion in an alloy. (Copper is the base metal in
brass)
( 2 ) The substrate metal that is coated or protected by a surface coating.
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Black Liquor:
The liquid material remaining from pulpwood cooking in the soda or sulfate papermaking
process.
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Bleeder Valve:
A valve designed to slowly relieve a liquid or gas from a system.
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Bleeding:
Slowly reducing the pressure of liquid or gas from a system or cylinder by slightly
opening a valve.
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Bleedoff:
The continuous removal of water from a re-circulating water system.
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Bleedoff Rate:
The rate at which water is continuously removed from a system.
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Blowdown:
( 1 ) In connection with boilers or cooling towers, the process of discharging a significant
portion of the aqueous solution in order to remove accumulated salts, deposits and
other impurities.
( 2 ) Boiler water that is removed from the boiler in order to maintain the desired
concentration levels of suspended and dissolved solids in the boiler and/or removal
of sludge.
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Blowdown Valve:
A specially designed, manually operated valve that connects to the boiler for the
purpose of reducing the concentration of solids in the boiler or for draining purposes.
(Often called bottom blowdown.)
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Blow-Off Valve:
A valve which permits a boiler control to be flushed out, and the function of same to be
checked.
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Boiler Crown:
The part of a boiler that forms the roof of the furnace in a firebox boiler, or the equivalent
surface in other types of boilers.
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Boiler Efficiency:
The term "boiler efficiency" is often substituted for combustion or thermal efficiency. True
boiler efficiency is the measure of fuel-to-steam efficiency.
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Boiler Feed Water:
The total water fed to a boiler. This water, usually, is the mixture of return steam
condensate and makeup water.
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Boiler Feed Water Pump:
A pump that is governed by a controller that monitors the actual boiler water level and
adds water to the boiler when the boiler needs it. The pump controller is mounted on the
boiler.
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Boiler Heating Surface:
The area of the heat transmitting surfaces in contact with the water (or steam) in the
boiler on one side and the fire or hot gases on the other.
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Boiler Horse Power:
( 1 ) The equivalent evaporation of 34.5 pounds of water per hour at 212°F to steam at
212°F. This is equal to a heat output of 33,475 Btu per hour, which is equal to
approximately 140 sq. ft. of steam radiation (EDR).
( 2 ) The work required to evaporate 34.5 lb of water per hour into steam from and at
100°C.
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Boiler Rating:
The heating capacity of a boiler expressed in boiler horsepower, Btu/hour, or pounds of
steam/hour.
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Boiler Water:
A term construed to mean a representative sample of the circulating boiler water, after
the generated steam has been separated and before the incoming feed water or added
chemical becomes mixed with it so that its composition is affected.
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Boiling Out:
The boiling of high alkaline water in boiler pressure parts for the removal of oil and
greases, prior to normal operation or after major repairs.
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Boiling Point:
The temperature at which the vapor pressure of a liquid equals the absolute external
pressure at the liquid-vapor interface.
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Boiling Temperature:
Temperature at which a fluid changes from a liquid to a gas.
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British Thermal Unit, (Btu):
The Btu is defined as the heat required to raise the temperature of 1 pound of
water 1°F.
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Bulge:
A local distortion or swelling outward caused by internal pressure on a tube wall or boiler
shell due to overheating.
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Burner Windbox:
A plenum chamber around a burner that maintains an air pressure sufficient for proper
distribution and discharge of secondary air.
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Burner Windbox Pressure:
The air pressure maintained in the windbox or plenum chamber measured above
atmospheric pressure.
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Bypass:
( 1 ) A pipe or duct, usually controlled by valve or damper, for conveying a fluid around
an element of a system.
( 2 ) Passage at one side of, or around, a regular passage.
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CO:
Carbon monoxide.
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CO2:
Carbon dioxide.
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Calcium:
A scale-forming element found in boiler feedwater.
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Calorimeter:
Device used to measure quantities of heat or determine specific heats.
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Caustic Soda:
A common water treatment chemical, sodium hydroxide.
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Cavitation:
The formation and collapse, within a liquid, of cavities or bubbles that contain vapour or gas or both. In general, cavitation originates from decreases in static pressure in the liquid. In order to erode a solid surface by cavitation, it is necessary for the cavitation bubbles to collapse on or close to that surface.
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Centrifugal Pump:
( 1 ) A pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing,
having an inlet and a discharge connection. The rotating impeller creates pressure
in the liquid by the velocity derived from centrifugal force.
( 2 ) Pump that produces fluid velocity and converts it to pressure head.
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Change of State:
Condition in which a substance changes from a solid to a liquid or a liquid to a gas caused by the addition of heat. Or the reverse, in which a substance changes from a gas to a liquid, or a liquid to a solid, caused by the removal of heat.
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Check Valve:
Device that permits fluid flow in one direction.
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Chemical Feedline:
The line that feeds the boiler treatment chemicals into the boiler.
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Chemical Precipitation:
When the chemicals react with the dissolved minerals in the water to produce a relative insoluble reaction product. A typical example of this takes place with a lime-soda softening process.
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Closed Re-Circulating Water System:
A system using as a heat-transfer medium water that continuously circulates through closed piping and heat exchanger without evaporation.
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Coefficient of Expansion:
A measure of the change in length or volume of an object. Specifically, a change measured by the increase in length or volume of an object per unit length or volume.
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Colloids:
Organic matter of very fine particle size, usually in the range of 10-5 to 10-7 cm in diameter. It tends to inhibit the formation of dense scale and results in the deposition of sludge, or causes it to remain in suspension, so that it may be blown from the boiler.
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Combined Feeder Cutoff:
A device that regulates makeup water to a boiler in combination with a low-water fuel cutoff.
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Combustion Air:
Air used in the combustion process. Air contains oxygen which is required to burn fuel.
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Combustion Chamber:
An enclosed space provided for the burning of fuel.
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Combustion Efficiency:
The effectiveness of the burner to completely burn the fuel. A well-designed burner will operate with as little as 10 to 20% excess air, while converting all combustibles in the fuel to useful energy.
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Condensate:
The liquid formed by condensation of a vapor. In steam heating, water condensed from steam; in air conditioning, water extracted from air, as by condensation on the cooling coil of a refrigeration machine. The capacity of traps, pumps, etc., is sometimes expressed in pounds of condensate they will handle per hour. One pound of condensate per hour is equal to approximately 4 sq. ft. of steam heating surface (240 Btu per hour per sq.ft.)
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Condensate Pump:
( 1 ) Device to remove water condensate that collects beneath an evaporator.
( 2 ) A pump that returns condensate from remote condensers (radiators, evaporators,
heat exchangers) to a hot well (condensate return tank) close to the boiler. In some
systems it adds water to the boiler when the condensate tank becomes full, whether
or not the boiler needs water.
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Continuous Blowdown:
The uninterrupted removal of concentrated boiler water from a boiler to control total concentration of solids in the remaining water.
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Controller:
A device that uses a signal from a sensor to measure and regulate, comparing the data with a desired value, and issues signals for corrective action.
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Corrosion:
The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties.
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Corrosion, External:
A chemical deterioration of the metal on the fireside of boiler heating surfaces.
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Corrosion, Inhibitors:
Substances that slow the rate of corrosion.
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Corrosion, Internal:
Usually refers to an electrochemical deterioration of the boiler surface at or below the water surface.
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Critical Point:
A point at which the saturated liquid and saturated vapor states are identical. Also, the latent heat of evaporization is zero at this point.
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Critical Pressure:
The pressure at the critical temperature above which the fluid no longer has the properties of a liquid, regardless of further increase of pressure.
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Critical Temperature:
That temperature above which the vapor phase cannot be condensed to liquid by an increase in pressure.
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Cycle:
A series of thermodynamic processes during which the working fluid can be made to undergo changes involving energy transition and is subsequently returned to its original state.
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Damper:
A device used to vary the volume of air passing through an air outlet, air inlet or duct.
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Deaerating Heaters:
Mechanical device using steam to strip dissolved gases from the boiler feedwater and heating the feedwater.
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Deaeration:
( 1 ) The act of separating air from substances.
( 2 ) The removal of air and other gases from boiler feed water prior to its introduction into a boiler.
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Deaerator:
An apparatus or device that is used to remove dissolved air or oxygen from water.
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Deconcentrator:
A cylindrical tank connected before the boiler to receive the boiler feedwater before entering the boiler. It is designed to promote settling of suspended solids, which then could be removed via its own blowdown device. Used for operation with very high-suspended solids.
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Degrees of Superheat:
The amount by which the temperature of a superheated vapor exceeds the temperature of the saturated vapor at the same pressure.
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De-ionization:
Deionization, a more general term than deashing, embraces the removal of all charged constituents or ionizable salts (both inorganic and organic) from solution.
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Demineralizer:
A process to remove dissolved matter from boiler pretreated water by contacting the water with ion-exchange resins.
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Desalination:
The removal of inorganic dissolved solids from water.
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Design Pressure:
Highest or most severe pressure expected during operation. Sometimes used as the calculated operating pressure plus an allowance for safety.
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Design Working Pressure:
The maximum allowable working pressure for which a specific part of a system is designed.
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Desilicizer:
An apparatus or device used to remove silica from a water supply.
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Diatomaceous Earth Filtration:
A process in which a filter cake or precoat of diatomaceous earth is used as a filter medium.
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Differential:
The temperature or pressure difference between cut-in and cut-out temperature or pressure of a control.
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Direct Acting:
Instruments that increase control pressure as the controlled variable (such as temperature or pressure) increases. Reverse acting instruments increase control pressure as the controlled variable decreases.
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Dissolved Gases:
Gases soluble in water.
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Dissolved Solids:
Those solids in water that are in solution.
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Distillation:
( 1 ) Vaporization of a substance with subsequent recovery of the vapor by condensation.
( 2 ) Often used in less precise sense to refer to vaporization of volatile constituents of a fuel without subsequent condensation.
( 3 ) Involves boiling water and condensing the vapor.
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Domestic Hot Water:
Potable hot water as distinguished from hot water used for house heating.
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Draft:
The difference between atmospheric pressure and some lower pressure existing in the furnace stack or gas passages of a steam-generating unit.
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Drum Water Level Line:
The water level in the steam drum during the normal operating mode.
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Dry Fire:
Insufficient water in a boiler to carry off the heat of combustion. It causes dry fire, which results in cracked cast iron sections and melted fire tubes.
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Dry Pipe:
A perforated or slotted pipe or box inside the steam drum and connected to the steam outlet.
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Dry Saturated Steam:
Saturated steam containing no water in suspension.
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Dry Steam:
Steam containing no moisture. Commercially dry steam containing not more than one half of one percent moisture.
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Economizer:
A series of tubes located in the path of flue gases. Feedwater is pumped through these tubes on its way to the boiler in order to absorb waste heat from the flue gas.
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Eddy Current Testing:
An electromagnetic nondestructive testing method in which eddy-current flow is induced in the test object. Changes in flow caused by variations in the object are deflected into a nearby coil or coils where they are measured.
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EDR:
Equivalent direct radiation is the rate of heat transfer from a radiator or convector. It is equivalent to the square feet of surface area necessary to transfer heat at the same rate at which it is produced by a generator. A single boiler horsepower equals 140 ft2 EDR.
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Efficiency:
The ratio of output to input.
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Electric Boiler:
A boiler that generates steam or hot water by the action of immersed electrodes, which conduct electricity through the boiler water, which in turn, generates heat by its resistance to electric current.
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Entrainment:
The transport of water or solids into a gas stream. In a boiler, this is carryover; in a cooling tower, drift.
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Excess Air:
Air supplied for combustion in excess of that theoretically required for complete oxidation.
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Expansion Joint:
Device in piping designed to allow movement of the pipe caused by the pipe's expansion and contraction.
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Expansion Tank:
A reservoir usually above a closed re-circulating water system that is blanketed with a gas to permit expansion and contraction of water in the system during temperature changes.
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Fahrenheit:
A thermometric scale in which 32 (°F) denotes freezing and 212 (°F) the boiling point of water under normal pressure at sea level (14.696 psi).
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Feedwater:
Water that is fed to a system such as a boiler. It includes makeup water and return condensate.
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Feedwater Line:
The piping leading to a system through which the feedwater flows, usually between the feedwater pump and boiler steam drum.
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Feedwater Heater:
A device used to heat feedwater with steam or other thermal energy source.
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Feedwater Treatment:
The treatment of boiler feed water by the addition of chemicals to prevent the formation of scale or to eliminate other objectionable characteristics.
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Fin:
An extended surface to increase the heat transfer area. Metal sheets attached to tubes.
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Firetube:
A tube, in a boiler, through which the hot gases flow and transfer heat to the water on the outside of the tube.
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Firetube Boiler:
This type of boiler has the water on the external side of the tube and the heat (fire) on the internal side of the tube.
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Fire Wall:
The back end of a boiler, opposite the burner, at which the hot gases change direction of flow.
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Firing Rate Control:
A pressure, temperature or flow controller that controls the firing rate of a burner according to the deviation from pressure or temperature set point. The system may be arranged to operate the burner on-off, high-low or in proportion to load demand.
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Flame Detector:
A device, which indicates if a fuel (liquid, gaseous, or pulverized) is burning, or if ignition has been lost. The indication should be transmitted as a signal to a control system that would shut off the fuel supply. A PRIMARY SAFETY DEVICE in a burner control system.
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Flame Safeguard:
A control that sequences the burner through several stages of operation to provide proper air purge, ignition, normal operation, and shutdown for safe operation.
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Flash:
The portion of a superheated fluid converted to vapor when its pressure is reduced.
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Flash (Steam):
The rapid passing into steam of water at a high temperature when the pressure it is under is reduced so that its temperature is above that of its boiling point for the reduced pressure. For example: if a trap into a low-pressure return or into the atmosphere discharges hot condensate, a certain percentage of the water will be immediately transformed into steam. It is also called re-evaporation.
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Flash Tank:
A vessel used for separating the liquid phase from the gaseous phase formed from a rise in temperature and/or a reduction of pressure on the flowing stream.
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Flue:
A passage for products of combustion.
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Flue Gas:
The gaseous product of combustion in the flue to the stack.
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Fluid Head:
The static pressure of fluid expressed in terms of the height of a column of the fluid, or of some manometric fluid, which it would support.
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Fly Ash:
A finely divided siliceous material formed during the combustion of coal, coke, or other solid fuels.
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FM:
Factory Mutual.
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Foaming:
( 1 ) Formation of steam bubbles on the surface of the boiler water due to high surface tension of the water.
( 2 ) A condition that occurs when an organic substance, usually oil, is floating on the surface of the water in a boiler. When the boiler is fired, a layer of foam develops on the surface of the water. This generally is indicated in the gauge glass by large swings in water level.
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Fouling:
Deposits of impurities, dirt or foreign matter that clog systems or restrict flow and interfere with heat transfer.
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Fouling Factor:
The degree of interference with heat transfer.
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Fuel - Air Mixture:
Mixture of fuel and air.
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Fuel - Air Ratio:
The ratio of the weight, or volume, of fuel to air.
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Furnace:
An enclosed space provided for the combustion of fuel.
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Furnace Pressure:
Pressure occurring inside the combustion chamber; positive if greater than atmospheric, negative if less than atmospheric, and neutral if equal to atmospheric.
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Furnace Volume:
The cubic contents of the furnace or combustion chamber.
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Fusible Plug:
Plug or fitting made with a metal of a known low-melting temperature. Used as a safety device to release pressures in case of fire.
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Gas Analysis:
The determination of the constituents of a gaseous mixture.
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Gas Pressure Regulator:
A spring loaded, dead weighted or pressure balanced device which will maintain the gas pressure to the burner supply line.
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Gas Valve:
Device in a pipeline for starting, stopping or regulating flow of gas.
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Gauge Glass:
The transparent part of a water gauge assembly connected directly or through a water column to the boiler, below and above the water line, to indicate the water level in a boiler.
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Gauge Pressure:
Absolute pressure minus atmospheric pressure.
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Gauge, Vacuum:
Instrument used to measure pressures below atmospheric pressure.
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Generating Tube:
A boiler tube used for evaporation.
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Grade:
Oil classification according to quality, generally based on ASTM specifications.
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Hard Water:
Water that contains dissolved compounds of calcium, magnesium or both.
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Hardness:
( 1 ) Generally refers to the presence of calcium and magnesium content of the water.
( 2 ) The scale-forming and lather-inhibiting qualities that water, high in calcium and
magnesium ions, possesses.
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Head:
( 1 ) Pressure, usually expressed in feet of water, inches of mercury or millimeters of
mercury.
( 2 ) The measure of the pressure of water expressed in feet of height of water:
1 psi = 2.31 feet of water.
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Header:
Length of pipe or vessel to which two or more pipelines are joined. Carries fluid from a common source to various points of use.
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Heat Exchanger:
Device used to transfer heat from a warm or hot surface to a cold or cooler surface. (Evaporators and condensers are heat exchangers.)
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Heat Of Vaporization:
The latent heat absorbed by a substance as it changes from a liquid to a vapor.
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Heat Transfer:
( 1 ) Flow of heat by conduction, convection or radiation.
( 2 ) Movement of heat from one body or substance to another. Heat may be transferred
by radiation, conduction, convection or a combination of these three methods.
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High Limit Control:
A device which normally monitors the condition of the controlled medium and interrupts system operation if the monitored condition becomes excessive (for example a high level of fluid in a storage tank).
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Hot Well:
A tank used to receive condensate from various sources on its passage back to the boiler through a feedwater system.
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Hot-Water Heating Boiler:
A boiler in which no steam is generated and from which hot water is circulated for heating purposes and then returned to the boiler.
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Hot-Water Re-Circulating System:
A heating system using water as a heat-transfer medium through a heat exchanger or boiler to terminal heating unit.
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Hydraulic Head:
The force exerted by a column of liquid expressed by the height of the liquid above the point at which the pressure is measured. Although head refers to a distance or height, it is used to express pressure, since the force of the liquid column is directly proportional to its height. Also called head or hydrostatic head.
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Hydrocarbons:
Organic compounds containing only hydrogen and carbon atoms in various combinations.
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Hydronic System:
A re-circulating water system used for heating and/or comfort cooling.
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Ignition:
The initiation of combustion.
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Ignition Temperature:
Lowest temperature of a fuel at which combustion becomes self-sustaining.
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Impingement:
High-velocity flow of water or gas over a metal surface, causing premature failure by abrasion.
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Incomplete Combustion:
The partial oxidation of the combustible constituents of a fuel.
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Induced Draft Fan:
A fan exhausting hot gases from the heat absorbing equipment.
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Inhibitor:
An additive used to retard undesirable chemical action in a product. An inhibitor is added to corrosive environments to decrease corrosive action. In boiler work, the inhibitor is used to remove scale and prevent the acid from attacking the boiler metal.
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Injector:
A device utilizing a steam jet to entrain and deliver feed water into a boiler.
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Insulation, Thermal:
Material which is a poor conductor of heat; used to retard or slow down flow of heat through wall or partition.
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Intermittent Blowdown:
Blowdown is taken from the mud drum, waterwall headers or the lowest point of circulation.
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IRI:
Industrial Risk Insurers.
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Joule:
The unit used to measure heat, work, and energy in the metric system. Its symbol is J. It is the amount of energy required to move an object of 1 kg mass to a height of 1 m. Also called a Newton-metre (Nm).
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kPa (kiloPascal):
A unit of pressure.
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Kilo Calorie:
This is the amount of heat (energy) necessary to raise the temperature of 1 kg of water 1°C. (Kilo calorie = kcal)
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Laminar Flow:
A non-turbulent flow regime in which the stream filaments glide along the pipe axially with essentially no transverse mixing.
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Leakage:
( 1 ) In water treatment, it refers to the passing of impure steam or boiler water through the drum internals.
( 2 ) In water treatment, the phenomenon in which some of the influent ions are not adsorbed and appear in the effluent when a solution is passed through an under regenerated exchange resin bed.
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Light Crude Oil:
A crude oil of relatively high API gravity (usually 40°C or higher).
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Longitudinal Seam:
A riveted or welded seam along the longitudinal axis of a boiler shell or drum.
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Low Pressure Steam:
As defined by ASME, low pressure steam is 15 PSIG or less.
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Magnesium:
A scale-forming element found in some boiler feed water.
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Makeup Water:
Water fed to a system to replace that which is lost - for example, water fed to a boiler to replace that lost as steam or condensate; water fed to a cooling tower to replace that lost by evaporation, drift, or other causes.
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Manometer:
( 1 ) A device to measure small to moderate pressure differentials; generally constructed
from glass or plastic tubes filled with water, oil, alcohol or other suitable fluids.
( 2 ) An instrument for measuring pressures, especially a U-tube partially filled with a
liquid, usually water, mercury, or a light oil, so constructed that the amount of
displacement of the liquid indicates the pressure being exerted on the instrument.
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Maximum Allowable Working Pressure:
The maximum gauge pressure permissible in a completed boiler. The MAWP of the completed boiler shall be less than or equal to the lowest design pressure determined for any of its parts. This pressure is based upon either proof tests or calculations for every pressure part of the boiler using nominal thickness exclusive of allowances for corrosion and thickness required for loadings other than pressure. It is the basis for the pressure setting of the pressure relieving devices protecting the boiler.
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Microfiltration:
A membrane filtration process, which forces water through a porous barrier. Pores are usually between 0.1 to 20 µm, when used for water purification. For filtering purposes, pore sizes are .045 µm.
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Minimum Safe Water Level:
Also know as safe operating level. The minimum level of water in a boiler where the burner will still operate. Below this level, the burner should be off due to low water.
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Modulating:
Type of device or control which tends to adjust by increments (minute changes) rather than by either "full on" or "full off" operation.
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Modulating Control:
A mode of automatic control in which the action of the final control element is proportional to the deviation from set point of the controlled medium.
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Mud Drum:
A pressure chamber of a drum or header type located at the lower extremity of a water tube boiler and fitted with a blow off valve.
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Multi-Fuel Burner:
A burner designed to efficiently burn more than one fuel.
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Natural Circulation:
The circulation of water in a boiler caused by differences in density. Also referred to as thermal or thermally induced circulation.
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Naturally Aspirated:
A term used to describe a diesel engine in which air flows into the engine by means of atmospheric pressure only.
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Non-Destructive Inspection (NDI):
A procedure such as ultrasonic or radiographic inspection, for determining the quality of a material without permanently altering anything.
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NOx:
Abbreviation for all of the family of oxides of nitrogen.
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Nucleate Boiling:
The even boiling of water in which steam bubbles are formed within the boiler water gradually and are evenly distributed rather than being suddenly formed and erratically distributed.
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Once-Through Boiler:
A steam-generating unit usually operated above the critical pressure in which there is no recirculation of the working fluid in any part of the unit.
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On-Off Control:
A two-position action that allows operation at either maximum or minimum condition, or on or off, depending on the position of the controller.
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Open Re-Circulating Water System:
A system, using continuously circulated water as a heat-transfer medium, in which the water is exposed at one point to the atmosphere for either discharge or absorption of heat.
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Operating Control:
A control to start and stop the burner - must be in addition to the high limit control.
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Operating Pressure:
Actual pressure at which the system works under normal conditions. This pressure may be positive or negative (vacuum).
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Orifice:
( 1 ) Accurate size opening for controlling fluid flow.
( 2 ) The opening from the whirling chamber of a mechanical atomizer or the mixing chamber of a steam atomizer through which the liquid fuel is discharged.
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Overfiring:
A situation where the burner does not turn off for a number of reasons. In this situation, the pressure of the system rises and the safety relief valve should open.
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Overpressure:
Minimum operating pressure of a hot water boiler sufficient to prevent the water from steaming.
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Oxygen Scavenger:
A substance that will absorb oxygen by chemical reaction.
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Packaged Boiler:
A boiler supplied with all of its components - burner, controls and auxiliary equipment. Designed as a single engineered package ready for on-site installation.
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Pass:
A confined passageway, containing heating surface, through which a fluid flows in essentially one direction.
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pH:
The negative logarithm of the hydrogen-ion concentration of a solution; simply a measure of the relative acidity or alkalinity of a water solution. (pH 1 very acidic; pH 14, very basic; pH 7, neutral).
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pH of Saturation (pHs):
The pH at which a sample of water is saturated with a specific salt; for example, the pH of saturation of calcium carbonate is the pH of a saturated solution of calcium carbonate.
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Phosphate Treatment:
An internal boiler water treatment method to reduce calcium in the boiler with low hardness feedwater.
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Physical Water Treatment:
Refers to the treatment of removing dissolved gases from the boiler feedwater using steam.
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Pilot:
A flame that is utilized to ignite the fuel at the main burner or burners.
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Pipe Scale:
Rust or mill scale found on the interior of water pipe.
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Post Purge:
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.
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Preheated Air:
Air at a temperature exceeding that of the ambient air.
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Pressure:
The normal force exerted by a homogeneous liquid or gas, per unit of area, on the wall of its container.
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Pressure Drop:
Pressure loss in fluid pressure, as from one end of a duct or pipe to the other, due to friction, dynamic losses, and changes in velocity pressure.
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Pressure Reducing Valve:
A piece of equipment for changing the pressure of a gas or liquid from a higher pressure to a lower one.
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Pressure, Operating:
Pressure at which a system is operating.
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Pretreatment:
Also referred to as external treatment, consisting of treating the raw makeup water. Includes removing dissolved oxygen, carbon dioxide, suspended solids, hardness, alkalinity, silica, dissolved solids, etc.
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Primary Air:
The initial air stream discharged by an air outlet (the air being supplied by a fan or supply duct) prior to any entrainment of the ambient air or for the purpose of combustion. Air introduced with the fuel at the burner.
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Process Hot Water:
Hot water needed for manufacturing processes over and above the "domestic hot water" that is for the personal use of industrial workers.
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Process Steam:
Steam used for industrial purposes other than for producing power.
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Products of Combustion:
The gases, vapors, and solids resulting form the combustion of fuel.
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Propane:
A paraffin hydrocarbon (C3H8) that is a gas at ordinary atmospheric conditions but easily liquefied under pressure.
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PSI:
Symbol or initials used to indicate pressure measured in pounds per square inch.
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PSIA:
Symbol or initials used to indicate pressure measured in pounds per square inch absolute. Absolute pressure equals gauge pressure plus atmospheric pressure. The "A" indicates that the gauge pressure is reading in absolute.
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PSIG:
Symbol or initials used to indicate pressure in pounds per square inch gauge. The
"G" indicates that it is gauge pressure and not absolute pressure.
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Pump:
A device that increases the pressure on a fluid or raises it to a higher level.
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Pump Discharge Pressure:
The point of highest pressure in a recirculating water system, which is at the discharge side of the recirculating pump.
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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.
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Radiation Loss:
A comprehensive term used in a boiler-unit heat balance to account for the conduction, radiation, and convection heat losses from the boiler to the ambient air.
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Rated Capacity:
The manufacturer's stated capacity rating for mechanical equipment; for instance, the maximum continuous capacity in pounds of steam per hour for which a boiler is designed.
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Rate of Blowdown:
A rate normally expressed as a percentage of the water fed.
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Raw Makeup Water:
Untreated water fed to a system to replace that lost.
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Raw Water:
With water treatment it means untreated feedwater or water in its natural state, prior to any treatment.
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Recuperator:
Equipment for transferring heat from gaseous products of combustion to incoming air or fuel. The incoming material passes through pipes surrounded by a chamber through which the outgoing gases pass.
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Refractory:
Brickwork or castable used in boilers to protect metal surfaces and for boiler baffles.
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Relief Valve:
Safety device on a sealed system. It opens to release fluids before dangerous pressure is reached. Also called pressure relief valve.
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Return-Steam Condensate:
That steam produced by a boiler that returns to the boiler after it has condensed.
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Safety Plug:
Device that will release the contents of a container before rupture pressures are reached.
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Safety Shut-Off Valve:
A manually opened, electrically latched, electrically operated safety shut-off valve designed to automatically shut off fuel when de-energized.
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Safety Valve:
A spring-loaded valve that automatically opens when pressure attains the valve setting. Used to prevent excessive pressure from building up in a boiler.
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Saturated Steam:
Steam at the temperature and pressure at which evaporation occurs.
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Saturation Pressure:
The pressure at which saturation takes place at a given temperature.
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Saturation Temperature:
The temperature at which a liquid boils under a given pressure. For any given saturation temperature, there is a corresponding saturation pressure.
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Scale:
Surface oxidation, consisting of partially adherent layers of corrosion products, left on metals by heating or casting in air or in other oxidizing atmosphere. Also a deposit on a heat-transfer surface resulting from precipitation of salts present in water in contact with that surface, forming a hard, dense material.
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Secondary Air:
Air for combustion supplied to the furnace to supplement the primary air.
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Sediment:
( 1 ) Matter in water that can be removed from suspension by gravity or mechanical
means.
( 2 ) A non-combustible solid matter which settles out at the bottom of a liquid; a small
percentage is present in residual fuel oils.
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Separator:
( 1 ) A tank type pressure vessel installed in a steam pipe to collect condensate to be
trapped off and thus providing comparatively dry steam to the connected machinery.
( 2 ) Device to separate one substance from another.
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Skimming:
A procedure for cleaning the surface of the water in a boiler. This procedure should be done on all new boiler installations, and when there is a foaming condition.
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Sludge:
( 1 ) A deposit on a heat-transfer surface that does not have the hard, crystalline structure of a scale but is softer and less dense.
( 2 ) A soft water-formed sedimentary deposit that normally can be removed by blowing down.
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Soot:
Unburned particles of carbon derived from hydrocarbons.
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Sparger:
An extension into the bottom of a tank of a pipe that has a distribution nozzle on the end for mixing one fluid with another.
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Specific Gravity:
( 1 ) The density of a substance compared to the density of a standard material such as
water.
( 2 ) Direct ratio of any liquid's weight to the weight of water at 62°F. Water at 62°F
weighs 8.33# per US gallon and is designated 1.0 sp. gr.
NOTE: A centrifugal pump develops head, not pressure. All pressure figures should
be converted to feet of head taking into consideration the specific gravity
(Ft. HD = PSI x 2.31 - Sp. Gr.)
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Specific Heat (Cp):
The ratio of the amount of heat required to raise a mass of material 1 degree in temperature to the amount required to raise an equal mass of reference substance, usually water, 1 degree in temperature.
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Stack Draft:
The magnitude of the draft measured at the inlet to the stack.
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Steam:
Water in vapor state. The vapor formed when water has been heated to its boiling point, corresponding to the pressure it is under. (See also Dry Saturated Steam, Wet Saturated Steam, and Superheated Steam).
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Steam Drum:
A pressure chamber located at the upper extremity of a boiler circulatory system in which the steam is generated in the boiler and separated from the water.
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Steam Quality:
The percentage by weight of vapor in a steam and water mixture.
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Steam Trap:
A device for allowing the passage of condensate and air but preventing the passage of steam.
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Superheated Steam:
Steam heated above its saturation temperature.
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Superheating:
The process of adding heat to a vapor in order to raise its temperature above saturation temperature. It is impossible to superheat a saturated vapor as long as it is in contact with the liquid from which it is being generated; hence the vapor must be led away from the liquid before it can be superheated.
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Surface Blowdown:
Removal of water, foam, etc. from the surface at the water level in a boiler.
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Suspended Solids:
Undissolved solids in boiler water.
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Tertiary Air:
Air for combustion supplied to the furnace to supplement the primary and secondary air.
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Therm:
( 1 ) Measurement used by gas utilities for billing purposes. 1 Therm = 100 cubic feet of gas = 100,000 Btu.
( 2 ) Quantity of heat equal to 100,000 Btu.
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Thermal Expansion:
The change in length of a material with change in temperature.
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Thermocouple:
( 1 ) Device for measuring temperature utilizing the fact that an electromotive force is
generated whenever two junctions of two dissimilar metals in an electric circuit are
at different temperature levels.
( 2 ) Device which generates electricity, using the principle that if two unlike metals are
welded together at one end and the junction is heated, voltage will develop across
the open ends.
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Treated Water:
Water that has been chemically treated to make it suitable for boiler feed.
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Tube Bundle:
A single tube (pipe) formed into a tight array so as to present a large surface area in a small space.
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Tube Sheet:
The portion of a heat exchanger or boiler into which the tubes are rolled or secured.
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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.
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Turndown Ratio:
Ratio of maximum to minimum fuel or steam input or boiler output.
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Unburned Combustible:
The combustible portion of the fuel that is not completely oxidized.
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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.
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Vacuum:
Pressure lower than atmospheric pressure.
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Valve, Modulating:
A valve which can be positioned anywhere between fully on and fully off to proportion the rate of flow in response to a modulating controller (see modulating control).
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Valve, Needle:
A form of globe valve that contains a sharp, pointed, needle-like plug that is driven into and out of a cone-shaped seat to accurately control a relatively small rate of flow of a fluid.
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Valve, Pop:
A spring-loaded safety valve that opens automatically when pressure exceeds the limits for which the valve is set. It is used as a safety device on pressurized vessels and other equipment to prevent damage from excessive pressure. (Also called relief valve or a safety valve.)
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Vent Valve (Steam):
A device for permitting air to be forced out of a heating unit or pipe and which closes against water and steam.
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Vent Valve (Water):
A device permitting air to be pushed out of a pipe or heating unit but which closes against water.
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Vertical Firing:
An arrangement of a burner such that air and fuel are discharged into the furnace in practically a vertical direction.
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Viscosity:
That property of semi-fluids, fluids, and gases by virtue of which they resist an instantaneous change of shape or arrangement of parts. It is the cause of fluid friction whenever adjacent layers of fluid move with relation to each other.
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Viscosity Index:
A commonly used measure of the change in viscosity of a fluid with temperature. The higher the viscosity index, the smaller the relative change in viscosity with temperature.
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Water Level:
The elevation of the surface of the water in a boiler.
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Watertube:
A boiler tube through which the fluid under pressure flows. The products of combustion surround the tube.
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Watertube Boilers:
This type of boiler has the water circulated through a tube bundle with the heat applied on the external side of the tube.
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Water, Potable:
Water that is safe to drink.
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Waterleg:
That space that is full of boiler water between two parallel plates. It usually forms one or more sides of internally fired boilers.
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Waterwall:
A row of water tubes lining a furnace or combustion chamber, exposed to the radiant heat of the fire.
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Wetback Boiler:
Firetube boiler design wherein the back portion of the boiler has a water jacket.
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Wet Return (Steam):
That part of a return main of a steam heating system that is completely filled with water of condensation.
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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.
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Wet Saturated Steam:
Steam containing moisture.
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Wet Standby:
Boiler is filled completely with water or maintained at normal operating level with a positive nitrogen pressure of 35 to 70 kPa.
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Windbox:
A chamber below the grate or surrounding a burner, through which air under pressure is supplied for combustion of the fuel.
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Windbox Pressure:
The static pressure in the windbox of a burner or stoker.
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