Glossary

Absolute Pressure  The sum of gauge pressure and atmospheric pressure.
Accumulation Test  Test used to establish the relieving capacity of boiler safety relief valves.
Acid Dew Point  Temperature at which acids begin to settle out of flue gases.
Alkalinity  Determined by boiler water analysis. Boiler water with a pH over 7 is considered alkaline.
Ambient Temperature  Temperature of the surrounding area.
Ampere  Unit of measure of electrical current.
Anion  Ion that has a negative electrical charge.
Area  The number of unit squares equal to the surface of an object.
ASME Code  Code written by the American Society of Mechanical Engineers that controls the construction, repairs and operation of boilers and their related equipment.
Atmospheric Pressure  Pressure at sea level (14.7 PSI).
Atomization  Process of breaking a liquid fuel stream into a mist of tiny droplets.
Atomize  To break up fluids into a fine mist.
Boiler  Closed vessel in which water under pressure is transformed into steam by application of heat.
Boiler Capacity  Pounds of steam of BTU=s of hot water a boiler is capable of producing.
Boiler Horsepower  The evaporation of 34.5 pounds of water per hour from and at a feedwater temperature of 212°F.
Boiler Lay-Up  Removing a boiler from service for a period of time. A boiler can be laid-up wet or dry.
Boiler Room Log  A data sheet to record pressures, temperatures of other operating conditions of a boiler on a continuous basis.
Boiler Shutdown  A sequence of operation completed when taking a boiler off line.
Boiler Startup  A sequence of operations completed when preparing a boiler for service.
Boiler Vent  Valved port coming off highest part of the waterside of the boiler that is used to vent air from the boiler when it is filled. Also used to prevent a vacuum from forming when the boiler is drained.
Boiling Point  Temperature at which water changes into steam.
Bottom Blowdown  Periodic draining of part of the water in the boiler to remove the heavy sludge that settle to the bottom of a vessel.
Breeching  Ducting from boiler flue gas outlet to stack (or chimney).
British Thermal Unit  (BTU) Amount of heat necessary to raise the temperature of 1 lb. Of water 1°F.
By-Pass Line  A pipeline that passes around a control. Used so a boiler can operate manually without use of the control.
Calibrate  Adjusting a gauge, control or piece of equipment to conform with a test gauge, control or piece of equipment.
Carryover  Particles of water that flow with steam into the system piping.
Cavitation  Condition caused when a portion of water or other liquid entering the eye of a pump impeller flashes intosteam bubbles. Causes pitting of pump impellers.
Celsius (Centigrade)  Temperature scale commonly used with the metric system of measurements. The freezing point of water on this scale is 0° and the boiling point of water is 100° at normal atmospheric pressure.
Centrifugal Force Force  caused by a rotating impeller that builds up in a centrifugal pump.
Check Valve  One-way flow valve for fluids.
Combustible Material  Any material that burns when it is exposed to oxygen and heat.
Combustion  The rapid union of oxygen with an element or compound that results in the release of heat.

 Complete Combustion – The burning of all supplied fuel using the minimum amount of excess air.
Compound Gauge  Combination pressure gauge and vacuum gauge.
Condensate  Steam that has lost its heat and returned to water.
Condense  Process whereby steam turns back to water after the removal of heat.
Conduction  A method of heat transfer in which heat moves from molecule to molecule.
Continuous Blowdown  Small stream of water that constantly drains from a boiler to control the quantities of impurities in a boiler on a continuous basis.
Convection  A method of heat transfer that occurs as heat moves through a fluid.
Cracking Open  Slowly opening a valve, generally to allow equalization.
Cross AT@  Used in water column piping for inspection for being clean and clear.
Cut-In Pressure  Automatic pressure control setting at which the boiler turns on.
Cut-Out Pressure  Automatic pressure control setting at which the boiler turns off.
Cycle of Concentration  Number of times solids in a particular volume of water are concentrated as compared to concentration of the solids in the original volume of water.
Deaerator  Pressure vessel that removes oxygen from the feedwater before going into the boiler.
Dealkalizer  Ion-exchange unit that works exactly like a sodium zeolite water softener, but removes anions and replaces them with chloride.
Differential Pressure  Difference between two pressures at different points.
Differential Setting  Difference between the pressure at which the automatic pressure control turns the burner on, and the pressure at which the automatic pressure control turns the burner off.
Dissolved Solids  Impurities that have passed into solution.
Draft  The difference in pressures between two points that cause air or gases to flow.

 Economizer – Uses the gases of combustion to heat boiler feedwater.
Element  A basic substance consisting of atoms.
Enthalpy  Total heat in steam.
Erosion  Wearing away of metal.
Excess Air  Air more than the theoretical amount needed for combustion.
Factor of Evaporation  Heat added to water in an actual boiler in BTU per pound and divided by 970.3.
Fahrenheit  Temperature scale commonly used with the U.S. system of measurements. The freezing point of water on this scale is 32° and the boiling point of water is 212° at normal atmospheric pressure.
Feedwater  Water that is supplied to a boiler.
Feedwater Treatment  Using softwater and chemicals in the boiler feedwater. Protects against scale and corrosion.
Fire Point  Temperature at which fuel oil burns continuously when exposed to an open flame.
Firetube Boiler  Has heat and gases of combustion passing through the furnace and boiler tubes surrounded by water.
Firing Rate  Amount of fuel the burner is capable of burning in a given unit of time.
Flame Failure  When the burner pilot or main flame goes out on its own.
Flame Scanner  Device that confirms that the pilot and main burner flame exists.
Flash Point  Temperature at which fuel oil, when heated produces a vapor that flashes when exposed to an open flame.
Flash Steam  Created when water at a high temperature has a sudden drop in pressure.
Foaming  Rapid fluctuations of the boiler water level that can lead to priming or carryover. Caused by impurities on the surface of the boiler water.
Foot Pound  Unit of measure that equals the movement of an object by a constant force (in pounds) to a specific distance (in feet).
Force  Energy exerted or brought to bear on.
Forced Draft  Mechanical draft produced by a fan.
Furnace Volume  Amount of space available in a boiler furnace to complete combustion.
Gate Valve – Valve used to shutoff or admit flow.
Gauge Glass  Glass connected to a water column or directly to a boiler that allows an operator to see the water level inside a boiler.
Gauge Pressure  Pressure above atmospheric pressure. Assumes atmospheric pressure being zero.
Gas Analyzer  Used to analyze the gases of combustion to determine combustion efficiency.
Gas Leak Detector  A device to locate gas leaks in the boiler room.
Gases of Combustion  Gases produced by the combustion process.
Globe Valve  Valve having a tapered rounded or flat disc held horizontally on the stem.
Gravity  Natural force that makes objects on earth fall to the lowest point possible.
Handhole  Small access hole, smaller than a manhole (manway), used for looking and reaching into the boiler shell during inspections.
Header  Manifold that feeds several branch pipes or takes in steam or water from several smaller pipes.
Heat Exchanger  Any piece of equipment where heat is transferred from one substance to another.
Heating Surface  Any part of a boiler metal that has hot gases or combustion on one side and water on the other.
Heat Recovery System  Equipment that is installed to reclaim heat that is normally lost.
Heat Transfer  Movement of heat from one substance to another that can be accomplished by radiation conduction or convection.
Heating Value  Expressed in BTU=s. Heating value of fuel varies with the type.
High Pressure Boiler  A boiler that operates over a steam pressure of 15 PSI.
Hot Water Boiler  Boiler that is completely full of water that produces only hot water, not steam.
Hydrostatic Pressure  Water pressure per vertical foot (.433) exerted at the base of a column of water.
Inches of Mercury (IN.Hg)  Unit of measure for vacuum.
Incomplete Combustion  Occurs when all the fuel is not burned, resulting in the formation of smoke or soot.
Infrared  Invisible light rays produced by the combustion process and detected by a flame scanner.
Latent Heat  Heat in BTU that is added so boiling water at a given temperature will change into steam at the same temperature.
Laying Up  Taking a boiler out of service for longer than a normal period of time.
Low Pressure Boiler  A boiler that operates at a steam pressure of not more than 15 PSI.
Low Water  Lower than acceptable water level in a boiler that is dangerous because it can cause over heating of a boiler.
Low Water Fuel Cutoff  Device located slightly below the NOWL of a boiler that shuts off the boiler burner in the event of low water.
Main Steam Stop Valve  Gate valve in the main steam line between the boiler and the steam header.
Makeup Water  Water that must be added to the boiler to make up for condensate that was dumped, lost through boiler blowdowns or leaks in the system.
Manhole (Manway)  Hole on the steam and waterside of a boiler used to clean, inspect and repair a boiler.

 Maximum Allowable (MAWP) – Highest legal pressure at which a pressure vessel may be working pressure operated.
Modulating Pressure  Control device that regulates the burner for a higher or lower fuel Control burning rate depending on steam pressure in the boiler.
Multiple-Pass Boiler  Boilers that are equipped with a means to direct the flow of the gases of combustion so that the gases make more than one pass over the heating surfaces.
Natural Draft  Caused by the difference in weight between a column of hot gases of combustion inside the chimney (stack) and a column of cold air of the same height outside the chimney.
Non-Condensable Gas  Any gas that will not change into a liquid when its temperature is reduced.
Non-Return Valve  Combustion shutoff and check valve that allows steam to pass out of the boiler, but a back flow of steam from a drop in pressure causes the valve to close.
Normal Operating Water Level (NOWL)  Level of the boiler water at normal operation.
Overfiring  Forcing a boiler beyond its designed steam producing capacity.
Package Boiler  Boiler that comes completely factory assembled, with exception of those items that have to be removed from the boiler for shipment.
Passes  Number of times gases or combustion flow the length of the pressure vessel as they transfer heat to the water.
Perfect Combustion  Burning of all the fuel with the theoretical amount of air. Can only be achieved in a laboratory.
PH  Value representing how acidic or alkaline water is.
Phosphates  Chemicals that cause hardness particles to settle out as a heavy sludge.
Power  Unit of measure that equals the amount of foot pounds of work in a given period of time.
Pneumatic System  A system of control that uses air as the operating medium.

 Pounds of Steam Per Hour (LB/HR) – Unit of measure that expresses the amount of steam produced by a boiler in one hour.
Popping Pressure  Predetermined pressure at which a safety relief valve opens and remains open until the pressuredrops.
Post-Purge  The passing of air through the boiler fireside after normal burner shutdown.
Pour Point  The lowest temperature at which a fuel oil flows as a liquid.
Pre-Purge  The passing of air throught the boiler fireside prior to pilot and main burner flame lightoff.
Pressure  Application of force commonly measured in PSI.
Pressure Reducing Station  Where higher pressure steam is reduced in pressure for lower pressure needs.
Primary Air  Air supplied to the burner that regulates the rate of combustion.
Priming  Severe form of carryover in which large slugs of water leave the boiler with the steam.
Process Steam  Steam used in a plant for manufacturing or processing purposes.
Products of Combustion  Gases that are formed as a fuel is burned in a furnace.
Programmer  Device that controls the burner sequence of operation.
Proving Pilot  Sighting the pilot through a flame scanner to verify that the pilot is lit.
Pounds Per Square Inch (PSI)  Number of pounds of pressure exerted on one square inch of a given area.
Purge Period  Before ignition and after burner shutdown when explosive combustibles are removed.
Quality of Steam  Term used to express the moisture content present in saturated steam. Quality of steam effects the BTU content of the steam.
Rate of Combustion  The amount of fuel that is being burned in the furnace per unit of time.
Raw Water  Untreated water.

 Reseat Pressure – The pressure at which a safety valve will reseat. It will pop above the pressure.
Ringlemann Chart -Chart used as a measure of determining smoke density.
Safety Valve  Valve that keeps the boiler from exceeding its maximum allowable working pressure.
Safety Valve Capacity  Measured in pounds of steam per hour safety valves can discharge.
Sample Cooler  Closed heat exchanger that cools a sample before it enters a sample container.
Saturated Steam  Steam at a temperature that corresponds with its pressure.
Scale  Deposits in the boiler waterside caused by improper boiler water treatment.
Scotch Marine Boiler  A firetube boiler with an internal furnace.
Secondary Air  Air that is needed to complete the combustion process.
Sediment  Particles of foreign matter present in the boiler water.
Sensible Heat  Heat that can be measured by a change in temperature.
Sludge  Accumulated residue produced from impurities in water.
Smoke Density  Varies from clear to dark. Determined by the amount of light that passes through the smoke as it leaves the boiler.
Sodium Zeolite Water Ion Softener  Exchange water softener that uses a bronze solution and resin
Softener beads to soften water.
Solid State  An electronic system using transistors in place of electronic tubes.
Soot  Fine powder consisting primarily of carbon that results from incomplete combustion.
Spalling  Hairline cracks in boiler refractory due to changes in fireside temperatures.
Specific Gravity  Weight of a given volume of a material divided by the weight of an equal volume of water measured at 60°F.

 Spontaneous Combustion – Occurs when combustible materials self-ignite.

 Stack – Outlet to the atmosphere for the gases of combustion. Used to create a draft.
Static Head Pressure (SHP)  Pressure at the bottom, or at some specified point, of a column of still liquid.
Steam  Gaseous form of water. Steam is odorless, colorless and tasteless.
Steam Boiler  A closed pressure vessel in which water is converted to steam by the application of heat.
Steambound  Condition that occurs when the temperature in the open feedwater heater gets too high and the feedwater pump cannot deliver water to the boiler.
Steam Space  The space above the water line in a steam boiler.
Steam Trap  Mechanical device used to remove condensate from steam piping.
Sulfur  A combustion element found in coal and fuel oil.
Superheated Steam  Steam at a temperature above its corresponding pressure.
Surface Tension  Caused by impurities on the top of the water in a steam boiler.
Tensile Stress  Occurs when two forces of equal intensity act on an object, pulling in opposite directions. Affects boiler plates and staybolts.
Therm  Unit used to measure BTU content of natural gas. A therm has 100,000 BTU.
Thermal Efficiency  The ratio of heat absorbed by the boiler to the heat available in the fuel per unit of time.
Thermal Shock  Stress imposed on boiler metal by a sudden and drastic change in temperature.
Total Force  Total pressure that is acting on an area, determined by diameter and pressure.
Total Heat  Sum of sensible heat and latent heat.

 Turbulence – Movement of water in the boiler.
Ultraviolet  A form of light that is produced during combustion.
Vacuum  A pressure below atmospheric pressure.
Vacuum Breaker  Vent on top of vessel that allows air to be pulled into the tank to prevent formation of a vacuum.
Vacuum Gauge  Pressure gauge used to measure pressures below atmospheric pressure.
Valve  Mechanical device that starts, stops or regulates flow of a liquid, gas or loose bulk material.
Vapor  Diffused matter in a gaseous state.
Vertical Firetube Boiler  One pass boiler that has firetubes in a vertical position.
Viscosity  Ability of a liquid or semi-liquid to resist flow.
Waste Heat Recovery Boiler  Boiler in which heat that would otherwise be discarded is used to make steam.
Water Column  Metal vessel installed on the outside of a boiler shell or drum at the NOWL that helps an operator determine the water level in a boiler.
Water Hammer  A banging condition that is caused by steam and water mixing in a steam line.
Wet-Lay-Up  Method of short term boiler storage that keeps the boiler free from oxygen on the inside, which prevents damage from corrosion.
Working Pressure  Maximum allowable working pressure or the pressure at which the boiler is normally operated.