Every Industry has its own unique terminology. Sometimes these terms can be confusing so we thought a boiler dictionary would be helpful. The following definitions can be found in a number of texts.
Glossary of Boiler Terms and Definitions
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Backing ring – A strip of thin plate used on the inner surfaces of the abutting ends of pipe, tubes, or plates which are butt-welded. Its purpose is to prevent irregularities at the base weld and to permit penetration at its root.
Baffle – A plate or wall for deflecting gases or liquids.
Bag – A deep bulge in the bottom of the shell or furnace of a boiler.
Bag filter – A device containing one or more cloth bags for recovering particles from dust laden gas or air which is blown through it.
Balanced draft – The maintenance of a fixed value of draft in a furnace at all combustion rates by control of incoming air and outgoing products of combustion.
Barometric pressure – Atmospheric pressure as determined by a barometer usually expressed in inches of mercury.
Barrel – The cylindrical portion of a firetube boiler shell that surrounds the tubes.
Base load – The term applied to that portion of a station or boiler load that is practically constant for long periods.
Beta Ratio – For a single orifice the beta ratio is the ratio of the orifice bore diameter to that of the upstream pipe diameter. However, since in burner designs typically there is more than one orifice at a riser pipe exit, the beta ratio is equal to the square root of the ratio between total area of the fuel ports to that of the upstream pipe area.
Bias – The output plus (or minus) some arbitrary value.
Black light – In magnetic particle inspection, light in the near ultraviolet range of wavelengths, just shorter than visible light.
Blast furnace gas – Lean combustible by-product gas resulting from burning coke with a deficiency of air in a blast furnace.
Blowback – The number of pounds per square inch of pressure drop in a boiler from the point where the safety valve pops to the point where the safety valve reseats.
Blowback ring – An adjustable ring in a safety valve, used to control the amount of blowback.
Blowdown – The drain connection including the pipe and the valve at the lowest practical part of a boiler, or at the normal water level in the case of a surface blowdown. The amount of water blown down.
Blowdown valve – A valve generally used to continuously regulate concentration of solids in the boiler, not the drain valve.
Blower – A fan used to force air under pressure.
Boiler – A closed vessel in which water is heated, steam is generated, steam is superheated, or any combination thereof, under pressure or vacuum by the application of heat from combustible fuels, electricity, or nuclear energy. The term dose not include such facilities of an integral part of a continuous processing unit but does include fired units of heating or vaporizing liquids other than water where these units are separate from processing systems and are complete within themselves.
Boiler header (box) – A pressure part of the boiler consisting of a flat tube sheet into which the ends of the water tubes are rolled. In a parallel plane is a tube cap or handhole sheet. The two sheets are spaced about 4 to 8 in. or more apart. The top and bottom and both ends are flanged together and riveted or may be closed by a narrow flanged strip of plate riveted to each sheet. Circulating nipples connect the top of the header and drum, or the header may be flanged and riveted directly to the drum. Welding would be used today instead of rivets.
Boiler, high-pressure, steam or vapor – A boiler in which steam or vapor is generated at a pressure exceeding 15 psig.
Boiler, hot-water-heating – A boiler in which no steam is generated and from which hot water is circulated for heating purposes and then returned to the boiler.
Boiler, hot-water-supply – A boiler functioning as a water heater.
Boiler, low-pressure-steam or vapor – A boiler in which steam or vapor is generated at a pressure not exceeding 15 psig.
Boiler horsepower – The evaporation of 34 ½ lbs. of water per hour from a temperature of 212oF into dry saturated steam at the same temperature. Equivalent to 33,475 Btu.
Boiler water – A term construed to mean a representative sample of the circulating boiler water, after generated steam has been separated and before the incoming feed water or added chemical becomes mixed with it so that its composition is affected. (ASTM – D860)
Boiling – The conversion of a liquid into vapor with the formation of bubbles.
Boiling out – The boiling of a highly alkaline water in boiler pressure parts for the removal of oils, greases, etc. prior to normal operation or after major repairs.
Bourdon tube – A hollow, metallic tube, bent semicircular, which forms the actuating medium of a pressure gauge.
Breeching – A duct for transport of the products of combustion between parts of a steam-generating unit to the stack.
Bridgewall – A wall in the furnace over which the products of combustion pass.
Brinell test – A hardness test performed by pressing a steel ball of standard hardness into a surface by a standard pressure.
Btu (British Thermal Unit) – A standard measure of energy in the British unit system. 1 Btu is the amount of heat required to raise the temperature of a liquid by 1 degree.
Brittle – A metal is brittle when it permits little or no plastic deformation prior to fracture.
Buckstay – A structural member placed against a furnace or boiler wall to limit the motion of the wall against furnace pressure.
Bulge – A local distortion or swelling outward caused by internal pressure on a tube wall or boiler shell due to overheating. Also applied to similar distortion of a cylindrical furnace due to external pressure when overheated, provided the distortion is of a degree that can be driven back.
Bunker C oil – Residual fuel oil (no. 6 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 – A burner that is factory-built as a single assembly or as two or more assemblies which include all parts necessary for its normal function when installed as intended.
Burner, atmospheric – A gas burner in which all air for combustion is supplied by natural draft, the inspiriting force being created by gas velocity.
Burner, natural-draft type – A burner which depends primarily on the natural draft created in the flue to induce the air required for combustion into the burner.
Burner, power – A burner in which all air for combustion is supplied by a power-driven fan that overcomes the resistance through the burner to deliver the quantity of air required for combustion.
Burner block – Also called “burner tile”, “muffler block,” or “quarl”. The specially formed refractory pieces which mount 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 heat release a burner can deliver (i.e., amount of fuel which can be completely burned through a burner) at a given set of operating conditions.
Burner windbox – A plenum chamber around a burner in which an air pressure is maintained to ensure proper distribution and discharge of secondary air.
Bypass temperature control – Control of vapor or air temperature by diverting part of or all the heating medium from passing over the heat-absorbing surfaces, usually by means of a bypass damper.
Sources:Sources for this listing were found in the ASME Boiler Codes, American Society of Mechanical Engineers, New York; ABMA; Metals Handbook, American Society for Metals; ASHRAE Handbooks; and Boiler Operator’s Guide by Anthony L. Kohan, The John Zink Combustion Handbook, Charles E. Baukal, Jr., editor.
