ME Boiler Operator key terms

The highest pressure at which a boiler or pressure vessel may legally operate, established by its design and stamped on the nameplate. Safety devices are set so that this limit is never exceeded in normal or abnormal operation.

An automatic pressure-relief device that opens at a preset pressure to discharge steam and protect the boiler from overpressure, then reseats itself as pressure drops back below the set point.

A pressure test in which the boiler is filled completely with water and raised to a specified test pressure, usually one and a half times the working pressure, to reveal leaks and weak areas without steam hazard.

The upper cylindrical vessel of a watertube boiler where steam separates from water, moisture is knocked out of the steam, and feedwater and treatment chemicals are introduced.

A rod, bolt, or brace that ties flat or stayed surfaces of a boiler together so that pressure loads are carried in tension instead of bending the plates.

A measure of boiler capacity defined as the evaporation of 34.5 pounds of water per hour from and at 212 degrees Fahrenheit, roughly equal to 33,475 Btu per hour of heat output.

A boiler design in which hot combustion gases travel through tubes surrounded by water, so the tubes carry the fire and the shell contains the water.

A boiler design in which water circulates inside tubes heated on the outside by combustion gases, permitting higher pressures and larger capacities than firetube designs.

The rapid chemical combination of fuel with oxygen that releases heat. In a boiler it must be complete enough to avoid carbon monoxide and unburned fuel leaving the stack.

The theoretical quantity of air that supplies exactly enough oxygen to burn all the fuel completely, leaving neither unused oxygen nor unburned fuel.

Air supplied beyond the theoretical amount needed for complete combustion. It ensures all fuel burns, but too much of it carries heat up the stack and lowers efficiency.

The proportion of combustion air to fuel delivered to a burner, adjusted so the flame stays stable and efficient across the full firing range.

The small pressure difference that pulls combustion air into the furnace and pushes flue gases out the stack. It may be natural, forced, induced, or balanced.

Breaking liquid fuel into a fine spray of small droplets so it mixes readily with air and burns completely. Poor atomization produces smoke, soot, and carbon buildup.

The relationship between a burner's highest and lowest stable firing rates. A wide range lets the boiler follow load changes without frequent on-off cycling.

Heat-resistant brick or castable material lining furnaces and flues to shield metal parts from flame and high temperature and to limit heat loss.

A safety control that senses water level and stops the burner when the water falls below a safe point, preventing overheating and damage to tubes or shell.

A system that proves a flame is present at the burner and shuts off fuel within seconds if the flame is lost, so unburned fuel cannot collect in the furnace.

A control that starts and stops or modulates the burner to hold steam pressure within the normal operating band. It is set below and separate from the high-limit control.

A safety control set above the normal operating range that cuts off the burner if pressure climbs too high, serving as a backup to the operating control.

A control method that continuously varies the burner firing rate to match steam or hot water demand, reducing pressure swings and improving fuel efficiency.

A transparent tube and fittings that show the actual water level inside the boiler, allowing the operator to confirm that the low-water cutoff is reading correctly.

A forced flow of air through the furnace and flues before light-off that clears any accumulated combustible gases and prevents a furnace explosion.

Opening the valve at the lowest point of the boiler to discharge water and settled sludge, removing solids that would otherwise bake onto heating surfaces.

Withdrawing a small amount of water from near the normal water level to remove dissolved solids and floating impurities, usually done while the boiler is firing.

Bringing a cold boiler up to operating temperature slowly, using low firing rates and open air vents, so thermal stress and uneven expansion are avoided.

A prompt, safe stop of the burner and fuel supply in response to a hazard such as low water, flame failure, a fuel leak, or a serious steam leak.

A banging shock in piping caused by steam collapsing into condensate or by abrupt valve closure. It can damage fittings, supports, and the boiler itself.

Hard mineral deposits, mainly calcium and magnesium compounds, that form on heated surfaces and resist heat transfer, causing overheating and eventual tube failure.

Carryover of boiler water into the steam, usually triggered by a high water level, foaming, or a sudden load surge. It can contaminate piping and superheaters.

Oxygen held in feedwater that causes pitting corrosion on boiler metal. It is removed mechanically by heating and chemically by an oxygen scavenger.

Equipment that heats feedwater with steam and strips out dissolved gases, chiefly oxygen and carbon dioxide, before the water is pumped to the boiler.

An examination of the water side and fire side of a boiler after it is opened, drained, and cleaned, looking for corrosion, cracking, scale, and other defects.

A document issued after a boiler passes its required inspection, authorizing operation until the next inspection date. It must be kept posted at the boiler.

A credential issued by the state that allows a person to operate boilers of a stated size and pressure, granted after meeting examination and experience requirements.

The state official who administers boiler and pressure vessel safety enforcement, directs the work of inspectors, and interprets the rules adopted under the state boiler law.

A written report the owner or operator must file with the state after a serious boiler or pressure vessel incident, such as a rupture, explosion, or injury.

The code published by the National Board that sets requirements for repairs, alterations, and inservice inspection of boilers and pressure vessels, and which state rules commonly adopt.