BD Second Class Boiler Attendant key terms

A national law that governs the registration, inspection, operation and repair of steam boilers, setting out the legal duties of owners and the powers of the inspecting authority.

A licence issued by the competent authority to a person who has passed the prescribed examination, authorising that holder to take charge of boilers of a stated class and size.

The licensed person on shift who is responsible for starting, running, feeding, watching and safely shutting down the boiler, and for recording pressures, water levels and any defects found.

An authorised official who examines boilers internally and externally, witnesses pressure tests, and certifies whether a boiler may lawfully continue in service and at what maximum working pressure.

The official record kept at the boiler house in which the attendant notes water level, steam pressure, blowdowns, tests, fuel used and any irregularities or defects observed during the shift.

A boiler in which hot combustion gases pass through tubes surrounded by water, so the shell contains the water and the tubes contain the fire; examples include the Lancashire and packaged shell boilers.

A boiler in which water circulates inside tubes that are heated externally by furnace gases, allowing higher pressures and faster steam raising than a fire-tube design of similar output.

A cylindrical pressure vessel holding a large body of water with the furnace and flue tubes inside it, characterised by large steam storage and suitability for moderate pressures and saturated steam.

A row of tubes lining the furnace or combustion chamber walls, filled with circulating water, that absorbs radiant heat and protects the refractory brickwork from overheating and slagging.

A spring- or weight-loaded valve fitted to the boiler that opens automatically at a set pressure and releases steam, preventing pressure from rising above the certified limit.

A brass plug with a low-melting alloy core screwed into the crown of a fire-tube boiler furnace, which melts and releases steam into the firebox if the water level falls dangerously low.

A protective control that senses an abnormally low water level in the boiler and automatically stops the burner or fuel supply before the metal becomes overheated.

A transparent tube or flat glass fitting connected to the boiler at steam and water spaces, showing the true water level so the attendant can confirm the level in the boiler.

A pressure test in which the boiler is filled with water and pressurised, usually to one and a half times the working pressure, to prove the strength and tightness of the pressure parts.

A test carried out with the boiler under normal steam pressure, with safety valves gagged or isolated as required, to check for leaks and confirm that all mountings function correctly.

A test that confirms the safety valves can discharge all the steam the boiler can generate at full firing without the pressure rising more than a small permitted percentage above the set pressure.

The deliberate discharge of water from the boiler, either from the bottom to remove sludge and sediment or from the surface to control dissolved solids and maintain steam purity.

A hard crust of mineral salts, mainly calcium and magnesium compounds, deposited on heating surfaces when dissolved solids concentrate, which reduces heat transfer and can cause overheating and tube failure.

The chemical and physical conditioning of water before it enters the boiler, including softening, deaeration and dosing, to prevent scale, corrosion, foaming and carry-over.

A vessel in which feed water is heated and sprayed or cascaded through steam to drive off dissolved oxygen and carbon dioxide, reducing internal corrosion of the boiler.

The concentration of dissolved salts in the boiler water, measured to decide how often blowdown is needed and to keep the water within limits that avoid foaming and carry-over.

The carry-over of boiler water, as a spray or foam, along with steam into the steam line, usually caused by high water level, excessive dissolved solids or sudden steam demand.

An automatic device that discharges condensate and air from steam lines and equipment while retaining live steam, allowing the system to run efficiently and avoid water hammer.

A sharp banging and pressure surge caused by slugs of condensate travelling at high speed and being stopped by a fitting, which can fracture pipes and joints.

A pump, often a reciprocating or centrifugal type, that forces treated feed water into the boiler against the steam pressure in the drum or shell.

A device that uses a jet of steam to draw in and force feed water into a boiler, commonly used as a standby feed appliance on smaller boilers.

A valve fitted on the feed line between the feed pump and the boiler that allows water to enter but prevents boiler water and steam from flowing back into the feed system.

The rapid chemical combination of fuel with oxygen, releasing heat, in which sufficient air, mixing time and temperature are needed for complete burning of the fuel.

The proportion of air supplied above the theoretical amount needed for complete combustion, kept just high enough to burn all fuel without excessive stack heat loss.

The combustion chamber of the boiler where fuel is burned and the hottest radiant heat is released to the surrounding water walls or fire-tube surfaces.

A mechanical device that feeds solid fuel onto a grate and removes ash, controlling the rate of firing and the distribution of fuel for even combustion.

The surface within the furnace on which solid fuel burns, supporting the fuel bed while admitting air from below and allowing ash to fall away.

The measurement of oxygen, carbon dioxide and carbon monoxide in the exhaust gases, used to judge combustion quality and set the correct amount of excess air.

The ratio of heat usefully absorbed by the steam to the heat released by the fuel, expressed as a percentage and reduced by stack losses, radiation and unburned fuel.

An accounting of all heat entering the boiler with the fuel and air against the heat leaving in steam, flue gases, radiation and blowdown, used to find where energy is wasted.

A form of cracking of stressed boiler steel in riveted seams and bends, caused by concentrated alkaline boiler water seeping into fine crevices, now largely prevented by water conditioning.

A sudden violent release of stored energy when the pressure vessel fails, usually from low water, overpressure or weakened metal, causing a flash of steam and widespread damage.