There have been a vast number of designs of steam boiler, particularly towards the end of the 19th century when the technology was evolving rapidly. A great many of these took the names of their originators or primary manufacturers, rather than a more descriptive name. Some large manufacturers also made boilers of several types. Accordingly it is difficult to identify their technical aspects from merely their name. This list presents these known, notable names and a brief description of their main characteristics.
auxiliary boiler: An auxiliary boiler, on a steam ship, supplies steam that is not used for main propulsion, but is necessary for some part of the essential machinery. See also donkey boiler. A small boiler may be used as an auxiliary boiler when at sea, or a donkey boiler in port. A composite auxiliary boiler does this, using waste heat from the main engines when at sea, or is separately fired when acting as a donkey boiler.
box boiler: An early marine boiler with flat sides. Owing to the flat sides, even with extensive rod stays, the boilers were only suitable for low pressures. These boilers were physically large and contained a few large flues, each heated by its own furnace. The flues were round, rectangular or arched and usually long and labyrinthine.
Brotan boiler: a rarely used boiler for steam locomotives that combined a conventional fire-tube boiler barrel with a water-tube firebox. There is a prominent steam drum above the boiler barrel, making it resemble a Flaman boiler.
Brotan-Defner boiler: a variant of the Brotan boiler. The steam drum was shortened and placed behind the boiler barrel, giving a much more conventional silhouette. Around a thousand of these were used in Hungary.
bundled-tube water-tube boiler; early large-tube water-tube boilers where the tubes were grouped into bundles (of 19, for geometrical reasons) that shared a common header, so as to improve shared access for tube cleaning.
De Poray boiler: patented French designs with a secondary combustion chamber to improve combustion efficiency. A vertical form of this uses field-tubes.
Doble steam-car boiler:
donkey boiler: A donkey boiler is used to supply non-essential steam to a ship for 'hotel' services such as heating or lighting when the main boilers are not in steam, for example, when in port. Donkey boilers were also used by the last sailing ships for working winches and anchor capstans. See also auxiliary boiler.
fire-tube boiler: A boiler with many narrow fire-tubes inside a water drum. A development of the flued boiler, where the many smaller tubes give a much larger heating surface area for the overall boiler volume.
Flaman boiler: an attempt to squeeze the largest possible locomotive boiler into the loading gauge by splitting the boiler into two drums: a fire-tube boiler beneath and a steam drum above.
forced-circulation boiler: boilers where circulation is forced by a pump, rather than relying on thermosyphon effect. These may use either forced-water-circulation (e.g. La Mont) or forced-steam-circulation (e.g. Löffler).
Galloway boiler: a Lancashire boiler fitted with Galloway tubes. Originally these fused the Lancashire boiler's original two flues into a single kidney-shaped flue, with the tubes mounted in the joined section. Later boilers kept the cylindrical flues separate and placed the tubes within them.
gothic boiler: an early locomotive boiler, where the outer firebox was particularly large and served as the steam dome, often highly decorated with polished brass. These were popular for early railway locomotives, from 1830 to 1850.
This is another form of boiler frequently described as a "haystack".
gunboat boiler: similar to the commonly known locomotive boiler, from steam locomotives. A horizontal boiler drum contains multiple fire-tubes and a separate furnace. However the furnace in a gunboat boiler has no opening at the bottom of the furnace to allow dumping of ash, the furnace is completely water cooled, similar to a scotch boiler furnace. These boilers were used in early torpedo boats and gunboats, having low height for protection from enemy gunfire.
Johnson boiler: one of the first "modern" classes of high-pressure marine oil-fired water-tube boilers. They have a single steam drum above a single water drum. Their small-diameter water-tubes curve outwards on each side to form a cylindrical furnace. As there is no grate or ashpan beneath, firing must be by oil. Return circulation is by external downcomers. Early versions also used water-walls at each end of the furnace, later ones had plain firebrick walls.
Kier: (sometimes Keeve or Kieve) an un-fired boiler, a pressure vessel heated by an external steam supply, used for bleaching in dyeworks and processing paper pulp. In use they were continuously rotated by an engine, steam being supplied through a rotating joint in the axle. They were usually spherical, sometimes cylindrical, and some were recycled from old boiler shells.
Kingdom boiler: an uncommon pattern of water-tube boiler.
large-tube water-tube boiler: early water-tube boilers with large diameter water-tubes, of 3 inches and above, rather than the later small-tube designs.
launch-type boiler: a small fire-tube boiler used in launches and smaller steam yachts. A horizontal cylinder in form, with a cylindrical furnace and multiple fire-tubes. They have some resemblance to a small Scotch boiler or Huber boiler, but with the fire-tubes extending beyond the furnace end, rather than folded back as a return-tube boiler.
monotube steam generator: A single tube, usually in a multi-layer spiral, that forms a once-through steam generator. The first of these was the Herreshoff steam generator of 1873.
multi-tube boiler: fire-tube boiler with multiple small fire-tubes, rather than a single large flue.
Mumford boiler: A form of three-drum water-tube boiler by Mumford of Colchester. The water-tubes are highly curved and the flue only covers the centre of the steam drum, not enclosing its whole length.
return-flue boiler: flued boiler with a single large flue that folds back on itself. Used in early steam locomotives.
return-tube boiler: fire-tube boiler with multiple small fire-tubes that reverse the direction of gas flow within the boiler. Individual tubes are not folded: there is usually a furnace, a combustion chamber that reverses the flow, then the tubes return from that. The Scotch is a well-known example of this type.
round-topped boilers are an early form of locomotive boiler, where the outer wrapper of the firebox is a semi-circular continuation of the cylindrical boiler barrel.
Schmidt boiler: a high-pressure locomotive boiler, as used for the experimental LMS 6399 Fury. To avoid the usual problems of scale formation in a highly-stressed firebox, the Schmidt system uses a separate primary circuit filled with distilled water.
small-tube water-tube boiler: water-tube boilers with small-diameter tubes, 2 inch or less, rather than the older large-tube designs, with tubes of 3 inch and above. Also termed Express or Speedy boilers.
Smithies boiler: A development of the pot boiler with added watertubes, used for model steam locomotives. The boiler was invented by F. Smithies in 1900 and developed by Greenly. It consists of a cylindrical water drum hidden inside a larger drum that forms the visible part of the model. Long slightly-sloping water-tubes are mounted beneath this water drum. The advantage of the boiler over similar model boilers is the use of almost the entire water drum surface for heating, although this also tends to scorch any paintwork on the outer drum, unless this is insulated. In a later development by Greenly, the backhead of the boiler becomes a double-walled water space and straight water-tubes are led into this at an angle.
Straker boiler: a vertical water-tube boiler for the Straker steam wagon.
submerged multi-tube boiler: a vertical multi-tubular fire-tube boiler, with the boiler shell extended upwards in an annular ring, so as to always maintain the whole length of the tubes submerged. Used in steam wagons and similar, where the water-level may be disturbed as the vehicle climbs a hill.
Sulzer boiler: a monotube "once-through" steam generator.
vertical boiler: flued or fire-tube designs where the main shell is a cylinder on a vertical axis, rather than horizontal. Boilers of this external form may have a great variety of internal arrangements.
Yorkshire steam wagon boiler: A double-ended transverse-mounted boiler used in steam wagons, to avoid problems of tilting when climbing hills. Internally it resembled a locomotive or Fairlie boiler with a central firebox and multiple fire-tubes to each end. In the Yorkshire though, a second bank of fire-tubes above returned to a central smokebox and a single chimney.