A mechanical stoker is a mechanical system that feeds solid fuel like

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

, coke or

anthracite Anthracite, also known as hard coal, and black coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the hig ...

into the

furnace A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings * Boiler, used t ...

of a steam boiler. They are common on

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

s after 1900 and are also used on ships and power stations. Known now as a spreader stoker they remain in use today especially in furnaces fueled by wood pellets or refuse. There are three types: the over feed, the under feed and the cross feed. The over feed delivers coal on to the top of the coals already in the furnace in the manner of a human working a shovel. The under feeder pushes fresh coal into the bottom of the furnace and then advances it upwards so that it mixes with the burning coal above. The mechanical means used are, depending on design, combinations of the screw feed, the conveyor belt, the bucket chain, the paddle and the ram. Steam jets from the boiler or a mechanical catapult may also be used to throw coal into the far reaches of the furnace.

Use in steam locomotives

The confined working conditions of a locomotive footplate meant that the earliest development of the stoker took place in this application. Designers sought to maximise power output in the locomotive by feeding coal at a rate faster than the

fireman A firefighter is a first responder and rescuer extensively trained in firefighting, primarily to extinguish hazardous fires that threaten life, property, and the environment as well as to rescue people and in some cases or jurisdictions also ...

could shovel. In

locomotives A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the ...

the stoker was usually powered by a small steam engine located in the tender which drew its steam from the main boiler. In early designs the coal would still be shovelled by the fireman into a hopper which would feed into a crusher and then a screw or bucket elevator would lift the pulverised coal to a position where it could be mechanically scattered across the burning coals of the furnace by a spreader. The spreader could be jets of steam, mechanical arms, or a fast rotating plate. Later designs also mechanised the retrieval of the coal from the tender using steam ram powered pushers and/or a helical screw.

Some notable types

*The earliest practical design is from 1905 and was known as the ''Crawford'' after D. F. Crawford, Superintendent of Lines West at the

Pennsylvania Railroad The Pennsylvania Railroad (reporting mark PRR), legal name The Pennsylvania Railroad Company also known as the "Pennsy", was an American Class I railroad that was established in 1846 and headquartered in Philadelphia, Pennsylvania. It was named ...

. This used a system of paddles to push coal forward and it was fed into the firebox at grate level.Hollingsworth, Brian, ''Illustrated Encyclopedia of the Worlds Passenger Steam Locomotives'', Salamander Books, London , 1982, K4 Class 4.6.2 , page 100, *The ''Street'' type, consisted of a coal crusher, hand-fed by the fireman, that was fitted to the front left hand side of the tender footplate and driven by a small steam engine mounted behind the hand brake column. The crushed coal then fell by gravity into a chute which led to a receiving bin that was fitted below the back buffer beam of the locomotive, from where it was picked up by a bucket elevator travelling in large tubes. The full buckets were carried up in the left hand side tube mounted on the back of the firebox, discharged into a central receiver and then travelled down the right hand side tube. *The ''Duplex'' type was manufactured by the Locomotive Stoker Company, Pittsburgh, PA. It used a screw feed to bring coal forward from the tender, and then two vertical screw feeds to raise it into the left and right hand sides of the firebox.

References

{{Reflist Steam locomotive technologies Locomotive parts Train-related introductions in 1905