BRITISH RAILWAYS 1920 - 1970
COMPONENT PARTS OF THE STEAM LOCOMOTIVE
Arch, brick: an arch of firebrick within the firebox, which spans the firebox for about half the distance between the firebox tubeplate (at the rear of the boiler barrel) and the back plate. This arch provides for complete combustion and an even draught for the firebed.
Ash ejector: a steam admission pipe at the base of the smokebox which enables accumulated ash to be lifted into the exhaust stream and thence be ejected through the chimney.
Ashpan: the ash receptacle which is fitted with dampers (swinging doors) before and behind to regulate the amount of air feeding the firebed.
Atomiser: an injector which provides a fine spray of lubricating oil to mix with the steam in the cylinders.
Axle-box: provides the bearing between the axle and the locomotive frame and is fitted in guides in the frame.
Balance weight: a solid mass added to the inner rim of a driving wheel (and in some cases to parts of the valve gear) to compensate for the inequilibrium of the various moving parts and reduce the 'hammer blow' effect (a vertical pulsating force acting on the rail, initially generated by the motion of the pistons).
Big end: the end of the connecting rod that bears on the crank pin of the driving wheel.
Blastpipe: the exhaust outlet for steam emitted from the cylinders. This is situated at the base of the smokebox exactly in alignment with the chimney. The position of the nozzle is critical because the exhaust steam influences the draught on the firebed; the size of the nozzle must be matched with the output of the cylinders in order to relieve the back pressure on the pistons when the locomotive is worked hard. A blastpipe of the Kylchap type consists of two blastpipes feeding a double chimney, thus increasing the area of orifice and minimising the back pressure.
Blowdown apparatus: an automatic water valve and a main stop-plug mounted at the back of the boiler which permits a limited quantity of water to be blown out of the boiler continuously when the regulator is open. This flushing effect tends to reduce the problem of priming consequent on the build-up of alkalis when softened water is used.
Blower: a jet, or series of jets, which provides steam directly from the boiler to the smokebox to induce draught up the chimney and thus improve the combustion at the firebed. There are many forms of blowers but they are commonly fitted in the cap of the blastpipe.
Bogie: an unpowered, weight-carrying wheel-set, designed to provide flexibility on curved track and improve riding-properties. A single wheel-set is termed a pony (-truck). A radial truck serves a similar purpose but the axle-boxes are allowed side-play within the mainframes.
Boiler: this comprises the barrel containing the flue tubes where the products of combustion from the firebox release their heat to the surrounding water for evaporating purposes. The firebox and smokebox form integral parts of the boiler.
Crosti boiler: in this design, the exhaust is fed backwards through a preheater (to heat the feed water) mounted beneath the boiler.
Taper boiler: a boiler which is tapered in profile so that more steam space is provided nearest to the firebox where steam is most liberally generated.
Booster: auxiliary cylinders which drive trailing bogie wheels or leading tender wheels and provide additional power for starting and in other situations where increased tractive effort is required.
Brakes: brakes are fitted to driving wheels and tender wheels of steam locomotives. Automatic vacuum or Westinghouse automatic air brakes were required for passenger train operation. In the former system, the power exerted by the brake blocks upon the vehicle is obtained from the atmospheric pressure on a piston. In the latter, the power is provided by compressed air furnished by a pump and stored in a main reservoir on the engine. The compressed air is also contained in auxiliary reservoirs on each vehicle. The reduction of pressure in the train pipe causes pistons of triple valves to move and permit some of the compressed air in the auxiliary reservoirs to pass to the brake cylinders. Steam brakes were used on freight locomotives and could be used in conjunction with the automatic brake. The power was obtained by admitting steam at boiler pressure behind a piston in a cylinder, placed below the footplate. The hand brake on a tender locomotive has a mechanical linkage to the tender wheels.
Buffing gear (or drawgear): the coupling between locomotive and tender. Capuchon: a raised edge on the forward part of a chimney to screen the mouth from air currents.
Carriage warming cock: this cock is fitted to the back plate and is provided with an independent steam pressure gauge and in some cases a reducing valve to give a pressure of about 40 to 50 lb. per sq.in.
Clack box: a box that holds the clack valve supplying water from the feed-water heater directly to the boiler.
Combination stand: a brass casting fitted in the cab against the firebox which collects steam from the dome and provides connections for the vacuum ejector, the whistle(s), carriage warming cock, steam gauge and sight-feed lubricators.
Combustion chamber: an extension of the firebox which fits inside the rear of the boiler barrel and promotes complete combustion of the fuel.
Compound locomotive: one in which steam at boiler pressure is first admitted to one or more high-pressure cylinders and then exhausted to one or more larger diameter low-pressure cylinders.
Condensers: tank locomotives working through the Underground system were fitted with condensers in order to reduce the exhaust steam: a flap in the blastpipe directed the exhaust back into the side tanks via external pipes.
Connecting rod: the rod connecting the crosshead to the crank-pin of the driving wheel.
Coupling or side rods: the rods which link the driving wheels and thus distribute the adhesion and optimise the tractive effort.
Crosshead: the bar between the piston rod and connecting rod which is guided by the slide bars and thus ensures that the small end of the connecting rod travels in a straight path.
Cut-off (regulator): see reversing gear.
Cylinders: the piston assembly where steam pressure is converted into mechanical energy. They may be placed inside or outside the frames.
Dampers: see ashpan.
Dome: the collecting chamber for 'dry' steam above the steam space in a boiler. It feeds the main steam pipe, and also other pipes which supply the injectors, the steam sanding cock, the jet cock and the vacuum ejector or steam brake valve.
Dragbox: the bracing at the rear of the main frames to which the drawgear is attached.
Drawgear: see buffing gear.
Drop-grate: a section of the grate which can be rotated to drop the fire or ashes.
Eccentric: a crank used on inside valve gear for transforming rotary into reciprocating motion.
Ejector: in air ejectors, which are used for creating a vacuum in the braking system, a jet of steam is discharged through nozzles to give a very high velocity. This jet combined with the reduction of pressure induces air from the surrounding chamber to form the vacuum (the Venturi effect). Two ejectors are commonly used: one large for rapid initial creation of vacuum and one small which is in continuous operation to maintain against leakage. The former is actuated by the driver's brake handle, when in the 'brake off' position.
Fall-plate: a hinged steel plate, covering the gap between locomotive and tender.
Feed water heater; a system whereby exhaust steam is taken from the blastpipe and fed to a mixing chamber to preheat the feed water for the boiler.
Firebox: this consists of a mild steel doorplate which is fitted to the outer firebox plate (or wrapper). a front tubeplate and saddle plate, and a copper inner firebox. The wrapper forms the outer casing for the water space surrounding the inner firebox. See also below.
Foundation ring: the connecting member between the inner and outer firebox shells which extends around the bottom of the inner box. The width of this ring defines the minimum water space.
Frames: the frame plates are placed vertically inside the wheels, the full length of the engine, and transversely stayed to form a strong deep framework to carry the engine and boiler. The plates are usually made of mild steel, about 1116 in thick.
Fusible plug: a lead alloy plug fitted to the firebox and designed to melt and allow steam to escape into the firebox if the water in the firebox were to fall to a dangerous level.
Giesl ejector: a system for improving the draught in the firebox, whereby the exhaust is passed through a series of parallel nozzles to provide the maximum freedom of the exhaust.
Guard iron: a downward projecting iron arm fitted before the leading wheels to remove small obstructions from the track.
Hornblocks: steel castings mounted in the frames to retain the axleboxes but allowing a vertical movement; thus, in conjunction with the springs, the vibration due to the jolting of the engine is reduced.
Injectors: these maintain the feed of water to the boiler against the pressure of steam in the boiler. They create a vacuum in the same way as ejectors (q.v.), which serves to lift the water supply ; the feed water is entrained in a jet of steam and injected into the boiler. Two injectors are fitted, one for a continuous feed and the other in a supplementary capacity for high usage of steam. Some injectors use steam from the exhaust, others including the supplementary type use live steam taken directly from the dome.
Lubricators: these are of a mechanical type (Silvertown or Wakefield pumps) or of the hydrostatic type (using condensed steam to displace the oil) and these feed the cylinders. See also atomiser, sight-feed lubricator.
Motion plate: a cross-plate of annealed cast steel which braces the frames at the rear of the inside cylinders and carries the slide bars and valve rod guides.
Petticoat (pipe): an extension of the chimney downwards into the smokebox.
Pick-up apparatus, water: this consists of a hinged scoop about 10in. wide which may be lowered when the engine passes over a water trough. This feeds a vertical pipe inside the tender which has a discharge end about 7in. above the maximum tank water-level. The scoop is lowered manually but is lifted by a steam cylinder or other device.
Piston rod: the rod which passes into a cylinder and to which is fixed the piston head. The admission of steam alternately to each end of the cylinder forces the piston head backward and forward, thus converting steam pressure into mechanical energy.
Piston valve: an assembly, comprising two pistons secured to one valve spindle, fitted in such a manner that they uncover steam ports and feed steam to each end of a cylinder alternately.
Pony: see bogie.
Poppet valves: valves which control the admission and exhaustion of steam in the cylinders. They provide for variable speed of opening and closure and are actuated by cams.
Ports, steam and exhaust: the inlet and outlet pathways, respectively, for steam in the cylinders.
Pressure relief valves: valves in the cylinders which serve to drain water introduced as a result of priming or condensation and thus prevent 'knocking'.
Radial truck: see bogie.
Regulator: the valve which regulates the supply of steam to the cylinders; it is controlled by a long rod which reaches from the dome (in the case of domed locomotives) through the doorplate.
Reversing gear: a mechanical linkage between the footplate and valve gear which serves not only to reverse the motion of the engine but also to vary the point of cut-off i.e. the point on the piston stroke at which the steam supply to the cylinders is cut off by the closure of the admission valve.
Rocking grate: a system whereby the firebars of the grate are hinged and can be 'rocked' to remove accumulations of clinker. These grates helped to alleviate the problems caused by inferior coal in post-war years.
Saddle plate: a steel casting which is secured between the frames and which holds a central spigot about which a bogie swivels.
Saddle, smokebox: a casting, fitted above the inside cylinder casting or between the frames, upon which a circular smokebox rests.
Safety valve: a valve mounted on the top of the boiler to prevent the build-up of excessive steam pressure. These are adjusted to the required blowing-off pressure. The most common forms used were the compact Ross 'pop' type and the older Ramsbottom type.
Sand gun, firebox: a steam jet mounted on the doorplate of the firebox which sprays sand at the tubeplate to remove accumulations of soot.
Sanding gear: the gear used to supply sand beneath the driving wheels to increase adhesion. The sand can be fed by gravity, by steam ejectors or in a wet form by a flush of water supplied from the boiler. Locomotives fitted with Westinghouse brake used compressed air.
Sight-feed lubricator: a displacement lubricator to feed oil to the cylinders which provides a visual indication (sight-feed) of the oil being supplied.
Slide bars: see crosshead.
Slide valve: see piston valve.
Smokebox: the section of the boiler where exhaust gases are collected. It contains the blastpipe, main steam pipes, blower and self-cleaning apparatus.
Snifting valves: vacuum relief valves, sometimes mounted on the smokebox behind the chimney. They allow cooling air to be drawn to the superheating elements when the regulator is closed.
Spark arrester: perforated steel plates are fitted immediately above the top row of tubes in the smokebox to prevent small particles of hot fuel from going up the chimney.
Speed indicator: a speedometer which may provide a record on a paper feed of time and speed; an electrical generator or mechanical transmission may be used to provide the information from the rear driving wheel.
Steam chest: the housing for the steam distribution valves which is sometimes integral with the cylinder casting.
Steam trap: a component of the feed-water heater system which ensures a supply of dry steam to the feed pump. It contains vanes on which the steam impinges and these throw off any water which may be carried in suspension.
Stoker, mechanical: the arrangement for a mechanical stoker typically takes the form of a rotating screw which carries the coal from the tender to a distribution plate on the doorplate of the firebox. From there it is blown by steam to the firegrate.
Superheater: superheating involves increasing the temperature of the steam, thus drying it and increasing its volume. The superheater consists of a header in the firebox which takes the steam from the regulator and distributes it to superheater elements, contained in large flue tubes within the boiler, before feeding it to the steam chests. Each of the elements consists of a continuous pipe in four sections connected by three return bends. Thus the steam makes two journeys in the direction of the firebox.
Thermic syphon: a Y-shaped funnel-like structure in the firebox through which boiler-water is circulated thus increasing the heating surface area.
'Top feed': the usual method of feeding water to the boiler was to take it to the lower front end, at the coolest portion. In the Churchward 'top feed' design, the water was fed from the top of the boiler and cascaded in fine streams via trays to the water level. Thus the temperature of all the water in the boiler was equalised.
Turbine locomotive: an engine fitted with turbines instead of the usual cylinders, pistons and rods. The L.M.S. design of 1935 used a non-condensing multistage turbine for forward running and an impulse type for reverse. The working pressure of the conventional boiler was 250lb per sq in and geared transmission was used to the coupled wheels.
Tyres: the wheel tyres are made from rolled steel and slightly undersize to the wheel centres. They are fitted by heating to permit the appropriate expansion. Studs or rivets are fitted later for additional security.
WALSCHAERTS VALVE GEAR
Valve gear: the mechanical linkage used to synchronise the movement of the pistons with the settings of the valves and to provide for reversal of movement. The Stephenson (and other link motions) and Walschaerts valve gears use eccentrics (which convert rotary into reciprocating motion) whereas Joy's and other radial valve gears dispense with eccentrics. The Caprotti and Lentz types utilise poppet valves (q.v.) and camshafts. In the case of Gresley conjugated valve gear, used on three-cylinder engines, the valve of the inner cylinder derives its motion from extensions on the outside valve spindles. Bulleid used a chain-drive immersed in an oil-bath for the valve gear on his light Pacific locomotives.
Water gauge: two sets of gauge glasses are commonly fitted to provide a cross-check on the water-level in the boiler. A protective glass case surrounds the vertical water tube which is connected to the steam and water spaces of the boiler. Ball and spring valves are fitted to shut off the steam and water supply in the event of breakage.
Whistle: in some cases two brass whistles of different size and tone were fitted to each engine. They were supplied separately with steam and had independent actuating valves.
COPYRIGHT © R.D.LAKE 2009