View source for Railway Technical Website - Steam Glossary

=== F ===

==== FAIRLIE LOCOMOTIVE ====
An articulated type of locomotive designed by Robert F Fairlie in 1865.  The design was popular on narrow gauge lines.  The frame was mounted on to one or two engine units which could move independently.  The engine units could have leading and trailing trucks.  A double Fairlie had two engine units, a single Fairlie one, the other being replaced by a bogie.  The double Fairlie appeared to have two boilers but this was not the case.  They had a single boiler with a firebox and cab in the middle and a smokebox at each end.  The cab was in the middle, and the boiler barrel ran right through it, with the driver on one side and the fireman on the other.  The driver on a double Fairlie controlled the water supply to the boiler as well as driving, leaving the fireman to look after the fire.  This saved space on the fireman's side of the cab.  Over 500 Fairlies were built in the USA including, in 1871 the Mason-Fairlie locomotive.  They were also used in Russia, India, Australia, and New Zealand.  The Fell locomotives used in New Zealand were Fairlies.

==== FEED PUMP ====
The means of getting fresh water into the boiler from the tank before injectors became common from the 1860s.  Pumps could be worked off an extension of the piston rod, the engine crosshead or from an eccentric on an axle.  Some designers added a steam driven pump or donkey engine to allow water to be fed to the boiler when the locomotive was stationary.

==== FEED WATER HEATING ====
Various means of pre-heating the water supplied to the boiler were tried over the 125 years of steam locomotive development.  In 1854 Joseph Beattie of the London & South Western Railway introduced a steam heated water supply system on his new locomotives and in 1862, Stephenson & Co.  built a locomotive with a tank under the footplate which was used to heat the feed water using live steam.  Sometimes, tender water heating was used.

The introduction of injectors provided some pre-heating of feed water in themselves but they would not work if the water had already been heated to above 120 F in the tender or before reaching the injector.

In later years some locomotives used feed water heating and had to have steam driven feed pumps.  The French ACFI system was a well-known example.

==== FELL SYSTEM ====
A system which allows locomotives to climb gradients at or over the limit of adhesion by means of a central third rail.  The locomotives are equipped with a second set of cylinders driving wheels parallel to the ground and forced against the centre rail by spring or screw pressure.  The Fell system differs from other mountain railway systems in that it depends on friction alone; the centre rail is a plain section unlike the Abt and other systems where the rail is toothed to correspond with toothed wheels on the locomotive.

==== FIRE HOLE ====
The opening in the rear wall of the firebox through which access to the fire is gained from the driver's cab.  Its principal use is for shovelling coal onto the fire.  It is normally kept closed and only opened for firing or cleaning the fire.

==== FIRE HOLE DEFLECTOR PLATE ====
An angled plate fitted inside the firebox over the fire hole to assist the flow of air over the fire so that the best gas heating rate is obtained.  It works in conjunction with the brick arch.

==== FIREBOX ====
The compartment at the rear of the boiler which houses the fire.  The firebox is where the fuel, usually coal, but it can be wood or oil, is burnt to provide the heat to boil the water in the boiler.  The firebox consists of two copper or steel enclosures, the outer firebox and the inner firebox.  They are connected by 'stays', bolts which keep the inner box rigid within the outer box.  Normally, the stays are threaded at each end and are screwed into the steel plates of the firebox.  The ends are hammered down as a seal.

Copper fireboxes were the normal practice for UK railways but in the US, steel was the usual material.  The steel firebox was first tried by Alexander Allan on the Scottish Central Railway in 1860.

Boiler water surrounds the firebox sides front and top to allow maximum benefit from the fire for heating.  The two side areas are often referred to as "legs", as they take on this appearance in cross section.  The outer firebox is really an extension to the boiler.  When the boiler is filled, water will enter the outer firebox legs and cover the roof or "crown" of the inner firebox.  The boiler's tubes are connected to the front wall of the inner firebox so that the hot gases from the fire pass through them to the smokebox.

Inside the firebox a brick arch is positioned over the fire so that the heat from the fire is deflected towards the back of the firebox to ensure the hot gases are distributed towards the tubes more evenly.  In their inspection, the lighting- up crew will check that the firebricks are secure and undamaged.

The two shells of the firebox are joined at the base by what is known as the 'foundation ring' or 'mud ring'.  This name arises from the sludge with tends to collect there during the time between boiler washouts, as it is the lowest point of the boiler where water reaches.

Firebox shape has developed over the years.  To get the required grate area to heat a large boiler, older fireboxes tended to be long but narrow, as they had to rest between the locomotive's frames.  This led to difficulties with manual firing, as the coal had to be thrown towards the rear in spite of a slope being provided.  Later designs had the frames lowered at the firebox end to allow a wider firebox with a shorter grate.  See also the Belpaire boiler.

==== FIREMAN ====
Second crew member for a locomotive responsible for the production of steam.  This requires that he looks after fire upkeep and the maintenance of sufficient water in the boiler.  He will also assist the driver with observation of the road, care of the locomotive, coupling and uncoupling etc.

==== FLANGE ====
The fundamental element of the wheel-on-rail guidance system. The inner edge of each wheel is shaped to a larger diameter than the wheel tread resting on the rail to act as a guide for the wheelset.  The two flanges of the wheels on an axle guide the wheelset to follow the route of the track.  A characteristic squealing sound can often be heard on sharp curves as the outer wheels' flanges slice along the inner edges of the rails.

==== FLANGELESS WHEELS ====
Common on many early locomotives to ease travel around curves.  Also used on later designs such as 2-8-0 locomotives for the same purpose.

==== FOUNDATION RING ====
The base upon which the firebox is built.  Originally circular, the foundation ring (also known as the 'mud ring') joins the outer and inner firebox shells and seals the water space around the inner firebox.  The name mud ring arises from the sludge which forms at the base of the water space due to the collection there of impurities in the water.

==== FRAMES ====
Locomotive frames were generally of two types, plate or bar. In the UK plate frames became standard whilst in the US bar frames were standard.

In the UK during the 19th century, locomotives were built with inside frames, outside frames and double frames.  The arrangements were tried by various designers offering various reasons for their choice.  Double frames gave better stability and strength and it was the practice to provide two sets of bearings for the driving wheels and one set for coupled wheels.  Double frames made locomotives heavier but, given the science of metallurgy in those days, they were preferred against single frames because the latter showed a tendency to fracture more readily.  There were some who believed that with double frames, the risk of broken crank axles was reduced and, even if they did break, the risk of derailment was reduced. Eventually, improvements in the quality of the steel used and the need to reduce weight led to the universal introduction of inside frames by the end of the First World War.

During the construction of frames it was essential to ensure that they were square, as any deviation would result in the cylinders, valve motion or cranks being out of line and thereby causing damage during running.  Some locomotives used cast frame beds ,particularly in the USA and by Beyer-Peacock where the engine frame was a single piece steel casting, thus guaranteeing the thing stayed square and true.  The South African GM-AM locomotives also have cast beds.

==== FULL GEAR ====
The position of the reverser where the maximum cut off is selected to allow the maximum amount of steam into the cylinders.  Usually used for starting, after which the cut off is reduced or shortened to allow more expansive working of the steam.  A locomotive may be in 'full forward gear' or 'full reverse gear'.

==== FUSIBLE PLUG ====
In the UK it became common to provide a plug in the crown sheet of the firebox which had a lead core in order to protect the boiler against failure if the water level was allowed to become too low.  If water failed to cover the crown of the firebox, the lead core of the fusible plug melted and steam and water would escape into the firebox to extinguish the fire.  Embarrassing for the crew, who were responsible for ensuring the safety of the boiler, but not fatal, as a boiler explosion could often be.