Friday, 11 September 2015

Railway Turntables


The turntable (or 'turnplate') appeared early in the development of railways, initially as a means of routing single wagons from one line to another at coal mines and similar installations and often narrow-gauge.

A cast narrow-gauge wagon turntable preserved at Black Country Living Museum (without the approach tracks).

When the first steam railways were built, the size of turntables was increased to allow shunting of passenger coaches and turning of the small locomotives then in use. No passenger station lacked a battery of turntables to assist in marshalling each train. The 'Roundhouse' design of locomotive shed using a turntable to access a number of radiating stabling roads was used as early as 1846 by the London and Birmingham Railway (there's a very brief description of that line here). The building of the roundhouse locomotive shed built at Camden survives as a Grade II* listed building and is now used as a performing arts and concert centre called Roundhouse. There are brief details of the building on Jack Whitehead's Local History website here.

Camden, showing the London and Birmingham locomotive roundhouse of 1846 (now the Roundhouse Theatre).

Eventually, small turntables became confined to goods yards and canal interchanges. They were often provided in large numbers, sometimes associated with capstans so that haulage ropes could be arranged allowing horses to move the wagons. The sketch map below shows the sidings and wagon turntables at the canal interchange basins at Bloomfield in the West Midland area of England in the early years of the 20th century.

A larger version of this sketch can be found here.

There's a brief write-up about the canals and sidings at Bloomfield in the post Rail and Canal at Bloomfield.

The picture below shows a typical standard-gauge wagon turntable, this one preserved in Birkenhead Docks.

Birkenhead: Wagon Turntable adjacent to Duke Street Lifting Bridge.

There's a write-up of my exploration of Birkenhead's Docks in the post Birkenhead and New Brighton by train (Part 2).


Developments in locomotive design produced larger engines which required longer turntables. In Britain, turntables up to 70 feet in length were made. There's a Wikipedia article here.

The following description is based on an article published in The Locomotive Magazine and Railway Carriage and Wagon Review, dated 15th February 1937. This article, in turn, was 'a brief abstract of the main points mentioned' in a paper on Locomotive Turntables read to a meeting of the Institution of Mechanical Engineers on 27th January 1937 by Associate Member Mr. J. H. A. Wilkins.

Modern locomotive turntables conform to one of three types:-
1. The cantilever, or centre balanced type: either 'through' or 'deck' pattern.
2. Articulated or centre hinged type.
3. Continuous girder type supported at three points (Mundt type).
Of more than 900 turntables in use in 1936, most were centre-balanced type with only around 20 ar and 20 of the continuous girder (Mundt) pattern. In the U.K, the largest turntable in use is 70 ft. diameter.

1. Cantilever or centre balanced type supported on the centre pivot

The turntable is balanced in the centre, the main girders acting as cantilevers. Two strong wrought iron or steel plate main girders are braced together by stretchers and securely attached to a middle framework which rests on and revolves around a centre pin fixed to a solid foundation. Large carrying wheels which travel on a rail laid round the circumference of the pit are attached to both ends of the main girders.

In use, the locomotive to be turned is centred or 'set' so that the majority of the weight is taken by the centre pivot, and a small force applied to the ends of the main girders is able to turn the table. To assist in achieving the necessary balance, the length of the table should be several feet longer than the wheel base of the locomotive.

During erection, the large carrying wheels are given a slight clearance from the circumferential rail and carry that part of the weight not supported by the centre pivot.

If a locomotive is perfectly balanced, all the weight is carried by the centre pivot, otherwise part of the weight is supported by the large carrying wheels at one end of the turntable.

The centre pivot comprises a cap or yoke cast in steel which supports the main girders by large suspension bolts. The cap rests on a pivot bearing, typically made of 'UBAS' case hardening steel supporting a bronze, gun-metal, or steel cup ('UBAS' was a trade mark used by W. T. Flather who manufactured special steels). If an anti-friction thrust bearing is incorporated, this is enclosed in a steel housing resting on, and positioned on, the stump or centre pivot. The centre pivot takes the full load of the turntable and locomotive when in use and is usually cast iron, secured by rag bolts or similar to a solid, normally concrete, foundation.

Because of the clearance given to the large carrying wheels, 'blocking pads' are provided to take the weight of the locomotive when running on or off the turntable. In some cases the hand lever for operating these blocking pads also operates the locking bolts for holding the table in position opposite the various roads radiating from the pit. In its horizontal position this lever is sometimes used for turning the table manually.

In some designs, levers to operate the blocking pads and locking bolts are replaced by hand wheels at each end of a shaft running the whole length of the turntable girder, so that turning the hand wheel at either end operates the blocking pads and locking bolts at both ends. The locking bolts also serve as blocking pads in some designs, engaging in a cast iron locking rest fixed in the pit wall where each track radiates.

The centre-balanced main girder may be of 'deck' (under girder) or 'through' (over girder) design.

In the 'deck' type, the rails are laid upon the top of the main girders, simplifiying construction but requiring a deep pit to accommodate the height of the main girders.

In the 'through' type, the rails are laid between the main girders, carried on cross members. This allows the use of a shallower pit. The G.W.R. normally use the 'through' type in outside locations (a 65 ft. turntable on the GWR at Oswestry was cited as an example) where a notice visible to the engineman reads "All engines must stop before going on to the turntable." so as to avoid shock as the locomotive runs on to the table, due to the clearance on the large carrying wheels). The 'through' type, although possessing the advantage of requiring only a shallow pit, weighs considerably more itself due to the heavier construction and greater width, and costs more than the 'deck' type.

2. Articulated or centre hinged type supported at three points

This design is credited to a Chief Inspector of Locomotives on a German railway called Herr Klensch who sold his patent to Messrs. Julius Vogele in Mannheim. They, in turn, granted licences to manufacturers in Germany and elsewhere.

The articulated turntable is divided into two beams, supporting the load over the centre pivot and the large carrying wheels at each end of the turntable which are always in contact with the circumferential rail. The large carrying wheels take at least half of the load on the turntable and it can be driven from either end.

Because the large carrying wheels remain in contact with the rail, the ends of the table are not violently depressed when a locomotive runs on to it, reducing the shocks which occur with the cantilever or centre balanced type descried above in which, when correctly balanced, the large carrying wheels remain clear of the rail.

One advantage of dividing the main girders in this design is that girder height can be reduced, allowing the use of a shallower pit.

The articulated or centre hinged design found favour in the U.S.A. where lattice girders were often used. Elsewhere riveted plate girders or rolled girders were generally used.

With an evenly-distributed load, the thrust bearing of the centre support carries half the total load the balance being carried by the large carrying wheels. The centre joint must be sufficiently robust to prevent slackness occurring which allows the large carrying wheels to skew, increasing the resistance to turning when the table is driven from one end only. A number of designs of centre joint using flexible hinge plates and laminated spring joints were evolved.

3. Continuous girder type supported at three points (Mundt type)

Mundt was an engineer with the Dutch State Railways and his improvement of the centre-hinged type eliminated the centre hinge by allowing a continuous girder to deform under load. The continuous girders are not of uniform section throughout, but are reinforced from each end to a certain distance short of the centre pivot. This allows of sufficient flexibility to prevent the rising of the unloaded end of the table with a unbalanced load (for instance, a short locomotive at one end).

The turntable may be driven from either end and no balancing is required - the locomotive can be turned immediately the last wheels of the engine or tender run on to it a no blocking up of the table is required.

Again, the design allows the use of reduced girder height, shallower pits and a centre support required to carry only half the total load.

A variation of the Mundt pattern, widely used in the U.S.A., uses unreinforced girders where bending throughout the length is provided. To ensure proper adhesion, these types are normally driven at both ends by electric motors.


Testing of locomotive turntables is usually carried out at the manufacturer's own works using a temporary track. The table is manufactured in sections (as in steel bridge construction) assembled with bolts in place of rivets to allow the structure to be taken apart for despatch to the customer. The test load is usually made up iron castings of known weight which are built up to the total weight required. The test load is stipulated on the contract, and is usually 25% above the weight of the heaviest locomotive which the table is designed to carry. The individual Loads are arranged to represent the axle loading of the heaviest class of locomotive which will use the turntable. Deflection tests of the main girders are made at the ends and between the ends and the centre. After the test load is removed, observations are made for any permanent set which may have taken place. The locking gear is carefully tested. This testing is usually witnessed by representatives of the customer.

When the turntable has been re-erected on its permanent site, it is then tested again by running the heaviest locomotive which will use the table on to it, and any final adjustments are made.


Early forms of turntable (before the use of anti-friction pivot bearings and carrying wheels became general) were operated by a winch driving gearing either fixed to the end carrier or directly to a toothed ring forming part of the wheel path. In some cases, the winch was driven by a small steam engine or hydraulic power.

Modern turntables may be operated:-
1. Manually
2. Electric motor
3. Vacuum motor
4. Compressed air motor.
1. Manual operation

The turntable is operated by a two-handled winch mounted at one end of the turntable deck. The crew of the engine to be turned provide the turning power. Extending beams are sometimes fitted to allow extra people to assist in pushing the turntable deck. In the 1930s, the majority of turntables in the UK were manually operated.

2. Electric operation

World-wide, this is the most common method of operation, particularly on larger turntables and almost universal in the U.S.A. At busy locations, the time saved by electric operation is significant. A control cabin is often mounted on the turntable deck and a man stationed in this cabin allows the engine crew to remain on the footplate during turning. In the U.K., both the GWR and LMS installed electrically-operated turntables but in 1935 there were under 30 in this country, compared with over 900 in the U.S.A. divided over 58 railway companies.

The electric motor is usually a totally-enclosed traction type. A tramway type controller with magnetic blowout, electric brake, current reverser and associated resistors is provided, often mounted within the control cabin. The controller usually has one handle for forward running and braking and another for reversing. A foot brake is provided working on a pulley keyed to the main or intermediate driving shaft.

Current collection to the rotating deck is either by electrical contacts in the pit or via an overhead cable to a gantry mounted at the centre of the deck provided with electrical slip-rings.

3. Vacuum operation

This method of driving is patented and manufactured by Messrs. Cowans, Sheldon & Co. Ltd. The apparatus consists briefly of a central valve chest mounting two double acting oscillating cylinders, each 4in. diameter by 6in. stroke, running at 350 rpm. and driving a crank shaft on which a pinion meshes with gearing which drives the large carrying wheels. All that is necessary when the locomotive is driven on to the table is for the vacuum brake pipe, either at the front or rear of the locomotive, to be connected to the flexible coupling of the tractor. The vacuum ejector on the engine is then opened and one of the engine men works the controls to operate the vacuum motor. There's a brief description of the 'Oscillating Cylinder Engine' here.

4. Compressed air operation

In the steam locomotive era, most British railway administrations used vacuum brakes but overseas air brakes were common. To cater for this market, the Cowans, Sheldon vacuum motor was adaptable to operate from the compressed air supply on an air braked locomotive.


There were two principal British manufacturers:-
Cowans, Sheldon and Company of Carlisle, perhaps better known as crane makers.
Ransomes and Rapier Limited of Norwich, also crane and machinery manufacturers.
Cowans, Sheldon and Company

A drawing of a Cowans, Shelton turntable in the collections of Tullie House Museum and Art Gallery, Carlisle. Click on the image for a larger view.

See also Grace's Guide.

Ransomes and Rapier Limited

A 1921 advert for 'Traversers and Turntables' (Grace's Guide).

See also Grace's Guide

Brief details of Ransomes and Rapier documents held by Ipswich Transport Museum on behalf of the National Archives are here.


Birmingham Railway Museum, Tyseley

Tyseley retains its turntable with radiating stabling roads from its former life as a Briitish Rail Motive Power Depot, although the building which originally covered both turntable and stabling roads had gone (along with a second building, turntable and stabling roads). For years, we operated this turntable by hand, although it had originally been electrically operated. Eventually, electric operation was restored. The turntable, a 'Mundt' type, had been supplied by Ransomes and Rapier Ltd. and the worksplate was marked:-
146 tons Mundt Turntable
Made For B.R. Contract No.1114-M&E
Ransomes and Rapier Ltd.
OR.G.J.4985 Ipswich England 1957.
There's a picture (by Stuart Axe) of this worksplate here.

Peak Rail, Rowsley

The original turntable here had been removed and the pit filled in. In a major restoration, the pit was dug out, re-bricked and a 60-foot turntable originally supplied to Mold Junction M.P.D. was installed. This is a Cowans and Sheldon turntable, operated by the original 2-cylinder vacuum motor.

The 60-foot turntable at Rowsley during installation. This Cowans Sheldon Co. Ltd turntable (O/N 6181 5-Mar-1937) was originally supplied to Mold Junction M.P.D.

There's a little more information on the Peak Rail website here.

The re-commissioned turntable at Peak Rail was inaugurated by Pete Waterman on 1st May 2010, as described here.

With Pete Waterman at the regulator, 8624 slowly reverses off the turntable (Photo: Sheila Rayson).

There is a collection of my pictures showing the Rowsley turntable in detail here.

Wolsztyn, Poland

'Piekna Helena' on the turntable at Wolsztyn.

There's a brief description of my visit here and my pictures are here.

Kolomia, Ukraine

Su 251-86 on the turntable at Kolomiya.

There's an introduction to my trip to Ukraine, with links to other posts and pictures here.

Kiev, Ukraine

A large turntable in Kiev serving an 8-stall roundhouse and the works. Note the overhead catenary.

There's an introduction to my trip to Ukraine, with links to other posts and pictures here.

Mahlwagon, Yangon, Myanmar

Mahlwagon Diesel Shed Turntable: 120 ton capacity metre gauge Mundt turntable built by Ransomes and Rapier in 1946.

There's a description of my visit to Mahlwagon Diesel Locomotive Shed here and my pictures showing the turntable at Mahlwagon are here.

A Model Turntable

A model turntable in 4mm/foot scale.

There are more details of this model railway here.

There's an article on Wikipedia about railway turntables here.

[Link to 'The Oscillating Cylinder Engine' added 25-Oct-2015]

Driving the 'Planet' replica

In the post 'Planet' at MOSI - The First 21 Years, I celebrated the 21st Birthday of the 'Planet' replica in October 2013.

When I was driving the 'Planet' replica, people sometimes asked if it was different from driving 'modern' steam locomotives. The answer is "not very, apart from the the fact she's a 'single wheeler', has a rather special braking system and an unusual method of reversing" ('Planet', like its immediate predecessor 'Rocket' has Slip Eccentric reversing). The basic principles of the steam locomotive haven't changed very much since the early days, although the appearance of the 'Planet' replica is very different from modern steam locomotives.

The 'Planet' replica being prepared for service with MOSI volunteer
Bev on the right.

I've already written about driving another early locomotive design in the post Driving 'Lion'. 'Lion' was built just eight years after the original 'Planet' and so there are many similarities, although 'Lion' incorporates Gab motion for reversing.


'Planet' has just one pair of driving wheels, which share the total weight of the locomotive with the leading pair of carrying wheels. Using Whyte's Notation, the arrangement is said to be a '2-2-0'. The total weight on the driving wheels is the 'adhesive weight'. With a single driving axle, not all of the locomotive weight can be adhesive. In the case of the original 'Planet' there was about 5 tons on the driving wheels, with about 3 tons on the carrying wheels. When the driver wants to get the train in motion, steam is used to generate sufficient torque at the driving wheels to move the load. But, if the torque applied to the driven wheels exceeds a critical value (related to the coefficient of friction between the wheels and the rails), the driving wheels slip on the rails and the train does not move.

This was more of a problem with goods trains, which tended to be heavier, so it was desirable to make all the locomotive weight adhesive to reduce the risk of slipping. On goods engines (then called 'luggage engines') the torque generated on the two driving wheels was shared with a similar pair of wheels linked to the driving wheels with coupling rods, giving a wheel arrangement of '0-4-0'. As the size and weight of locomotives increased, further coupled wheels were often used, although 'single-wheelers' weren't eliminated for some years as they could be free-running and, with large driving wheels, fast.

Because the 'Planet' replica only has one pair of driving wheels, it can be 'light on its feet' and prone to slipping so the driver has to take care when starting not to open the regulator too far.


In the early days of steam locomotives, effort was concentrated on making machines powerful enough to pull a useful load and braking technology was rather neglected. On both the original 'Planet' and the replica, there are two hand brakes, one on each side of the tender, and these are applied by 'screwing down' the handles which project from the top of the tender. Wooden brake blocks are provided which rub against the tyres of the tender wheels to provide braking. On the original 'Planet' that was it! This arrangement wasn't terribly effective in 1830 (severe braking could set the brake blocks on fire!) and, in the replica, the hand brakes are normally used only as a 'parking brake'.

Left side of replica tender showing the cast decorated panel and wooden brake blocks which are pulled against the tyres of the tender wheels by the screw handbrake to provide braking. Brake discs and calipers for the modern air brakes are visible between the wheel spokes.

To be acceptable for hauling passenger trains today, the 'Planet' replica also has an Air Brake system. This operates a disc brake on the leading axle of the locomotive, disc brakes on both tender axles and the train brakes. The regulator should always be closed before attempting to brake. I talk a bit about braking and the use of the automatic Vacuum Brake here. Air Brakes form another type of automatic braking (which I've not, to date, described). With the withdrawal of steam traction in the U.K., British Railways started to change over from vacuum braking to air braking and the 'Planet' replica has a version of what became the standard British Railways Two-Pipe Air Braking system.

Converting steam into rotary motion

This part of the locomotive has changed little since the early days. The 'Planet' had two horizontal cylinders at the front between the frames. When the regulator is at least partly open, steam flows through the main steam pipe to feed the two cylinders. The principle is simple - the steam under pressure is used to push a piston to the far end of a steam-tight cylinder. The picture below shows a deliberately 'sectioned' cylinder making the construction clearer. The piston is attached to a Piston Rod which sticks out of one end of the cylinder (through a steam-tight piston gland) and it's the motion of the piston rod which allows the cylinder to do useful work.

'Sectioned' cylinder on Beyer Peacock locomotive 'Pender' on display at MOSI. The piston is shown in its rearmost position in the cylinder and the Piston Rod extends to the left.

As the piston approaches the end of the cylinder, it's necessary to cut off the supply of steam and divert the steam to the other end of the cylinder so as to push the piston back again. This requires a valve in between the steam supply and the cylinder called (logically enough) the Steam Valve. The opening and closing of this valve must be synchronised with the movement of the piston. The two pictures below of the 'Planet' replica give an idea this was engineered in 1830, using complicated iron castings which were at the limit of what was technically possible.

The first picture below is taken inside the smokebox of the 'Planet' replica looking down onto the top of the left hand cylinder with the steam chest removed from the threaded mounting studs so as to show the flat port face area with two rectangular steam ports (connected to each end of the cylinder) and the larger rectangular exhaust port (connected through a passage to the blast pipe).

Top view of cylinder showing the cylinder ports (2 steam, 1 exhaust).

The second picture shows the underside of the steam chest which has been removed in the first picture. The steam chest is complete with the cast rectangular steam valve attached to the valve rod which sticks out of one end of the steam chest (through a steam-tight valve gland). The flat face of the valve bears slides to and fro against the flat port face so this type of valve is called a Slide Valve.

Steam chest complete with slide valve and valve rod.

The reciprocating motion of the two piston rods is converted to rotary motion of the driving axle by connecting rods linking the end of the pistons which pull and push a double-crank driving axle, as shown in the picture below. Practical locomotives have at least two cylinders and, on a 2-cylinder design, the cranks are set 90 degrees apart so that both cylinders cannot be on dead centre. This means that a locomotive can always be started (using the effort from at least one cylinder), whatever the position of the cranks.
More than a century after the building of the original 'Planet', similar arrangements remained in use. An increasingly common variation was to move the cylinders outside the frames where the connecting rods drove onto crankpins fitted to the driving wheels, but both inside cylinder and outside cylinder designs lasted until the end of steam. Some designs had additional cylinders and a locomotive might have both inside and outside cylinders. As locomotives became larger, slide valves were replaced by balanced slide valves and then piston valves. A variety of other valves (poppet, sleeve) were tried but piston valves emerged as the most practical form of valve. A few attempts were made using quite different techniques, like steam turbines, but double-acting reciprocating cylinder designs remained virtually unchallenged.
Valve Gear

As remarked above, the opening and closing of the steam valve to admit steam from the boiler to either end of the cylinder must be synchronised with the movement of the piston. Since the piston is used to turn the driving axle, if the motion of the steam valve is derived from the turning of the driving axle, the necessary synchronisation is obtained. The motion of the steam valve is derived from the rotation of the driving axle on this design by a special eccentric. A simple eccentric is a type of crank with a small 'throw' - see Wikipedia here. A simple eccentric is fixed to the axle which turns it so as to produce the correct valve events to rotate the driving axle in one direction.

But a locomotive must be able to move in both directions and this was achieved in 'Planet' and other early locomotives by the use of a Slip Eccentric for each cylinder mounted in the middle of the crank axle, as shown in the picture below. A Slip Eccentric is an eccentric which can engage with the crankshaft in two positions where one provides the correct movements of the eccentric rod and the valve rod for clockwise rotation of the driving axle whilst the other position produces anticlockwise rotation of the driving axle. This is achieved by providing lugs or 'dogs' which can engage with one of two mating recesses or pits. A transverse shaft operated from a foot pedal on the footplate is used slide each eccentric across the axle so as to disengage one lug and allow the other lug to engage when the axle has turned so as to bring the other recess in line.

"Planet's" driving axle and eccentrics viewed from below. L-R: RH driving wheel, intermediate axlebox, RH crank driven by (black) connecting rod, inside axlebox, RH eccentric and rod, LH eccentric and rod, inside axlebox, LH crank driven by (black) connecting rod.
Click here for a larger view

So, reversing the locomotive involves disengaging one lug in the slip eccentrics and turning the driving axle until the other lug engages. Achieving this probably provides the biggest challenge to the driver. There are two ways of achieving this changeover:-
1. Turn the driving axle by controlling the valves manually.
2. Perform a 'flying reverse'.
Reversing by controlling the valves manually involves operating the foot pedal to the other position, disengaging both valves from the eccentric rods (by operating the two small valve locking levers mounted on top of the left and right footplate railing) and operating the valves appropriately by hand (using the two curved levers mounted on the boiler backhead facing the driver) so as to move the locomotive. When the eccentrics have re-engaged, the two small valve locking levers are used to re-connect the eccentric rods with the valves, allowing the locomotive to be driven normally.

The 'flying reverse' is potentially simpler but requires careful judgment. This can be used if the locomotive is already in motion in one direction and requires to stop and then re-start in the opposite direction. The driver closes the regulator and uses the brakes so as to stop in the correct position. Before actually stopping, the foot pedal is operated to the other position. If judged correctly, the slip eccentrics will engage for the opposite direction before the locomotive comes to a stand. The 'flying reverse' can also be used if the locomotive is stationary but on a sufficient gradient so that it will roll when the brakes are released.

The view below of the footplate of the 'Planet' replica, shows the location of the controls used by the driver when reversing.

The 'Planet' replica in the Power Hall at MOSI. L-R: Steam chest pressure gauge, valve locking lever (on top of railing), two long curved levers (for manual operation of valves), foot pedal (for reversing), water gauge, regulator, water gauge, blower valve with injector steam cock below, boiler pressure gauge, valve locking lever (on top of railing).
Click here for a larger view

The two valve locking levers and the two long curved levers for the manual operation of the valves connect to the front of the locomotive via a series of rods. The picture below shows the two rocking shafts (top of picture) which operate the valve spindles controlling the valves in the steam chests described above. When the small valve locking levers are engaged, each rocking shaft is driven by the associated eccentric rod. To allow manual operation of the valves, the small valve locking levers disengage the eccentric rods from the rocking shafts by two shafts operating lifting links (near the bottom of the picture, painted green) which disengage each eccentric rod from its valve spindle.

Looking at the front of the cylinders from underneath the locomotive showing the method of disengaging the valves from the eccentric rods. The cylinder front covers are dummy, made to the diameter of the original 'Planet'. The replica 'Planet' has smaller cylinders because of the increased working pressure (100 p.s.i. compared with 50 p.s.i. in the original).
Click here for a larger view

Development of Valve Gear

Slip eccentric reversing of locomotives did not survive. By providing four fixed eccentrics and eccentric rods, rather than two, the correct valve movements for both directions of movements on two cylinders could be provided. Initially, a mechanism connected to a simple reversing lever on the footplate connected two of the four eccentric rods to the valve spindles. For instance, 'Lion' of 1838 features Gab motion.

But, by 1842, Stephenson's link motion appeared in the U.K. offering not only reversing but variable cut-off allowing steam to be used expansively for greater efficiency. This became the predominant valve gear in the U.K. for many years. Don Ashton's authoritative review of Stephenson Link Motion can be found here,

For comparison with the picture above showing "Planet's" driving axle and eccentrics, the picture below shows "Sapper's" driving axle and eccentrics. "Sapper" is an 0-6-0 'Austerity' tank built more than a century after the original "Planet". Stephenson Link Motion had replaced slip eccentric reversing but otherwise the layout is similar.

"Sapper's" driving axle and eccentrics viewed from below. L-R: RH axlebox and underhung laminated spring, RH crank driven by (red) connecting rod, RH fore eccentric and rod, RH back eccentric and rod, LH back eccentric and rod, LH fore eccentric and rod, LH crank driven by (red) connecting rod, LH axlebox and underhung laminated spring.
Click here for a larger view

Design issues

In general, materials and manufacturing techniques now are far superior to anything available in 1830. Steel was not available then - wrought iron was the best material but quality was very variable and only limited size sheets were available which required joining by riveting. Cast iron in the complex forms required for cylinders and valve chests was pushing at the limits of the technology available at the time.

The 'Planet' replica incorporates a number of features which were not possible in 1830 (for instance, air brakes, blower, injector, whistle, water gauges, pressure gauges) but that discussion I'll defer to a later article.

Related posts on this website

Early Locomotive Design.
The Planet Replica.

If your interest is broader than just the 'Planet' replica, there's a series of articles describing working on preserved railways and driving various steam locomotives. Most of these articles can be found here

My Pictures of the 'Planet' replica