By Andy Joel
This is an article about British Rail from about 1972 to about 1985, often referred to by modellers as era 7. It lists N gauge wagons because that is what I model in. If you model in another scale, I would be delighted to know what is available in it from that era.
It is very much a work in progress. If you see any errors or have suggestions or further information, do please let my know (do please say if you are happy for me to use your text; be aware I may edit it to fit the writing style).
The TOPS Code
In the early 70’s, British Rail (BR) introduced TOPS (Total Operations Processing System), a computerised system for tracking stock on the rail system. This required everything on the network to be readily identified, and this required a classification system. As I am sure you know, locos were given a class from 01 upwards, DMUs from 101, etc.
All rolling stock was also classified, and given a TOPS code. This was made up of three letters, the first letter being the general type, the last denoting the brakes on the unit, whilst the second character was a somewhat arbitrary assignment of the subclass.
This was all rolling stock, so, for example, coaches were type A and N (N if not passenger carrying). The codes very much reflect the time, hence one letter for brakes, which was very complicated back then. I find it remarkable that the APT got its own class, L!
There are a few codes of interest under this topic.
B Bogie Steel-Carrying Wagons C Brake vans and covered hoppers F Flat wagons H Hopper wagons J Bogie steel coil carrying (until 10/83) K 2 axle steel coil carrying (until 10/83) M Mineral wagons (not hoppers) O Open wagons P Private own, not tanks S 2 axle steel carrying (not coil until 10/83) T Private owner, tanks U Uncovered open bulk-carrying wagons (until 10/83) V Vans W Containers (until 1984)
The classifications reflect what was important to railway operations, so many different wagon diagrams might be lumped under one code as long as they are for the same material in the same form and with the same capacity and handling requirements at start and destination (and brakes).
Ensuring a rake of goods wagons had the proper brakes – and was marshalled to allow them to be used effectively – was something of a nightmare back then, and it is possible this was one reason BR looked to a computerised system.
Air Brakes and Vacuum Brakes
With vacuum braking, air is sucked out of a pipe that runs the length of the train (giving a vacuum, or at least a much reduced pressure) to release the brakes; to apply brakes, air is allowed back into the pipe. With air brakes, air is pumped into the pipe, giving a high pressure, to release the brakes; the air is allowed to escape to apply the brakes. I fact in practice both systems are rather more complicated than that, but that explanation will suit our purposes here. In either system, if the pipe breaks open – say the back of the train breaks away – the pipe returns to atmospheric pressure, and the brakes are applied, so they are “fail safe”.
In the early days there was no train braking. It became standard for passenger trains in the pre-grouping era (I think it was a legal requirement from 1889), mostly – but not exclusively – vacuum braking. On grouping, the “big four” all standardised on vacuum braking; I would guess for the simple reason that a vacuum is readily created by a steam engine using an ejector, while high pressure is not.
However, air braking is technically superior, as greater braking force can be applied. For vacuum brakes, the best possible difference between on and off states is 1 bar, i.e., between vacuum and atmospheric pressure (in practice probably rather less). Air braked freight trains typically work at 5 or 6 bar so have a lot more force behind them applying brakes (passenger trains are higher still).
While unfitted trains (no continuous brakes) might be limited to 25 mph, fully air-braked trains might run at up to 75 mph. From the earlier seventies, BR started to introduce air-braked freight stock.
Speedlink was a wagon-load service BR offered from 1977 to 1991. It used exclusively air-braked wagons, so the trains were fast, and avoided some marshalling issues. Trains ran to a specific timetable between a limited number of destinations. Speedlink (and Freightliner) became part of Railfreight Distribution on sectorisation in 1988.
Braking Types and Marshalling
We can start to get a feel for the complexities of marshalling a train when we look at the number of codes in use.
A Air brakes B Air brakes with through vacuum pipe F Vacuum brakes with Accelerated Freight Inshot (AFI) G Vacuum brakes with AFI and through air pipe H Dual (air and vacuum) brakes with vacuum AFI O No continuous brake (unfitted) P No continuous brake, through vacuum pipe Q No continuous brake, through air pipe R No continuous brake, through air and vacuum pipes V Vacuum brakes W Vacuum brakes with through air pipe X Dual (air and vacuum) brakes Y No continuous brake (for track machines)
A quick note about terminology. A wagon is considered “fitted” if it has either air- or vacuum-brakes, and unfitted otherwise. A wagon is considered “piped” if it has a pipe allowing the vacuum or air to be continued through it, but not the brakes.
AFI was a system that enhanced the vacuum brakes, but can be safely considered ordinary vacuum brakes for our purpose. They could be mixed with other vacuum-braked wagons.
If your rake is of identical wagons (or rather, the TOPS code of all the wagons ends with the same letter), there is no problem. just put a brake van on the end if the wagon TOPS code ends O, P, Q or R.
For mixed trains, it gets complicated…
Trains can have a “fitted” section and an “unfitted” section, the former being continuously braked. Either section is optional, but if there is an unfitted section, you need a brake van on the end.
The fitted section must be next to the loco. It will be either vacuum braked or air braked (you cannot have both), and your loco needs the equipment for that. Class 56 and 87 had only air brakes. All earlier locos had vacuum brakes; some also had air brakes:
Dual braked from build: 33, 50, 71, 73, 81-86
Some dual braked from build: 20, 25, 47
All converted to dual braked: 37, 45-47, 55
Mostly converted to dual braked: 20, 26, 27, 31, 52
Many converted to dual braked: 25, 40, 76
Later some classes were converted to air braked only (I think after this era): 20, 31, 33, 37, 47, 73, 86. More on locos here.
Brakes on a wagon can be turned off, so a fitted wagon can be treated as an unfitted wagon. In the seventies, air-braked wagons were rare, so the single air-braked wagon might have the brakes turned off and treated as unfitted, and the vacuum-braked wagons used in the fitted section. If you had several air-braked wagons, however, you would be more likely to turn off the brakes on the vacuum-braked wagons as they are less effective.
Your fitted section could have up to five piped wagons in a row, followed by two braked up to around 1980, thereafter the rules was only three piped and you needed three braked following.
BR-owned wagons were generally painted grey if unfitted and bauxite if fitted.
I think this web site was a book; very informative:
Another excellent site:
An amazing collection of photos of wagons; if you are building or painting models, you need to see this:
Different Wagons, as Classified by TOPS
This is a bit patchy, reflecting those areas that interest me! It may get updated in the future, as I do more research.
Note that a lowercase ‘x’ is used to indicate any or multiple braking types.
B: Bogie Steel-Carrying Wagons
Graham Farish do BDA and BAA wagons.
C Brake vans and covered hoppers
This is a weird grouping! Brake vans were all CAx (they perhaps were all CAO, though some may have been piped; they had a man inside to apply the brakes).
CBx were limestone hoppers, CCx were sand hoppers, CGx were grain hoppers, CZx sugar hoppers and CHx general covered hoppers (COVHOP).
CXx were gunpowder van – so why were they in the hoppers section? I think these were all inherited unfitted (which I find a bit scary), but some later had vacuum brakes. These were replaced by VEAs in the early 80’s.
Presflo cement were CPV/W, while prestwin were CQV. Other cent wagons were privately owned, so in the P group.
Dapol do a grain hopper.
Peco do a grain wagon, china clay hopper (CDA)
F Flat wagons
There were many different types. FFA were Freightliner inner wagons, FGA/B were outer wagons, FJA/B were single wagons.
H Hopper wagons
Hopper wagons are designed for transporting loose bulk material, including coal, aggregates, gravel and powdered chemicals. The shape of the wagon directs the material to one or more discharge points between the wheels. This requires a bigger investment at the destination, but makes emptying much simpler.
Hopper wagons can be divided into open and closed. Salt will dissolve in rainwater and sand stops being free flowing, so these and main other substance need to be transported in closed hoppers. Coal and aggregates are fine in open hoppers.
It looks like hoppers were much more common for coal trains in the NE of England. This was because the NE Railway liked them and encouraged their use. Sites in that area were set up for it, so even decades after grouping the effects were still apparent.
The original BR design that was inherited from LNER can be seen here (HTO and HTV). Many were later re-bodied with larger sections, and so less ribbing, see here. It is not that difficult to remove the extraneous ribbing from an N-gauge Dapol hopper.
An air-braked design was built from 1964, HAA, and was still being built in the 80’s. HCA (from 91), HDA (from 82) and HFA (from 92) were all similar. These were used on merry-go-round trains, and required specialist equipment at the destination to unload them; they were generally kept together in a single rake.
Merry-go-round trains were designed to be loaded and unloaded without stopping, and in theory would continue round a loop and back on to the railway system a the end of each operation. In practice most collieries lacked the facilities to do this. It was reckoned that one merry-go-round hopper could replace nearly twenty conventional wagons.
Some were fitted with a top canopy, increasing the capacity somewhat, but few collieries could handle the extra height. Seems to have been more common in Scotland.
Iron ore seems to be the other main commodity transported in hopper wagons (HKV, HJV, HJO). Coke and domestic coal were sometimes carried in specialised hoppers too.
Dapol do a 21t hopper. As far as I can see, only in PO liveries, and the original design, but see the note above.
Graham Farish do a 24 t iron ore hopper, and HAA/HEA/HFA/HSA hoppers.
Peco do MGR hopper.
M Mineral wagons
Like hoppers, mineral wagons are designed for transporting loose bulk material, but are designed to be emptied from the side or end, rather than the bottom.
The 16t version was very common on BR for carrying coal. These were originally fitted with vacuum brakes (MCV), so painted brown, but the brakes often fouled in the mechanisms at the colliery or (more likely I guess) the destination, so the vast majority were unfitted (MCO).
A diagonal white strip indicated the end with a door. This was used at coal hoists; a wagon would be detached from the train, pushed onto the hoist, raised up, then tilted to about 45 degrees to discharge its contents into a waiting ship. The wagon would then be lowered, and pushed out onto a second line for the empties. All this was done by manual labour and capstans, I would guess (the hoist was usually hydraulic).
There is a preserved coal hoist in Goole.
This is a 16t wagon being tipped at Preston dock:
And a plan of the dock here, showing the track arrangement on the north side:
The maximum size of a wagon was therefore determined by what the coal hoists could fit, which is why the vast majority of these wagons had such a short wheelbase.
In coal yards, the side doors would be used, together with a man and shovel.
A 21t version was also quite common (MDV, MDO, MDW).
Some wagon types were designed to be emptied by tipping the wagon to one side. These so-called tipplers seem to have been more common for PO wagons, so discussed later.
Air braked versions seem not to exist.
Graham Farish do a variety of 16 t wagons and 27 t tipplers
Peco do Butterly steel type wagon (Butterley being the manufacturer), 27 t tippler, 16 t
Revolution do MMA
O Open wagons
This not an area I have looked at much, but will note that open wagons here refers to wagons designed to carry discrete units, such as a pallet of bricks or steels tubes.
Air braked versions, OAA and OBA date from 1971. The OBA appears to have had raised ends. Steel-sided OCA date from early 80’s. Some OBAs were later re-built, for example as OTAs in 1985 for carrying timber.
Graham Farish do OBA and OCA wagons.
Peco do Ferry Open Wagon BR ‘Hybar’, tube wagon, open wagon, ferry tube wagon
P Private owner, not tanks
This covers a lot of diverse wagons – including tank wagons! It would be better to say it excludes tank wagons for liquids and gases, but includes powder wagons.
PCA and PCV were powder tank wagons of various designs, some centre-depressed, some parallel. PDV is a CemFlo wagon (as opposed to PresFlo and PresTwin, which are in the C group, being owned by BR).
Graham Farish do POA wagons.
Revolution do PFA wagons (container wagons dating from 87), PDV
T Private owner, tanks
These actually have some kind of system. TBx to TEx are bogie wagons, with the letter indicating the gross laden weight (GLW) in a 10 t band, from 70-79 for TBx to over 100 t for TEx. Two axle are similar, going from TRx (20-29 t) to TUx (over 50 t).
TMV are 3 axle milk tanks (TRV was used for two axle). The last two proper milk trains were from Fishguard and Penzance, both to Express Dairies at Kensington Olympia, and they both ended in 1981. Nevertheless, some were rebuilt in 1981 by the Milk Marketing Board for use was on a service from Chard Junction to Stowmarket; it lasted less than a year. They were retained for some years for emergence use if there was problems with road transport.
TIx are RIV tank wagons (RIV seems to stand for Regolamento Internazionale Veicoli; these would be tank wagons rated for European railways).
Dapol do a three wheel milk tanker, it is unlike the rebuilt version, but may be suitable for pre-1981 milk trains.
Graham Farish do a TEA tank wagon and TTA.
Revolution do a TEA
Dapol do Ferry wagons
GF do VGA vans. They also do a 12 t and a 1o t insulated
Peco do “Railfrieght van”, Pallet van, ford, box van (dubious railfreight livery)
Sonic Models (Revolution) do a VEA
Appendix 1: More on vacuum and air brakes
Appendix 2: A note about the units used for pressure
Sure you can buy milk in pints or litres, and you might describe your height in feet and inches, or in metres, but when it comes to the number of units, pressure wins by a mile. Or 1.61 km.
I would guess it stems from different approaches to the issue.
Relative to atmospheric pressure
An easy way to think about pressure is to compare it to atmospheric pressure, and take that as 1. Even there, we have two units, that are almost – but not quite – the same, that is atmosphere (atm) or bar.
1 atm = 1.01 bar.
The reason there are not quite the same is that 1 atm is defined as 760 mmHg, while 1 bar is defined as 100 kPa, both of which are discussed later.
It is common to measure high pressure (say greater than three or four atmospheres) in atm. Tank wagons designed for carrying gases will usually have a maximum pressure stated in atmospheres.
We also have mbar, with a thousand mbar in 1 bar. This is also one hectopascal (hPa), by the way, which will be discussed later.
1 atm = 1010 mbar.
Meterologists usually use mbar, for example, see here.
Measured with mercury
An easy way to measure pressure is with a U tube containing mercury, and note the difference in height. That difference can then be measured in millimetres or inches. You have the system you want to measure connected to one side of the U. The other side could be under vacuum to give an absolute measure, or to the atmosphere for the relative pressure.
The chemical symbol for mercury in Hg, so the units are mmHg and in Hg or just Hg. One millimeter of mercury is also called 1 Torr.
1 atm = 760 mmHg (by definition) 1 atm = 29.9 in Hg 1 atm = 760 Torr (by definition)
Measured with water
You might also measure pressure using water instead of mercury. Mercury is 13.6 times denser than water, so the height of the water will be 13.6 times greater. To measure a vacuum you need a device over 33 foot high!
1 atm = 407 in H2O
The only time I have heard about using water gauge is BNFL measuring the pressure of fluorine produced from a cell, which I would guess was because it dated from decades ago and the pressure difference was very small, so using water would be rather more accurate than mercury (I cannot remember if they used inches or millimeters).
Force per area
Pressure is, in a technical sense, the force being applied to an area, so this is another approach to pressure. In the imperial system, this is the force in pounds on a square inch, or PSI. In the metric system, it is the force in newtons per square meter, N/m2, which is also called a pascal, Pa. One pascal is pretty small, and it is often more convenient to use kPa, which is a thousand pascals.
1 atm = 14.7 psi 1 atm = 101000 N/m2 1 atm = 101000 Pa 1 atm = 101 kPa 1 bar = 100 kPa (by definition)
One hundred pascal, also called one hectopascal (hPa), is almost one millibar, and I suspect modern weather maps use hectopascals rather than millibars, but they are so close it makes little odds.
Steam pressure in a loco is usually quoted in psi.
Relative or absolute
A further complication is that sometimes it is convenient to describe pressure relative to atmospheric pressure and sometimes relative to a perfect vacuum. When looking at figures for pressure, you need to check carefully which it is. Sometimes “bar” is written as “bara” for the absolute value or “barg” for the relative pressure (bar gauge), but generally it is left to the read to guess for himself!
You may also find with relative pressure, a vacuum is described as a positive or negative number.