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Stock Formation
The idea for this page has has come, as is often the case, from some correspondence I've received, and it's both apparent and hardly surprising that it's an area which causes some confusion - not least of all amongst new Train Operators during the course of their training!
So I thought I'd spend some time trying to make it all a little clearer.
To try to demonstrate the differences between different London Underground stocks I'm going to use both the C69/77 and D78 trains. As with many things there are further variations, but I hope this will help you get a grasp on the principles involved.
Back to basics!
I think that much of the confusion arises because there is an understandable assumption that a train is a train - no more and no less. In terms of 'conventional' trains - that is a locomotive hauling a rake of coaches or wagons - this is correct, but where 'Multiple Unit' trains are concerned, be they electric or diesel powered, it is less clear cut.
On London Underground we are dealing with Electric Multiple Units - EMU's. Each train is made up of two or more units which are then coupled together to form the service train, but each unit is, in its own right, a train! It has all the components needed to propel it and brake it and, at least in theory, it could run in passenger service.
So, let's start putting our train together!
C69/77 Stock Formation
As I will be making some reference to the numbering of cars, it's worth being aware of the following.
The 'C' Stock units were built in two batches, the C69 and the C77, but, to all intents and purposes, they are identical and interchangeable.
The batches are numbered as follows:
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C69/77 Stock Numbering
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Car Type
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C69 Stock
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C77 Stock
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Driving Motor Car
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5501 - 5605
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5701 - 5733
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Trailer
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6501 - 6605
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6701 - 6733
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One Unit
This has all the equipment needed to stop and move the train. It has a full drivers cab at one end (the Driving Motor Car - DMC) and a shunting position - an abbreviated cab - at the other (The Trailer Car -T). It has motors, heaters, the means of picking up traction current, motor alternators to provide lighting and electrical supplies to the various equipment and to recharge the batteries that are fitted. It also has compressors to supply air to various components including the doors and brakes. It should also be noted that our DMC and T cars are, what we call, semi-permanently coupled together. The two cars can be divided, but this can only be done in a depot, and DMC number 5602 will always be paired with T number 6602.
It wouldn't really be practical to try to run this train in service though, as there are only door controls in the cab, so if driven from the shunting position the driver wouldn't be able to open the doors - not much good for a passenger service! Similarly if driven from the shunting position normal 'line speeds' cannot be obtained - the controls are such that they don't allow it. It should also be noted that a train like this wouldn't actually be allowed on the 'main line' as there are requirement for the duplication of systems and components in the event of failures!
So, we have to couple at least one more unit to this one to make things more realistic!
Two Units
In this next diagram we have two units, now coupled together - the second is a mirror of the first. Coupling is achieved by means of the Auto (or Wedgelock) coupler between our two units. An explanation of the coupling process is discussed here. Our train is now taking shape and we have a train formed of a DMC (5602) +T (6602) + T (6703) + DMC (5703). It has a cab at both ends, with all the controls required for a 'proper' service and all the equipment is duplicated. It would be perfectly in order for this train to run in passenger service.
So we could run this train in passenger service, at normal speeds. All equipment is duplicated, the doors can be opened from both ends and so on. Our problem now is our passenger capacity - it's not ideal for the number of passengers that need to be moved, particularly during the service 'peaks'. In the past London Underground did reduce the length of trains 'of peak', but this practise was abandoned some years ago prior to the introduction of the C69 stock.
So, to increase our capacity, a third unit is added.
Three Units
This is a repeat of the process described above, with a third two car unit being attached.
(Note that this a 'clickable' link to a larger image)
This now gives us our 'normal' service train. It is three, two car units coupled together, and in this orientation gives a train formed by:
DMC (5602) + T (6602) + T (6703) + DMC (5703) + T (6501) + DMC (5501).
One further point to note is that C69 stock units are a little unusual, in that they can, and are, routinely turned round, so we could form this same train, using the same units, but in a different order as follows!
(Again note that this is a 'clickable' link to a larger image)
You will see that the three units employed are the same ones, but DMC 5501 and T 6501 has been 'turned' and is now on the 'west' end of the train, whereas it had been on the 'east' end of our train previously. But, as can be seen, the end result is the same - we have a six car train formed of three, two car units.
On a final point, you will also notice that 'our' train has been formed of two C69 units and one C77 unit. It could have been formed by any combination of the stock available!
So, that is the formation of a train of C69/77 Stock - let us now look at a train of D78 Stock.
D78 Stock Formation
The formation of a train of D78 stock is, at least at first sight, a little simpler, but there are some variable factors of which account needs to be taken.
Again, a D78 stock train is made up of six cars, but this time formed of two units, rather than three.
Although this time I will not be referring to car numbers in this section, it is, nevertheless. helpful (and, I hope, interesting!) to have an understanding of the numbering system employed.
Car numbers
The 4/5 digit car numbers on a D78 Stock train provides the following information:
- The first digit denotes the car type.
- The end three or four digits denote the cars unique number and type of unit.
If the last digit in the numbering sequence is an even number it denotes an 'A' end unit. In District Line terms, this means it's facing west.
If the last digit in the numbering sequence is an odd number it denotes a 'D' end unit. In District Line terms, this means it's facing east.
There are two types of D78 units - single ended and double ended.
A single ended unit has a Driving Motor Car (DMC) at one end, then a Trailer Car (T) and then an Uncoupling Non Driving Motor Car (UNDM) at the other. To run in passenger service this must be coupled to another unit - either another single ended unit or a double ended unit.
A double ended unit has a Driving Motor Car, a Trailer Car and then another Driving Motor Car. A double ended unit could operate in passenger service, and indeed has done so on the East London Line.
Further comment is made on this later!
Single ended unit numbering
Driving Motor Car:
The first digit will always be a '7' followed by 3 digits. The second digit will either be an '0' or a '1'. The third and fourth digits are the cars' number - e.g. 70xx, 71xx.
Trailer Car:
The first two digits will always be '17'. The third number can either be an '0' or a '1'. The last two digits are the cars' number - e.g. 170xx, 171xx.
U.N.D.M. (Uncoupling Non Driving Motor Cars)
The first digit will always be an '8' followed by three digits. The second digit will be either an '0' or a '1'. The third and fourth digits are the cars' numbers - e.g. 80xx, 81xx.
Double ended unit numbering
Driving Motor Car
The first digit will always be a '7', followed by a second digit that will be a '5'. The third and fourth digits are the cars' number - e.g. 75xx
Trailer Car
The first three digits will always be '175'. The last two digits are the cars' number - e.g. 175xx, which will always be an even number taken from the 'A' (west end) DMC.
Driving Motor Car
The first digit will always be a '7', followed by a second digit that will be a '5'. The third and fourth digits are the cars' number - e.g. 75xx.
So, the D78 stock fleet is comprised as follows:
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Single ended units
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'A' Driving Motor Cars (west end units)
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7000 to 7128
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even numbers
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'D' Driving Motor Cars (east end units)
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7001 to 7129
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odd numbers
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'A' Trailer cars (west end units)
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17000 to 17128
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even numbers
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'D' Trailer cars (east end units)
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17001 to 17129
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odd numbers
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'A' Uncoupling non-driving motor cars (west end units)
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8000 to 8128
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even numbers
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'D' Uncoupling non-driving motor cars (east end units)
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8001 to 8128
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odd numbers
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Note: Trailer cars numbered 17000 to 17048 (even numbers only) are equipped for the laying of de-icing fluid.
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Double ended units
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'A' driving motor cars (west end)
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7500 to 7538
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even numbers
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'D' Driving motor cars (east end)
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7501 to 7539
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odd numbers
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Trailer cars
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17500 to 17538
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even numbers
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Stock formation
D78 Stock trains are known as 'Unit Stock'. Each unit is comprised of three cars. As mentioned above, a unit can either be:
- Single ended
- Double ended
A single ended unit is non reversible and consists of:
- A Driving Motor Car (DMC) at one end.
- A Trailer Car (T) in the middle.
- An Uncoupling Non Driving Motor Car (UNDM) at the other end.
A double ended unit is also non reversible and consists of:
- A Driving Motor Car (DMC) at each end.
- A Trailer Car (T) in the middle.
A 6 car train can consist of:
- 2 single ended units.
- 2 double ended units.
- 1 single ended unit, 1 double ended unit.
A double ended unit may be used to provide a three car train.
Wedgelock Automatic couplers are fitted to all UNDMs and the DMC's of double ended units.
So, now that you can see that things are not quite as simple as may have been thought at first sight, let's put our train together!
One Unit - Single Ended 'A' Unit
The first thing that you may notice is that the cab and shunting position are not indicated on this diagram. This isn't really to important, but the car to the left is the DMC (so the cab will be to the extreme left), that in the middle is the T and that to the right is the UNDM, so this is an 'A' unit. So, let us say that this is formed of the following:
DMC 7000 + T 17000 + UNDM 8000
This in turn can either be coupled to a single ended 'D' unit, or to the 'A' end of a double ended unit, which will be illustrated later.
One Unit - Single Ended 'D' Unit
This is our 'D' unit, and is simply a mirror image of the 'A' unit which will have the DMC 7001, so now - left to right - goes:
UNDM 8001 + T 17001 + DMC 7001
If this unit were to be coupled to a double ended unit, it would be coupled to the 'D' end of the double ended unit.
Both Units Coupled
(Note that this is a 'clickable' link to a larger image)
So, here is our complete train, formed of two single ended units. Thus it comprises:
DMC 7000 + T 17000 + UNDM 8000 + UNDM 8001 + T 17001 + DMC 7001
Double Ended Unit
Really just included for information, this is a double ended unit. The main difference to note from the diagram is that there are two compressors. This is required were the unit to run in service in its own right.
So the formation of this unit is:
DMC 7500 + T 17500 + DMC 7501
The only other thing to note is that the 'D' (east end) DMC will always be numbered one digit higher than the 'A' (west end) DMC.
And that's about it as far as the formation of trains is concerned. I hope it answers a few questions, but if it raises any which are relevant I'll add to this in the future!
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