DIESEL MULTIPLE UNITS and DIESEL ELECTRIC MULTIPLE UNITS
(DMUs and DEMUs)

Updated 2 May 06
Added images 14 August 06

How this page is supposed to work….

This page contains seven entries corresponding to the seven DMU and DEMU vehicles we have on site. For each entry there is an illustration on the left, whilst on the right is a link to further information which is held on the Vintage Carriages Trust Carriages Register (VCT) site. The link gives a broad description of the coach, whilst we add a bit of narrative below. Selecting the link will take you to the VCT site where formal, and rather technical details of the vehicles are held – and another better (but older) photo. If you need to know things about the lot number or diagram number this is the link to follow. To return from the link, use the RETURN button on your browser. Our photos were taken in the depths of winter, (20 December 2005) and we will replace them as soon as possible so you have an up-to-date and brighter image.

What’s a Diesel Multiple Unit? A short train of coaches, very nearly always with a driving cab at each end. These trains can be coupled together and driven by one driver from one cab, so, for example, an six-coach train can be formed from two three-car units, or an eight-car train from two four-car units - or even a five car train from a three-car and a two-car unit! Needless to say a unit can run by itself if conditions so demand. DMUs are properly called Diesel Mechanical Multiple Units or DMMUs and are powered by diesel engines slung underneath the coaches. Power is transmitted to the axles through a system of clutches and fluid flywheels, together with a mechanical epicyclic gearbox. The engines are similar to those found in the larger buses (mainly double deckers). All ours are powered by 150 horsepower Leyland 680s, two under each coach, so that one of our two-car trains (a single unit) is powered by four engines – just what we need for our steep inclines. Other engines were made by British Union Traction (BUT) , AEC, Rolls-Royce and Albion. The four-engine configuration that we use is called a power-twin, and was rare on the main-line being confined to South Wales and across the Pennines. The ‘motor-trailer’ was more common, especially on quiet country branches. We are currently running one Class 108 ‘cross-country’ unit, with a second Class 117 ‘high-density’ suburban unit expected into service during 2006. Another Class 108 motor-trailer set awaits restoration, but is unlikely to work on the railway alone – though a future doing what it was supposed to do – that is, work in multiple, is a distinct possibility.

The Class 108 Units on the railway are operated by the Gwent 108 Group. For more info click HERE

A blow-by-blow, rather technical account, of restoration work on the Class 117 DMU, appears on John Down's DMU page HERE

Real DMU fans should try the Railcar Association website HERE

We turn now to the Diesel Electric Multiple Unit or DEMU. By far the most common DEMUs were worked by the BR(Southern Region). At the time of their introduction in 1957 the Southern Railway and its predecessors had best part of half a century of experience of electric trains, all of which collected their power through a third rail. The DEMU was designed to work where there was no third rail, and the BR(S) simply took an electric train and fitted it with a big motor-generator (and lost a few compartments in the bargain). The output from the generator was then fed through the controls direct to the traction motors attached to the wheel axles – that was it then, an electric train carrying its own power station! The BR(S) DEMUs (called classes 201 to 207) were all powered by the same engine – the English Electric 600 horsepower supercharged 4SRKT (indeed, all the electrical equipment was supplied by English Electric). The unforgettable sound of these engines when working under load, has attracted to the trains the soubriquet ‘Thumpers’ – and a large army of fans. All have now gone from the national network.

We are fortunate to have secured a Class 205 Thumper for our railway, carrying the unit number 205 018, we accepted it onto the PBR as a two-car unit (we didn’t think a three-car unit would make it up the bank!). As received it carried the awful white and yellow Connex livery but it has now been returned to its original livery. 205 018 derived from unit 1118, but the unit has had a rather turbulent history and as a result its trailer car originated from unit 1129.

	BR 50632 Class 108 DMU: Driving Motor Composite Lavatory built 1958 DMU Class 108 DMCL This is the older style of Class 108 driving car with the smaller (and more attractive) headcode box. This car forms one half of our second-tier service formation deputising for locomotive hauled stock. Since she is rarely called upon for such duties, the unit is sometimes timetabled for its own sake, particularly for the many DMU fans – and for those who like to sit behind the driver and see the line ahead (or behind) from the forward facing windows. This unit is finished in the 1965 blue-grey livery, with full yellow ends.
	BR 52044 Class 108 DMU: Driving Motor Composite Lavatory built 1960 DMU Class 108 DMCL This is the newer style of Class 108 driving car with the larger headcode box. This car forms the second half of the ‘power-twin’ in our second-tier service formation. Both this car and that shown above belong to the Gwent 108 Group.
	BR 56270 Class 108 DMU: Driving Trailer Composite Lavatory built 1959 DMU Class 108 DMCL This is the only driving trailer of the four Class 108 cars on site. It will be some years before this unit sees service on the railway, since it will need the driving motor car shown below to be completed. The Gwent 108 Group, who own this unit, are considering returning her to green, which explains the presence of areas of green undercoat.
	BR 51942 Class 108 DMU: Driving Motor Brake Second built 1961 DMU Class 108 DMBS
	BR 59520 Class 117 DMU: Trailer Composite Lavatory built 1960 DMU Class 117 TCL. This is the middle trailer car, that is, without driving cabs,
	BR 51397 Class 117 DMU: Driving Motor Second built 1960 DMU Class 117 DMS
	BR 51351 Class 117 DMU: Driving Motor Brake Second built 1959 DMU Class 117 DMBS
	BR 60828 SR DEMU Class 205 Driving Trailer: "Hampshire" Unit built 1960 DEMU Class 205 DTCL This is the trailer car of our ‘Thumper’ unit. It came originally from unit 1129 and is therefore not exactly a ‘Hampshire’ unit, but a ‘Berkshire’ unit. It is seen on 8 Aug 2006, shortly after a repaint into something approximating its original colour. The bars on the windows have now been removed, allowing the committed ‘anorak’ to lean out of the window, without the risk of losing his head on our line!
	BR 60117 SR DEMU Class 205 DMBSO ("Hampshire" Unit) built 1957 DEMU Class 205 DMBS This is the motor car of our ‘Thumper’ unit, on its last day at Selhurst before delivery to South Wales. The space taken up by the motor-generator set is clear to see.

Unit 205 018 (ex 1118) at the top of the line. The trailer coach 60828 leads motor coach 60117, which has propelled it up the incline, into Whistle Inn platform, on an early proving trial during Summer 2005. The unit still wears its Connex livery of white and yellow. It will be replaced by British Railways green over the winter. At the same time the window bars ( a late BR modification) will be removed, so that our passengers can admire our wonderful scenery without hindrance Photo: Alistair Grieve The motor coach 60117 stands at Furnace Sidings on 6 August 2006, shortly after a repaint into BR(S) green. The position of the ‘luggage end’ triangle has been reproduced partly obscured by the headlamp. This is exactly how it appeared shortly after headlamps were fitted.