British Rail Class 74
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The British Rail Class 74 was an electro-diesel locomotive that operated on the Southern Region of British Railways. An electro-diesel locomotive is one that can operate either from an electrical supply, such as overhead catenary or an energized 3rd rail, or from an onboard diesel engine.
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[edit] History
The ten examples of Class 74 electro-diesel were rebuilt from the Class 71 (pre-TOPS type HA) straight electric locomotives. Twenty-four examples of Class 71 were built in 1958 at the British Rail works in Doncaster.
In the 1960s, ten examples of Class 71 were deemed surplus to requirements, withdrawn from service and placed in storage. The Southern Region were highly impressed with the "little-ED" HA/class 73 locomotives and were keen to see a locomotive with higher power when running on its diesel engine. Instead of scrapping the ten moth-balled class 71, they were sent to the British Rail works at Crewe, where they were rebuilt into type HB, later class 74, electro-diesels.
They were intended especially for use on the Southampton and Weymouth boat trains, the routes of which included sections of non-electrified track (actually tramway) to reach the destination. With the elimination of the engine change (at either Southampton or Bournemouth) it was envisaged, their dual power capability would greatly accelerate timings and reduce operational requirements.
Originally, plans had been to number them E7001 - E7010, but once rebuilt they were numbered E6101 - E6110 instead, later being renumbered 74001 - 74010 under the TOPS system.
[edit] Power supply
In common with the first SR DC electric locomotives (class 70) Class 74 utilised a 'booster' set (a motor-generator and flywheel combination) to overcome the problem of gapping. Booster set 836/2D had been designed by English Electric for use in class 71 and this was retained in the rebuild. The compact size of the booster permitted a small diesel engine and generator inside the body shell (only a single booster was used in classes 71 & 74 unlike the two of class 70). Thus, these locomotives could operate either from an energized 3rd rail at 650V DC (Eastern & Central sections) or 750V DC (Western section) or from their Paxman 6YJXL diesel engine that produced 650 hp.
[edit] Operations
The diesel engine of class 74 was marginally more powerful than the English Electric engine of the class 73 electro-diesels but nowhere near as reliable. The former was also difficult to start on occasion - rather negating the novel change-over whilst in motion and subsequent flexibility off the third rail. Excessive engine noise in the cab was a problem too.
In reality, they were rare visitors to Weymouth and were usually replaced at Bournemouth with class 33 for the final leg of the journey. This was almost directly attributable to their problems when running on diesel power and totally negated their original raison d'être - the intention being they would continue over the non-electrified lines to Weymouth eliminating the need for the engine change at Bournemouth. Thus, in all practicality, they offered none of the expected advantages of a higher power (than class 73) electro-diesel. Services to Southampton Ocean terminal did utilise them heavily over non-electrified lines, but the exposure was to only a few miles of diesel haulage rather than 60+ on the round trip to Weymouth and back. Class 73 has a simpler electrical system arrangement for control of the dual power sources - even to the point of two separate throttles on the desk; one for diesel and one for electric supply. The complex control system of the 74s (with only a single throttle controlling whichever source power was drawn from) was also problematic, and the class was dogged with electrical system failures up to their last days. Modern micro-processor based control electronics could easily solve the problems, but, in the 1970's, individuals were often parked up "failed", awaiting retrieval. Together, the three complaints of poor reliability, difficult engine starting and excessive noise made class 74 unpopular with crew and fitters alike.
When in good order they were promising performers and running on third rail with the full 2552HP (the original class 71 traction equipment having been down-rated slightly from 2700HP to extend service intervals) brought to bear, many 100+ mph runs were noted despite a stated maximum of 90 mph - though nothing approaching this was achievable on diesel power.
They were regular visitors to the London area, often running on Midland and Western Region tracks. In the early half of the 1970s, Milk trains for the Southern Region were a staple for the class as far as Acton Yard, requiring diesel power from Clapham Junction through Kensington and onto the Western Region mainline (Class 52 or occasionally 47 used for the major haul west of Acton to & from Cornwall and Devon ). This would often produce two trains per weekday and usually two different examples of the class.
The entire class was allocated to Eastleigh depot for their operational life, and 74003 was the last locomotive to enter Eastleigh works for repairs. In common with class 73, class 74 were sent to Crewe for heavy maintenance up until 1972, when Eastleigh took over all treatment of both classes.
[edit] The end
In 1976 the first example was withdrawn. This was 74006 which was damaged by fire. The other nine remained in service until 1977 when they were all taken out of service as a result of a motive power rationalisation.
[edit] Departmental use
In 1978 one example, 74010, was sent to Derby for Departmental use at the Railway Technical Centre. It remained there for a short while before being scrapped.
| Type HB | Previous Type HA |
TOPS | Disposition |
|---|---|---|---|
| E6101 | E5015 | 74001 | Scrapped |
| E6102 | E5016 | 74002 | Scrapped |
| E6103 | E5006 | 74003 | Scrapped |
| E6104 | E5024 | 74004 | Scrapped |
| E6105 | E5019 | 74005 | Scrapped |
| E6106 | E5023 | 74006 | Scrapped |
| E6107 | E5003 | 74007 | Scrapped |
| E6108 | E5005 | 74008 | Scrapped |
| E6109 | E5017 | 74009 | Scrapped |
| E6110 | E5021 | 74010 | Departmental then scrapped |
[edit] External links
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| Pre-1955 type: | 10000-10001 - 10100 - 10201-10203 - 10800 | |
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| Classes: | 70 - 71 - 73 - 74 - 76 - 77 - 80 - 81 - 82 - 83 - 84 - 85 - 86 - 87 - 89 - 90 - 91 - 92 | |
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| Demonstrators: | D0226/D0227 - D0260 - D0280 - D9998 - DHP1 - DP1 - DP2 - GT3 - HS4000 - Janus/Taurus | |
