INTRO: Many developing railways face problems of locomotive availability; simple design changes to overcome common faults may have significant returns in reduced failures and quicker maintenance
BYLINE: S Gopalan*
Advisor, MechanicalIrcon International
BYLINE: * Mr S Gopalan was previously Chief Motive Power Engineer for India’s Southern Railway, and spent four years at Takoradi acting as Senior Diesel Loco Consultant to Ghana Railways Corp under a World Bank aided rehabilitation programme
THE WAVE of concessioning that swept through Latin America in the early 1990s is now moving on to Africa. Several of the former state-owned railways have recently been handed over to private-sector operators, typically for periods of 20 or 30 years. One of the many problem areas that the new operators must tackle is poor locomotive availability, which in some cases has had a near-catastrophic effect on the railways’ ability to handle the traffic on offer.
Over the past two decades, a combination of the need for fuel economy and the availability of tied overseas aid has seen the near-universal replacement of steam traction by imported diesel locomotives. Unfortunately, diesels are generally more complex machines than the steam engines they replaced, and various factors have conspired to prevent the railways from maintaining them correctly.
Based on the experiences of a four-year World Bank rehabilitation project for Ghana Railways Corp, this article is intended to draw out some statistics about the kind of problems which affect diesel loco operation on an African railway, which may assist manufacturers to adapt their designs to suit the needs of railways in developing countries.
The principal factors influencing the efficient operation and maintenance of diesel locos include the availability of spare parts, and the usual high reliance on imported material. It can be difficult to recruit highly-trained maintenance staff, particularly to deal with electrical and electronic control systems, and the maintenance depot facilities are often poor. Extreme weather conditions simply add to the problem.
On the road, inadequate driving skills and poor track conditions lead to loco failures, which can be compounded by poor communications. There is also damage from frequent derailments, collisions and loco fires. In nearly all these areas, the overriding problem is the lack of adequate funding for maintenance - or even for efficient railway operation.
Table I gives a breakdown of the various types of failures recorded by Ghana Railways’ 42 main line diesel locos over a one-year period. The vast majority of these were caused by problems with the power and control systems, air brakes, cooling circuit, lubrication or fuel supply.
Causes of failure
The biggest single cause relates to failures in the low-voltage electrical control systems. Well-trained and skilled manpower is essential for electrical work, as former steam depot staff are generally unable to deal with sophisticated equipment. Ideally, the railway should be recruiting from technical institutes or engineering colleges, but financial or manpower limitations usually preclude this.
Importing spare parts is another minefield. Inadequate foreign exchange, complicated import procedures and long lead times are the main problems, but it is not unknown for the manufacturers to supply the wrong parts. Financing and import problems also affect the availability of suitable equipment for the maintenance depots, but even when new machinery is installed it may not be able to tolerate the climate. Extreme humidity and rain cause exposed components to rust, and electrical equipment to fail, both on the locos and in the workshops.
GRC’s fleet comprised six types of diesel-electric loco and two classes of diesel-hydraulic shunter, of differing ages. Certain types seem to have performed better than others, with higher availability and lower maintenance and out-of-course repairs.
Catalogue of failures
On an ideal locomotive, sub-assemblies should be easily replaceable without the need for removal of other components. On one GRC class, attention to the injectors usually required removal of the cylinder head. On another class, no crankcase doors were provided for periodic inspection of the connecting rods and big ends.
The most reliable power packs were medium-speed two-stroke engines with air blowers rather than turbochargers. Auxiliaries tend to work better when driven directly by a shaft than when coupled through belts or clutches. One loco class had a long transmission shaft and clutch to drive the compressor/exhauster and radiator fan, and these suffered from frequent shaft breakages. Electrically-driven auxiliaries suffered from motor defects because of the prevailing climate.
Another cause of frequent failures on the road was fuel starvation. The locos in question had a very long suction pipe from the tank to the fuel pump, with four intermediate joints. Inadequate clamping led to these joints working loose on rough track, leading to the pump drawing in air. A simple redesign enabled the pipe to be shortened and made as a single piece. High-pressure fuel lines mounted above the engine proved prone to leaking, which diluted the engine oil, whilst motor-driven pumps proved better than belt-driven ones.
Pneumatic engine governors frequently malfunction as a result of humidity and condensation in the pneumatic lines, and we preferred to use electro-hydraulic governors. Similarly, sensitive microswitches proved difficult to adjust.
Cooling circuit problems are not unique to railways in hot countries, but extreme temperatures can aggravate the position. One particularly poor design had a roof-mounted radiator of inadequate capacity and tended to leak oil from the fan gearbox all over the cooling fins. The mounting prevented adequate cleaning from the fan side, meaning that the radiator had to be removed regularly for cleaning. After the manufacturer refused to modify the design, the railway rebuilt several locos with a pair of accessible side-mounted radiators, increasing the cooling area and reducing the maintenance requirement significantly.
Locomotive fires have a variety of causes. One GRC class had a hot exhaust pipe passing close to the traction motor cables below the underframe, where they were regularly soaked with leaking oil running down the exhaust pipe. Sparks from the nearby brake blocks were sufficient to ignite the hot oil. After four locos had self-combusted the railway decided to re-route the exhaust pipe well away from the traction motor cables. Another source of fire was fuel leaks from the top of the engine block; these were solved by shifting the exhaust manifold away from the fuel lines.
Similarly, problems arose from a loco design which ran the engine exhaust close to the electrical control cubicle. Overheating of the components resulted in premature insulation failure, burnt out resistances and coils, and even electrical fires. It is preferable for the electrical transmission circuit to be relatively simple and foolproof, avoiding the regular problems of transition defects. Speed sensing through an axle generator may be easier than voltage sensing to trigger the transition.
Rubber hoses for water and lubrication oil can often burst or leak, particularly where they are subject to vibration or rubbing in inaccessible locations where they cannot be checked regularly. Hot exhaust pipes can also lead to rapid deterioration of rubber hoses. A related problem is loco failures on the line through shortage of fuel, lubricating oil or cooling water. These are often the result of failures in consumable spares such as gaskets, seals or hoses which have not been replaced in time or are of poor quality. Ideally, suppliers should provide certified quality spares and give the railway detailed specifications to allow for subsequent local manufacture.
Finally, the running gear also needs to be as simple as possible. A bogie that rides well, with a straightforward suspension able to cope with indifferently maintained track, will reduce collateral damage from derailments; in many cases a Bo-Bo rides better than a Co-Co. When one class began dropping between the rails on a regular basis, the track and mechanical engineers blamed each other. Widening the wheel treads and fitting high-capacity shock absorbers, together with minor improvements to the track, solved the problem.
Feedback to aid design
Any new locomotive for developing railways should be designed from the outset for easy maintenance and high reliability in the face of the often difficult operating conditions. Generally, a single-cabbed loco is preferable, as any operating disadvantages are more than overcome by the improved reliability that comes from eliminating the duplicate controls, cabling and related electrical equipment.
Manufacturers need to engage in a constant dialogue with operators to address the various problems which often come to light after the end of the warranty period. Rather than insisting on a standard design which works well in European or North American conditions, suppliers would do well to encourage feedback from the operators and design a loco to meet the specific needs of a low-technology railway, at a price which reflects their ability to pay.
CAPTION: GRC took delivery of eight Class 2601 main-line diesel locos from GEC Alsthom in early 1993; powered by Caterpillar 3606 engines, they are rated at 1700 kW
CAPTION: In 1995 GRC acquired three GM-engined 1120 kW Co-Cos of Class 1661 from ABB Henschel, identical to the 10 units of Class 1651 supplied by Thyssen-Henschel in 1978
CAPTION: Mainstay of the GRC main line fleet for many years were the 18 Class 1851 Co-Cos of 1850hp supplied by English Electric in 1969; only two of these Ruston-engined units remain in service
CAPTION: Brush Traction supplied six Rolls-Royce engined Bo-Bos of Class 701 to GRC in 1982; rated at 675hp, they are used for shunting and short-distance trip freight
TABLE: Table I. Analysis of main line diesel loco failures in one year
Components Occur- % of rences failures
Power control system 71 18·6
Compressor/Exhauster and airbrakes 68 17·8
Cooling circuit 43 11·3
Lubrication 27 7·1
Traction motors 23 6·0
Fuel system 20 5·2
Power pack 18 4·7
Bogie assembly 18 4·7
Turbocharger 17 4·5
Traction generators 5 1·3
Miscellaneous 61 16·0
Crew mismanagement 10 2·6
Total 381 100