FRUSTRATIONS OF FUEL EFFICIENCY: FEED-WATER HEATERS PART THREE TWENTIETH CENTURY

n 1915 one British locomotive Chief Mechanical Engineer was faced with a particular problem and so he tried to make a success of F. H. Trevithick’s Phase D heat exchanger version by adding a waste gas heater to a simple exhauststeam heat exchanger. Peter Drummond’s 6ft 4-4-0s known as the ‘Big Bens’ were a class of six engines built for the Highland Railway in 1908/9. The wheels, cylinders and frames were the same as the successful ‘Small Bens’, but the ‘Big Bens’ were fitted with a much larger boiler and firebox, while retaining the same small grate area. This mismatch resulted in very high fuel consumption, particularly when war broke out and quality coals were prioritised for the Royal Navy. Drummond’s successor, F. G. Smith, tried to rectify this by incorporating a dual feed-water heater of his own design. This combined an exhaust steam heatexchanger located externally with a narrow, multi-tubular waste gas heater mounted in the smokebox against the lower part of the boiler. The coincidence with the small flue tubes of the latter meant that both could be cleaned at the same time without dismantling. Reports of comparative coal consumption with No.62 for two months in 1914 (before fitting) and the same two months a year later (after fitting) showed average savings of 33%, but within eighteen months the heaters had all been removed. One can only surmise that the waste gas elements had suffered