Keeping it warm
The locomotives might have been powered by diesel, but steam was still needed to heat the coaches. The Class 40s, like other designs, needed Steam Heat Generators, referred to as ‘boilers’, and two types were used: D200-259/267-286/305-324 were fitted with Stones-vapor boilers, whereas D260-266/287-304/325-399 received Clayton boilers. Although enclosed within the body, there were some tell-tale differences: Stones-vapor-fitted machines had a rectangular exhaust port and a square access panel with a top hinge; the Clayton boilers had a circular exhaust port and a rectangular access hatch with side hinges. D255 entered service with Electric Train Heating equipment installed for trial purposes. However, once tests were complete this was removed and the ‘blue star’ multiple working equipment added in the standard position.