Hedley's Engine, Wylam Railway, 1815.
HedleyÕs 0-8-0, Wylam Railway, 1813-14.
This engine was practically the same as the "Puffing Billy," but was of greater power as the cast iron rails, then employed, were only able to support them when their weight was distributed upon eight wheels, also geared to work together so as obtain the adhesion of them all. These engines embodied two improvements of much importance, the first being the return flue boiler to give additional heating surface and to render the course of the flame more effective, the other of adopting a chimney of small diameter (12 inches) which materially increased the draft. Trevethick was perhaps, the author of both these improvements but Hedley was the first to bring both into practical use.
WescottÕs description of the 0-8-0 is as follows: from an engraving in Wood's A Practical Treatise on Railroads, 1825. Three similar engines were made. One, Puffing Billy, had two vertical cylinders, 9 in. by 36 in., one on each side of the boiler and partly enclosed in it, and drove a single crankshaft coupled to the wheels by spur gearing. Wrought-iron return flue boiler having 77 sq. ft. heating surface and working at 50 lb. per sq. in. Weight 8.3 tons. Slide valves worked by tappets. Separate inside wooden frames and tender for fuel and water.