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.