Snowdon: Why the Sloping Boilers?

Awkward though they may seem, the sloping boilers of SMR's steam engines are actually a clever solution to a difficult problem. Were a conventional horizontal-boilered locomotive to attempt to climb the near-20% grades found on some stretches of the SMR line, the fireman and driver would soon find the water shifting to the rear of the boiler, puddling over the firebox and crownsheet, and ultimately climbing into the steam dome. Once in the steam dome, the unevaporated water might well be sucked into the drypipe and thus pass into the cylinders themselves. This would rob the engine of power at best, and at worst could spell disaster. Unlike steam, liquid water is highly incompressible. When the piston began its return stroke and attempted to compress the remaining liquid in the cylinder, the cylinder would most likely burst. With their built-in droop, however, the boilers of SMR's mountain goats get more rather than less level as the engine tilts on its way up the grades, and so are at perfect working trim when the engine is grinding up the mountain slopes. The only difficulty the fireman faces is to keep sufficient water over the crownsheet when the engine is on level or nearly level ground, and the boiler is drooping forward.