ESSENTIALS FOR GOOD-STEAMING ENGINES.
To steam freely, an engine must be built according to sound mechanical principles. The locomotives constructed by our best manufacturers, the engines which keep the trains on our first-class roads moving like clock-work, are designed according to proportions which experience has demonstrated to be productive of the most satisfactory results for power and speed, combined with economy. There are certain characteristics common to all good makers. The valve-motion is planned to apply steam to the pistons at nearly boiler pressure, with the means of cutting off early in the stroke, and retaining the steam long enough in the cylinders to obtain tangible benefits from its expansive principle. Liberal heating-surface is provided in the boiler, its extent being regulated by the size of the cylinders to be supplied with steam. With a good valve-motion, and plenty of heating-surface served with the products of good coal, an engine must steam freely if it is not prevented from doing so by malconstruction or adjustment of minor parts, or by the wasting of heat in the boiler or in the cylinders.
An engine of that kind will steam if it is managed with any degree of skill. But as the best lathe ever constructed will turn out poor work under the hands of a blundering machinist, so the best of locomotives will make a bad record when run without care or skill. Regular feeding—the water supplied at a rate to equal the quantity evaporated, which will maintain a nearly level gauge—is an essential point in successful running. It is hardly second in importance to skillful firing.