2?2

MODERN STEAM PRACTICE.

Fig . 1S2.—Section through Steam Valves.

, Slide valve. E, Expansion valve. F, Small valve for moving the engine.

through a stuffing box on the underside of the valve casing. Theexpansion valve rod also passesthrough stuffing boxes at the topand bottom, and may be actuatedby an eccentric or cam motion.The pedestal for bolting the cylin-der to rests on massive frames ofcast iron, and is raised somewhatabove the line of the crank shaft;the Castings under the cylinderweigh 75 tons, and the foundationscontain 10,000 cubic feet of lime-stone in large blocks; thus securinga firm bedding for the machinery.When the main parts of such heavyCastings can be run from smeltingfurnaces where the engine is to befitted up, of course cast iron islargely used; but where transportis necessary recourse must be hadto the usual mode of building thefoundations with stone or brick-work laid in cement.

The crank is of cast iron, but theshaft is better of wrought iron, al-though many cast-iron ones arein use. The pillow block for thecrank end rests on one of theframes to which the cylinder pe-destal is bolted; the other end ofthe shaft passes through the side ofthe engine house, and is supportedby a pillow block resting on a mas-sive wall plate.

The fly wheel is 22 feet in dia-meter, weighs about 35 tons, and^ is fitted up in Segments in the usualmanner, the arms being fitted into