Steam Expansion

—Steam admitted to a cylinder during a portion of the stroke, then cut off, and expanded in the cylinder upon the piston, for the remainder of the stroke. If the flow of steam to an engine be cut off when the piston has made half its stroke, that is, if it is used expamnsively, it has been ascertained that the efficiency will be increased one and sixty-nine hundredths times beyond what it would have been if the steam at half stroke had been released into the atmosphere, and so on, as expre ed in the following (approximate): TABLE. Cutting off at yy the stroke, efficiency is increased 3.3 times. rene Cutting off at 4 the stroke, efficiency is increased 3 times.: pee Cutting off at % the stroke, efficiency is increased.6 times. K Iy: Cutting off at + the stroke, efficiency is increased.386 times. f E Cutting off at 4% the stroke, efficiency is increased.2 times. y ae Cutting off at ł the-stroke,-efficiency is increased 1.08 times.; prt Cutting off at fs the stroke, efficiency is increased 1.02 times. ar Cutting off at 4 the stroke, efficiency is increased 1.69 times. i Pai. Cutting off at ~ the stroke, efficiency is increased 1.5 times. a ay Cutting off at § the stroke, efficiency is increased 1.47 times. ’ bay Cutting off at ip the stroke, efficiency is increased 1.35 times. ` Š Cutting off at ł the stroke, efficiency is increased 1.28 times. The theoretical values given in the above table are largely reduced in practice, chiefy by condensation which increases with the expansion ratio. On this account it is not advisable to expand steam more than four or five times in one cylinder non-condensing, nor more than six or seven times condensing. Tests have shown that the efficiency is not increased by exceeding these limits. For higher expansions additional cylinders are used, thus dividing the temperature range and reducing the total condensation.