One in which the action of the piston is transmitted directly to the crank-shaft. Nearly all engines are of this type.
One in which the motion of the piston is communicated to the crank-shaft by means of intermediate levers. In the beam-engine, the connection between the piston and the connecting rods consists of a beam, the oscillating point of which is placed midway between the two rods. They are chiefly employed for pumping purposes and for driving paddle-wheel steamers. Other than in this lim ited field, they are becoming obsolete.
Expansive Working An engine is worked expansively when the steam, instead of being admitted at full pressure into the cylinder until the termination of the stroke, is cut off at some fractional part of the stroke and thus caused to do work simply by its own expansion. The steam may be expanded in one or more cylinders. The amount of steam consumed is low as compared to the amount of work done. It is universally used where circumstances will permit, on account of its greater economy as compared with the engines of the non-expansive working type.
Working An en gine in which the steam is allowed to enter the cylinder at boiler pressure and is maintained at that pressure behind the piston during the whole of the stroke. The amount of steam consumed is disproportionately high as com pared to the work done.
Condensing Engine (called also low-pres sure or vacuum engine).—One in which the spent steam in the cylinder is exhausted into a vacuum and condensed into water, thus oblit erating the back pressure of the atmosphere and consequently effecting a gain of pressure equivalent to 14.7 pounds per square inch in the effective working pressure of the steam.
Non-condensing Engine (called also high pressure engine).— One in which the spent steam in the cylinder is exhausted into the air at atmosphenc pressure, thus entailing the work of forcing the piston against a back pressure of 14.7 pounds per square inch, at the expense of the effective working pressure of the steam. This disadvantage is offset by using steam at higher pressures.
Simple Engine.— One in which the steam after having forced the piston through its stroke is exhausted into the air or into a vacuum or condenser.
Compound Engine.— An engine with two or more cylinders in which the steam after having expanded and performed its work in one cylin der passes into the next cylinder, of larger size, and continues to expand and perform worlc. The different types of compound engines are distinguished as “series-expansioe engines or by the number of cylinders employed for the expansive working of the steam, and are desig nated as the two-cylinder compound engine, the three-cylinder or triple-expansion engine and the four-cylinder or quadruple-expansion engine. The cylinders are usualbr arranged side by side or parallel with each other. Some times, as in the case of the 4tandem-compound,D they are placed in line one behind the other, and also vertically one above the other as in the case of the 4steeple-compound.° In a across compound') the cylinders are placed side by side and parallel to each other, but sufficiently far apart to allow space for a fly-wheel between them. Up to the present time the quadruple expansion engine appears to be the limit beyond Which the numbers of expansions have not been carried with success. The great practical ad vantage of the multiple-expansion engines lies in their high steam economy.
Air (or Hot Air) Engine.— An engine in which the worlcing fluid is air expanded by heat. It is only of experimental interest.
Horizontal Engine.— One in which the axis of the cylinder and piston rod is horizontal.
Vertical Engine, One in which the axis of the cylinder and piston rod is vertical. Vertical engines are made in a great variety of forms and are usually arranged with the cylinders uppermost. Very few of them are constructed with the cylinders lowermost and those are only of the smallest sizes. The principal ad vantages of the vertical engine consist in the small space required for their foundations and the uniformity of wear on the cylinders, pistons and rods. The type includes many forms of steam hammers, launch engines, screw engines and inverted cylinder engines.