Page:The New International Encyclopædia 1st ed. v. 18.djvu/608

STEAM ENGINE. 522 STEAM ENGINE. The cylinder was placed over a boiler, B, and was connected with it by a pipe provided with a stop-cock, V, to cut otf or admit the steam. Suppose the pump-rod depressed, and the piston raised to the top of the cylinder — which was ef- fected by weights suspended at the pump end of the beam — the steam cock was then turned to cut off the steam, and a dash of cold water was thrown into the cylinder by turning a cock, K, was used as a condenser. The principal improve- ments since have been either in matters relating to the boiler or in details of construction conse- quent on increased facilities, improved macliin- ery, and greater knowledge of the strength of materials. Analysis. The motor element of the engine is the cylinder and piston (Fig. 2). The cylin- der, C, is a hollow cylinder of metal closed at Fig. 1. NEWCOMEN'8 ENGISE. on a water pipe. A, connected with a cistern, C. This condensed the steam in the cylinder, and caused a vacuum below the piston, which was then forced down by the pressure of the atmos- phere, bringing with it the end of the beam to which it was attached, and raising the other along with the pump-rod. The cock was then turned to admit fresh steam below the piston, which was raised by the counterpoise; and thus the motion began anew. The opening and shut- ting of the cocks was at first performed by an attendant, but in 171.3 a boy named Humphrey Potter devised a system of strings and levers liy which the engine was made to work its own valves. In 1717 Henry Beighton invented a simpler and more scientific system of 'hand- gear,' which rendered the engine completely self- acting. The next essential improvements on the steam engine were those of Watt. The first and most important improvement made by AVatt was the separate condenser, patented in 1769. He had observed that the Jet of cold water thrown into the cylinder to condense the steam necessarily reduced the temperature of the cylinder so much that a great deal of the steam flowing in at each npward stroke of the piston was condensed be- fore the cylinder got back the heat abstracted from it by the spurt of cold water used for con- densing the steam in the cylinder. The loss of steam arising from this was so great that only about one-fourth of what was admitted into the cylinder was actually available as motive power. Watt, therefore, provided a separate vessel in which to condense the steam, and which could b^ kept constantly in a state of vacmim, with- out the loss which arose when the cylinder itself both ends, e.xcapt for small openings for the en- trance and escape of steam and for the passage of the piston rod. Inside the cylinder is the piston, P. a circular disk of metal fitting steam- tight and capable of movement lengthwise of the cylinder. The openings Sj and S, provide for the admission of steam into the cylinder, and the openings E, and E, provide for the exhaust of steam from the cylinder. These passages are opened and closed by valves. These valves oper- ate in pairs; when valves S, and E, are open valves S, and E, are closed and vice versa. If steam be admitted by opening valve S, its pres- sure forces the piston P to the opposite end of the cylinder. Valves Si and E^ now close and valves S, and E„ open, and steam entering at Sj forces the pislon to return and press, as it advances, the previous cylinderful of steam out of the exhaust port E,. The repeated and alter- nate opening and closing of the two pairs of valves, as described, causes the piston to recip- rocate back and forth in the cylinder. This motion is carried outside of the cylinder by means of the piston rod R. This is a cylindrical rod attached rigidly to the piston and passing out of the cylinder through a steam-tight orifice in the cylinder head. At its outer end the pis- ton, rod is attached to a rectangular piece H, called the crosshead, which slides between two guides, GG. To the opposite end of the cross- head is hinged the rod S, called the connecting rod, the forward end of which is journaled to a crank K, which operates the fly-wheel W. In the steam engine, as actually constructed, these different parts and their movements are variously modified, but the essential operating parts of all reciprocating steam engines are: The c.vlinder and piston; the valves and valve gear; the piston rod ; the crosshead and guides ; the connecting rod; the crank and crank-shaft or fly-wheel. The ordinary unit of measure of the work done by a steam engine is the horse power, and it was originated by Watt. As defined by att a horse power is the work done in lifting 3,3.000 poimds one foot high in one minute. Now if the area of the piston P. Fig. 2, is it' square inches and the pressiire of the steam admitted to the cylinder is i/ pounds per square inch, then the pressure exerted by the steam against the pis-