Piston, Connecting-Rod, and Crank Connections. An idea very generally prevails among engineers that the crank of a steam-engine travels faster at one part of the stroke than at the other. This is evidently a mistake. The crank travels at a uniform speed throughout its revolution, but the piston travels farther to make one-half its stroke than the other. If the connectingrod were indefinitely long, or a slotted yoke were substituted for it, the movement of the piston would be determined by the crank alone; its points of mid-travel would correspond exactly with the corresponding points in the travel of the crank, and the piston would occupy the same position at the first and last half of each stroke. But in consequence of the distorting action of the connecting-rod, the piston travels farther during the half of each stroke farthest from the crank, and consequently, when the crank is at its point of mid-travel, that is, when it is perpendicular to the axial line of the cylinder, the piston is nearer the crank than its point of mid-travel by an amount which varies inversely with the length of the connecting-rod, and which is equal to the difference between the base and the hypothenuse of the right-angled triangle formed by the connecting-rod, crank, and the included portion of the line. Now the square of the hypothenuse of a right-angled triangle is equal to the sum of the squares of the other two sides. The crank of a steam-engine moves six times as far while the piston is travelling the first inch of the stroke as while it is making the middle inch; a little over twice as far while the piston is moving the second inch; a trifle over 11⁄2 times as far while the piston moves the third inch; and less than 11⁄2 times as far while the piston is making the fourth inch. The crank also travels less when the piston is making the last inch of the stroke than it does while it is making the first. Another fact, not generally recognized by inexperienced persons, is that the crank of a steamengine at certain points travels a considerable distance, while the cross-head has a motion which is hardly perceptible. Rule for finding the distance the piston is ahead of a central position in the cylinder on the forward stroke, and also the distance which it lags behind on the backward stroke. Subtract the square of the length of the crank from the square of the length of the connecting-rod; find the square root of the difference or remainder, and subtract it from the length of the connecting-rod. The remainder will be the variation of the piston from a central position when the crank is at right angles to the centre line of the engine. Example.-Length of crank, 12 in. Length of connecting-rod, 72" Then 7225184 in. 122 144 " Difference = 5040" ✔504070·992 in.; and 70.992 1.008, which is the variation in inches. The Reynolds Corliss Engine. The cuts on pages 178, 179, represent the front and back views of the Reynolds Corliss Engine. It will be observed that the frame is of the girder pattern, the front end of which is faced up to receive the cylinder and slides, while the back end contains the pillow-block bearing; the whole being supported by three pair of legs, which insures rigidity and prevents the possibility of springing, in case the engine should be run at a high rate of speed or loaded beyond its rated capacity. The cross-head has its support on the slides, directly opposite the centre of the crosshead pin, thus avoiding the springing and final breaking of pistonrods, as is often the case where the support is carried back of the centre of the cross-head, as is done in most engines of this type. It is provided with convenient mechanical arrangements for easy and accurate adjustment in case of wear. The valves are of such construction that they have double the wearing surface ordinarily found in engines of this type. This obviates the rapid wear of the seats, which must occur where the wearing surfaces are small; while, in consequence of the peculiar construction of the valve-gear of these engines, they can be run at any desired speed. The valves open with perfect regularity and close instantaneously, which is a feature of great importance in itself, especially in flouring-mills, as it admits of the line-shafting being coupled directly to the engine-shaft, thus avoiding the use of expensive counter-gearing, and still giving the fly-wheel sufficient motion to properly "lead" the stone and avoid "backlash." No springs are required on either steam- or exhaust-valves. The steel catches used for opening and liberating the steam-valves are so constructed and arranged as to give eight wearing faces on each piece; while by unhooking the eccentric-rod, all the valves can be easily moved and the engine worked by hand, which prevents the liability of its catching on the centre, which is a source of annoyance, especially in the case of large engines. The liberating portion of the valve-gear is claimed to be an improvement on any M |