230 and 231. PROELL'S GOVERNOR.-In 230 the balls, aside from lifting a weight, act to compress a spiral spring. In 231 the outward movement of the balls is controlled by an air dashpot. 232. COSINE GOVERNOR.-A cross arm governor which acts to raise a weight. balls 233. PARABOLIC GOVERNOR.-The move on parabolic guide arms, which modify the effect of the centrifugal force, and produce equal valve movement, which is exactly proportional to the speed of the engine. 234. OSCILLATING LEVER GOVERNOR.The balls are secured to the ends of a lever, which assumes a more horizontal position as the speed of the engine increases. A spring normally holds the arm in the tilted position illustrated. 235. SWEET'S FLYWHEEL GOVERNOR.-The centrifugal action of the ball moves the eccentric toward the center, thus reducing the stroke of the slide valve. A leaf spring resists the centrifugal action of the ball. 236. HARTNELL'S EXPANSION GOVERNOR.— The balls are thrown out by centrifugal force against the action of a spring raising the block in the link and thus varying the stroke of the valve. 237. HARTNELL'S CRANK SHAFT GOVERNOR. -The weights operate against the spring to move a toothed sector, which moves the eccentric toward the center of the crank shaft, thus varying the stroke of the slide valve. 238. TURNER'S CRANK SHAFT GOVERNOR.The weights have bearings in the side plates of the governor. They also carry pins by which they are connected to the eccentric. When the weights are thrown out by centrifugal action, they move the eccentric toward the center of the crank shaft. 239 and 240. VANE GOVERNORS.-The shaft is prevented from rotating too rapidly by the atmospheric resistance acting on a pair of vanes. This resistance may be varied by adjusting the vanes to different angles. In some types of vane governors the inclined vanes serve to lift a sleeve, cutting off the supply of power. THE TENACITY OF GOOD NEW BELT LEATHER varies from 3,000 lb. to 5,000 lb. per square inch of sectional area. THE COEFFICIENT OF FRICTION between ordinary belting and cast-iron pulleys is about .423. THE THICKNESS OF BELTS varies from three-sixteenths to five-sixteenths of an inch, or an average of one-fourth of an inch. TENACITY OF RIVETING AND LACING.-The ultimate tenacity of good single leather belting may be taken at about 1,000 lb. per inch in width; the corresponding strength of a riveted joint being about 400 lb., a butt laced joint about 250 lb., and an ordinary overlap laced joint 470 lb. It is not customary, however, to allow an effective strain of more than one-fourth these amounts. WORKING STRESS OF BELTS.-The following are the effective working stresses allowed SPRINGS. or CARRIAGE 241 and 242. LAMINATED SPRINGS, used on carriages to take up the jolts of the wheels in passing over uneven roads. 241 shows the elliptical form, and 242 the semi-elliptical form. They are built up of flat spring metal strips. 243. WATCH or CLOCK SPRING, used to drive a watch or clock train. The spring is formed of a flat spring metal strip, wound into a flat coil. 244. RIBBON SPRING.-A strip of flat spring metal mounted to exert a torsional pressure. 245. SPIRAL SPRING.-A length of round spring wire wound into spiral form. This spring could be used either as a tension or as a compression spring, though usually it has the form shown in Figure 247 when used as a tension spring. A spiral spring should never be extended or compressed more than onethird of its length. 246. SEAR SPRING.-This spring gets its name from its use in gun locks for causing the sear to catch in the notch of the tumbler. However, the spring is here shown as holding apart the arms of a compass. 247. TENSION SPIRAL SPRING.-A spiral spring which tapers toward the ends so that the pull will come centrally on the spring, thus giving an even tension and avoiding side strains. 248. FLAT or LEAF SPRING.-A strip of flat spring metal used chiefly as a compression spring. A spring of this type is apt to lose its resiliency after continued use. 249. DISK SPRING.-A compression spring made up of a series of dished disks or plates. 250. HELICAL SPRING.-This spring differs from the spiral spring, Figure 245, in that it is formed by being wrapped around a cone, whereas a spiral spring is formed by being wrapped around a cylinder. The helical spring may safely be compressed until it lies flat like a clock spring. 251. VOLUTE SPRING.-A compression spring formed by coiling a flat spring ribbon into a helix. 252. FURNITURE SPRING.-A compression spring comprising a double helical spring used in furniture to support the cushioned backs or seats of chairs. This spring is also used in bed springs. |