po n the two barrels is wound a steel rope with a snatch-bloek suspended in the bight between the two barrels. The smaller bar rel is rotated directly by a chain wheel and dependent chain. By it one man can lift 440 lb. The large barrel is provided with double purchase-gear, so propor tioned that two men can lift a ton. Further, upon the shaft of the large barrel is a coupling, and when this is put into gear both barrels are coupled together by means of a pitch-chain, a differential raising or lowering action results, by which two men are able to hoist a load of 5 tons. When the two barrels are coupled together, the pawl must be lifted out of the ratchet-wheel of the small barrel.
When a workman has to lift a small weight. he pulls the chain of the small barrel. If he finds the load too heavy, he applies himself to the second chain, without any coupling or uncoupling being necessary. It is only in the case of very heavy loads that any adjustment of the mechanism is required. All the motions can be worked from below by hand-chains.
Electric Trarelin6r-Cranos.—Electrically driven traveling-cranes have come into extensive use during the past. three or four years, the convenience of transmitting power by a wire, its eompared with transmission hy square shafts, belting, or ropes, being its clUel recommenda tion for this service. Any form of traveling-crane may be converted into all electric crane NV1111011t either the track, the bridge, or the trolley, simply by substituting for the belt, rope, or square shaft, which gives motion to the first rotating shaft, whence all the mo tions of longitudinal and vertical transverse travel are derived. an electric motor with suita ble spurgearing. Preference is now given, however, to cranes tilted with three independent motors, one for each of the three of the All the movements are controlled by swilehes bundled by tie operator stationed in a carriage at one end of the bridge.
L'opP-brit.en Trrieeling-ermle (Figs. ti and 7) illustrate a rot w-driven traveling-erane made by the Philadelphia Engineering Works. In this crane ropes and belts are used as far as jaissible, instead if and :dialling. The trolley has the full traverse motion of the hridge. l'he power is applied by two endless cotton ropes (5, 5) along I he full length of the shop, being guided by pullt‘y-wliccls ut iutPrvals. These ropes nre kept tent on one end by
passing over a movable sheave suspended upon guide-bars, and pass over driving-sheaves (a, 7) plaved zigzag in relation to a pair of guitle-slwaves, upon either side of the main girders (I„ By this arrangement a long grip on the driving-sheaves is obtained. One of these driving sheaves (6) is fitted to a shaft, working in adjustable bearings, and carrying three pulleys for the lifting-gear. The power is transmitted from these pulleys, through belts, to a counter-shaft (13) fitted up with three sets of tight and loose pulleys, thereby obtaining three lifting and three lowering speeds. From this counter-shaft (13) the motion is trans mitted, through a pair of spur-gears, to a square shaft (21) (provided with tumbling bearings), extending the full length of the bridge (1). The motion is then transmitted to the lifting-drum (23), from any part of the square shaft (21), by means of tangent gear (24 and 25) carefully cut by special machinery. and spur-gears (26, 27). The sides of the trolley (23) are made of cast iron, secured to each other by distance bolts and bars (OS, 29). The drum (23) is made of cast iron, and has a right and left handed groove for the chains. By this arrangement the load always hangs in the cen ter, between the girders. A driv ing-sheave (7) is fitted to a shaft (33) working in adjustable ball bearings (34), and carrying four pulleys, two for giving motion to the bridge (1) up and down the shop, and two for giving trans verse motion to the trolley. The power is transmitted from two of these pulleys (one being smaller than the other), through belts, to a square shaft extending the full length of the bridge (1). with two sets of tight and loose pulleys. The power is transmitted from this square shaft to the trolley-wheel through bevel and spur gear-wheels. thereby obtaining two speeds for the trolley travel. The other two pulleys (one being smaller or larger than the other) are belted to two sets of tight and loose pulleys, working on a round shaft (44). and extending the fnll length of the bridge. The power is transmitted to the bridge girder-wheels on both sides from this shaft (44) by means of compounded gear-wheels, thereby obtaining two speeds for the bridge, and insuring a parallel motion for the same.