334. Source of Power. In each case the source of power for operating the mixer, conveyors, hoists, derricks, or cableways must be considered. If it is possible to run the machinery by electricity, it is generally economical to do so. But this will depend a great deal upon the local price of electricity. When all the machinery can be supplied with steam from one centrally located boiler, this arrange ment will be found perhaps more efficient.
In the construction of.some reinforced-concrete buildings, a part of the machinery was operated by steam and part by electricity. In constructing the Ingalls Building, Cincinnati, the machinery was operated by a gas engine, electric motor, and a steam engine. The mixer was generally run by a motor; but by slid ting the belt, it could be run by the gas engine. The hoisting was done by a 20-horse power Lidgerwood engine. This engine was also connected up to a boom derrick, to hoist lumber and steel. The practice of operating the machinery of one plant by power from different sources, is to be questioned; but the practice of operating the mixer by steam and the hoist by electricity seems to be very common in the construction of buildings. A contractor, before purchasing machinery for concrete work, should carefully investigate the different sources of power for operating the machinery, not forgetting to consider the local conditions as well as general conditions.
335. Power for Mixing Concrete. A ver tical steam engine is generally used to operate the mixer. The smaller sizes of engines and mixers are mounted on the same frame; but on account of the weight, it is necessary to mount the larger sizes on separate frames. Fig. 132 shows a Ransome disc crank vertical engine, and Table XIX is taken from a Ran :, some catalogue on concrete machinery. These engines arc well-built, heavy in construction, and will stand hard work and high speed.
336. Gasoline Engines. Gasoline engines are used to some extent to operate concrete mixers. Their use so far has been limited chiefly to portable plants such as are used for street work. The fuel for the gasoline engine is much easier moved from place to place than the fuel for a steam engine. Another advantage that the gaso line engine has over the steam engine is that it does not require the constant attention of an engineer.
There are two types of engines—the horizontal and the vertical.
The vertical engines occupy much less floor space for a given horse power than the horizontal. While each type has its advantages and disadvantages, there does not really appear to be any very great advantage fo one type over the other. Both types of engines are what is commonly known as four-cycle engines. In the operation of a 4-cycle engine, four strokes of the piston are required to draw in a charge of fuel, COM press and ignite it, and discharge the exhaust gases. Fig. 133 shows a vertical gasoline engine made by the In ternational Harvester Company.
The quantity of gasoline con sumed in ten hours, on an average, is about one gallon for each rated horse-power for any given size of engine. At 15 cents per gallon for gasoline, the hourly expense per horse-power will be 1.5 cents.
337. Hoisting Concrete. When the concrete requires hoisting, it is done sometimes by the same engine that is used in mixing the concrete. It is generally con sidered better practice on large buildings to have a separate unit to do the hoisting. If it is possible to use a standard hoist, it is usually economical to do so. These hoists are equipped with automatic dump buckets.
Fig. 134 shows a standard double-cylinder, double-friction-drum hoisting engine of the Lambert type. This type of engine is designed to fulfil the requirements of a general contractor for all classes of derrick work and hoisting. Steam can be applied by a single boiler, or from a boiler that supplies various engines with steam. The double friction drums are independent of each other; therefore one or two derricks can be handled at the same time, if desired. This hoist is fitted with ratchets and pawls, and winch-heads attached to the end of each drum-shaft. The winch-heads can be used for any hoisting or hauling desired, independent of the drums. These engines are also geared with reversible link motion.
338. Friction Crab Hoist. A friction crab hoist of the Ransome type is illustrated in Fig. 135. The same engine that drives the mixer can be used to operate the crab hoist. By means of a sprocket wheel and chain, this crab hoist can be geared to any engine, and, when so geared, is ready for hoisting purposes. The hoisting drum is controlled by one lever. This hoist can be run by an electric motor, if desired. On account of the low price, the friction crab has found much favor with contractors.