The Mechanical Handling and Storing of Material

58o THE MECHANICAL HANDLING OF MATERLAL The result shows that the efficiency of the hoists had considerably improved during the two years’ working, and, as it was obtained at half-load, further clearly demonstrates the high efficiency of electricity over wide ranges of working. Working Cost.—Wte cost of the electrical energy, including coal, water, stores, and oil, wages, repairs, etc., is -89d. per unit. Phis cost is estimated as an average, with a consumption of approximately 560,000 units per annum. I he capital charges increase this figure to about 2d. per unit. The particulars obtainable for hydraulic power, variously estimated at from 2d. to Is. 9d. per 1,000 gals, at a pressure of 750 lb., cannot obviously be on the common basis, but in any case the fact must be recognised that whereas the supply of electricity to any given quantity of work is a direct measure of work done, the supplj of water in the case of hydraulics is always more than the quantity required, and therefore some of it is wasted; this waste may vary from 5 to 50 per cent, (what is here termed waste does, in a modern installation, however, not exactly apply, as such water is always returned to a second set of accumulators). Two gals, of water per minute, at a pressure of 750 lb. per square inch, is reckoned equal to 1 H.P. The conclusions to which Messrs Baxter and Dixon came were : Firstly—Electric and hydraulic systems are equally reliable. Secondly-The cost of working with electrical and hydraulic power is equal for full loads, but under variable and low load conditions electric power is cheaper. Thirdly—Electrical power has now the equivalent of a hydraulic accumulator. Fourthly—Electrical power can be applied to all dock appliances, and has greater flexibility than hydraulic power. It must be mentioned here, with regard to the first conclusion, that we have only five or six years’ experience with electrical tips, whilst with hydraulic ones we have, thanks to the genius of Lord Armstrong, an experience of over sixty years, and we know that some of the earliest tips, though perhaps not up to date, are still as serviceable as ever they were. With regard to cost under the second conclusion, this was based on the cost ot 9d. per 1,000 gals, of pressure water. This estimate is considered excessive by hydraulic experts, and it is asserted that hydraulic power can be produced at from '2d. to 3d. per 1,000 gals. In addition it might here be mentioned that hydraulic coal hoists or tips have an advantage over electric hoists, as it is not necessary to employ wire ropes either foi lifting, tipping, or balancing, the wire rope being oftén a source of anxiety to those in charge. Working Results.—The coal and other material shipped by the two hoists during twelve months was 556,419 tons. The units consumed during this period totalled 80,164, and the number of wagons dealt with 70,604. During this period as many as 23 tons of coal per unit have been shipped, while, including all distribution losses and