A Treatise On The Principles And Practice Of Dock Engineering

PETROLEUM STORAGE. 545 Dumps would do in the way of getting rid of obstructive débris. The alligator was undamaged except where it had been severed.* Oentrifugal pumps are of two types—the vertical and the horizontal. The latter is perhaps more generally known as the turbine. The turbine has an advantage over the centrifugal proper, in that the machinery for driving it can be placed at or about the quay level, whereas the other has its motive power applied near the middle of its lift, about half of which is done by suction, and the other half by propulsion. This involves an expensive watertight chamber below the level of the surface of the dock. On the other hand, the centrifugal pump is simpler in construc- tion, being driven by the main shaft direct, while the turbine pump necessitates the interposition of gearing. The maintenance of a centri- fugal pump is therefore less expensive, and on this ground it cornmends itself to the favour of engineers. It is not proposed to enter here into details of pumping machinery. The subject is so extensive as to call for separate and specialised treatment, which may be found elsewhere. Some brief particulars relating to installations at several graving docks are given in Chap. xi. Petroleum Storage.—Petroleum is imported into this country either in barrels or in bulk—the latter by means of specially constructed tank steamers. The barrel system is the less economical of the two, owing to the depreciation in the value of the imported barrels, which may amount to as much as 20 or 30 per cent. An ordinary barrel is some 33 inches long and 25 inches middle diameter; it weighs about 64 Ibs. when empty, 400 Ibs. when full, and contains 42 imperial gallons. Barrels can be most conveniently and effectively landed or shipped by means of parallel tracks of angle iron, set up on trestles, where necessary, to give the requisite inclination. It is found that there is no disposition on the part of the barrels to leave the tracks, however great the speed. Petroleum in bulk from a tank steamer is usually pumped through conduit pipes into a storage tank or tanks ashore. These tanks are cylindrical in form, built of plates of wrought iron, or steel, and suitably stiffened. A settling tank of similar construction is often included in the equipment. The following particulars relate to the petroleum storage depot at Barrow Docks :— There are two installations. The smaller consists of two tanks, with a capacity of 2,500 tons each. In the other installation there are six large tanks, two small tanks, and a settling tank, with a total capacity of 16,360 tons. The tanks are of wrought iron, cylindrical in shape, 64 feet in diameter and 33 feet high, with flat bottoms and low-pitched conical roofs of iron plates, supported by iron principals resting on an angle-iron ring, 2 feet * Min. Proc. Inst. C.B., vol. xcii., p. 178. 35