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Progressive gravel pit operators are awakening to the importance of providing a large surge pile at some point between the pit and the recrushing, screening, and washing section of the plant. It is not always practicable to place this surge pile ahead of the primary crusher; large boulders cannot be handled economically on field conveyors, nor can they be handled through storage unless large and expensive feeding apparatus is installed. Where the operation involves boulders larger than 12 to 15 in. the primary crusher is almost always installed ahead of the surge pile. This of course calls for reserve crusher capacity, but this is usually taken care of automatically, because a crusher that is large enough to receive these large boulders will generally have plenty of excess capacity to handle the rock component of any gravel deposit. This excess should be not less than 25 percent for such operations. Where the large surge can be located ahead of the primary, a reserve of 10 to 15 percent is sufficient. It is quite common practice, in some basic products plants, to design the original installation so that it may readily be expanded to take care of anticipated increases in product sales. Such expansion might involve doubling or tripling the initial output. |
