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It is not always necessary nor advisable to install a single-unit primary crushing department. Occasionally the required plant capacity is so high that the load can be divided between two primary crushers of ample receiving opening to handle shovel-Ioaded, quarry-run, or mine-run rock. So me successful high-capacity crushing plants have been built in this manner. In general, the dual primary arrangement is not economically applicable to shovel-Ioading quarry operations unless the required capacity is in excess of 800 to 1000 t P h. For plants above this range the duplicate set-up has some definite advantages: the two crushers can be set to turn out a smaller product than the one huge machine which would be required for the single-unit installation; trains or trucks can be handled through the crusher house more rapidly because of the duplication of dumping points; and the arrangement has the inherent flexibility, which has long been recognized as being an important and desirable feature in the succeeding stages of the crushing and screening plant.
For plants handling a smaller size of primary feed, for, example, gravel plants,
and those connected with underground mining operations, the dual, or multiple, unit primary crushing arrangement is more widely applicable, and the advantages are much the same as we have outlined in the preceding paragraph. Probably the most important¡ single advantage is the smaller product obtainable from
the smaller primary crushers as opposed to the larger single unit. It is possible in some cases to eliminate one stage of reduction by utilizing such an arrangement.
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