| 摘要 |
Particulate material such as sand is classified in two or more classifying devices (13 and 15) which operate on the principle of "hindered settling" each to provide a coarse underflow fraction and a fine overflow fraction. A chosen blend 12 of the underflow fractions is provided by pneumatic control circuitry (FIGS. 2,5,6) which actuates flow control valves (14 and 16) to open, by amounts in accordance with a chosen blend ratio, only when there is sufficient material available for blending.
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