Grading machines produce high Weir type single spiral low Weir type single and double spiral, spirals and double spirals, and immersed single and double spiral classifier, low Weir type, now rarely used, mainly high Weir type and the sinking type. Low Weir type overflow weir below helical axis of rotation. The grading machine due to the small settlement area, actual production is only used for washing mud not much sand and coarse dehydration, grinding cycle rarely apply