Keeping the ‘Class’ in Classifying Tanks
Better Roads Staff
Long-term operation and maintenance of your classifying tanks can be achieved by following five simple tips.
By Tom Moore and Dave Schellberg
Sand classifying tanks have been used for more than 50 years for refining glacial/alluvial ‘natural’ and ‘manufactured’ sands and sand slurries. They have been used primarily in North America for three typical reasons:
Concentrating or ‘scalping’ water in a low-percent solids slurry for more efficient dewatering by downstream equipment;
Removal of excess intermediate sand grain sizes to produce a uniformly graded product for many common construction sand specifications; and
The production of two controlled and one uncontrolled sand product from a single feed.
As with any process equipment, periodic operational and maintenance checks are recommended to optimize a machine’s operation. Your manufacturer’s installation and maintenance manual can be used as a guide to allow the most efficient performance and yield of desired sand products.
This type of sand tank is not a ‘set it once and walk away’ device, as sand feeds can vary due to changing pit feeds or the performance of crushers and other equipment that may precede it.
Periodic sampling of the sand discharging from the sand tank valves, particularly at the first two or three stations, is recommended to make sure that the product is mostly coarse sand particles. If a specification concrete sand gradation is found in the product valve sampling, adjustments to the rising current water injection and tank overflow weirs should be made to move finer sand particles further down the sand tank. This provides a more controlled blending of coarse, intermediate, and fine sands being made by the PLC control system.
During a non-operational period, an empty sand tank’s operating system should be inspected to assure that the valves at each station are opening and closing as programmed by the controller. This would include stalling the torque motor paddle at each valve station.
To assure fine product-sized sand retention, make sure that all weirs are level, allowing uniform depth of silt slurry overflow.
To minimize downtime during peak production, periodic inspections of key components should be made.
All sands cause wear on components to varying degrees. Valves and valve seats are among the most commonly replaced items. While some original components are hard cast-iron alloys intended for abrasion resistance, these parts are often replaced by polyurethane components, which offer extended wear life in most instances.
Valve rods, torque motor paddles, and paddle rods should be periodically inspected for wear and replaced when needed.
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