For secondary clarifiers that require rapid sludge removal, suction headers of rectangular cross section may be applied. Tapered suction headers are fully tapered, varying in cross sectional area from a maximum at the inner end, near the tank center, to a minimum at the outer end to provide a uniform velocity of sludge in the header.
For greater flows and the resultant larger basins, higher torque capacities, a spur gear driven pier-supported collector is best applied. Walker Process pier-supported collectors are built around a center pier which supports the entire rotating portion of the machine plus half of the access bridge load. In addition to providing support, the pier resists the torque developed by the collector's sludge plowing action.
Bridge-supported collectors have as their basic support a bridge that spans the entire clarifier basin diameter. The entire rotating mechanism is supported mid-span by the bridge that must be designed to limit deflection to less than ½ inch to prevent the scraper arms from contacting the floor.
Bridge supported collector mechanisms may be designed with Segmented Plow type scrapers, Spiral Rakes, Tapered Suction Headers, or SightWell type sludge removal arrangements.

Clarifiers - Spiral Rakes

Clarifiers - Thickener