Filter Sand

Fifty Years of Progress in Water Purification, 1913–63

“…To permit the use of uniform filter granules, Camp 28 replaced perforated piping, embedded in graded gravel tapering into coarse sand, as support for the filtering sand proper, with a false bottom constructed of porous plates. Bed depth could then conform to sand size in accordance with the principles developed by Allen and Armstrong 29,30 at Baltimore and Toron to: the coarser the sand, the greater the depth for equal performance. The most successful method of reversing size stratification in order to distribute the load of work vertically through the filter was the creation of density stratification.…”

Filtration

“…Fine sand is applicable when: [1] pretreatment is sometimes poor; [2] the maximum removal of turbidity is needed; [3] the maximum removal of bacteria is needed to safeguard health; [4] benefits of longer filter runs and lower wash water consumption are not of great importance; [5] backwash is limited by filter plant design to rates sufficient for cleaning fine sand only; [6] rapid buildup of grain size with calcium carbonate following softening is expected.…”

Specifications for Filtering Materials

“…Data on the hydraulic grading of filters during washing, and the penetration of floc during filtration were presented by J. W. Armstrong (16), who suggested that as the 10 per cent size is not an index of the action of the filter in operation, it should be dropped from use. He recommended "top size" as a better index of filter performance.…”