Experiments were conducted to characterise the clean bed headloss of commercial sand and anthracite filter media over sizes ranging from 0.5 to 1.7 mm and over filter rates ranging from 1 to 20 gpm/sf (2.45–49 m/h). Limited tests were also conducted with glass beads. For an equivalent size, the glass beads showed the highest headloss, followed by the sand and then the anthracite. The headloss through granular media was shown to be sensitive to the porosity of the media bed and the size of the media grains. Over the range of filter rates examined in this study, the headloss was not proportional to the filter rate in a simple way as is suggested by Darcy's law.

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