... surface property, a great amount of pollutant entrapment,less water head loss in the filter bed, lower consumption of back-flush ... ball, normally, its filtering velocity is 15-20m3/h, with small head loss,it lowers filtering tank’s height and saves electric ... ~ 1.5 times as quartz sand filtering. 4.High strength,small abrasion,usage life is over 15 years. 5.Well distributed ...