Abstract: A filter medium comprising first and second filter mediums joined together. The first filter medium provides relatively large voids and has high porosity, while the second filter medium provides relatively small voids and has low porosity. Raw water is mainly introduced into the first filter medium, and water branching therefrom flows through the second filter medium, at which biological filtering is conducted by aerobic microorganisms breeding therein.

Abstract: A water filtering device has a substantially horizontal rotatable drum having a filter layer composed of a granular filter material and a space therein, the rotatable drum being rotatable about its own axis, a first water flow pipe extending axially into the rotatable drum in coaxial relationship, the first water flow pipe having a first branch extending radially outwardly in the space for introducing crude water to be filtered into the rotatable drum and discharging waste washing water out of the rotatable drum, and a second water flow pipe extending axially into the rotatable drum in coaxial relationship, the second water flow pipe having a second branch extending radially outwardly in the filter layer for discharging filtered water out of the rotatable drum and introducing washing water into the rotatable drum. The rotatable drum is rotatably mounted on the first and second water flow pipes. The first and second water flow pipes are fixedly mounted on a support base.

Abstract: A water purification device comprises a raw water channel forming plate extending spirally along the inner wall of a filter tank. A collector for collecting filtered water, positioned in the layer of the filter medium substantially at the center of the raw water channel forming plate, is also disclosed. Since the raw water is filtered from the periphery of the layer of the filter medium and the continuous raw water channel formed by the spirally extending raw water channel forming plate enables the number of influx points of raw water into the raw water channel to be reduced to one at a minimum, the structure is simplified and manufacture costs are reduced.

Abstract: In a water purification apparatus in which a granular filter medium is washed by agitation imparted to the filter medium, a pipe adapted for collection of purified water is mounted within the heap of precipitated granular filter medium and enclosed by a filter mesh to prevent outflow of the filter medium. Sliding contact elements such as turns of a wire wound about the collecting pipe or linear brush-like members inserted on the collecting pipe are also provided between the pipe and the filter mesh so that both the inner and outer surfaces of the filter mesh may be cleaned during countercurrent washing of the filter medium for assuring optimum water permeation at all times.

Abstract: A water purification device includes a plurality of tiers of flow channel or passage defining plates along the inner surface of the wall of a filter tank, a water collecting strainer at about the center of the tank for collecting purified water, and raw water distribution conduit means for distributing and supplying raw water to the respective flow channels. Since raw water permeates into the filter layer in the tank not only from above but from below and from the peripheral zone of the tank, and the purified water is collected at the center and drawn to the outside, the filtration efficiency is improved as compared to the case where raw water is permeated into the filter medium from above and the purified water is collected at the bottom of the tank.

Abstract: A water purification device wherein a separation tank is placed in a space of a filter tank above a mass of granular filter material, the separation tank having an inlet through which washing water which has been supplied into the filter tank for washing the filter material and the entrained granular filter material is supplied into the separation tank during washing of the filter material. The water and entrained filter material are caused to descend in a vortex flow and the granular filter material is separated and collects at an outlet at the bottom of the separation tank which is closed by a cover member. A rod- or cylinder-like member is mounted generally along the central vertical axis of the separation tank. The vortex flow of the washing water is reversed and caused to flow in a gyratory flow along the outer peripheral surface of the rod-like member and to be discharged from the filter tank through a water outlet.