VALVELESS FILTERING DEVICE

PROBLEM TO BE SOLVED: To correctly control flow rate of clean water by providing a plurality of air sealing traps for making a clean water conduit and a filtering chamber parallelly communicate with each other and controlling each of the air sealing traps by using two values of 'communicating' and 'sealed' and carrying out flow rate control on the basis of number or combination of the air sealing traps to be set to 'communicating'. SOLUTION: In a filtering process, a raw water air sealing trap 3 and a clean water air sealing trap 16 are set to a communicating state and a filtering pond water discharging siphon 26 and a filtering pond water casting siphon 29 are set to an air sealing state and an air washing blower 31 is stopped. Then, raw water is introduced into a raw water conduit 2s from a raw water conduit 2p through the raw water air sealing trap 3, is made to overflow an overflowing dam 6 into an influent conduit 7 and is made to flow into the filtering pond 1 through an influent pipe 8. The raw water retained in the filtering pond 1 is filtered by a filtering material layer 11 in a filtering chamber 9 to be changed into clean water, which is guided into a water collecting conduit 14 through an air washing nozzle 12 via a water collecting chamber 13. After that, the cleaned water is guided into a clean water conduit 20 via the clean water air sealing trap 16 and overflows an outflow dam 21 into an outflow conduit 22 and retained there.