Filtering device and method of manufacturing same

1. A filtering device comprising:

a primary filtration unit for filtering a raw water, which unit includes

a filtering medium including a depth filter having a pore size within a range of 1 to 25 μm, and

a housing for accommodating the filtering medium, the housing having defined therein

a port that serves as a raw water supplying port for supplying the raw water into the filtering medium and alternately serves as a drain port for discharging a fluid used for backwashing and the raw water,

a filtrate water outlet port, and

a fluid supplying port for supplying the fluid for backwashing into the filtering medium,

a filtrate passage for discharging filtrate water from the filter;

a conveyance valve disposed on the filtrate passage for conveyance of filtrate water;

a drain passage in fluid connection with the drain port;

a drain valve disposed on the drain passage for passage of the fluid used for backwashing and the raw water;

a communication passage for communicating the filtrate passage with the drain passage, the communication passage branching off from the filtrate passage upstream of the conveyance valve and is in fluid connection with the drain passage;

a switching valve for selectively opening or closing the communication passage; and

a controller that controls the conveyance valve, the switching valve, and the drain valve, and controls the operation of the port in the housing that alternately serves as a raw water supplying port and as the drain port.

2. The filtering device as claimed in claim 1 , further comprising a secondary filtration unit for filtering again the filtrate water, which has been filtered by the primary filtration unit, by means of a filtering medium including an ultrafiltration membrane or a reverse osmosis membrane.

3. The filtering device as claimed in claim 1 , wherein the fluid supplying port and the filtrate water outlet port are co-located such that use thereof may be alternately switched by the controller.

4. A method of making filtrated water with a filtering device as claimed in claim 1 , which comprises:

a filtering step for supplying raw water from the raw water supplying port to cause the filtrate water to be transported towards the filtrate passage in a condition in which the conveyance valve is open, the drain valve is closed and the supply of the fluid for backwashing from the fluid supplying port is interrupted;

a backwashing step for supplying the fluid for backwashing from the fluid supplying port and then discharging the fluid from the drain port through the drain passage with the drain valve open and in conditions in which the supply of the filtrate water toward the filtrate passage is interrupted by closing the conveyance valve;

a priming step for discharging the fluid for backwashing, by supplying raw water from the raw water supply from the raw water supplying port, through the filtrate water outlet port, and through the communication passage and finally through the drain passage, in a condition in which the switching valve is opened while the supply of filtrate water toward the filtrate passage is interrupted by closing conveyance valve and the supply of fluid for backwashing from the backwashing fluid supplying port is interrupted; and

further starting the filtering step.