Automatic flushing type pre-filtering device

An automatic flushing type pre-filtering device, comprising:

• a valve head set,
• a filter cartridge set, including:
• a cylinder body,
• a filter cartridge, disposed in the cylinder body, the filter cartridge includes a filter net rack and a filter net disposed on the filter net rack, a first chamber is formed between the filter cartridge and the cylinder body, and a second chamber is formed inside the filter cartridge, and
• a movable rod piece, having a hollow portion inside, and the movable rod piece is disposed in the second chamber, a water separation piece is disposed between the movable rod piece and the filter net rack, a plurality of through holes are disposed on the movable rod piece corresponding to a position of the second chamber, the hollow portion and the second chamber are connected and in communication with each other through the through holes, a seal boss is disposed around an outer periphery of the movable rod piece, and the seal boss is located on an upper end of the water separation piece, a bulge ring is disposed between the movable rod piece and the cylinder body, to act in a seal cooperation with the seal boss;
• a drain valve set, disposed at a lower end of the filter cartridge set;
• and
• a spring, to sleeve around the water separation piece and the movable rod piece.