To provide a filter having a large surface area and long life.
A filter member 10 is formed from a material folded so as to form pleats 11 and having a thickness(t) at the inner and outer ends in the radial direction of each of the pleats 11. Therefore, the pleats 11 become slightly round. As a result, a small triangular gap 11f is formed between the opposed inner surfaces 11d of the adjacent leg parts 11a of the pleats 11 at the inner ends in the radial direction of the pleats 11 and a small triangular gap 11g is formed between the opposed outer surfaces 11c of the adjacent leg parts 11b of the pleats 11 at the outer ends in the radial direction of the pleats 11. It is preferable that the heights of these gaps 11f, 11g measured along the height of the pleats 11 are extremely small. As the pleats 11 become sharper, the roundness at the inner and outer ends in the radial direction of the pleats becomes small and the heights of the gaps 11f, 11g also become small and the ratio of the volume between the inner and outer peripheries of the filter member 10 capable of being utilized in filtering also becomes large.
WILLIAMSON KENNETH M
HOPKINS SCOTT D
GEIBEL STEPHEN A
WOLFF TERRY L
