Abstract: A method of making a liquid filter includes the steps of providing a spiral roll of filtering material on a central tubular member, providing a housing member into which the roll is to be placed and laying a bead of thermoplastic material having a given softening point on an outer surface of the roll at least around the circumference of the roll close to an end thereof. The bead is pressed with cooled forming jaws, while in a warm state, to suitable dimensions corresponding to inside dimensions of the housing member. The housing member is heated to a temperature above the softening point of the thermoplastic material, the roll is inserted into the housing member and thereafter, the housing member is cooled. The thermoplastic material cools, acts as a glue and constitutes a tight, rigid connection between the housing member and the roll of filtering material.

Abstract: A strip of filter material is folded so as to form two closely adjacent strip portions which are of one piece and have aligned longitudinally extending free edges and longitudinally extending second edges transversely spaced from the free edges and unitary with one another. The strip is coiled so that each of the strip portions forms a plurality of convolutions which alternate with the convolutions of the other strip portion. Means is provided in the region of the second edges for preventing liquid being filtered from forcing contaminant particles through the filter material.