Patent ID: 8561810

Claim:
A positioning sheet to be rolled up in cylindrical form for being disposed between a filter element and a housing, the positioning sheet comprising: a rollable sheet, having two elongated flat edges extending in a longitudinal direction of the rollable sheet and a supporting surface between the two elongated flat edges, the rollable sheet capable of being rolled up along the longitudinal direction thereof, thereby forming a cylinder enclosing a passageway for the reception of the filter element passing through; and a plurality of bulging portions vertically protruding from the supporting surface of the rollable sheet toward the same direction, bulging portions co-defining a horizontal level higher than a horizontal level of the elongated flat edges of the rollable sheet; wherein when the rollable sheet is rolled up into the form of the cylinder with the supporting surface facing inward, the cylinder has a first diameter at an inlet of the cylinder and a second diameter at a location of the cylinder wherein the bulging portions is, and the first diameter is greater than the second diameter, such that the filter element is allowed to pass through the passageway of the cylinder from the inlet of the cylinder and the bulging portions are against the filter element.