Abstract: Disclosed is a cylindrical closed strainer molded of a plastic in a unitary structure, which comprises a top plate, a bottom plate disposed opposite said top plate at a fixed interval therefrom and a cylindrical net stretched between the peripheries of said top plate and bottom plate, said top plate being possessed of snap fastening means on the upper surface thereof and provided with a through hole which has a diameter larger than the outside diameter of a suction pipe intended to be connected with the strainer body and is provided on the inner circumference of said through hole with a thin seal member coaxially containing a circular hole of a diameter smaller than said outside diameter of the suction pipe. Said suction pipe is provided with a flange which is adapted to rest stably on the upper surface of said top plate.

Abstract: Disclosed are a strainer and a method of injection-moulding the strainer of plastics. A strainer according to this invention comprises a pair of semi-cylindric shells integrally and movably connected along their adjacent longitudinal sides in the state of being developed; top and bottom circular boards integrally connected to the top and bottom frames of one of said semi-cylindric shells; and nets integrally connected to each of said semi-cylindric shells. This developed structure of the strainer makes it possible to injection-mould a semi-product of strainer as a whole in a single injection-mould die, and a so moulded and developed strainer is easily assembled in the final and complete cylindric shape by simply closing the semi-cylindric shells and integrally connecting them along their abutting longitudinal sides.