Filter element for circulating air systems

Claim 1

A reusable air filter assembly for removing solid particles entrained in and flowing with an air stream to be filtered, comprising, an inlet stage filter medium consisting of a single layer of fabric woven from polypropylene yarn in an egg-crate pattern producing high and low surface areas in the direction of air flow through the filter assembly, an outlet stage filter medium consisting of two layers of fabric woven from polypropylene yarn in an egg-crate pattern producing high and low surface areas in the direction of air flow through the filter, said two layers being in overlying relation with the egg-crate pattern producing air spaces between the two layers, the polypropylene yarn employed to weave the outlet stage filter medium being smaller and the weave substantially closer than in the first stage filter medium, a low velocity precipitation chamber between said inlet stage filter medium and said outlet stage filter medium, said low velocity precipitation chamber being defined and maintained by a layer of corrugated metal screen engaging and separating said inlet and outlet layer filter media, said low velocity precipitation chamber having a thickness, measured in the direction of flow of air through the filter, which is at least equal to the combined thickness of the filter media of the inlet and outlet stages, expanded metal grid members extending over the inlet side of the inlet stage filter medium and the outlet side of the outlet stage filter medium, and a rigid, corrosion resistant frame extending around the periphery of and supporting the filter assembly and said grid members.