Air filter

In an air filter, a housing defining a chamber therewithin, an annular filter cartridge in said chamber having a circumferentially extending permeable outer wall cooperating with the wall of the housing to define an annular inlet compartment therebetween within said chamber, inlet means for communicating air into said inlet compartment, said annular filter cartridge defining an outlet compartment, outlet means for communicating air from said outlet compartment after the air has passed through said filter cartridge, means in said inlet compartment circumscribing said permeable outer wall of said cartridge and extending transversely across said inlet chamber between the wall of the housing and said permeable outer wall for inducing a spiral flow component to at least a portion of the air communicated through said inlet and dividing said inlet compartment into one section upstream from said spiral flow inducing means and another section downstream from said spiral flow inducing means, said inlet communicating with said upstream section, said filter cartridge including a first filtering medium for filtering larger particles from the air communicated to said housing and a second filtering medium separate from said filtering medium for filtering finer particles from the air communicated to said housing, said second filtering medium being carried on said permeable outer wall of said filter cartridge, said upstream section and said first and second filtering media defining a first flow path between said inlet and outlet, said upstream section, said spiral flow inducing means, said downstream section, and at least one of said filtering media defining a second flow path between said inlet and outlet in parallel with said first flow path.