Patent ID: 7520910

Claim:
An air purification unit, comprising: a filter section, comprising: an air inlet on a first end, a rigidly framed filter inside said filter section and attached to said filter section on said first end such that the rigid frame is sealed with respect to said air inlet such that the only available flow path through said filter section is through said filter, and a fan coupling extending from a second end of said filter section; and a blower section, comprising: an air outlet, and an internally mounted motor and fan, said fan being configured to provide a pressure differential boundary between a high pressure on a discharge side of the fan and a low pressure on an inlet side of the fan when said fan is in operation, wherein the fan coupling of said filter section extends sufficiently into said blower section when said filter section is joined to said blower section such that the pressure differential boundary of said fan is no further downstream than the free end of said fan coupling and wherein the fan coupling is configured such that a section joining interface between said filter section and said blower section is located on the high pressure side of said pressure differential boundary such that risk of ingress of contaminated air from exterior of the air purification unit in the event of an imperfect seal at the section joining interface between said filter section and said blower section is eliminated.