An air intake assembly for a centrifugal blower having a casing having an axial inlet and a radial outlet, an impeller disposed within the casing for drawing a gaseous medium at a first pressure into the axial inlet and expelling gaseous medium at a second higher pressure through the radial outlet, and a motor for driving the impeller, including an air intake assembly casing having an air inlet and an air outlet, the air outlet connectable to the axial inlet of the blower casing of the centrifugal blower, and a check valve mounted within the air intake assembly casing positioned to permit air flow from the air inlet through the air intake assembly casing to the air outlet and prevent air flow from the air outlet through the air intake assembly casing to the air inlet.