A regenerative blower includes an annular housing assembly that surrounds a rotating impeller and defines a toroidal flow channel, an inlet to admit fluid to the toroidal flow channel, an outlet to discharge fluid from the toroidal flow channel, a low fluid-pressure region of the toroidal flow channel proximate to the inlet, and a high fluid-pressure region of the toroidal flow channel proximate to the outlet. A non-contact interaction between concentric surface contours of the impeller and the housing assembly form opposed concentric fluid pathways between the impeller and the housing assembly from the high to low fluid-pressure regions of the toroidal flow channel. The opposed concentric fluid pathways are so convoluted as to restrict fluid from flowing therethrough from the high fluid-pressure region of the toroidal flow channel to the low fluid-pressure region of the toroidal flow channel.