The basic unit consists of two figure eight shaped impellers mounted on parallel shafts. The impellers rotate in opposite directions within a cylindrical casing. As each impeller passes the inlet, it traps a definite volume of air/gas and caries it around the casing to the discharge where the gas is expelled. The cycle repeats four times with every revolution.
All Roots rotary positive blowers have close tolerances between the impellers and casing to minimize back-slippage of gas and to improve efficiency.