Roots blower, sometimes called a Positive Displacement, or PD blower, is a machine which " pushes" a relatively constant volume of the gas handled at the inlet through to the discharge. It applies to conditions requiring high vacuum or high pressure especially in the waste water treatment plant.

The main purpose of the blower is to provide constant flow of gas at different pressures. The blower consists of a cast iron casing in which two rotors with conjugate shapes rotate and are synchornised by a set of timing gears. During rotation, there is no contact between the lobes or between the lobes and the casing.