English: A labelled cross-section of a Roots blower with 2-lobed rotors. The rotor form is cycloidal, and in this drawing is drawn accurately. In fact, it is part epicycloidal and part hypocycloidal, and in both cases the smaller generating circle is 1/4 the diameter of the circle it rolls around. Roots blowers find uses in superchargers and gas pumps which need a high volume at a low differential pressure. See the key below.