Named after the Roots brothers who invented it, this pump displaces the liquid trapped between two long helical rotors, each fitted into the other when perpendicular at 90°, rotating inside a triangular shaped sealing line configuration, both at the point of suction and at the point of discharge. This design produces a continuous flow with equal volume and no vortex. It can work at low pulsation rates, and offers gentle performance that some applications require.

Applications include:

High capacity industrial air compressors
Roots superchargers on internal combustion engines.
A brand of civil defense siren, the Federal Signal Corporation's Thunderbolt.