Screw Pump. Two opposing screws rotate to create gas flow. Direction of flow is axial from inlet to exhaust.

Hook & Claw. Clawed rotors spin in opposite directions to trap and compress gas and vapor. Gas flow is directed through multiple stages and then exhausted.

Roots Mechanism. Interlocking lobed rotors use positive displacement to move gas and vapor.

Scroll Pump. Uses two opposing scroll shaped disks. One is fixed while the other rotates and uses an eccentric cam. Gases are trapped compressed and moved towards the exhaust.

The above mentioned pumps may be placed in series combinations for specific pumping characteristics. Many manufacturers use multiple stages of the Hook & Claw, and Roots device in a single pump.