Roots Blower
Definition and meaning of Roots Blower in chemistry.
A Roots blower is a positive displacement gas mover consisting of two counter-rotating rotors, each with a figure-eight (peanut) shaped cross-section, that carry gas from inlet to outlet without internally compressing it. It is commonly used in vacuum systems to move large gas volumes efficiently.
In more detail
The twin rotors turn synchronously in opposite directions, kept apart from each other and from the housing walls by a small clearance that prevents contact. As they rotate, each rotor pocket carries a fixed volume of gas from the low-pressure side to the high-pressure side per revolution, producing a pulsating flow well suited to evacuating large quantities of air or vapor. Because a Roots blower has a limited compression ratio and cannot exhaust directly to atmosphere, it is staged as a booster pump in the vacuum foreline: it sits between the vacuum chamber (or a diffusion or turbomolecular pump) and a separate backing (roughing) pump, typically a rotary vane pump, which maintains the outlet-side pressure the Roots blower discharges into. This staged arrangement substantially raises the overall pumping speed of the system in the medium-vacuum range.
Key facts
| Field | Physical Chemistry |
|---|---|
| Type | Positive displacement blower with two counter-rotating, figure-eight shaped rotors |
| Primary use | Booster pump in the foreline of a vacuum system, paired with a rotary vane backing pump |
| Advantage | Handles large gas volumes at moderate pressures without internal compression |
A laboratory vacuum system might use a Roots blower as a booster pump positioned between a large reaction vessel and a rotary vane backing pump, allowing the combination to evacuate the vessel far more rapidly than the rotary vane pump could achieve alone.
Frequently asked questions
How is a Roots blower different from a rotary vane pump?
A Roots blower moves much larger volumes of gas per cycle and generates less frictional heat because its rotors never touch, making it effective as a booster ahead of a rotary vane pump, while the rotary vane pump itself is better suited to reaching low final pressures and exhausting to atmosphere.
Why use a Roots blower in a vacuum system?
Its ability to move large quantities of gas without internal compression, combined with oil-free operation in many designs, makes it effective as a booster pump that increases the pumping speed of a system backed by a rotary vane pump, ahead of a diffusion or turbomolecular pump.