Opens in a new tab
Clear, accurate chemistry definitions
1,500+ terms6 topics118-element periodic table
Physical Chemistry

Roots Blower

Definition and meaning of Roots Blower in chemistry.
A Roots blower is a mechanical pump that moves large volumes of gas. It uses two spinning peanut-shaped rotors to push gas from the inlet to the outlet. This device is commonly used to create a vacuum in modern chemistry labs.

In more detail

The two rotors turn inside a metal housing in opposite directions. They spin at the exact same speed to stay perfectly in sync. A tiny gap keeps the rotors from ever touching each other or the walls.

This gap prevents friction and allows the pump to run without any messy oil inside. Each time the rotors turn, they trap a specific pocket of gas. They carry this fixed volume of gas from the low-pressure side to the high-pressure side.

The blower does not actually squeeze or compress the gas inside the pumping chamber. It just moves the gas very quickly to create a steady flowing stream. Students often confuse this specific device with a standard industrial air compressor.

A normal air compressor squeezes gas to physically raise its internal pressure. A Roots blower simply shoves the gas forward to quickly clear out a space. Because it cannot compress gas well, it cannot push gas directly out into the normal room air.

Instead, it must push the gathered gas into another pump that can finish the job. This second pump in the sequence is typically called a backing pump. The backing pump handles the final push to exhaust the gas into the room.

Key facts

Field
Physical Chemistry
Type
Positive displacement mechanical gas blower
Rotor Shape
Figure-eight or peanut shaped
Primary Use
Booster pump in a multi-stage vacuum system
Key Advantage
Moves large gas volumes without needing internal oil
Limitation
Cannot exhaust gas directly into the normal atmosphere
Example
A laboratory vacuum system often pairs a Roots blower with a rotary vane backing pump. The Roots blower rapidly pulls huge amounts of gas out of a large chemical reaction vessel. It then shoves all of this collected gas directly into the rotary vane pump. The rotary vane pump squeezes the gas and pushes it out into the room. This team approach empties the vessel much faster than one pump could work alone.

Frequently asked questions

How is a Roots blower different from a normal air compressor?

An air compressor squeezes gas to increase its pressure, while a Roots blower simply moves gas from one place to another without squeezing it.

Why do Roots blowers need a second backing pump?

They cannot compress gas enough to push it against normal atmospheric pressure, so they need a second pump to finish the job.

Why are Roots blowers good for clean chemistry labs?

The rotors never touch each other, so the main pumping chamber does not need any messy lubricating oil that could contaminate the chemical samples.
By the Chemistry Dictionary editorial team · Reviewed July 16, 2026