The roots type vacuum pump is a mechanical vacuum pump consisting of two inter-digitated rotors in close face-to-face contact with each other. The pumping action is created by the rotors displacing air as they rotate, exposing the pumping chambers alternately to atmospheric pressure and a vacuum. Roots pumps are rugged, simple, and capable of a long life under continuous-duty conditions. They have low rotational speeds, which permit flexible shafts and the use of reasonably large-diameter rotors with consequent large pumping capacity.

In 1869, the brothers Philander and Francis Marion Roots took out patents on a new type of high vacuum pump that proved essential in the development of the internal combustion engine. The Roots pump was first used in gas-producing wells to displace the water that had been flooding these operations. Today it is a standard piece of equipment for any laboratory, but it is being used more and more in large-scale industrial plants.

The following article provides an insight into the Roots vacuum pump for medical application.

The Root vacuum pumps used in medical applications provide a relatively clean, ultra-high vacuum for the majority of applications. They are ideal for evacuating reaction systems or pre-pumping after a turbomolecular pump or a dry pump. Unlike the forepump, they have no effect on system pressure.

In medical applications, these pumps are typically used in the following applications:

• Venting low-pressure sources, typically in control or interface vacuum gauges, semiconductor chambers, or aerospace purge systems.
• Pre-pumping after a smaller roughing pump, typically used in semiconductor processes.
• Vacuum bakeout of chambers and components.
• Pre-pumping for ultra-high vacuum systems in medical and analytical instruments.

Roots Vacuum Pumps are characterized by high pumping speed, high vacuum endurance, easy control characteristics, and trouble-free running. These pumps are particularly suited to the high vacuum requirements of ultra-high performance gas chromatographs and mass spectrometers. In addition, these pumps are ideal for pre-pumping desorption or cryotrapping systems. They are also used in the food, aerospace, and semiconductor industries and the production of thin-film heads.

Principle:

The rotor assembly consists of two flat rotors that rotate about a center shaft and are offset to accommodate the spaces in which atmospheric pressure may be present. Gaskets provide an airtight seal. The pumping action is created alternately when each flat rotor is positioned to expose the pumping chambers to atmospheric pressure and then to a vacuum. The rotor assembly is contained in a housing that provides an airtight seal and mounts on flanges to be connected to the application system.

The Roots vacuum pump uses the flow of air to perform vacuum pumping tasks. This is in contrast to most other types of vacuum pumps, where a mechanical drive system is used to achieve the flow of air. This mechanical drive system typically consists of a series, or trains, of rotating and/or reciprocating components. The pump rotor assembly consists of two inter-digitated rotors, often called teeth or lobes, which create the pumping action.

The rotor assembly is contained within a housing and connected to flanges so it can be connected to the application system, typically using quick-connect/disconnect flanges. 

The Roots vacuum pump is a mechanical rotary-piston single-stage high vacuum pump. It is used in many applications requiring a source of ultra-high vacuum. It provides the necessary pumping action with air and has minimal pressure effects on the vacuum system. It is typically used in medical applications for evacuating low-pressure sources, pre-pumping ultra-high vacuum systems, and venting non-vacuum systems.