VACUUM SCIENCE BLOG

Cryopumps offer several advantages compared to other high-vacuum pumps. For instance, their pumping speed for water vapour is up to 4x higher than any other vacuum pump with the same inlet diameter. Furthermore, unlike gas transfer pumps, i.e. turbomolecular pumps or oil diffusion pumps, cryopumps condense all the gasses within them. The goal of this blog is to explain to you how they operate and where their capabilities are beneficial to the vacuum process. 

Screw pumps belong to the family of dry compressing gas transfer pumps. They are positive-displacement pumps that use two screw shaped intermeshing rotors to move gas along the screw’s axis. They are frequently used in industrial vacuum applications, often in combination with roots blowers and as oil-free roughing pumps in high and ultrahigh vacuum systems.

The presence of gaseous molecules, whether slow or fast moving, is what gives rise to pressure. A vacuum is created by reducing the number of molecules that exist within, for example, a chamber or a flask. However, by reducing the number of molecules that exert a pressure on the internal surface of such a chamber, one reduces the pressure. Unfortunately, this causes “additional” molecules to enter into play.

There are several types of pumps that can deliver high and ultra-high vacuum pressures; diffusion pumps, cryo pumps; ion getter pumps (IGP); titanium sublimation pumps (TSP); non-evaporable getter (NEG) pumps; and turbomolecular pumps (TMP).

The methods whereby these pumps are capable of producing high and ultra-high vacuum pressures (between 10^-3 and 10^-11 mbar) are either by momentum transfer of gas molecules or by capturing them (either physically or chemically).

Multistage roots pumps are dry vacuum pumps used in low, medium, high and ultra-high vacuum systems to produce “dry” conditions.

The simple (single-stage) roots pump is most commonly employed as a booster pump for several types of fore-pumps (such as rotary vane pumps, screw and liquid ring pumps) to improve ultimate pressure and pumping speeds. When multistage roots pumps are employed, no fore pump is required and they can operate from atmospheric pressure. Roots pumps are suitable where a dry and clean atmosphere is important or more likely essential. Consequently, they are frequently used in the manufacture of semiconductors and solar panels, as well as for coatings and other industrial applications.

Vacuum simulation (or modelling) is an essential part of vacuum system design. It is now a well-established practice and is primarily concerned with the prediction and calculation of how vacuum pumps and systems will perform in specific scenarios.

These simulations enable engineers to identify anomalies in the design stage and acquire the right components, rather than building a vacuum system that later needs to be redesigned.

For a vacuum pump system, a vital consideration in its design is the conductance. Conductance in vacuum systems is the characteristic of a vacuum component or system to readily allow the flow of gas and can be thought of as the inverse of resistance to flow. Its units are that of the volumetric capacity of gas flow in a passive component (or aggregate component of a vacuum system), such as an opening or a pipe, divided by time.

When working with high vacuum (HV) and ultra-high vacuum (UHV), there are specific aspects to consider to ensure an efficient and safe system.

To clarify, the pressure range of UHV conditions are defined as between 10^-7 and 10^-12 mbar, whereas HV conditions are defined as between 10^-3 and 10^-7 mbar. Some of the main applications of HV include metallurgical processes, nuclear physics, space simulation and analytical instruments. On the other hand, UHVs are used for surface analysis, in high-energy physics and Molecular Beam Epitaxy (MBE). 

In this blog, we discuss the three main considerations you need to bear in mind when working under HV or UHV conditions.

working principle 

Turbomolecular pumps (TMPs) are kinetic vacuum pumps which operate using a very fast spinning rotor (usually rotating at between 24,000 and 90,000 RPM). Their typical operating pressures are in the high to ultra-high pressure range between 10^-3 and 10^-11 mbar, employing pumping speeds of between 10 and 4,000 l/s.

Wherever and whenever a vacuum needs to be created, it is essential to ensure its integrity (i.e. the “tightness” of the system). If the system is not tight, then time is squandered and effort is pointlessly spent trying to create a vacuum in an “open system” which could never support a vacuum in the first place.