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. 

Over the years, vacuum pumps have evolved to dry versions (no oil in the swept volume), robust, process specific, low power consumption and reduced footprint. With this shift in the industry, it was great to hear a range of discussions around this during the 10^th Vacuum Symposium UK.

Screw pumps belong to the family of dry compressing gas transfer pumps. (Learn more about the origins of dry pumps here) 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.

When pumping atmospheric air (or gas) in a vacuum system, however “pure” it may appear to be, it will invariably contain some vapour.

During the compression process in the pump , this vapour will condense. Failure to remove it will form a contaminant which will prevent the pump from achieving its optimum vacuum pressure. Also, the condensate can enter the pump’s mechanism, for example the oil in oil-sealed rotary pumps, where, as a contaminant, it can have a detrimental effect.

In simple terms, a gas ballast valve incorporated into the system will allow a flow of air into the final part of the compression cycle and allow the vapour to be expelled without condensation or affecting the pump's overall performance.

There are several types of pumps that can deliver high and ultra-high vacuum pressures; diffusion pumps, cryo pumps; ion getter pumps (IGP) Large TiTan Ion Pumps | Products | Gamma Vacuum | The Science of Advanced Vacuum; titanium sublimation pumps (TSP) Titanium Sublimation (TSP) | Products | Gamma Vacuum | The Science of Advanced Vacuum; non-evaporable getter (NEG) Non-Evaporable Getters (NEG) | Products | Gamma Vacuum | The Science of Advanced Vacuum 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).

In the world of vacuum systems, scroll pumps hold a valuable place as one of the few pumps that are traditionally employed in low (i.e. 1000 mbar to 1 mbar) and medium (i.e. 1 mbar to 10^-3 mbar) systems, and yet are now also frequently being employed as fore (or backing) pumps in high and ultra-high (i.e. 10^-3 to 10^-12 mbar) vacuum systems.

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.

Ion getter pumps (also called sputter ion pumps or simply ion pumps) produce ultra-high vacuum (UHV) without the aid of moving parts or valves. This makes them highly effective, quiet and low maintenance.

What do you need to consider when choosing vacuum pumps?

Anyone without a deep understanding or knowledge of pumps might think that vacuum generation is simply a question of “plugging in a pump”, starting it up and waiting for the vacuum to drop to the required level.