Scroll pumps play a valuable role in the world of vacuum systems as they are one of ...
Scroll pumps play a valuable role in the world of vacuum systems as they are one of a few pumps that have generally been used in medium (1mbar to 10-3mbar) and low (1000mbar to 1mbar) systems, and, in more recent days, are being used as backing or fore pumps in ultra-high and high vacuum systems (10-3mbar to 10-12mbar).
One of the main benefits of a dry scroll pump is they present no contamination risks. However, to counter this characteristic, we have to acknowledge that the pumps are intolerant to particles. With that being said, it’s worth noting that there’s a potential for particle generation caused by tip seal wear.
A scroll pump’s main working parts consist of two spiral-shaped, co-wound scrolls that are contained within the pump’s vacuum housing. The housing has an exit valve located at the center of the assembly. One of the spirals is fixed while the other, known as an ‘orbiter,’ moves without rotating, and in the opposite direction of the other. Gases enter the open end (outside) of the spirals, and, as the other spiral orbits, the gas gets trapped between the two and is transported towards the center. When this happens, the void initially occupied by the gas gets squeezed and moves between the spirals.
As the restricted ‘slug’ of gas starts moving towards the center, the amount of volume it initially occupied decreases. This continually compresses the ‘captive’ gas at the center of the housing until it’s forcefully expelled through a non-return valve. While no moving parts within the pump’s chamber require any lubrication, the PTFE (polytetrafluoroethylene) tip seals do wear out and will need to be replaced periodically.
Scroll pump performance characteristics vary depending on a variety of factors, including the speed of operation, unit size, characteristics of the vapor/gas being pumped, and ambient temperature. The following listings highlight some of the typical performance characteristics of a scroll pump:
Additionally, these pumps come with a frequency converter designed to ensure that they work anywhere in the world. Furthermore, there are electronic-free, three-phase scroll pump variants designed to work in environments with high levels of radiation and strong magnetic fields.
These pumps are one of few dry fore/oil-free pumps (the others being screw, diaphragm, and multi-stage root pumps) that are generally used as fore pumps in high and ultra-high vacuum systems. When choosing a scroll pump, your final selection will as always, come down to the advantages and disadvantages of the pump, its limitations, and its intended purpose.
While scroll pumps are used in various applications, they are mostly used to compress and pump vapors and gases in applications where clean, dry vacuum pumping is required. They’re also used for surface analysis, sample preparation, and non-hazardous/non-corrosive applications. Apart from being used for analytical purposes like in electron microscopes or leak detection equipment, they are often employed as fore pumps in turbomolecular systems where clean final products are required.
Like with other types of vacuum pumps, scroll pumps do have their fair share of benefits and – though few but not insignificant – drawbacks, as well as limitations that should be considered when choosing a pump to use in a vacuum system.
Feasibly, their most significant benefits are that even though their initial cost is relatively-high, their operating costs are considerably lower since they don’t require oil (something that also makes them environmentally-friendly).
Below is a look at some of the advantages and disadvantages of using a scroll pump.