February 1, 2021
5 MIN READ
When the time comes to select a new vacuum pump, it's important to take a thoughtful approach. At first glance, it might seem like a simple task, but there are several factors to consider.
Various factors affect a vacuum pump’s overall efficiency and capabilities. Each pump requires its own process conditions, has its own operating range, and offers its own set of benefits and limitations. These characteristics depend on four factors:
Process or application impact on pump
Pump impact on process or application
Cost and maintenance
Vacuum level is perhaps the most critical consideration as it affects each of the other factors.
Typical classifications and ranges include:
Rough vacuum: from from 10 3 mbar to 1 mbar
Medium vacuum: 1 mbar to 10 -3 mbar
High vacuum: 10 -3 mbar to 10 -7 mbar
Ultra-high vacuum: 10 -7 mbar to 10 -12 mbar
Extreme high vacuum: less than 10 -12 mbar
Different pump technologies are required to achieve different vacuum pressure ranges. Depending on the target vacuum level, a mix of different vacuum pump technologies might be necessary.
Forevacuum pumps — those operating in the rough and medium vacuum ranges — exhaust to the atmosphere and can operate in isolation.
High and ultra-high vacuum pumps — such as turbopumps and diffusion pumps — need to exhaust to, or operate with, a forevacuum pump.
Ion, non-evaporable getter pumps, and cryopumps need initial evacuation and occasional forevacuum and high vacuum pump support at certain stages.
Related: Brush up on the unique demands of working with high vacuum ranges on this resource page by Vacuum Science World, The Fundamentals of High, Ultra-High & Extreme High Vacuum. Or, check out this guide by Vacuum Science World, to Understand the Different Types of Vacuum Pumps in more detail.
The way processes can impact pumps plays a significant role in selection. The impact of the application on the selected pump technology needs to be evaluated carefully, as well as the potential impact of:
Dust or debris from the process
Corrosive gases like chlorine or acidic mixtures in the presence of water vapor
High gas throughputs
Mechanical movements and shocks
Heat radiation on the pump
Particle or X-ray radiation
Magnetic and electric fields
As an example, rotary vane pumps are well-suited for many low and medium vacuum applications, such as:
Research and development
Industrial and coating activities
On the other hand, scroll pumps provide hydrocarbon-free vacuums by compressing gases using two tip-sealed spirals rotating eccentrically against each other. This results in low operation and maintenance costs.
Compared to RV pumps, scroll pump applications are mainly limited to processes without dust or dirt that could damage the tip seals.
Related: Learn more about the evolution of freeze drying in the food industry on our resource page, Vacuum Pumps and Freeze-Drying Technology.
Evaluating the impact of the vacuum pump on the application or process is just as important. Several variables can influence vacuum pump choice, including — but not limited to:
Oil or hydrocarbon emissions or backstreaming
Vibrations produced/induced by the pump
Magnetic fields produced by the pump (rare)
Rotary Vane pumps are at a disadvantage because they cannot generate a hydrocarbon-free vacuum due to oil vapor emission.
On the other hand, while capable of producing a hydrocarbon-free vacuum, scroll technology carries the risk of particle emission due to tip seal wear.
Related: Check out this blog post with 5 Quick Facts About Noise Pollution in Your Lab, that can help keep you and your team safe.
Beyond initial capital costs, there is cost associated with operation and maintenance or service.
Diffusion pump operation is likely much more expensive when compared with a turbomolecular pump. Also, the cost of ownership over five years also includes factors like higher energy and maintenance costs.
Diffusion pumps can deal with dirtier, industrial processes, whereas turbo pumps are used mainly in clean processes.
Related: Calculate and compare the total cost of ownership between wet and dry vacuum technology with our free online calculator. Click the button below and see how much you could save when using dry vacuum technology.
There are two overarching categories of vacuum pumps: forevacuum pumps and high vacuum pumps.
Forevacuum pumps exhaust directly to atmospheric pressure. They include:
Rotary vane pumps
Related: Check out this blog post for 5 Tips to Make Your Rotary Vane Pumps Last Longer.
Secondary pumps rely on primary pumps to continuously support their operation as they cannot exhaust atmosphere, and require a low pressure at their exhaust, known as "backing."
Continuously supported (backed) high vacuum pumps include turbomolecular and diffusion pumps.
Ultra-High vacuum pumps include ion getter, titanium sublimation, non-evaporable getter, and cryogenic pumps.
Roots blower pumps are often combined with forevacuum pumps to act as a pump pair, but they are strictly classified as secondary pumps, as they are not designed to be used without a forevacuum pump.
Related: Explore our range of turbomolecular pumps on our resource page, introducing the Leybold TURBOVAC i.
Making the right pump choice for effective vacuum generation requires an understanding of how pumps impact processes — and how processes impact pumps. Vacuum level needs, cost, and maintenance also impact vacuum pump choice.
Choosing the wrong pump can be expensive and potentially damaging to your operation if the pump doesn't perform as required. A quick chat with our team can help you avoid those pitfalls and advise on which pumps best suit your requirements. Click the button below and start the conversation — we're always happy to lend a hand!
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