Glossary
Performance criteria
What is the most suitable vacuum pump technology (or combination of technologies) for any given application? Essential performance measures in a given task include the level of vacuum you need to reach, and the time in which you need to reach this operating vacuum. Then there is the power requirement to be considered.
Degree of vacuum produced
The vacuum that the pump is capable of producing is a figure that will be provided by the manufacturer. Note whether this figure is for continuous duty or intermittent duty. Note also any temperature considerations that may limit ultimate performance. Also, figures are relative to standard atmospheric pressure, so consider where you are going to be operating the pump - at lower ambient pressures (for example at higher altitudes) it will only be capable of reduced vacuum.
Rate of gas removal
Time to reach a given vacuum is defined by the rate of gas removal. Note that while flow rate might be constant, the relationship between flow rate and actual mass of gas removed is non-linear for many pump technologies. Manufacturers will supply curves of vacuum levels against time for given pumping speeds. These curves can prove key in evaluating the performance of one pumping technology against another, and of pumps from different manufacturers.
Power requirements
Power is proportional to flow and the pressure differential.
Mechanical and environmental considerations
Pumps differ significantly in details such as manufacturing tolerances, levels of vibration, audible noise, service intervals and overall size, all of which impact on the performance and the suitability for a given application.
Corrosive materials and contaminants
The medium being evacuated can have significant implications for vacuum pumps, affecting both the materials that can be used within the pump and the level of filtration required. Corrosive chemicals, water, dust and other contaminants all have to be taken into account in choosing the most appropriate pump or compressor for the application. By considering the contaminants that are present, you can begin to eliminate inappropriate designs of vacuum pump, to ensure the product you actually end up using will give you the optimum lifespan in your application.
Dry running and oil-lubricated
Dry running pumps are essential in applications that cannot allow any oil mist to be exhausted with the gas, but they can also provide a lower maintenance option since there is no ongoing refilling of an oil reservoir. There are many dry running pump options available these days. Oil-lubricated pumps have their own advantages, however. They can generally provide a higher vacuum because the lubricant acts as a sealant between the moving parts. And they can offer long lifespans by running cooler than dry pumps.
