The Difference Between Vacuum Pumps

There are multiple types of vacuum pumps on the market, including; rotary vane vacuum pumps, diaphragm vacuum pumps, scroll pumps and direct drive vacuum pumps. When choosing a vacuum pump for your application it’s important to take into consideration any chemicals you will be using and in what concentrations. Every pump has specific characteristics and can be used for various applications depending upon your requirements. It’s crucial to choose the correct model, size, and level of vacuum, as well as the quality to insure the pump longevity and your system operations on a day to day basis. 

Level of Vacuum

You must understand the level of vacuum required for your application when choosing the correct pump for the job.

  • Low vacuum is often used for moving liquids around through filtration (filter flasks)
  • Medium vacuum is used for applications similar to solvent recovery where you would be evaporating solvents or reconditioning them.
  • Medium to high vacuum has a range of uses where it’s important to lower the boiling points of certain compounds to become gaslike.
  • High vacuum applications are best suited for the semiconductor industry.
  • Ultra-high vacuum (UHV) is used in theoretical applications when studying space and certain nuclear reactions.

Choosing the correct vacuum depth and precise flow rate will have a notable impact your system. For oven applications, and if the oven is small, a small direct-drive pump can be used to quickly remove air from the system. If you were to have a larger oven, a bigger pump should be used.

 Corrosion Resistant – Do you need oil or not?

Again, if the application is using an oven, depending on the items that are being purged/degassed in the oven, a corrosion resistant pump may be required to extend the lifetime of the pump. Understanding driving forces behind the application is necessary when selecting a pump. Free air displacement relates to the flow rate though a given pump and describes how fast it will reach its ultimate vacuum. High flow rates for distillation can cause the molecules to condense into unpleasant areas when the pump is pulling vapors past where they’re intended to collect.

Rotary Vanes

Rotary vane pumps offer high performance with lower costs. Even though the pump itself may be on the lower cost spectrum- the oil which has to be replaced can be expensive. The life expectancy of a rotary vane pump revolves around and is extremely dependant on the maintenance of the pump. Because rotary vane pumps can reach deep ultimate vacuum levels and have variable displacement capabilities, it’s crucial that maintenance on the pumps is performed regularly.

Direct Drive

Direct drive units are powered by an electric or gas motor to achieve a deep vacuum. Because the motor spins at a constant speed, the pump is connected to the drive shaft of the motor to the pump mirrors the motor’s RPM’s. When the direct drive pump spins at a higher RPM the motor can endure stress from wear and tear faster than what would normally be considered acceptable. When the direct drive is at a constant high RPM is can result in a reduced lifespan of the overall machine.

Common applicators for the direct drive pumps are vacuum ovens, centrifugal concentrators and freeze dryers.


Diaphragm pumps are ‘dry’ meaning they do not use oil to run. The elimination of oil from the diaphragm pump means it is also relatively environmentally friendly. Diaphragm pumps reduce the hydrocarbon output from the pump. Because Diaphragm pumps have valves that pulse in an open and closing motion creating movement of the air- this allows the pump to operate without oil. These pumps often run in low-to-medium vacuum levels, but there are some diaphragm pumps that are designed for medium-to-high vacuum.

Dry Scroll

These ‘dry’ oil-free pumps incorporate two spiral scrolls to compress air and vapors- often directed towards the exhaust. While dry scroll pumps may be expensive they can often save you time and maintenance down the road. When you have a dry scroll pump the maintenance and downtime is significantly less compared to any other pump because they do not require any oil. Dry scroll pumps have lower hydrocarbon output and are more ecologically sound; they are also better at handling water vapor compared to most pumps. Dry scroll pumps are often used in degassing, distillation, and/or any type of concentrate applications.


 While diffusion pumps were the first ever type of vacuum pumps referred to as ‘gas-jet’ pumps, there are no moving parts in these pumps! Gas-jet pumps often work off of the act of diffusion itself rather than a conventional fluid. The gas cannot diffuse against the vapor stream and is carried towards the exhaust, which creates a vacuum. Because the diffusion pumps heat the oil, it boils and captures the gas molecules while pushing particles with it- eventually creating a vacuum. While refilling the fluid in this pump may be extremely costly, the reliability is incomparable to any other pump. The main use for diffusion pumps frequently is a mass spectrometer or other similar applications which require an extremely high vacuum.

While high quality, long lasting vacuum pumps can often be expensive, it is important to thoroughly research the pump and take all factors into consideration when choosing it. If you are not sure which vacuum pump you need, feel free to give us a call or email us and we’ll be glad to help.

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