Sterlitech Corporation

How to Choose the Best Vacuum Pump for Your Lab

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Courtesy of Sterlitech Corporation

Vacuum pumps are a versatile piece of laboratory equipment for suctioning via negative pressure. They are routinely used in biological sciences for filtration, distillation and concentration of volatile solvents, solid phase extraction, freeze drying, and more. Even though vacuum pumps share a common function, there are many considerations to take into account when choosing a new pump. The following article will explain some important attributes to look for when comparing different vacuum pumps.

What type of pump do you need?
First, evaluate which type of pump is best suited to your laboratory needs. Vacuum pumps differ in their design and components, and each type performs best for specific applications. For example, a chemically resistant diaphragm pump is more appropriate for work that involves suction with corrosive solvents, such as solid phase extraction. A rotary vane or gear pump is more appropriate for work that requires a stronger vacuum such as freeze drying or rotary evaporation (1).

How to Choose the Best Vacuum Pump for Your Lab

Oil Free Vacuum Pumps
As the name suggests, oil free pumps use a dry lubricant instead of oil to prevent friction between the internal components. These include piston, diaphragm and scroll pumps. Chemically resistant models are coated with PTFE and are safe to use with most corrosive gases. Applications for oil free pumps include large or small-scale extraction and membrane filtration. These pumps are often portable and low maintenance, but come with a tradeoff in weaker max vacuum power. The Rocker 300 and Rocker 400 are all oil free pumps that will work best for filtration applications with noncorrosive solvents. The Lafil 300C, Chemker 300, and Rocker 300C are chemical resistant options for a wider range of vacuum filtration applications.

Rotary Vane Vacuum Pumps
Rotary vane vacuum pumps are oil-sealed and used for lab applications that require a stronger, consistent vacuum pressure below 10-3 mbar. Hydraulic braking systems, freeze dryers, and mass spectrometry typically use rotary vane vacuum pumps. Some drawbacks of oil-sealed pumps involve disposing of toxic oil waste and difficulty finding replacement spare parts (3). The Tanker series includes several different sized pumps with Tanker 130on the small end and Tanker 230 on the larger end.

Water Aspirators
Aspirators create suction with negative water pressure. The aspirator is connected to a tap and suction is created through a hose when the tap water flows through a nozzle at high speed. The fluid being aspirated mixes with the waste water into the sink or a separate collection bucket. While aspirators are generally inexpensive and easy to use, they require continuous water flow to run and should not be used with hazardous materials. They are not as strong as a wet or dry vacuum pump, and the performance varies depending on the water flow and temperature. The polypropylene aspirator vacuum pump is an inexpensive, easy to use alternative to an electric pump.

Which Model Should You Buy?

After deciding what kind of pump you need, there are usually a few makes and models to choose from. The relationship between Max vacuum and Max flow rate is the most important for determining pump performance. As the vacuum increases, the flow rate approaches a maximum value. Balancing these two factors to suit your lab needs can minimize sample loss from bumping or over evaporation and maximize the evaporative speed.

  • Max vacuum (mbar) - also called “ultimate vacuum”, this is the lowest pressure level that the vacuum can pull. A pump with a max vacuum of 0.1 mbar can evaporate gases with a vapor pressure greater than 0.1 mbar at room temperature.
  • Max flow rate (lpm) - also called “pumping speed”, this is the highest rate that the vacuum can evacuate vapors. A pump with a max flow rate of 10 lpm can potentially pump 10 liters (or 10 cubic meters) of vapors per minute at atmospheric pressure.

Other specifications to help you choose the best pump for your lab include:

  • Motor speed (rpm) - how many revolutions the motor makes per minute. This varies mostly between the 110V/60Hz and 220V/50Hz variants and ranges from 1275 rpm to 1750 rpm.
  • Horsepower (hp) - the rate of mechanical energy used by the pump. Horse power is correlated to the max vacuum. Rotary vane pumps pull a strong vacuum and use ½ hp  to ⅓ hp. Oil-free pumps use ⅙ hp to ⅛ hp.
  • Noise level (dB) - how much noise the pump makes when operating. Oil-free pumps are generally quieter ranging from 50 dB to about 68 dB for oil-sealed pumps. Water aspirators are the quietest since they do not have a motor.
  • Hose barb (mm) - internal diameter of hose barb fittings and is consistent across different makes and models at 8-10 mm.
  • Net weight (Kg) - weight of the vacuum pump unit, generally ranging from 4 - 14 Kg.

Final considerations

Vacuum pumps are a vital piece of laboratory equipment. Simplify your search by narrowing down the options. First, decide which type of pump will best suit your lab needs by evaluating the required max vacuum, corrosive chemicals, and toxic oil disposal. Then, compare different models based on pump performance (vacuum vs. flow rate), noise level, weight, and cost.

In summary, oil-free pumps offer environmentally friendly, dependable performance for small to medium scale vacuum applications. The cost varies between different models with chemical resistant pumps on the more expensive end. Rotary vane pumps are high performing, but come with increased maintenance responsibilities from oil-changes and wet seals. They are generally more expensive than a standard oil-free pump, but less expensive than the chemically resistant diaphragm models. Finally, the aspirator vacuum pump is best suited for aqueous filtration work with non-hazardous chemicals. It is by far the least expensive device, but is relatively limited in performance.

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