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Loss of oil from oil-sealed rotary vane pumps

How to predict when my vacuum pump needs an oil refill?

Let us consider a typical laboratory system where a 1 litre volume flask is being evacuated from atmospheric pressure every hour.

  • At a temperature of 295 K the mass of air transferred/ pumped in each cycle is ~ 1.2 g 
  • A typical ‘small’ Oil sealed rotary vane pump has an oil charge of approximately 1 litre. With unit density this is a mass of ~ 1,000 g 

If 25% of the mass of oil, compared to the mass of the pumped air, is carried over (i.e. transferred with the pumped air) during each flask evacuation then

  • During each cycle the oil loss ~ 0.3 g 

This suggests that in ~ 3300 cycles all the oil will be lost from the pump. At a rate of one cycle per hour this occurs in approximately 4 to 5 months. (Note that this could be confirmed by checking how often the oil in the Oil sealed rotary vane pump needs to be re-filled) and or we can surmise that in 3 months we would expect > 600 g of oil to be lost from the pump.

This will result in a layer of aromatic (smelly) oil of 0.1 mm thickness coating an area of 60,000 cm2 of the laboratory. As a comparison operating a pump at ultimate pressure (< 1 Pa) the mass flow of air is <0.001 g/h

RV Group

When using oil sealed rotary vane pumps we also need to consider

  • The cost (financial and environmental) of the safe disposal of oil
  • The potential contamination of a laboratory system from the back-migration of oil in a oil sealed rotary vane pump
  • The required maintenance such as oil re-filling and seals replacement 
  • Oil contamination versus time
  • The required configuration and equipment to prevent oil loss
  • The potential for contamination of a sterile laboratory environment by any oil being present within it 
  • The risk of the oil sealed rotary vane pump becoming a potential source of ignition if it is operated below the minimum level of oil

 

Edwards nXDS20i Scroll Pump

nXDS scroll pumps are completely oil-free, hermetically sealed. They have no oil in the gas pathway so there is no potential contamination of the process nor of the laboratory environment. They can be configured to pump a wide range of laboratory applications and maintenance intervention is 2.5 years or more