Fundamentals of Vacuum Pumps (High Vacuum)

What is a Diffusion Pump?

This pump exhausts gas molecules by imparting momentum to the gas molecules, which enter from the inlet port due to diffusion phenomena, toward the exhaust port by using high-speed and high-density oil vapor jet flow from a nozzle. The jet flow also prevents gas molecules from flowing back into the inlet port.

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Diffusion Pump's Application:

  • FPD manufacturing equipment
  • Semiconductor manufacturing equipment
  • Vacuum distillation
  • Purification degassing
  • Sterilization
  • Drying
  • Dehydration
  • Disinfection


The diffusion pump consists of a boiler heating oil and generating steam, an umbrella-shaped nozzle to jet the steam in a direction, and cold side walls to condense the steam. Despite such a simple structure, the pumping speed is quite high. This pump does not work alone, and it has to combine with oil rotary vacuum pumps.

Advantage Disadvantage
Simple structure and high pumping speed/ Presence of oil vapor flowing back from the nozzle to the high vacuum side.

How Diffusion Pump Works

The oil at the bottom of the pump is heated and turns into vapor. The vapor is ejected from the jet at supersonic speed, pushed out from the upper jet to the lower, and heading toward the exhaust port. The emitted oil vapor is cooled and condensed on the inner wall, turning into oil, and returns to the heating section.



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