Types of high vacuum pumps

High vacuum pumps operate in low pressure ranges, usually below 1 × 10-3 mbar. Depending on the operating conditions (quality of seals and surfaces, baking, materials used), pressures below 1 × 10-9 mbar are typically achievable.

Despite their high compression capability most high vacuum pumps cannot compress to atmospheric pressure. Depending on their design and the application conditions they need a single or multi-stage backing system. The definition of the preferred pump type itself depends in turn on the respective requirements for the pressure level, the quality of the vacuum and the additional boundary conditions given by the respective application. Leybold offers the right high vacuum pumps for a variety of applications. The product portfolio includes turbomolecular pumps, cryogenic pumps and diffusion pumps.

Turbomolecular pump

Turbomolecular pumps are mechanical high-vacuum pumps that work according to the principle of the molecular pump invented by Wolfgang Gaede in 1913. The principle of the pumps is based on the transmission of momentum from the rapidly moving surfaces of a rotor to the individual gas particles to be pumped. In the classical version, the turbomolecular pump consists of several pairs of rotor/stator blades. In comparison to those classic turbomolecular pumps the so-called compound or wide range pumps can be operated at higher backing pressures. Which means, smaller fore vacuum pumps can be used then. In addition to the classic turbo part, these pumps have one or more downstream friction stages. Basically, it can be said that compound or wide range pumps are used if high compression is required and classic turbomolecular pumps will be preferred if high pumping speeds are decisive.

Another important distinguishing feature of turbomolecular pumps is the bearing of the rotor. A basic distinction is made between magnetically levitated and mechanically supported pumps. Pumps equipped with active magnetic bearings are particularly low in vibration and wear-free. On the other hand, they can interfere with sensitive instruments. Another advantage is the generation of a hydrocarbon-free vacuum. Mechanically supported turbomolecular pumps are characterised by their great robustness against mechanical, radiation and magnetic field influences. Bearings of Leybold’s mechanical pumps are grease-lubricated. This makes the pumps easy to maintain and, unlike oil-lubricated pumps from other manufacturers, they can be used in any installation position. Leybold turbomolecular pumps are very flexible and can be used in a variety of applications.

Turbomolecular pump

  • Achievable pumping speed: 20 up to 4000 l/s
  • Clean vacuum
  • Small installation space
  • Different mounting positions applicable
  • Low energy consumption
Turbo molecular pumps

Cryo pumps

Cryogenic vacuum pumps are gas-binding pumps that bind gaseous substances to the cold surfaces inside the pump, e.g. by cryo condensation. The inner surfaces of the cryo pump are cooled down to a few Kelvin and thus are able to bind the molecules of various gases. These extremely low temperatures make cryo pumps especially suitable for pumping light gases. Due to their design and the large flange diameters extremely high pumping speeds can be achieved. The use of cryo pumps is the only way to evacuate large-volume vacuum chambers in a realistic time frame under clean conditions to very low pressure levels.

A major disadvantage of cryogenic pumps is that the pumped gases are not transported away, but remain bound in the pump until it is "regenerated". In order to maximize the time until the next regeneration, cryo pumps should only be switched on at very low pressures, as the gas load is too high at higher pressures. During regeneration itself, the pump is cut off from the actual vacuum system and heated to ambient temperature or higher. This desorbs the previously pumped amount of gas which leaves the pump through a pressure relief valve. Subsequently, the cryo pump is again evacuated by a separate backing pump. The temperature can be increased by heating the pump housing and/or by flushing with heated purge gas. After pumping flammable or dangerous gases and large quantities of water it is advisable to purge with nitrogen.

Cryo pumps

Cryo pumps

  • Very high pumping speeds attainable (up to ~60.000 l/s)
  • Extremely low pressure level attainable
  • Particularly suitable for light gases
  • Very clean vacuum
  • Suitable for relatively small gas flows only
  • Store the pumped gas and must be regenerated
  • Low cut-in pressures. Usually, additional high vacuum pumps are required to pre-evacuate the vacuum system, e.g. turbomolecular pumps

Diffusion pumps

Diffusion pumps are high vacuum pumps that work on the principle of a jet pump. In oil diffusion pumps, the pumping effect is produced by diffusing the gas to be pumped into an oil vapor jet. The great advantage of diffusion pumps lies in their simple design without moving parts. This makes these pumps very reliable, easy to maintain and cost-effective. Depending on the size, they can provide very high pumping speeds at pressures below 1 × 10-3 mbar. Due to the working principle the pumping speed at lower pressures is almost constant. At the same time, diffusion pumps have good fore vacuum persistence, so that relatively small fore vacuum pumps can be used. Special vapor barriers and baffles are used to prevent oil from flowing back into the recipient. A disadvantage is the high energy requirement resulting from the heating of the blowing agent. However, the DIJ series from Leybold achieves a significant reduction in heating power consumption by its innovative control. This minimizes the power demand compared to conventional diffusion pumps.

Diffusion pumps

  • Very high pumping speeds attainable (up to ~60.000 l/s)
  • Particularly suitable for light gases
  • No moving parts: robust, reliable, easy to maintain
  • Can be operated in vertical mounting position only
  • Additionally installed parts for holding back the working fluid
  • High energy consumption due to heating of the working fluid
  • Long preheating and cooling times needed
Diffusion pumps

Videos

Leybold TURBOVAC i - Turbomolecular vacuum pumps
Leybold COOLVAC iCL - Cryogenic technology
Leybold DIP Oil diffusion pumps - Function principles
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