Fore-vacuum pumps

Fore vacuum pumps always work against atmospheric pressure or a similarly high pressure into an exhaust pipe. They are used in almost every vacuum system and are a prerequisite for achieving low pressures by the use of high-vacuum pumps. Depending on the operating principle and design pumping speed and ultimate pressure vary significantly. Individual backing pumps can achieve ultimate pressures of down to 1 × 10-3.

A general distinction is made between dry-running and oil-sealed pumps. I.e., the pump's suction chamber is sealed either by minimal gaps or by oil or another liquid. While dry-running backing pumps have the advantage of generating a hydrocarbon-free vacuum oil-sealed pumps are often more robust and able to pump different kinds of gas almost equally well. Leybold offers a variety of different fore vacuum pumps. Dry-running pumps include screw pumps, multi-stage roots pumps, diaphragm pumps and scroll pumps. As oil-sealed backing pumps Leybold primarily offers single-stage and two-stage rotary vane pumps.

Screw vacuum pumps

Dry-running screw vacuum pumps are twin-shaft rotary displacement pumps. The intermeshing screw rotors are sealed against each other as well as against the pump casing by very narrow gaps. Therefore, there will be no oil in the pump's suction chamber which could enter the recipient and interfere with the process. As a regular oil change is not necessary any more, the maintenance effort will be also reduced. Screw vacuum pumps from Leybold operate with internal compression, which enables quiet and energy-efficient operation. They are available in different sizes, are robust and are used in a variety of applications.

Screw vacuum pumps

  • For pumping speeds up to approx. 700m³/h
  • Dry running / gap sealed
  • Very clean, hydrocarbon-free vacuum
  • Attainable ultimate pressure level about 1 × 10-3 mbar
  • Pumping speed depends on type of gas
Dry screw vacuum pumps

Multi-stage Roots pumps

Roots pumps are rotary displacement pumps without internal compression. The basic principle of multi-stage Roots pumps is not different from that of single-stage Roots pumps. The high compression ratio of multi-stage Roots pumps is achieved by connecting several Roots stages in series. This enables the pumps to operate directly against atmospheric pressure and to work as backing pumps within a wide range of applications. Just like dry-running screw vacuum pumps, multi-stage Roots pumps are gap-sealed and do not require oil as a sealant in the pump's suction chamber. They are therefore ideally suited for clean processes and environments and have low operating costs due to long service intervals. Multi-stage Roots pumps of the ECODRY series are exceptionally quiet running, air-cooled, easy to handle and thus are also ideal for lab applications.

Multi-stage Rootspumpen

Multi-stage Roots pumps

  • Dry running / gap sealed
  • Very clean, hydrocarbon-free vacuum
  • Quiet and low-vibration
  • Maintenance-friendly
  • Low running costs
  • Susceptible to dusts and particles

Scroll pumps

Scroll pumps are dry-running displacement pumps where two or more Archimedean spirals are nested in each other and compress the gas by a counter-rotating movement. One of the spirals moves eccentrically on a circular path, while the other spiral stands still. As the spirals rotate the chambers formed by the spiral segments becoming smaller and smaller and "move" towards the center. This takes place without the spirals touching each other. Therefore, Scroll pumps are dry compressing and do not require any oil in the pump's suction chamber. For the axial sealing of the spirals, however, mechanical seals (so-called tip seals) are used. These are wear parts to be replaced regularly. The latest generation of the SCROLLVAC series offers a considerably extended service life between the replacement of the tip seals.

With scroll pumps, high pumping speeds and low ultimate pressures can be achieved in a small space. Compared to the multi-stage roots technology, scroll pumps have the advantage of providing a high pumping speed even at high suction pressures. Therefore, they are better suited for rapid pumping even at atmospheric pressure. Like multi-stage roots pumps, scroll pumps are low in vibration and noise, energy efficient and well suited for environments with special requirements for cleanliness and low emissions.

Scroll pumps

  • Dry running / gap sealed
  • Very clean, hydrocarbon-free vacuum
  • Quiet and low-vibration
  • Low running costs
Scroll pumps

Diaphragm pumps

Diaphragm pumps are intermittently working dry displacement pumps where the pump's suction chamber is separated from the drive part by a diaphragm. This means they are leakage-free, generate a hydrocarbon-free vacuum and are insensitive to mechanical and chemical influences emanating from the medium to be pumped.

Due to their design single stage pumps do not achieve large compression ratios. Thus, usually two, three and even four-stage versions are found in real life. With their environmentally friendly design and low running costs, they are particularly suitable as backing pumps for turbo molecular pumps and as corrosion-resistant backing pumps in the laboratory.

Membran vacuum pumps

Diaphragm pumps

  • Dry running / gap sealed
  • Very clean, hydrocarbon-free vacuum
  • Low running costs
  • Rather small pumping speeds up to approx. 100 m³/h

Rotary vane pumps

Rotary vane pumps are by far the most common type of displacement pumps. Due to their technically mature design they offer excellent reliability and robustness in a wide range of applications. Further advantages are their compactness and low acquisition costs. They can be used as backing pumps for virtually any type of high and fine vacuum pump.

The pump's suction chamber is defined by movable vanes mounted in the rotor and sealed by an oil film. The oil also lubricates the moving parts, carries the internal cooling and serves to collect dirt and condensate. This requires a regular oil change. The operating behavior of the pumps can be favorably influenced with additional equipment. For example, the gas ballast option is used to prevent the condensation of corresponding gases within the pump or to reduce noise during ultimate pressure operation. A wide variety of oil, dust and condensate filters can reduce the load on the pump or also reduce the contamination of the exhaust air by corresponding substances.

Rotary vane pumps

  • Large range of pumping speeds up to approx. 650 m³/h
  • Low ultimate pressure levels achievable
  • Pumping speed almost independent of gas type
  • Pumping speed nearly constant over the entire working pressure range
  • Vacuum not hydrocarbon-free
  • Oil change on a regular basis necessary
Rotary vane vacuum pumps

Videos

Leybold ECODRY Plus - Multi-stage Roots vacuum pump
Leybold SOGEVAC - Oil sealed vacuum Pump
Leybold SCROLLVAC plus - Function principle
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