Vacuum pumps

1. Rotary vane pumps

The rotary vane pump consists of a housing in which a rotor rotates eccentrically. In this housing, vanes are loaded by springs, which are pressed against, and slide along, the inner wall of the housing. The gas trapped on the suction side is compressed until it exceeds the ambient pressure and then the exhaust valve opens to the high-pressure side.

The pump runs in an oil bath. This has the following advantages:

• Sealing of the suction and high-pressure sides
• Reduction of friction

Rotary vane pumps are used in particular for our standard systems. The larger the pump, the shorter the process time.

If it is to be used with oxygen, the pumps must be prepared for this. Oil mistis formed in the pump housing. When using mineral oil, mist combined with pure oxygen is explosive.

There are two ways to solve this problem:

1. The pumps are filled with PFPE oil. This oil is incombustible. But it has some serious drawbacks:

• PFPE oil is extremely expensive
• PFPE oil contains fluorine. In plasma processes, this oil can decompose and extremely toxic compounds can arise(e.g. perfluoroisobutene). Dangerous accidents have already occurred due to this oil compound.
• PFPE oil must be disposed of as hazardous waste.

3. Roots vacuum pumps (Roots pumps)

The pressure which can be generated with a rotary vane pump is limited. To reinforce the suction we recommend combination with a roots vacuum pump. These form a so-called pump stand. A typical combination is made up as follows:

1. The first pump (e.g. a rotary vane pump) produces an initial vacuum. It is referred to as a "fore-pump".

2. A roots vacuum pump is used as a second pump.