Vacuum pumps are compressors that generate spaces without air, liquid, and gas molecules. Whether for hardening materials, microchip production or in particle accelerators: Countless processes in science, research, and production would be inconceivable without a vacuum. Vacuum pumps ensure degassing. But how is a vacuum generated?
Vacuum: definition and importance
In everyday usage, “vacuum” refers to a space without air; that is, a space where there are no particles. The term comes from the Latin adjective vacuus for “empty.” And actually a complete vacuum cannot be generated technically nor is there any such according to human knowledge: Even outer space is a slightly but partially filled space.
According to the DIN standard DIN 28400-1, we speak of a vacuum as soon as a pressure of less than 300 mbar is reached. Technically, gas states at a pressure much lower than atmospheric pressure are referred to as vacuums. Here, there is a distinction of various degrees depending on the residual pressure:
• Rough vacuum (300 to 1 hPa)
• Fine vacuum (1 to 10-3 hPa)
• High vacuum (10-3 to 10-7 hPa), and
• Ultra-high vacuum (10-7 to 10-12 hPa)
The range of the different degrees of a vacuum is very wide. While “vacuum-packed” food doesn’t even reach the residual pressure of the rough vacuum, pressures that are otherwise only found in outer space are achieved by, for example, the ultra-high vacuums generated in particle accelerators.
Vacuum pumps: Operating principle is the same for all pump types
There are many different types of vacuum pumps, depending on the application and task. However, there are only two basic principles involved, and therefore vacuum pumps are divided into
• gas transfer vacuum pumps
• and gas-binding vacuum pumps.
The designs are thus distinguished in principle from actual pumps that serve to handle fluids. From a technical perspective, therefore, vacuum pumps are not pumps, but compressors.
Gas transfer vacuum pumps convey gases through impulses that are transferred to the particles or in a closed working space.
Gas-binding vacuum pumps, by contrast, convey gas molecules in a closed chamber.
Both designs are aimed at removing as many particles as possible from a chamber. The result is an extreme negative pressure.
Positive displacement pumps generate a vacuum in a closed working space whose size changes in the course of the working process: Low pressure arises during the intake and transporting of gases, high pressure during the expelling and pressure change. The gas enters the working space, which is then sealed off. In the process, it is compressed and then expelled again. The variants of positive displacement pumps for vacuum generation include the rotary piston pump and the rotary vane pump. The principle of the diaphragm pump is also used to generate a vacuum.
Molecular pumps consist of a quickly rotating rotor disk in a round housing, a suction nozzle as inlet, and a pre-vacuum nozzle as outlet. If particles are taken in, they are adsorbed and desorbed on the rotor and escape through the pre-vacuum nozzle. Turbomolecular pumps (also called turbopumps for short) have rotors and stators arranged in alternation. The rotors achieve speeds of up to 90,000 revolutions per minute so that a very high pump capacity can be achieved.
Cryopumps contain a sharply cooled surface for gas condensation and are therefore also called condensation pumps. Helium is often used for cooling; hydrogen or nitrogen are used for some models.
Sorption pumps use active carbon or so-called zeoliths so that the gas to be evacuated evaporates on the inside surface of the pump.
Jet pumps, by contrast, expel gas with a nozzle. The impulse is transferred to particles so that they are transported.
Liquid ring pumps are a special type: This design also works according to the principle of the condenser. The name comes from the fact that liquid ring pumps not only serve to generate a vacuum but convey gases into a vacuum.
From rough vacuum to high vacuum and ultra-high vacuum, vacuum pumps are used for a wide variety of applications in production and research. The areas of application range from science to pharmaceutical and medical technology, and general process engineering to the manufacturing of photovoltaic modules and microchips.
Many products whose use has become a matter of course could not be manufactured without compression in a vacuum; examples are computers and smartphones. However vacuum technology is important even in everyday life: for example for refrigeration and air conditioning technology.
Usually for these applications, the point is to generate a space that is as clean as possible in which small particles do not disturb production quality. Even the least contamination in semiconductor production can make the product unusable since microchips have extremely small structures. In the test space of an electron microscope, gas molecules would influence the sample examined.
While a simple vacuum pump is sufficient to generate a rough vacuum, it is necessary to switch several pumps in a row for more extreme negative pressures. The first pump in the row – frequently a rotary vane pump is used for this – generates a so-called pre-vacuum, so that the following pump – usually a turbomolecular pump – must convey fewer gas molecules from the space.
Whether in everyday life or scientific research: Vacuum pumps are indispensable in many areas. By generating a space without air where there are as few disturbing gas molecules as possible, they make processes safer, more reliable, and efficient.
Since these machines are not pumps in the usual sense, there are specialized manufacturers of vacuum pumps on the market.