Vacuum pump technologies are considered either wet (lubricated) or dry (oil free or dry running), depending on whether or not the gas is exposed to oil or water during the compression process.
Wet pumps lubricate and/or sealing themselves using either oil or water; this fluid can contaminate the pumped (swept) gas. Whereas, Dry vacuum pumps have no fluid in the pumped gas, relying on precise clearances between the rotating and static parts of the pump, dry polymer (PTFE) seals, or a diaphragm to separate the pumping mechanism from the gas and ensure a tight seal.
However, dry are not completely oil-free, as oil or grease is often used in the pump gears and bearings. This is kept separate from the vacuum compression side. Dry pumps reduce the risk of contamination and oil mist. They also have environmental benefits of not requiring the disposal of oils like lubricated pumps.
Centrifugal pumps
Centrifugal pumps are hydraulically operated machines characterised by their ability to transmit energy to fluids (in particular to liquids) through the work of a field of centrifugal forces. Their main purpose is to transfer fluids through an increase in pressure. Centrifugal pumps can have different structures, but their operating principle and fluid dynamic characteristics are always the same.
Liquid Ring Vacuum Pumps
Liquid ring vacuum pumps are similar to a rotary vane pump, with the difference being that the vanes are an integral part of the rotor and churn a rotating ring of liquid to form the compression-chamber seal. They are an inherently low-friction design, with the rotor being the only moving part. Sliding friction is limited to the shaft seals. Liquid-ring pumps are typically powered by an induction motor.
Liquid-ring systems can be either single or multistage.
Rotary Claw
Rotary Claw vacuum pumps generate contact-free vacuum efficiently and economically. This is possible because of the principle of internal compression in the rotary claw design. The claw vacuum pumps are based on a static compression system. In contrast to rotary lobes, compression happens internally by volume contraction.
A claw pump consists of two rotors. They turn in opposite directions in a compressor housing without contact observing very tight clearances. They are synchronised via a precision gear. As the claw moves over the suction connection and the axial suction channel inlet gas is sucked into the compression chamber. The gas is pre-compressed within the compressing chamber and is then discharged.
Rotary screw pumps
A screw vacuum pump consists of two parallel, screw-shaped rotors, one with a right-hand thread and the other with a left-hand thread. Both screws turn in the compressor housing without friction and at very tight clearances.
They are synchronized via a precision gear. The compression housing and the special shape of the screws form the compression chambers. Due to the opposite rotation of both screws the chamber connected with the suction port is enlarged and the gas is transported into the compression chamber. Then the chamber moves axially from the suction side to the pressure side (arrow).
In variable pitch models, the gas is compressed at each pitch change and cooled before the next pitch change, resulting in greater efficiency. On the pressure side the chamber is moved against the axial housing wall and the volume is reduced until the front surface of the screw opens the pressure channel and the pre-compressed gas is discharged through the pressure connection. Cooling is achieved using a water cooled outer chamber. For some pump sizes additional cooling gas can be introduced into the pump.
