In S-Series screw vacuum pumps compression is achieved by internal volume contraction.
A screw vacuum pump consists of two screws, one with a right-hand thread and the other with a left-hand thread. Both screws turn in the compression housing without friction with very tight clearances. They are synchronised 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). During this transportation the mass of the gas in the chamber increases.
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.