A screw compressor is one where rotary helical screws are used to compress the air. These compressors are a replacement for the piston type compressors where vibrations and surges are more due to reciprocating action.
The air is sucked from the suction port and is made to pass through the threads of the screws and is pushed towards the compressor.
This type of compressors are used where high quantity of air is needed and using high power tools such as jack hammer.