Posted by IR Compressed Air on 5/14/2014
Rotary helical screw compressors utilize two intermeshing helical rotors in a twin-bore case. In a
single-stage design, the air inlet is usually located at the top of the cylinder near the drive shaft
end. The discharge port is located at the bottom of the opposite end of the cylinder. As the rotors
unmesh at the air inlet end of the cylinder, air is drawn into the cavity between the main rotor
lobes and the secondary rotor grooves. As rotation continues, the rotor tips pass the edges of the
inlet ports, trapping air in a cell formed by the rotor cavities and the cylinder wall. Compression
begins as further rotation causes the main rotor lobes to roll into the secondary rotor grooves,
reducing the volume and raising cell pressure. Oil is injected after cell closing to seal clearances
and removes heat of compression. Compression continues until the rotor tips pass the discharge
porting and release of the compressed air and oil mixture. (Cut away picture of a rotary machine)
