Within the compressor housing, a pair of interlocking helical rotors are arranged side by side. The rotor featuring protruding teeth outside the pitch circle is commonly referred to as the male rotor or male screw, while the one with concave teeth inside the pitch circle is known as the female rotor or female screw. Typically, the male rotor is connected to the prime mover, which drives the female rotor to rotate in tandem.
The final pair of bearings on the rotors is responsible for axial positioning and withstanding the axial forces within the compressor. Cylindrical roller bearings positioned at both ends of the rotors provide radial positioning and bear the radial forces encountered during operation. At each end of the compressor housing, there are orifices of specific shapes and sizes. One serves as the intake port, while the other functions as the exhaust port.
Intake
A closer look at the intake process of a screw air compressor reveals the following: As the rotors rotate, the space between the teeth of the male and female rotors reaches its maximum when they align with the opening at the intake end wall. At this precise moment, the tooth groove spaces of the rotors are connected to the intake port. Since the gas within the tooth grooves is fully expelled during the exhaust phase, the tooth grooves are in a vacuum state once exhaust is complete. Upon reaching the intake port during rotation, external gas is drawn in and enters the tooth grooves of both the male and female rotors in an axial direction. Once the gas completely fills the tooth grooves, the intake-side end face of the rotors rotates away from the intake port of the housing, effectively sealing the gas within the tooth grooves.
Compression
Delving into the compression process of a screw air compressor, we find that at the conclusion of the intake phase, the tips of the male and female rotor teeth form a seal with the housing. At this point, the gas trapped within the tooth grooves ceases to flow outward. As the meshing surface gradually progresses towards the exhaust end, the space between the meshing surface and the exhaust port within the tooth grooves progressively diminishes. Consequently, the gas within the tooth grooves is compressed, leading to an increase in pressure.
Exhaust
An in-depth examination of the exhaust process in a screw air compressor reveals the following sequence: When the meshing end face of the rotors rotates to establish a connection with the exhaust port of the housing, the compressed gas begins to be discharged. This discharge continues until the meshing surface between the tooth tips and tooth grooves reaches the exhaust end face. At this juncture, the space between the meshing surface of the male and female rotors and the tooth groove of the exhaust port in the housing is reduced to zero, thereby completing the exhaust process. Simultaneously, the length of the tooth groove between the meshing surface of the rotors and the air inlet of the housing reaches its maximum once again, signaling the commencement of a new intake cycle.
