Important Screw Compressor Working Principle

The core working components of a screw compressor consist of a pair of intermeshing helical male and female rotors within the cylinder. Both rotors feature multiple concave tooth grooves and rotate at high speeds in opposite directions during operation. The clearance between the rotors and between the rotors and the inner wall of the housing is only 5 to 10 thousandths of an inch (0.05 to 0.10 millimeters), ensuring the sealing integrity of the gas compression process.

Regarding the drive system, the main rotor (also known as the male or convex rotor) is typically driven by an electric motor (though engine-driven configurations exist in some applications). Power transmission to the secondary rotor (also known as the female or concave rotor) is primarily achieved through two methods: flexible drive via an oil film formed by oil injection, or rigid transmission via synchronous gears at the ends of both rotors. Both drive methods ensure no direct metal-to-metal contact during rotor operation (in theory), effectively reducing wear and enhancing operational stability.

The compressor's discharge volume (flow rate) and discharge pressure are primarily determined by the rotor's structural parameters: longer rotors enhance pressure-building capacity during the compression stroke, resulting in higher discharge pressure; larger rotor diameters increase the gas volume per intake cycle, leading to greater discharge volume.

The operational cycle follows the “intake – compression – discharge” sequence, detailed as follows: When the screw rotor's tooth cavity rotates to the intake port position, its volume gradually expands. Ambient gas is drawn in by the pressure differential and fills the cavity. As the rotor continues rotating, the gas-filled tooth cavity is sealed by the casing wall, forming an independent compression chamber. At this point, lubricating oil is injected into the chamber under high pressure, simultaneously serving the three functions of sealing, cooling, and lubrication. The continuous rotation of the rotor causes the volume of the compression chamber to steadily decrease, gradually compressing the oil-gas mixture (a blend of lubricating oil and gas) within the chamber, resulting in a sustained increase in pressure. When the compression chamber rotates to align with the discharge port, the high-pressure oil-gas mixture is expelled from the compressor under pressure, completing a full working cycle.

The stable operation of the rotors is supported by a friction-reducing bearing system: The bearings are fixed and positioned via end caps near the shaft ends. The inlet end typically employs roller bearings, primarily bearing radial loads; The discharge end features a pair of opposing tapered roller bearings. These bearings serve a dual function: acting as thrust bearings to counteract the axial thrust generated by rotor operation while also bearing radial loads. Simultaneously, they provide the minimal axial clearance required for rotor movement, ensuring precise operation within specified limits.

Notably, as the rotor continuously rotates, each pair of meshing tooth slots sequentially repeats the “intake—compression—exhaust” process. The working cycles of multiple tooth slots interlock and alternate continuously, enabling the compressor to deliver a steady and stable gas output.