Working Principle of Air Compressor

Working Principle of Screw Air Compressor and In-depth Analysis of Each System

一. Overall Work Logical Framework

Screw air compressors are positive displacement rotary compressors. Their core principle relies on the meshing of male and female rotors to achieve gas compression. They are equipped with four coordinated systems: the host/motor system for power supply, the cooling/separation system for maintaining operating temperature and medium cleanliness, the gas circuit regulation system for pressure and flow control, and the control circuit system for automated operation and safety protection. These four systems work together to complete the full process of "air filtration → compression → oil-gas separation → cooling → stable pressure output".

二,Main unit / motor system: Power core and compression execution

(1) Core Structure Composition

Host Assembly

Composed of an ∞-shaped casing, male and female rotors, suction/exhaust end caps, and bearings. The casing provides a sealed working chamber, with the end-face suction port precisely matched to the rotor rotation angle; the suction/exhaust end caps not only seal the body but also provide assembly and positioning for the rotors and bearings.

Rotor Group: The male rotor (convex teeth, driving) and female rotor (concave teeth, driven) adopt a single-sided asymmetric cycloid-arc profile, operating through two transmission methods:

① The male rotor is directly connected to the motor to drive the female rotor;

② Both rotors mesh with the motor's driving gear via driven gears.

Bearing System: Roller bearings on the motor end provide radial support, while tapered roller bearings on the other end counteract both axial thrust and radial force, ensuring stable high-speed rotation of the rotors.

Motor and Transmission

Adopts a rigid connection, transmitting motor torque to the rotors through gear transmission. Some models offer optional belt transmission to adapt to different speed requirements.

(二)Compression Three-Stage Process Mechanism

Suction Process: When the rotors rotate, the teeth of the male rotor disengage from the tooth grooves of the female rotor, expanding the inter-tooth volume and connecting it to the suction port. Air is drawn in until the volume reaches its maximum, then the volume is sealed. At this point, the inter-tooth volumes of the male and female rotors are not connected to each other.

Compression Process: As the rotors continue to rotate, the teeth of the female rotor intrude into the inter-tooth volume of the male rotor for preliminary compression. Subsequently, a "V"-shaped elementary volume is formed, which gradually shrinks as the teeth engage, achieving pressure increase.

Exhaust Process: The elementary volume shrinks until it connects to the exhaust port, and high-pressure gas is discharged until the volume reaches its minimum, completing the exhaust and forming a continuous cycle.

(三)Comparison of Lubrication Methods

三,Cooling / Separation System: Temperature Control and Medium Purification

(一)Air-cooled System

Structure: An aluminum plate-fin oil cooler (front cooler) and air cooler (aftercooler) are connected in parallel, with a separate fan motor driving the fan for forced heat exchange.

Intelligent Regulation: A temperature control valve enables adaptive oil temperature control-when the temperature is below 40℃, oil flows directly to the host; when above 55℃, all oil enters the cooler for temperature reduction.

Maintenance Points: Ambient temperature should be ≤40℃; regularly blow dust off the fin surfaces with compressed air to avoid reduced heat exchange efficiency.

Water-cooled System

Structure: A shell-and-tube cooler is divided into two circuits. Cooling water flows inside the copper tubes, while hot oil or hot air flows outside the tubes, and heat is removed through heat exchange.

Operating Parameters: Cooling water must meet the requirements of 0.2-0.5MPa water pressure and ≤32℃ inlet water temperature. Water softening devices and filters should be installed in areas with hard water.

(二)   Oil separation system operation process

Three-stage Separation Mechanism

Primary Separation: The oil-gas mixture enters the separation cylinder. Through impact, cyclonic separation, and reduced flow velocity, large oil droplets are separated and deposited at the bottom.

Precision Separation: The oil passes through an oil separation element made of multi-layer micron-grade glass fiber, reducing oil content to below 3ppm.

Oil Return Cycle: The separated lubricating oil is discharged to the low-pressure end of the host through the oil return pipe, re-participating in lubrication and cooling.

Core Component Functions

Oil Cut-off Solenoid Valve: Conducts the oil circuit to supply oil when the unit starts; cuts off the oil circuit when shutting down to prevent oil from overflowing from the suction port.

Check Valve: Prevents unit reverse rotation and lubricating oil backflow into the host when shutting down.

Oil Filter: Filtration precision ≤15μm, protecting bearings and rotors. A differential pressure indicator signals clogging. Replace for the first time after 150 hours, and subsequently every 2000 hours.

四,Gas path regulation system: Pressure stabilization and flow control

(1) Core Control Components

Two Types of Intake Valves

Butterfly Valve Type: When loading, the solenoid valve drives the servo cylinder to open the valve plate. During capacity regulation, the proportional-integral valve adjusts the control pressure to keep the valve plate half-open, balancing air supply and consumption.

Piston Valve Type: Controls the opening and closing of the valve port through piston movement, realizing no-load/full-load switching. It links with the blow-off valve to release pressure during unloading.

Key Pressure Control Valves

Minimum Pressure Valve: Set to open at 0.4-0.45MPa, ensuring stable pressure of the oil separation element, preventing backflow of pipeline network pressure, and providing power for lubricating oil circulation.

Proportional-Integral Valve: The higher the system pressure, the lower the output control pressure. It achieves stepless air volume regulation by adjusting the intake valve opening, with the set value lower than the unloading pressure.

Safety Valve: Automatically pops open to release pressure when the pressure exceeds the rated value by 10%. Calibrated before delivery; regularly manually pull to test effectiveness.

(二)Gas Path Complete Process

Air → Air Filter (dust removal) → Intake Valve → Host Compression → Oil-Gas Mixture → Separation Cylinder (primary separation) → Oil Separation Element (precision separation) → Minimum Pressure Valve → Aftercooler (70% water separation) → Outlet Valve → Air Supply Pipeline Network.

五,Control circuit system: Intelligent operation and safety protection

(1) Loading / Unloading Closed-loop Control

Core Logic: Based on signals from the pressure sensor, the controller compares the loading (lower limit) and unloading (upper limit) pressure thresholds to achieve automatic switching. For example, setting loading at 0.6MPa and unloading at 0.8MPa to maintain stable system pressure.

Working Process

Loading: Pressure below lower limit → Controller instructs loading solenoid valve to act → Intake valve fully opens → Air is compressed and output → Minimum pressure valve opens for air supply.

Unloading: Pressure above upper limit → Solenoid valve de-energizes → Intake valve closes → Blow-off valve opens to release pressure → Unit idles, and automatically shuts down after timeout (e.g., 10 minutes).

(二)Four-tier safety protection system

(三)Frequency conversion control upgrade (optional)

Inverter-equipped models adjust motor speed via an inverter, replacing traditional intake valve on-off control: when pressure approaches the upper limit, the speed decreases to reduce exhaust volume, avoiding frequent loading and unloading. Idle energy consumption drops to zero, and energy efficiency increases by more than 30%.

六,Key Maintenance and Operation Points

Regular Component Replacement: Replace the oil separation element every 2 years, coolant every 8000 hours or 2 years, and oil filter every 2000 hours after the first replacement at 150 hours.

Daily Inspection Items: Clean cooler fins, regularly inspect safety valves, calibrate pressure sensors, and monitor lubricating oil level and quality.

Fault Warning Focus: Pay attention to signals such as abnormal oil temperature (>95℃), excessive exhaust oil content (>3ppm), and large pressure fluctuations. Timely troubleshoot issues like solenoid valve jamming and separation element clogging.