What is an oil-injected screw air compressor? Its operating principle, advantages, applications, and maintenance.

What is an oil-injected screw air compressor?

An oil-injected screw air compressor is a positive-displacement rotary compressor that operates by rotating two intermeshing helical rotors within the compressor housing, thereby reducing the gas volume and increasing the gas pressure. During compression, lubricating oil is directly injected into the compression chamber, serving to cool, seal, lubricate, and reduce noise.

Working principle

The operating cycle of an oil-injected screw air compressor is primarily divided into three stages: intake, compression, and exhaust.

• Inhalation process: As the rotor rotates, the tooth-slot spaces communicate with the intake port, and external gas is drawn into the tooth slots.
• Compression processAs the rotor continues to rotate, the tooth‑groove volume gradually decreases, causing the injected lubricating oil to mix with the gas and be compressed. During this process, the oil absorbs substantial compression heat, effectively controlling the discharge temperature.
• Exhaust processWhen the crankcase volume reaches its minimum and connects with the exhaust port, the high-pressure oil–gas mixture is discharged from the compressor and then enters the oil–gas separator for oil–gas separation.

Core Advantages

• Operates smoothly and reliably: There is no direct contact between the rotors or between the rotor and the housing, resulting in minimal wear, smooth operation, and a long service life.
• Good cooling performance: The injected lubricating oil directly absorbs the compression heat, enabling a higher single-stage compression ratio and lower discharge temperatures.
• Low noise and vibrationThe damping effect of the lubricant, combined with the precision-designed rotor profile, significantly reduces operating noise and vibration.
• Low maintenance costs: The structure is relatively simple, with a small number of components; routine maintenance primarily involves replacing the filter element and lubricating oil.

Main application areas

Oil-injected screw air compressors, owing to their high efficiency and stable performance, are widely used across various industrial sectors.

• Mechanical manufacturing: Provides a power source for pneumatic tools, pneumatic fixtures, paint-spraying equipment, and more.
• Textile industry: Used for air-jet spinning, pneumatic control of looms, and material conveying.
• Chemical Engineering and Pharmaceuticals: Provides process gases and participates in material mixing, fermentation, and packaging processes (must be used in conjunction with downstream processing equipment to meet gas purity requirements).
• Mining and Construction: Operates rock‑drilling equipment such as pneumatic drills and jackhammers, as well as sandblasting and cleaning operations.

Key Points for Daily Maintenance

Proper maintenance is key to ensuring efficient equipment operation and extending its service life.

• Regularly replace consumables.: Replace the air filter element, oil filter element, oil–gas separator filter element, and dedicated lubricating oil strictly according to the prescribed service intervals to prevent contaminants from entering the compression chamber.
• Monitor operating parametersDuring routine inspections, carefully monitor the discharge pressure, discharge temperature, and motor current; if any abnormalities are detected, immediately shut down the equipment and perform a thorough troubleshooting.
• Keep the environment clean.Ensure that the air compressor room is well-ventilated and maintains an appropriate ambient temperature, and regularly clean dust from the radiator surfaces to prevent equipment shutdowns due to overheating.
• Inspect the piping system: Regularly inspect all connecting pipelines, valves, and fittings to prevent air or oil leaks and ensure stable system pressure.