Introduction

It has become an inevitable trend to replace piston air compressors— which have many vulnerable parts and poor reliability— with highly reliable screw air compressors. According to statistics, the market share of screw compressors in Japan was only 27% in 1976, and rose to 85% in 1985. In developed countries in the West, the market share of screw air compressors has reached 80% and continues to show an upward trend. Screw air compressors boast advantages such as simple structure, small size, no vulnerable parts, reliable operation, long service life, and easy maintenance.

Single-Screw Air Compressors

A single-screw air compressor, also known as a worm air compressor, has a meshing pair consisting of one 6-lobe screw and two 11-tooth star wheels. The worm meshes with the two star wheels simultaneously, which not only balances the force on the worm but also doubles the displacement. The air compressor is compact in size; for example, a worm air compressor with a displacement of 9 cubic meters per minute (9m³/min) weighs only 1/6 of that of a piston air compressor. The balanced force on the worm endows the worm air compressor with a series of advantages, as detailed below:

High Performance and Efficiency

• Air Compressor Equipment: Screw air compressors adopt high-capacity compression components. The outer circumferential speed of their rotors is low, and excellent oil injection is achieved, resulting in high efficiency and high reliability. By 2012, manufacturers’ designs had ensured extremely low system temperatures and compressed air temperatures, which guarantees better cooling effects and longer service life for all components.

Foldable Drive Concept

• Air Compressor Equipment: Screw air compressors drive the compression components at the optimal speed for their intended use through a high-efficiency transmission system. No maintenance is required at all during normal operation, featuring maintenance-free performance, high reliability, and high efficiency.

Built-in Intelligent Control

To reduce operating costs, precise operation control is essential. All screw compressors are equipped with intelligent control systems, and their control menus are simple and easy to use.

Working Processes of Screw Air Compressors

1. Intake Process

A detailed analysis of the intake process in screw air compressors: When the rotor rotates, the tooth groove space of the male and female rotors reaches its maximum volume when it aligns with the opening of the intake end wall. At this point, the tooth groove space of the rotor connects to the intake port. Since the gas in the tooth grooves is completely discharged during the exhaust process, the tooth grooves are in a vacuum state once exhaust is completed. When the tooth grooves rotate to align with the intake port, external gas is sucked in and enters the tooth grooves of the male and female rotors along the axial direction. When the tooth grooves are fully filled with gas, the intake-side end face of the rotor rotates away from the intake port of the machine housing, and the gas in the tooth grooves is then sealed.

2. Exhaust Process

A detailed analysis of the exhaust process in screw air compressors: When the meshing end face of the rotor rotates to connect with the exhaust port of the machine housing, the compressed gas begins to be discharged. This process continues until the meshing surface of the tooth tips and tooth grooves moves to the exhaust end face. At this point, the volume of the tooth groove space between the meshing surface of the male and female rotors and the exhaust port of the machine housing becomes zero, marking the completion of the exhaust process. Meanwhile, the length of the tooth groove between the meshing surface of the rotor and the intake port of the machine housing reaches its maximum again, and the intake process resumes.

Key Technical Parameters

1. Working Pressure

There are various ways to express pressure units; here, we mainly introduce the pressure units commonly used for screw air compressors:① Working pressure, often referred to as "exhaust pressure" by domestic users, refers to the maximum pressure of the gas discharged by the air compressor.② Common working pressure units are bar or MPa, with 1 bar = 0.1 MPa.③ Generally, users often refer to the pressure unit as "Kg (kilogram)". In fact, "Kg" is an abbreviation of "kgf/cm²" (kilogram-force per square centimeter), and approximately 1 bar = 1 kgf/cm².

2. Power

① Generally, the power of an air compressor refers to the rated power of the matched drive motor or diesel engine (as indicated on the nameplate).② The units of power are KW (kilowatt) or HP (horsepower), with 1 KW ≈ 1.333 HP.

Maintenance

1. Intake Air Filter Element

The air filter is a component that filters out dust and dirt from the air. The filtered clean air enters the compression chamber of the screw rotor for compression. Since the internal clearance of the screw machine only allows particles smaller than 15 μm to pass through, if the air filter element is blocked or damaged, a large number of particles larger than 15 μm will enter the internal circulation of the screw machine. This not only significantly shortens the service life of the oil filter element and oil-gas separation element but also causes a large number of particles to directly enter the bearing chamber— accelerating bearing wear, increasing rotor clearance, reducing compression efficiency, and even leading to dry seizure of the rotor.

2. Oil Filter

The oil filter element of a new machine should be replaced after the first 500 hours of operation. Use a special wrench to unscrew the oil filter element counterclockwise to remove it. Before installing the new filter element, it is recommended to apply screw oil to it; then, use both hands to screw the new filter element back into the oil filter seat and tighten it firmly. It is advisable to replace the filter element with a new one every 1500–2000 hours. When changing the oil, it is better to replace the oil filter element at the same time. In harsh environments, the replacement cycle should be shortened.Note: Using the oil filter element beyond its service life is strictly prohibited. Otherwise, severe blockage of the filter element will cause the pressure difference to exceed the tolerance limit of the bypass valve, triggering the automatic opening of the bypass valve. As a result, a large amount of dirt and particles will directly enter the screw main unit along with the oil, leading to serious consequences.For diesel-driven screw machines, the replacement of the diesel engine oil filter element and diesel filter element should be carried out in accordance with the diesel engine maintenance requirements, and the replacement method is similar to that of the screw machine oil filter element.

3. Oil-Gas Separator

The oil-gas separator is a component that separates the screw lubricating oil from the compressed air. Under normal operation, the service life of the oil-gas separator is approximately 3000 hours. However, the quality of the lubricating oil and the filtration accuracy of the air have a significant impact on its service life. It is therefore evident that in harsh operating environments, the maintenance and replacement cycle of the air filter element must be shortened, and consideration should even be given to installing a pre-air filter.The oil-gas separator must be replaced when it reaches the end of its service life or when the pressure difference between its inlet and outlet exceeds 0.12 MPa. Failure to do so will cause motor overload and damage to the oil-gas separator, resulting in oil leakage.Replacement Method:

1. Remove all control pipe joints installed on the cover of the oil-gas barrel.

2. Take out the oil return pipe that extends into the oil-gas barrel from the barrel cover, and remove the fastening bolts of the oil-gas barrel cover.

3. Remove the oil-gas barrel cover and take out the oil-gas separator. Clean off the asbestos gasket and dirt adhering to the upper cover plate.

4. Install the new oil-gas separator. Note that staples must be used to secure the upper and lower asbestos gaskets, and the gaskets must be arranged neatly when compressing— otherwise, gasket blowout may occur.

5. Reinstall the upper cover plate, oil return pipe, and all control pipes, and check for any leaks.

4. Oil Replacement

The quality of the screw oil has a decisive impact on the performance of the oil-injected screw machine. High-quality oil exhibits good oxidation stability, fast separation speed, excellent foam resistance, high viscosity, and strong corrosion resistance. Therefore, users must use genuine special screw oil provided by our company.The first oil change for a new machine should be performed after 500 hours of running-in, and subsequent oil changes should be carried out every 2000 hours of operation. When changing the oil, it is better to replace the oil filter element at the same time. In harsh environments, the oil replacement cycle should be shortened.Replacement Method:

1. Start the air compressor and run it for 5 minutes to raise the oil temperature to above 50°C, which reduces the viscosity of the oil.

2. Stop the machine. When the pressure inside the oil-gas barrel reaches 0.1 MPa, open the oil drain valve at the bottom of the barrel and connect it to an oil storage tank. Open the oil drain valve slowly to prevent the pressurized and heated lubricating oil from splashing and causing injury or contamination. Close the oil drain valve when the lubricating oil begins to drip.

3. Unscrew the oil filter element, drain all the lubricating oil from the pipelines, and install a new oil filter element.

4. Open the oil filler plug, inject new oil, and ensure the oil level falls within the scale range of the oil level gauge. Tighten the oil filler plug and check for any leaks.

During the use of the lubricating oil, regular inspections are necessary. If the oil level is too low, add new oil in a timely manner. Condensed water in the lubricating oil must also be drained regularly— generally once a week, or every 2–3 days in high-temperature weather. If the machine is shut down for more than 4 hours, open the oil drain valve to drain the condensed water when there is no pressure in the oil-gas barrel, and close the valve immediately when oil begins to flow out.Important Notes:

• Mixing lubricating oils of different brands is strictly prohibited.

• Using lubricating oil beyond its service life is strictly forbidden. Otherwise, the oil quality will deteriorate, lubricity will decrease, the flash point will lower, which may easily cause high-temperature shutdown and even spontaneous combustion of the oil.