Screw compressor: we understand what it consists of and how it works - Setafi

In this article, you will learn what a screw compressor is, what is the design of a screw compressor, how a screw compressor works, pluses of screw compressor models.

Screw compressor - what is it. Features and characteristics of rotary compressors

A screw compressor is a type of compressor, a device for compressing air and storing it for later use. In screw models, gas / air is compressed by two rotors. Rotors are also called screws, hence the name.

The first patented screw compressor was constructed in the 1930s. Screw compressors are second only to piston compressors in popularity. This is due to their efficiency, small size, low weight, reliability, autonomy, energy efficiency, ease of installation, low vibration. Due to the latter, screw models do not need a special foundation to work properly, so they are used by first responders, in shipbuilding / placement on ships.

In terms of characteristics, rotary devices are superior to analogues - the maximum air pressure is 15 atmospheres, the productivity reaches 100 cubic meters per minute.

Advantages of screw compressors

Advantages of rotary compressors over reciprocating ones:

1. Less oil consumption. Oil consumption in rotary compressors is from two to three milligrams per cubic meter of pumped air.
2. Cleaner air, no need for filters to power pneumatic equipment. This comes from less oil consumption.
3. Less vibration and noise than reciprocating compressors. No special foundation is needed to dampen vibrations.
4. Lighter than piston models.
5. There is air cooling. That is, water supply is not required to cool the compressed air, and the heat released during the operation of the compressor can be reused - for space heating.
6. More reliable and secure.
7. Ease of management, operation.
8. They can work for a long time without interruption.
9. They don't need maintenance for a long time.
10. There are systems of automatic operation and self-shutdown.

Screw compressor design

Elements of a classic rotary compressor:

• Primary Air Filters. When air enters the unit, it passes through one or more filters to get rid of dust and coarse dirt. The filters themselves consist of several layers. One is mounted on top of the housing on the air intake pipe, the second is installed on the pipe with a valve.
• check valve. Thanks to him, the oil from the working chamber and compressed air do not go back into the atmosphere - it blocks the exit. It works mechanically - it closes from air pressure, opens from low pressure in the chamber. Equipped with a spring.
• Working block - main chamber and two propellers / rotors. In this chamber, the rotors compress the air. The rotors themselves are two large threaded screws that, when rotated, hermetically close part of the space. The screws are the most expensive part of the compressor. There are several sensors in the chamber, one of them is for adjusting the temperature of the screws. It is located at the air outlet pipe / pipe. The compressor automatically shuts off at an outlet temperature of 105 degrees at the propellers. Otherwise, the equipment will become unusable due to overheating of the device.
• Drive unit. It can be direct (torque from the motor / engine is transmitted immediately to the screws) and belt (the belt is securely tensioned between the shafts of the screws and the engine; when the motor shaft rotates, the rotor shaft also rotates). Straight ones are more efficient, but they also take up more space, they are more difficult to repair, so belt-driven models are more common. The belt itself consists of two connected pulleys. Belt models with a high speed of rotation increase productivity and reduce pressure.
• Belt/Pulleys. The kit comes with several belts / pulleys of different sizes. Thanks to them, you can adjust the speed of rotation.
• Motor or Engine. A classic electric motor that drives propellers directly through a shaft or with a belt. To protect it, a thermal sensor is provided - when it warms up to the maximum allowable temperature (depends on specific engine model), the sensor sends a signal to the control panel, then the engine contacts open until it cool down. This solution extends the life of the engine and prevents accidents.
• Oil filter. It is needed to clean the oil from large contaminants before it enters the rotors. Stands in front of the oil supply pipe in the working chamber.
• Oil separation chamber. Air enters here after compression. After the compression process, it contains a lot of oil. In order not to contaminate the pneumatic equipment, you need to clean it. To do this, the air is swirled, and due to centrifugal force, different weights, and density, oil drops are separated from the air masses. They scoop into a container, from where the oil is fed back.
• Oil cleaning filter. This is the second stage of air purification from oil. After separating most of the oil from it, the air passes through this filter. At the outlet, the oil content in it does not exceed 1.4 milligrams per cubic meter of air. No other reciprocating compressor cleans the air this way.
• Safety valve. Often referred to as a safety valve. It is triggered when the pressure in the oil separation chamber exceeds the allowable level. This valve closes the air supply to the compartment, after which the compressor stops working.
• Thermostat. The device bypasses non-hot oil so that it cools faster.
• oil cooler. When air is compressed, it heats up. The temperature rises to 107-180 degrees Celsius. The oil comes into contact with air, so it also heats up. Hot oil enters the cooler, where it cools down.
• Air cooling chamber. Here the air is cooled. Above we mentioned that in the compressor compressed air is heated to a temperature of 107-180 degrees. It is not safe to use such hot compressed air, so the compressor is provided with an air cooler. Here the compressed gas is cooled to a temperature exceeding the ambient temperature by 10-20 degrees Celsius.
• Fan. The main task of the fan in the compressor is to take in air for compression. The device is set so that it additionally cools the equipment.
• Pressure switch. Automates the operation of the compressor - measures the pressure in the system when it reaches a certain level, opens the motor contacts, and the compressor stops. The latest models put electronic panels.
• pressure gauge. Measures the pressure in the compressor. It is mounted on the front panel so that the user can monitor the pressure.
• Air outlet tube.

How a screw compressor works

The principle of operation of a rotary compressor is as follows:

The electric motor rotates the screw shaft through the belt. Above the working chamber with rotors there is an opening or a tube with a fan for air intake. The screws themselves are designed in such a way that when you connect their sides, a sealed section is formed. Air enters this section. The screws portionwise move the air to the air outlet tube. The rotors are lubricated with oil to make it easier to turn, so that the outgoing air is mixed with the oil. The mixture enters the cleaning chamber through the outlet tube. There, the air is swirled, due to centrifugal force, different masses, density and density, the oil flows down, the air masses rise. There they pass through the oil filter, almost completely cleared of oil. When a gas is compressed, it heats up. The air in the compressor is heated to 107-180 degrees Celsius, so it needs to be cooled. After the cleaning chamber, it enters the radiator through the tube, where it is cooled. Compressed gas exits through the pipe. The oil comes into contact with air, so it also heats up. After the cleaning chamber, it also enters the radiator, where it is cooled. Further, the mixture flows back through the tubes to the rotors for reuse. On the way, it passes through an oil filter. For automatic shutdown, there is a pressure switch on the tubes, which turns off the motor when a certain indicator is reached.