Screw compressor: understand what it consists of and how it works

This article will provide you with information about the functionality and design of screw compressors. Additionally, it will delve into how these compressors work and examine the advantages that screw compressor models offer.

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

A screw compressor is a type of air compressor that compresses air and stores it for later use. In this type of compressor, air is compressed by two rotating screws. These screws are also known as rotors, which is why the compressor is named as such.

The first patent for a screw compressor was filed in the 1930s. Screw compressors are the second most popular type of compressor after piston compressors. This is because they are highly efficient, compact, lightweight, reliable, autonomous, energy-efficient, easy to install, and produce minimal vibrations. Due to their low vibration levels, screw compressors do not require a special foundation to operate smoothly, making them ideal for use by first responders and in shipbuilding.

When compared to other rotary devices, screw compressors have superior characteristics. They can achieve a maximum air pressure of 15 atmospheres and have a productivity rate of up to 100 cubic meters per minute.

Pros of screw compressors

Advantages of rotary compressors compared to piston compressors:

1. Reduced oil consumption: Rotary compressors only consume two to three milligrams of oil per cubic meter of pumped air.
2. Cleaner air: No filters are required to power pneumatic equipment due to the lower oil consumption.
3. Reduced vibration and noise: Rotary compressors produce less vibration and noise compared to reciprocating compressors, eliminating the need for a special foundation to dampen vibrations.
4. Lightweight design: Rotary compressors are lighter than piston models.
5. Air cooling: Rotary compressors feature air cooling, eliminating the need for a water supply to cool the compressed air. The heat generated during compressor operation can also be reused for space heating.
6. Increased reliability and safety.
7. Simple control and operation.
8. Continuous operation: Rotary compressors can work for extended periods without interruption.
9. Minimal maintenance requirements: Rotary compressors do not need frequent maintenance.

Screw compressor design

Essential components of a traditional rotary compressor:

• Primary air filters. When air is drawn into the unit, it passes through one or more filters to remove dust and larger particles. These filters consist of multiple layers, with one being located on top of the unit’s housing on the air intake tube, while the other is positioned on the valve tube.
• Check valve. The check valve plays a role in preventing the escape of oil from the working chamber and compressed air into the atmosphere. It operates mechanically, closing under air pressure and opening when the chamber reaches a low pressure level. The check valve is equipped with a spring mechanism.
• The main part of the working unit is the chamber, which includes two screws or rotors. Inside this chamber, the rotors are responsible for compressing the air. These rotors are like large screws with threads that, when rotated, help to seal off a specific section of the chamber. Interestingly, the screws happen to be the most costly component of the compressor. Within the chamber, there are multiple sensors, one of which is designed to regulate the temperature of the screws. This particular sensor is located at the air outlet pipe. If the screws reach a temperature of 105 degrees, the compressor will automatically shut down in order to prevent any damage caused by overheating. Failure to do so could result in the breakdown of the entire equipment.
• Belt/Pulleys. There are multiple belts and pulleys of various sizes included, which allow for adjustable rotation speed.
• Motor or engine. This is a traditional electric motor that directly powers the propellers through a shaft or belt. To safeguard the motor, a temperature sensor is incorporated. If the motor reaches its maximum permissible temperature (which varies depending on the specific model), the sensor sends a signal to the control panel, which then opens the motor contacts until it cools down. This feature helps prolong the motor’s lifespan and prevents accidents.
• Oil filter. The oil filter is essential for removing large contaminants from the oil before it enters the rotors. It is positioned in front of the oil supply connection in the working chamber.
• The oil separation chamber is responsible for removing oil from the compressed air. When the air is compressed, it becomes contaminated with oil. To prevent this oil from damaging pneumatic equipment, it must be removed. This is done by swirling the air in the chamber, which causes the oil droplets to separate from the air due to centrifugal force. The separated oil then flows into a container to be reused.
• The oil purification filter is the second stage of air purification in the compressor. After most of the oil has been removed in the separation chamber, the air passes through this filter. By the time it exits the filter, the oil content in the air is reduced to just 1.4 milligrams per cubic meter. This unique method of air cleaning is not found in any other reciprocating compressor.
• Safety Valve. Referred to as a safety valve, this component activates when the pressure in the oil separation chamber exceeds the acceptable limit. Its main function is to shut off the air supply to the compartment, thereby stopping the compressor from operating.
• Thermostat. Designed to expedite the cooling process, the thermostat is responsible for diverting non-heated oil to facilitate faster cooling.
• Oil cooler. As air is compressed, it generates heat, causing the temperature to rise significantly (107 to 180 degrees Celsius). The oil, being in direct contact with the air, also tends to heat up. To counter this, the hot oil is directed to the oil cooler, where it is effectively cooled down.
• An air cooling chamber is responsible for cooling the air. As mentioned earlier, the compressed air in the compressor is heated to a temperature of 107-180 degrees Celsius, which is not suitable for use. To rectify this, the compressor is equipped with an air cooler. In this chamber, the compressed gas is cooled to a temperature that is 10-20 degrees Celsius above the surrounding environment.
• The fan in the compressor plays a crucial role in both the intake of air for compression and the cooling of the equipment. Its positioning allows for additional cooling.
• A pressure switch automates the operation of the compressor by measuring the pressure in the system. Once it reaches a certain level, the contacts of the motor open and the compressor stops. Some of the latest models are equipped with electronic panels for this functionality.
• A pressure gauge is responsible for measuring the pressure in the compressor. It is mounted on the front panel, allowing the user to monitor the pressure easily.

How a rotary screw compressor functions

The operational principle of a rotary screw compressor is as follows:

An electric motor utilizes a belt to rotate the shaft of the screws. Above the working chamber where the rotors are located, there is an opening or tube with a fan to intake air. The design of the screws enables the formation of a sealed section when their sides are connected. This section forces air into it. The screws divide the air into the air exhaust tube. To facilitate the rotation of the rotors, they are lubricated, causing the discharged air to mix with oil. The mixture enters the cleaning chamber through the diverter tube. Inside, the air is swirled due to centrifugal force, different mass, density, and density. The oil flows downwards while the air masses rise. They then pass through an oil filter, effectively removing most of the oil. As the gas is compressed, it becomes heated. The air in the compressor reaches temperatures of 107-180 degrees Celsius, necessitating cooling. After the purification chamber, the air is directed through a tube to the radiator for cooling. The compressed gas exits through a nozzle. Since the oil comes into contact with the air, it also becomes heated. After the cleaning chamber, it enters the radiator for cooling. The mixture is subsequently piped back to the rotors for reuse, passing through an oil filter along the way. To enable automatic shutdown, there is a pressure switch on the tubes that stops the motor when a specific value is reached.