Why you need a Rotary Screw Air Compressor?

We have a complete range of oil-lubricated and oil-free industrial screw compressors suitable for any industry and application.

You could be someone who owns a piston compressor but you’re looking for other options because your requirements have changed.

Whatever the case may be, when picking an air compressor you consider things like the pressure and volume requirements of your tools, the frequency of use, space constraints and the mobility of your operation.

If you’re running heavy-duty applications that continue over long periods of time, like in a factory, industrial plant or workshop, then you should consider upgrading to a rotary screw air compressor.

Here’s why:

• They are designed to work 24/7
• They can operate at higher flow capacities while dissipating the heat generated
• They are relatively less noisy than piston compressors
• They receive less wear and tear
• They tend to require less space
• They outperform piston compressors in terms of efficiency at about 15 kW (20 hp)
• They discharge less oil and contaminants with the compressed air

Rotary screw air compressors use the principle of positive displacement.

Positive-displacement happens when a constant flow of air is forced into a chamber as the volume of the chamber is decreased. This causes the air to get compressed and increases the air pressure within the chamber. When maximum pressure is reached a valve or port opens and the air is discharged into an outlet system for productive use. Just imagine a bicycle tire pump. It uses positive displacement and a piston to compress air within a chamber.

Now in a rotary screw compressor the words ‘rotary screw’ refer to two helical screws that are meshed closely together and fitted inside the chamber. The idea is that once air is pushed into the chamber it then gets trapped between the two rotating helical screws, resulting in decreased volume and increased pressure. As the helical screws rotate in sync with each other the air is compressed and pushed along the grooves until it is discharged from the other end.

Have a look at how it works in this video.

The air compression process generates heat so injecting some oil into the chamber helps to dissipate that heat by cooling the rotary screw element. The oil also acts as a lubricant and sealant for the compressor.

You can learn about this more by reading the PDFs for the Atlas Copco GA (VSD+) Oil-Injected Screw Compressor.

When comparing oil injected and oil free rotary screw compressors it’s not necessarily true that one is better than the other. The type of compressor you choose depends on the application you need it for and the quality of the air you require from the outlet system. Oil free rotary screw compressors are a better option when air purity matters to you. The oil could contaminate the end product. This is usually a concern for anyone using air compression during food preparation, pharmaceutical synthesis, agricultural processing etc.

The oil free rotary screw compressor operates on the same working principle of positive displacement. The difference is that you get ‘wet type’ and ‘dry type’ variants.

A ‘wet type’ of oil free rotary screw compressor is where water is injected instead of oil to dissipate heat and act as a sealant inside the chamber.

A ‘dry type’ of oil free rotary screw compressor is where oil never enters the chamber. Instead oil is only used outside of the chamber where it lubricates the parts of screw compressor like bearings and timing gears.

You can learn more by reading the PDFs for Atlas Copco ZR & ZT (VSD) Dry Type Screw Compressor  and the AQ Wet Type Screw Compressor.

As a buyer, being aware of the essential parts for a properly functioning rotary screw air compressor is important.

Here’s a quick list that you can refer to:

1. Rotary screw element

Drives the air to the outlet and creates the pressure.

2. Compression chamber

Encloses the rotary screw element. It’s possible to have multiple stages for more pressurization.

3. Inlet suction air filter

Set at the inlet of the compression chamber where it’s possible to catch and reduce dust, and ingress of damaging particles. Necessary for cleaning and protection of the compressor stage/s.

4. Oil filter

Oil Filters are set within the oil system to gradually remove contamination in the oil that is used for lubrication or compression.

5. Anti-friction roller and ball Bearings

These secure the rotary screws, making sure they are balanced and rotate evenly.

6. Suction valve or load / unload valve

This is usually set at the top of the compressing unit. Responsible for drawing the raw air inward to be processed by the rotary screw element. Opens fully when system pressure drops below the minimum set limit also called as loading and closes the valves called as unloading when the system pressure reaches the maximum set limit.

7. Discharge valve

This is usually set at the end of the compression process. It only opens once the correct minimum pressure is achieved and ensures enough pressure is maintained within the system to ensure good lubrication of the compression stages.

8. Compressor motor

This drives the rotary screws and powers the unit’s compression cycle. It is controlled by the compressor microprocessor controller.

9. System control

This takes the form of a display and input panel. Necessary for operating, automating and monitoring the compressor unit.

10. Separator vessel

This is a tank where compressed air is sent for separation of oil from compressed air, it has dual use, it's a reservoir for oil at the same time holds air pressure with the aid of the min pressure valve to ensure lubrication pressure is maintained within the system.

11. Separators

Specifically for oil-injected compressors, its embedded inside the separator vessel and filters the excess oil to ensure that the compressed air leaves the system with minimum residual oil content.

12. Gaskets and seals

Necessary to maintain maximum pressure and make sure the overall compressor is leak-free at critical points in the unit.

13. Non return valve / check valve

This valve ensures that when the compressor unloads or stops generating air, it retains the pressure in the downstream system.

14. After cooler

This cools down the compressed air and removes the heat generated by the compression process. The coolers can be either cooled by ambient air or with water in water cooled compressors. Selection of either air cooling or water cooling is made based on individual customer requirements and location of the installation.

15. Water separator

One of the critical screw air compressor components, the water separator  is installed downstream of the after cooler and separates liquid moisture from compressed air and ensures air leaving the compressor is saturated by free of any liquid water.

Understanding the function of rotary screw air compressor parts will help you optimize the performance of your equipment by replacing and maintaining them as and when needed. 

1. Rotary screw element

Interlocking twin rotors are placed inside lined cylinders wherein their complementary and circulatory rotations occur. As soon as the machine is switched on, rotors will operate, receiving suctioned air from the opening valve. Connected to the compressor’s motors, rotors will start spinning through a wide distribution system of belts, bearings, and the motor drive. Air is sucked and compressed between the rotors while the spinning continues. 

The air will be transformed to a fully compressed state once the grooves will reach the finishing of the rotation length. Lastly, the compressed air will be released through the discharge valve into the storage tank. 

2. Inlet air filter

These are required for regulatory maintenance and an important component of a compressor. When it comes to oil-injected units, the air filters clean up moisture and oil residue from the opening valve and cooling injection processes. Regular inspection of air filters is crucial for your equipment’s performance. 

Air filters are located near the intake valves for the oil-free units. They form the primary defense line from pressurized air impurities and are thus the most common maintenance filters. 

3. Oil filter

Oil filters help keep the compressed air’s gas purity clean and intact and ensure proper lubrication and cooling functions of the entire machine. Belt and pulley run in sync with those nestling within the oil separator. Also, since contemporary oil filters have a spin on installation, they are easy to assess and replace. 

Most oil filters are equipped with bypass valves that send alerts when oil filters are too jammed or internal operating temperatures are hot. They will allow raw oil to infiltrate the compression chamber but without entering the oil filters.

4. Bearing

Bearings help in reducing friction, balancing part movements, regulating the overall compressor’s temperature. Although there are several bearing nested in crucial places, axial and radial-load bearings are the most important among all. Radial-load bearings help ensure the compressor’s smooth rotations and horizontal circular roller motions without creating noises. Axial bearings keep the complementary and perpendicular spinning of the rollers in load and balanced. 

5. Suction valve 

Suction valves get triggered by your machine’s programmed stage settings to close and open, which ensures the efficiency of the rotary screw units. As they are engineered to suit different design elements for maximizing airflow, suction valves are available in different configurations. The poppet valve, the ring valve, and the plate valve are the three types of suction valves. Each of them has its distinct concentric layers to ensure ideal air flows for specific operation types. 

6. Discharge valve

Being the endpoint of your compressor system, the discharge valves offer a safe and steady release of pure and fresh concentrated air. Whether the air is released into the final storage tank or connected to the air hoses, the discharge valve serves as the critical regulatory agent. Inspecting these valves and their performance is important to avoid any kind of malfunctioning. 

7. Compressor motor

It is important to remember that the bigger the motor the better the performance does not always hold true for ensuring optimal productivity. The horsepower generated and maintained by massive motors may court efficiency problems. 

You would want to test your motors frequently and check if it’s being productive, thereby gauging the overall performance of your compressor. 

8. System control

A compressor’s system and stage control can regulate, monitor, and track the machine’s performance by assessing functionality and checkpoints throughout multiple unit features. 

Particular unit designs may have internal sensors for automatically powering off the motor upon the completion of a programmed cycle or when the storage container is saturated. This is a smart technological feature for high-capacity equipment pieces. 

9. Oil separator

Some compressor models may need to infuse oil in their chambers for cooling and lubrication, but they also require oil separators to filter and wash off excess oil from compressed air. 

High temperatures can be the natural by-product of an equipment’s compressor capabilities. This makes use of oil and coolant fluids necessary for accelerating the machine’s performance. But an oil separator makes sure oil does not get mixed with the final compressed air. Oil separators can be installed when it wears out or you have to optimize your equipment.

10. Gaskets and seals

Gaskets and seals boast an air-tight design to prevent leakage of compressed air. Chamber lining and bearing rings around compression rotors and bearings are as critical as any other big or major compressor parts. As they are oil-injected or self-lubricated, sliding seals reduce natural friction building between rotors. 

Regulatory maintenance of compressor parts should not be seen as some burdensome chore. Instead, this task should be taken seriously if you want to extend the life of your air compressor. 

Air filter checks – These parts require thorough inspections as they are most commonly worn-out or replace parts of the compressor. Although they are easy to maintain and clean, complete filter replacement may be required after a period of optimal utilization. 

System control testing – A system controller can monitor your equipment by providing safety readings of load settings, tank capacity, and temperature checks. Moreover, it can control the entire production system automatically. Checking pre-set limits regularly is important to make sure that the motor shuts off or operates at low capacity and reads pressure levels correctly. 

Oil filter & separate inspections – When your rotary screw air compressor is oil-injected, inspecting daily oil levels can reduce wearing out from friction. 

Rotor compression inspections – Checking your compressor’s rotors is the key to optimize the productivity of the machine. You may use belt tension gauges for the activity level measurement. While high readings indicate that motor bolts should be loosened, low readings mean these components need tightening. 

Routine maintenance schedules – An in-depth compressor system check should be conducted every few weeks to keep the machine’s performance intact for a longer time. 

Depending on the manufacturer’s design there may be additional parts and systems that give their products an edge over the competition.

For example, many Atlas Copco screw compressors come with Variable Speed Drive technology built in.

Most industrial applications of screw compressors have fluctuating air demand and that is where variable speed drive technology helps.

A compressor with  VSD technology simply adjusts its motor and elements speed to match your demand.

Atlas Copco screw compressors can come with remote monitoring software as well.

Remote monitoring software gives the customer real-time data insights.

With this data they can observe their equipment closely, correct inefficiencies, schedule maintenance in advance, and improve their uptime overall.

Atlas Copco’s Compressor Technique business area provides compressed air solutions to over 180 countries. We’ve been making products for the manufacturing and process industries since 1873. Our rotary screw air compressors are market leaders in terms of energy efficiency and innovation. We have budget and premium designs that work on a variety of standardized kW/HP ranges.

The brand of rotary screw compressor you chose can either help or hurt your bottom line.

10% to 30% of all energy used in the average industrial facility goes towards generating compressed air.

In the worst cases we’ve found that up to 90% of that energy can be lost through: 

• Heat
• Air leakage
• Friction between screw compressor parts
• Bad compressor design

The good news is that Atlas Copco specializes in energy savings.

Our award-winning compressor technology is designed to improve your energy efficiency, increase uptimes and reduce your costs.

Book a free consultation with us today and let’s talk about how we can help you.