Rotary screw air compressors or twin-screw compressors as they are also known are some of the most popular mobile compressors available. A longtime staple in numerous manufacturing processes, the rotary screw compressor is a true workhorse that makes many amazing accomplishments of modern technology possible.
This page will provide you with all the relevant information on a rotary screw-type air compressor so that you can better understand them, including how they work, their advantages and disadvantages, where to buy them, and a comparison with other types of air compressors.
Table of Contents
- What Is a Rotary Screw Air Compressor?
- How Does a Screw Compressor Work?
- Rotary Air Compressors Advantages and Disadvantages
- Rotary Screw Compressor Applications
- Rotary Screw Compressor Manufacturers & Where to Buy
- Reciprocating Air Compressor vs Rotary Screw Air Compressor
- FAQs (Frequently Asked Questions)
- Other Types of Air Compressors
What Is a Rotary Screw Air Compressor?
A rotary screw air compressor is a compressor that uses a rotary-type positive displacement mechanism, called a rotary screw, air-end. Rotary screw compressors are commonly used as a replacement for piston compressors, in commercial and industrial applications, where larger volumes of high-pressure air are a requirement.
Sometimes referred to as a “twin-screw compressor”, they are ideal for both mobile and standalone applications and can be found on vehicles and trailers as well as in production, industrial, and medical facilities where there is a need for very high-quality equipment.
How Does a Screw Compressor Work?
The rotary screw compressor process is fairly different from the reciprocating piston compressor. It works by generating the compression continuously at the rotary screw drive air end of the compressor.
Air enters the unit at the inlet port of one of the two large screws rotating against one another, also known as the rotors or rotary screws. This air then moves down the length of the screws and compresses the air towards the outlet due to the air gaps in the rotors getting smaller and smaller.
These rotary screws are machined with low tolerances to very highly accurate finished products through which the vanes on the rotary screws can be as low as a thousandth of an inch apart.
These pressurized rotary screw air systems consist of many components that interconnect and work together to compress air. Atmospheric air is used to provide the end goal of quality compressed air however, oil can be a very important characteristic of a rotary compressor.
Oil lubricates compressed air systems and allows for the rotary screws to be far more efficient with the bonus of saving the user significant costs. Though oil brings these benefits, it does also require additional mechanisms resulting in a far more complex system.
The oil performs four crucial functions:
- Noise dissipation
These mechanisms must be able to circulate, filter out and recycle the oil that enters the rotary-screw compressor.
The oil-fed rotary compressor provides a hydraulic seal between the rotary screw vanes and this allows for mechanical energy to be transported between the two rotary screws. Air enters the system in the same way as that of the oil-less system and moves down the length of the screws towards the outlet with the oil.
The oil and air then pass through a separation process to ensure clean air. The oil is cooled, filtered, and returned back into the air end within its closed loop system. The air is cooled and transferred to airlines and a receiver, ready for use with your tools.
Rotary screw compressors are also available as oil-free versions, these types will inject water to remove the heat of compression. The injected water is then removed from the discharged compressed air by a conventional moisture separation device.
Rotary Air Compressors Advantages and Disadvantages
|Rotary Screw Compressor Advantages||Rotary Screw Compressor Disadvantages|
Advantages of Rotary Screw Air Compressors
- Duty cycle
- Reduced wear
Rotary screw air compressors hold some very important advantages over reciprocating air compressors. Generally, they can deliver more compressed air in comparison to reciprocating ones of the same size allowing for jobs to be completed faster and more on a day-by-day basis.
Reciprocating compressors create air pulses in the compression process and require reservoir tanks to try to reduce these and also to be able to withhold greater quantities of air, which rotary screw compressors do not require for either reason.
Another key advantage that Rotary screw compressors hold is their ability to operate at 100% duty cycle. This allows for the continuous production of compressed air meaning you can work for longer and get jobs done without needing to wait around. The duty cycle in air compressors can be described as the amount of time that an air compressor can successfully operate without having to stop for any reason like overheating.
For example, if you were to have a 10-hour working day period where the compressor runs for the full 10 hours then it is a 100% duty cycle. If it was only able to operate for 7.5 hours then it would be 75% duty cycle and so on.
The key importance here is that in comparison to the rotary compressors, the majority of reciprocating compressors are only 50% duty cycle meaning that they can only operate for half the time which can cause significant reductions in completed work.
Reciprocating compressors also wear significantly over time due to their engine-like parts coming in contact with each other. This wear then causes a detrimental reduction in the performance of the compressor, increased oil carryover, and an even greater amount of heat generation.
Rotary screw compressors allow you to work with so many more products due to their lighter weight and advantageous capacity when small in comparison to reciprocating air compressors.
They can provide enough air flow to power and operate numerous very common pneumatic hand-held tools and allow vehicles to haul more equipment, tools, and materials. These all combine to an overall result of getting jobs completed a lot faster and more of them.
Disadvantages of Rotary Screw Air Compressors
On the other hand, they do have a couple of disadvantages.. first of all, they can have a higher upfront cost than reciprocating compressors.
They can generally be upwards of twice the cost, but as you’ve learned can operate at twice the duty cycle so you essentially get what you pay for. This makes them a solid investment for long-term business operations that require air compression.
Another disadvantage is that due to their complex nature, they require a far higher level of expertise to conduct maintenance on them in comparison to reciprocating compressors.
Rotary Screw Compressor Applications
- Food packaging
Common industries where screw air compressors support you are manufacturing sectors such as automotive, brewing, food packaging, aerospace, construction, and more, along with commercial applications where a requirement for high pressurized air in large volumes is essential.
Rotary screw air compressors are commonly found in industrial facilities and construction sites across the whole world providing an on-demand supply of compressed air for everything from food packaging to pneumatic pumps and jackhammers.
Many businesses rely on rotary screw compressors for their everyday production capacity. They are highly suited to heavy-duty industrial operations due to their lack of a duty cycle, robust design, and their ability to handle a wide variety of operating conditions!
Rotary Screw Compressor Manufacturers & Where to Buy
- Quincy Air Compressors
- Sullair Air Compressors
- Ingersoll Rand Air Compressors
- Chicago Pneumatic Compressors
- Compair Air Compressors
If you’re looking for a rotary screw compressor for sale, I would recommend visiting the above company’s websites to browse their catalog of screw compressors.
Alternatively, you may be able to find what you’re after on Amazon. I have picked out a couple of examples of rotary screw air compressors you may come across in your search.
The first is a 5 HP 18.5 CFM rated rotary screw compressor for sale from Ingersoll Rand. It includes an air-cooled aftercooler to reduce discharge air temperatures.
The second is a 10 HP Chicago Pneumatic quiet rotary screw air compressor with a maximum pressure of 132 PSI.
Reciprocating Air Compressor vs Rotary Screw Air Compressor
Two of the most common mobile compressors are reciprocating (piston) and rotary screw air compressors. But what sets them apart and which is better?
Reciprocating air compressors, which are also referred to as “piston” air compressors, boast great price and availability and thus are widely used throughout various service industries. Numerous commercial vehicle operators request reciprocating air compressors simply because they do not understand the difference between a rotary screw and a reciprocating air compressor.
Rotary screw air compressors provide better performance and often require less space, which makes them an attractive alternate option that you should be aware of. Rotary screw air compressors can work faster and deliver more air compared to reciprocating compressors of the same size.
Rotary screw compressors do not create the same type of air pulses that reciprocating compressors do, and therefore they do not need a reservoir tank like their counterparts, and so, provide you with the ability to get your jobs done faster as you do not have to wait for your compressor to keep up.
This relates to their duty cycle also, rotary screw compressors can operate at 100% duty cycle, and are continuous use without the need to stop. In comparison, most reciprocating air compressors are only capable of a 20-30% duty cycle or 50% at best. This means that you must give the compressor time to rest between operations. For example, a 50% duty cycle would mean that the compressor can only run for 15 minutes every 30 minutes.
Rotary screw compressors last a lot longer than reciprocating air compressors as they’re designed in a way to prevent parts from wearing out, of course with a cost. Unlike a reciprocating compressor that loses performance with age, the rotary screw compressor maintains the same performance throughout its long life.
FAQs (Frequently Asked Questions)
Rotary screw air compressors are used for both mobile and standalone applications and can be found on vehicles and trailers. Not only this but rotary screw air compressors are very popular in production, industrial, and medical facilities where there is a need for very high-quality equipment.
Rotary screw compressors are so expensive because their rotors are of superior quality and leave very little space between them. The precision and accuracy to ensure that they don’t touch come at a cost.
Rotary screw compressors are predicted to last anywhere between 60,000 – 80,000 hours before a rebuild is necessary. This is around 6-8 times longer than reciprocating air compressors.
When comparing them with reciprocating air compressors, they have some distinct advantages. Rotary screw air compressors are known to deliver more air compared to reciprocating compressors of the same size along with providing a quieter operation.
A rotary screw compressor is a rotary-type positive displacement air compressor. It uses two rotating screws (rotors) to produce clean, quiet, and efficient compressed air.
Other Types of Air Compressors
If you’re interested in finding out more information on other types of air compressors please visit our specific pages:
- Reciprocating Air Compressors Explained
- Rotary Vane Compressors Explained
- Centrifugal Compressors Explained
- Axial Flow Compressors Explained
- Scroll Air Compressors Explained
- Oilless Air Compressors vs. Oil Compressors
If you have any questions regarding rotary screw air compressors, please leave a comment below, with any photos if applicable, so that someone may help you!