Tag: positive displacement compressor

Should You Consider Rotary Screw Air Compressors For Your Process?

Published on by jasonkirbyLeave a comment
Rotary Screw

Rotary screw compressors are efficient, positive-displacement machines specifically engineered for continuous industrial air supply. Utilizing two interlocking helical rotors, these compressors provide a 100% duty cycle, operate quietly, and require less maintenance than traditional piston compressors. They are particularly well-suited for high-demand environments such as manufacturing and construction.

Rotary air compressors are positive displacement devices engineered for continuous, high-capacity industrial applications, employing rotational motion to capture and compress air. The primary types include rotary screw, sliding vane, scroll, root blower, and liquid ring compressors. These machines are categorized based on their cooling methods, which can be either air-cooled or water-cooled, as well as their efficiency control mechanisms.

Rotary screw compressors, characterized by their two interlocking helical rotors, are the most prevalent type used in various industrial settings. These compressors effectively trap and compress air, making them highly efficient for continuous operation. Their robust design ensures exceptional durability, which is essential for meeting the demands of industrial applications.

Sliding vane compressors operate by utilizing a rotor equipped with several sliding vanes that extend radially. This design facilitates the formation of air pockets between the rotor and the housing, which effectively reduces the volume of air and simultaneously increases its pressure.

Scroll compressors utilize two interleaved spiral scrolls—one stationary and the other orbiting—to compress air without any rotational movement. This design is particularly suited for smaller applications where quiet operation and energy efficiency are essential.

Lobe compressors operate by utilizing two precisely matched lobes to move air from the intake to the discharge port. This mechanism ensures a steady and continuous flow of low-pressure air (4.4 to 14.5 psig).

Liquid ring compressors are a specialized rotary compressor that utilizes a liquid, typically water, as the sealing medium to compress gas. This design is particularly advantageous in applications where it is essential to avoid oil contamination in the process.

Advantages: Rotary compressors, especially screw models, are known for their exceptional energy efficiency, achieving savings of up to 60%. They are designed for continuous operation around the clock, which makes them suitable for demanding industrial, HVAC, and refrigeration applications. With fewer moving parts, these compressors require minimal maintenance and operate quietly with low vibration levels. This combination ensures a consistent and reliable airflow while minimizing oil carryover, making them an excellent choice for environments that prioritize efficiency and performance.

Disadvantages: Rotary compressors, especially the rotary screw variety, entail significant upfront costs and require specialized maintenance. Their efficiency tends to decrease during periods of low air demand, which can result in condensation if the units do not operate at sufficiently high temperatures. Although these compressors are engineered for continuous use, they can incur substantial repair expenses in the event of a failure, particularly due to the high costs associated with air end replacements.

If you have questions about the rotary compressors, or anything regarding EXAIR and our products, please do not hesitate to reach out.

Jason Kirby
Application Engineer
Email: jasonkirby@exair.com
Twitter: @EXAIR_jk

Air Compressors: Rotary Type

Published on by John BallLeave a comment

What is an air compressor? In simple terms, it is a machine that increases fluid pressure.  It works by either changing the volume of air, positive displacement, or by changing the velocity of the air dynamics.  Many industries use air compressors to operate pneumatic equipment.  In this blog, I wish to cover the Rotary Compressor.

The Rotary Screw Compressor is a very common type of air compressor. This compressor uses dual rotors with meshing lobes that trap air while rotating. The rotation continues to push air toward a discharge port while decreasing the space the air takes up, thus increasing pressure. The rotary type of air compressor has five different sub-categories, reference image above.  This style of air compressor has some clear advantages and disadvantages:

Advantages:

  • Quiet Operations
  • Durability and Low Maintenance
  • High Efficiency
  • Continuous duty Cycle

Disadvantages:

  • High initial cost
  • Specialized maintenance

No matter the type of air compressor you use, they are very costly to operate.  To help you use them efficiently and safely, EXAIR offers a range of products that can clean, cool, blow, conserve, and convey.  This would include our Super Air Knives, Super Air Nozzles, Safety Air Guns, Cabinet Coolers, and much more.  If you want to save energy, increase safety, and cut costs no matter what size air compressor you have, you can contact an Application Engineer at EXAIR.  We will be happy to help. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Images Courtesy of the Compressed Air Challenge

Intelligent Compressed Air: Double-Acting Reciprocating Compressor

Published on by Tyler DanielLeave a comment

Evaluating all of the different types of compressors and which is right for you can seem like a daunting task. Today, I’d like to take some time to talk about the Double-Acting Reciprocating type of air compressor.

double acting compressor
Cut-out of a double-acting reciprocating compressor

Double-Acting Reciprocating compressors are a subset of the larger family of positive displacement compressor types. In positive displacement compressors, air is drawn into a chamber where the volume is then mechanically reduced. The energy used to displace the air volume is converted to an increase in air pressure. Dynamic compressors operate a little differently. They utilize an increase in air velocity to create the change in pressure. Air is accelerated to a high velocity through an impeller. The kinetic energy of the air is converted to an increase in potential (pressure) energy.

The Double-Acting Reciprocating compressor is a close relative to the Single-Acting Reciprocating compressor. In these types of compressors, an “automotive-type” piston driven by a crankshaft provides the compression. In a Double-Acting Reciprocating compressor, air is compressed as the piston moves in each direction. Hence the name, “double-acting”. In a Single-Acting Reciprocating compressor, air is only compressed on each full revolution of the piston. This makes the Double-Acting Reciprocating compressor much more efficient than its brethren.

Double Acting Recip
Double Acting Reciprocating Air Compressor

Double-Acting Reciprocating compressors are also available in much larger sizes. While Single-Acting compressors can be found up to 150HP, generally they’re much less common any larger than 25HP. Whereas a Double-Acting compressor is available from 10HP-1,000HP, making it a better choice for larger plants that require a significantly greater volume of compressed air. While they’re a bit more expensive due to the added mechanisms to produce the double-action compression, this cost is quickly offset by the increase in efficiency. At a performance of 15-16 kW/100 cfm, they’re 32% more efficient than a single-acting reciprocating compressor.

If you’re in the market for a new compressor and are struggling to determine the most suitable compressor, talk with your local compressor sales representative. Once you’re up an running, EXAIR has a wide-range of products that’ll make sure you’re using your compressed air safely and efficiently!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD
Image courtesy of Best Practices for Compressed Air Systems – second edition

 

What is an Air Compressor?

Published on by John BallLeave a comment

Internals of an air compressor

What is an air compressor?  This may seem like a simple question, but it is the heartbeat for most industries.  So, let’s dive into the requirements, myths, and types of air compressors that are commonly used.  Like the name states, air compressors are designed to compress air.  Unlike liquid, air is compressible which means that it can be “squished” into a smaller volume by pressure.  With this stored energy, it can do work for your pneumatic system.

There are two types of air compressors, positive displacement and dynamic.  The core component for most air compressors is an electric motor that spins a shaft.  Positive displacement uses the energy from the motor and the shaft to change volume in an area, like a piston in a reciprocating air compressor or like rotors in a rotary air compressor.  The dynamic types use the energy from the motor and the shaft to create a velocity energy with an impeller.  (You can read more about types of air compressors HERE).

Compressed air is a clean utility that is used in many different ways, and it is much safer than electrical or hydraulic systems.  But most people think that compressed air is free, and it is most certainly not.  Because of the expense, compressed air is considered to be a fourth utility in manufacturing plants.  For an electrical motor to reduce a volume of air by compressing it.  It takes roughly 1 horsepower (746 watts) of power to compress 4 cubic feet (113L) of air every minute to 125 PSI (8.5 bar).  With almost every manufacturing plant in the world utilizing air compressors much larger than 1 horsepower, the amount of energy needed to compress air is extraordinary.

Let’s determine the energy cost to operate an air compressor to make compressed air by Equation 1:

Equation 1:

Cost = hp * 0.746 * hours * rate / (motor efficiency)

where:

Cost – US$

hp – horsepower of motor

0.746 – conversion KW/hp

hours – running time

rate – cost for electricity, US$/KWh

motor efficiency – average for an electric motor is 95%.

As an example, a manufacturing plant operates a 100 HP air compressor in their facility.  The cycle time for the air compressor is roughly 60%.  To calculate the hours of running time per year, I used 250 days/year at 16 hours/day for shifts.  So operating hours equal 250 * 16 * 0.60 = 2,400 hours per year.  The electrical rate at this facility is $0.10/KWh. With these factors, the annual cost to operate the air compressor can be calculated by Equation 1:

Cost = 100hp * 0.746 KW/hp * 2,400hr * $0.10/KWh / 0.95 = $18,846 per year in just electrical costs.

So, what is an air compressor?  The answer is an expensive system to compress air to operate pneumatic systems.  So, efficiency in using compressed air is very important.  EXAIR has been manufacturing Intelligent Compressed Air Products since 1983.  If you need alternative ways to save money when you are using your air compressor, an Application Engineer at EXAIR will be happy to help you.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Compressor internals image courtesy of h080, Creative Commons License.