Rotary Air Compressors: How Do They Work?

Ingersoll Rand Rotary Screw Compressor

One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, control systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.

There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. In a dynamic compressor, velocity energy is imparted to continuously flowing air by a means of impellers rotating at a very high speed. The velocity energy is then converted into pressure energy. We’ve discussed the different styles of air compressors here on the EXAIR Blog in the past. Today I’d like to highlight the rotary compressors, one of the positive-displacement types of compressors.

Positive-displacement compressors are broken into two categories: reciprocating and rotary. The rotary compressors are available in lubricant-injected or lubricant-free varieties. Both styles utilize two inter-meshing rotors that have an inlet port at one end and a discharge port at the other. Air flows through the inlet port and is trapped between the lobes and the stator. As the rotation continues, the point inter-meshing begins to move along the length of the rotors. This reduces the space that is occupied by the air, resulting in an increase in pressure.

In the lubricant-injected varieties, the compression chamber is lubricated between the inter-meshing rotors and bearings. This lubricant protects the inter-meshing rotors and associated bearings. It eliminates most of the heat caused by compression and acts as a seal between the meshing rotors and between the rotor and stator. Some advantages of the lubricant-injected rotary compressor include a compact size, relatively low initial cost, vibration free operation, and simple routine maintenance (replacing lubricant and filter changes). Some drawbacks to this style of compressor include lower efficiency when compared with water-cooled reciprocating compressors, lubricant carry over must be removed from the air supply with a coalescing filter, and varying efficiency depending on the control mode used.

In the lubricant-free varieties, the inter-meshing rotors have very tight tolerances and are not allowed to touch. Since there is no fluid to remove the heat of compression, they typically have two stages of compression with an inter-cooler between and an after cooler after the second stage. Lubricant-free compressors are beneficial as they supply clean, oil-free compressed air. They are, however, more expensive and less efficient to operate than the lubricant-injected variety.

Each of these compressors can deliver air to your Intelligent Compressed Air Products. If you’re looking to reduce your compressed air consumption and increase the safety of your processes contact an EXAIR Application Engineer today. We’ll be happy to discuss the options with you and make sure you’re getting the most out of your compressed air usage.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD




Photo courtesy of Ingersoll Rand CC BY 3.0, https://en.wikipedia.org/w/index.php?curid=32093890

The Impressive ROI of an Engineered Air Nozzle

You may have asked…why should I switch over to an engineered air nozzle if my system already works? Or…How can air nozzles be much different?

Manufacturing has always been an advocate for cost savings, where they even have job positions solely focused on cost savings. Return on Investment (ROI) is a metric they look toward to help make good decisions for cost savings.  The term is used to determine the financial benefits associated with the use of more efficient products or processes compared to what you are currently using. This is like looking at your homes heating costs and then changing out to energy efficient windows and better insulation. The upfront cost might be high but the amount of money you will save over time is worth it.

Model 1100 Super Air Nozzles can save compressed air dollars and increase safety

But how is ROI calculated? It is very simple to calculate out your potential savings of using one of EXAIR’s Intelligent Engineered Compressed Air Products. If you would rather not do the calculations out yourself then we can do it for you by sending the item in question to our Efficiency Lab Testing. The Efficiency Lab Testing is a free service that we offer to show you the possible savings by switching to one of our products.

The following is a simple ROI  calculation for replacing open blowoffs with an EXAIR Super Air Nozzle:

  • ¼” Copper Pipe consumes 33 SCFM at 80 psig (denoted below as CP)
  • A Model 1100 ¼” Super Air Nozzle can be used to replace and only uses 14 SCFM at 80 psig (denoted below as EP)

Calculation:

(CP air consumption) * (60 min/hr) * (8 hr/day) * (5 days/week) * (52 weeks/year) = SCF used per year for Copper Pipe  

(33) * (60) * (8) * (5) * (52) = 4,118,400 SCF

(EP air consumption) * (60 min/hr) * (8 hr/day) * (5 days/week) * (52 weeks/year) = SCF used per year for EXAIR Product  

               (14) * (60) * (8) * (5) * (52) = 1,747,200 SCF

Air Savings:

SCF used per year for Copper Pipe – SCF used per year for EXAIR Product = SCF Savings

               4,118,400 SCF – 1,747,200 SCF = 2,371,200 SCF in savings

If you know the facilities cost to generate 1,000 SCF of compressed air you can calculate out how much this will cost you would save. If not, you can us $0.25 to generate 1,000 SCF which is the value used by the U.S. Department of Energy to estimate costs.

Yearly Savings:

                (SCF Saved) * (Cost / 1000 SCF) = Yearly Savings

                                (2,371,200 SCF) * ($0.25 / 1000 SCF) = $592.80 annual Savings

With the simple investment of $42 (as of date published) you can calculate out the time it will take to pay off the unit.

Time Until payoff:

                (Yearly Savings) / (5 days/week * 52 weeks/year) = Daily Savings

                                ($592.80/year) / (5 days/week * 52 weeks/year) = $2.28 per day

                (Cost of EXAIR Unit) / (Daily Savings) = Days until product has been paid off

                                ($42) / ($2.28/day) = 17.9 days  

As you can see it doesn’t have to take long for the nozzle to pay for itself, and then continue to contribute toward your bottom line. 

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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A Simple Explanation of the Venturi Effect

The Venturi Effect was discovered by Italian physicist Giovanni Battista Venturi who lived between 1746 and 1822. In practice, there were a number of other physicists who were involved in the Venturi Effect but Giovanni Venturi is generally accepted as the first person to discover and explain the effect. So, what is the Venturi Effect, and how does it affect practical everyday living?

“A Venturi is a system for speeding the flow of the fluid by constricting it in a cone shape tube. In the restriction, the fluid increases its velocity, which reduces its pressure and produces a partial vacuum. As the fluid leaves the constriction, its pressure increases back to the ambient or pipe level.”

Any substance that flows is considered a fluid. This includes such things as water, shampoo, sunscreen, and even honey. Although not necessarily obvious, even gases, such as air, can be classified as fluids. So why would someone at EXAIR be talking about Venturi? Our E-Vacs use the Venturi Effect to create vacuum

This image has an empty alt attribute; its file name is in-line-e-vac-how-it-works.jpg

For most people the Venturi Effect is difficult to understand because you might expect the pressure to increase when a fluid is pushed through a restricted area. The fact that the increase in velocity is greater than any potential increase in pressure means that there is a net increase in velocity and a net reduction in pressure. The ability to mix-and-match certain fluids and gases via this process is relatively straightforward because the reduced pressure allows other substances to be sucked in through a connecting pipe at a rate of your choice.

EXAIR uses the Venturi Effect and other principles within the development of our engineered products. If you have questions or need a solution please call 800.903.9247 or visit us on www.EXAIR.com and let us help you.

Eric Kuhnash
Application Engineer
E-mail: EricKuhnash@exair.com
Twitter: @EXAIR_EK

 

Photo: Venturi Tube with labels by ComputerGeezer an Geof.  GNU Free Documentation License

Compressed Air Membrane Dryers: What are They? How do They Work?

A critical component on the supply side of your compressor system is the dryer. Atmospheric air contained within a compressed air system contains water vapor. The higher the temperature of the air, the more volume of moisture that air is capable of holding. As air is cooled, this water vapor can no longer be contained and this water falls out in the form of condensation. The temperature where this water will drop out is referred to as the dew point.

At a temperature of 75°F and 75% relative humidity, approximately 20 gallons of water will enter a 25HP compressor during a 24-hour period. As air is compressed, this water becomes concentrated. Since it’s heated during the compression process, this water stays in a vapor form. When this air cools further downstream, this vapor condenses into droplet form.

Moisture within the compressed air system can result in rust forming on the inside of the distribution piping, process failure due to clogged frozen lines in colder weather, false readings from instruments and controls, as well as issues with the point of use products installed within the system.

The solution to this problem is to install a dryer system. We’ve spent some time here on the EXAIR blog reviewing refrigerant dryers , desiccant dryersdeliquescent dryers, and heat of compression dryers. For the purposes of this blog, I’m going to focus on one of the newer styles on the market today: the membrane dryer.

Membrane Dryer

In a membrane dryer, compressed air is forced through a specially designed membrane that permits water vapor to pass through faster than the air. The water vapor is then purged along with a small amount of air while the rest of the compressed air passes through downstream. Generally, the dew point after the membrane dryer is reduced to about 40°F with even lower dew points also possible down to as low as -40°F!

With such low dew points possible, it makes a membrane dryer an optimal choice in outdoor applications that are susceptible to frost in colder climates. Membrane dryers also are able to be used in medical and dental applications where consistent reliability is critical.

A membrane dryer does not require a source of electricity in order to operate. The compact size makes it simple to install without requiring a lot of downtime and floor space. Since they have no moving parts, maintenance needed is minimal. Most often, this maintenance takes the form of checking/replacing filter elements just upstream of the membrane dryer. The membrane itself does need to be periodically replaced, an indicator on the membrane dryer will display when it needs to be changed. If particular instruments or processes in your facility are sensitive to moisture, a membrane dryer might be the best option.

However, there are some drawbacks to these types of dryers. They’re limited to low capacity installations, with models ranging from less than 1 SCFM up to 200 SCFM. This makes them more applicable for point-of-use installations than for an entire compressed air system. The nature in which the membrane dryer works necessitates some of the air to be purged out of the system along with the moisture. To achieve dew points as low as -40°F, this can equate to as much as 20% of the total airflow. When proper filtration isn’t installed upstream, oils and lubricants can ruin the dryer membrane and require premature replacement.

Make sure and ask plenty of questions of your compressor supplier during installation and maintenance of your system so you’re aware of the options out there. You’ll of course want to make sure that you’re using this air efficiently. For that, EXAIR’s wide range of engineered Intelligent Compressed Air Products fit the bill. With a variety of products available for same-day shipment from stock, we’ve got you covered.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD