About Double Acting Reciprocating Air Compressors

My colleague, Lee Evans, wrote a blog “About Single Acting Reciprocating Compressors”, and I wanted to extend that conversation to a more efficient relative, the double acting reciprocating compressor.   As you see in the chart below, this type of compressor falls within the same family under the category of positive displacement compressors.

Compressor Types

Positive displacement compressors increase air pressure by reducing air volume within a confined space.  The reciprocating type of air compressor uses a motor that turns a crank which pushes a piston inside a cylinder; like the engine in your car.  In a basic cycle, an intake valve opens to allow the ambient air into the cylinder, the gas gets trapped, and once it is compressed by the piston, the exhaust valve opens to discharge the compressed volume into a tank.  This method of compression happens for both the single and double acting reciprocating compressors.  With a single acting compressor, the air is compressed only on the up-stroke of the piston inside the cylinder.  The double acting compressor compresses the air on both the up-stroke and the down-stroke of the piston, doubling the capacity of a given cylinder size.  This “double” compression cycle is what makes this type of air compressor very efficient.  A single acting compressor will have an operating efficiency between 22 – 24 kW/100 cfm of air while the double acting compressor has an operating efficiency between 15 – 16 kW/100 cfm.  Therefore, electricity cost is less with a double-acting reciprocating air compressor to make the same amount of compressed air.

To explore the internals a bit closer, the mechanical linkage used to move the piston is slightly different as well as the additional intake and exhaust valves.   Instead of the connecting rod being attached directly to the piston as seen inside a single acting compressor, a crosshead is added between the compression piston and the connecting rod (view picture below).  The rod that connects the crosshead to the compression piston can be sealed to keep the cylinder completely encapsulated.  For every rotation of the electric motor, the air is being compressed twice.  With the added heat of compression, the double acting compressors are generally water-cooled.  Also, with the added mechanism between the crank and the piston, the rotational speeds are typically less.  Because of the larger size, water jackets, and added parts, the initial cost is more expensive than the single acting compressor, but the efficiency is much higher.

Double Acting Reciprocating Air Compressor

Double acting compressors are generally designed for rugged 100% continuous operations.  Dubbed the work horse of the compressor family, they are also known for their long service life.  They are commonly used in high pressure services in multistage styles and can come in lubricated and non-lubricated configurations.   With the dual compression, slow speed and inter-cooling, it makes this type of air compressor very proficient in making compressed air.

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


Photos:  used from Compressed Air Challenge Handbook

Finding Leaks and Saving Money with the Ultrasonic Leak Detector

Locate costly leaks in your compressed air system!  Sounds like the right thing to do.

The EXAIR Ultrasonic Leak Detector is a hand-held, high quality instrument that is used to locate costly leaks in a compressed air system.

Ultrasonic sound is the term applied to sound that is above the frequencies of normal human hearing capacity.  This typically begins at sounds over 20,000 Hz in frequency.  The Ultrasonic Leak Detector can detect sounds in this upper range and convert them to a range that is audible to people.

When a leak is present, the compressed air moves from the high pressure condition through the opening to the low pressure environment.  As the air passes through the opening, it speeds up and becomes turbulent in flow, and generates ultrasonic sound components. Because the audible sound of a small leak is very low and quiet, it typically gets drowned out by by surrounding plant noises, making leak detection by the human ear difficult if not impossible.


Detecting a Leak with the Ultrasonic Leak Detector

By using the Ultrasonic Leak Detector, the background noise can be filtered out and the ultrasonic noises can be detected, thus locating a leakage in the compressed air system. There are (3) sensitivity settings, x1, x10, and x100 along with an on/off thumb-wheel for fine sensitivity.  The unit comes with a parabola and tubular extension for added flexibility.


Model 9061 – Ultrasonic Leak Detector and Included Accessories

Finding just one small leak can pay for the unit-

A small leak equivalent to a 1/16″ diameter hole will leak approx 3.8 SCFM at 80 PSIG of line pressure.  Using a reasonable average cost of $0.25 per 1000 SCF of compressed air generation, we can calculate the cost of the leak as follows-


It is easy to see that utilizing the Ultrasonic Leak Detector, and identifying and fixing leaks is the right thing to do.  It is possible to find and fix enough leaks that a new compressor purchase can be avoided or an auxiliary back-up is not needed any more.

If you have questions regarding the Ultrasonic Leak Detector, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Estimating the Cost of Compressed Air Systems Leaks

Leaks in a compressed air system can waste thousands of dollars of electricity per year. In fact, in many plants, the leakage can account for up to 30% of the total operational cost of the compressor. Some of the most common areas where you might find a leak would be at connection joints like valves, unions, couplings, fittings, etc. This not only wastes energy but it can also cause the compressed air system to lose pressure which reduces the end use product’s performance, like an air operated actuator being unable to close a valve, for instance.

One way to estimate how much leakage a system has is to turn off all of the point-of-use devices / pneumatic tools, then start the compressor and record the average time it takes for the compressor to cycle on and off. The total percentage of leakage can be calculated as follows:

Percentage = [(T x 100) / (T + t)]

T = on time in minutes
t = off time in minutes

The percentage of compressor capacity that is lost should be under 10% for a system that is properly maintained.

Another method to calculate the amount of leakage in a system is by using a downstream pressure gauge from a receiver tank. You would need to know the total volume in the system at this point though to accurately estimate the leakage. As the compressor starts to cycle on,  you want to allow the system to reach the nominal operating pressure for the process and record the length of time it takes for the pressure to drop to a lower level. As stated above, any leakage more than 10% shows that improvements could be made in the system.


(V x (P1 – P2) / T x 14.7) x 1.25

V= Volumetric Flow (CFM)
P1 = Operating Pressure (PSIG)
P2 =  Lower Pressure (PSIG)
T = Time (minutes)
14.7 = Atmospheric Pressure
1.25 = correction factor to figure the amount of leakage as the pressure drops in the system

Now that we’ve covered how to estimate the amount of leakage there might be in a system, we can now look at the cost of a leak. For this example, we will consider a leak point to be the equivalent to a 1/16″ diameter hole.

A 1/16″ diameter hole is going to flow close to 3.8 SCFM @ 80 PSIG supply pressure. An industrial sized air compressor uses about 1 horsepower of energy to make roughly 4 SCFM of compressed air. Many plants know their actual energy costs but if not, a reasonable average to use is $0.25/1,000 SCF generated.

Calculation :

3.8 SCFM (consumed) x 60 minutes x $ 0.25 divided by 1,000 SCF

= $ 0.06 per hour
= $ 0.48 per 8 hour work shift
= $ 2.40 per 5-day work week
= $ 124.80 per year (based on 52 weeks)

As you can see, that’s a lot of money and energy being lost to just one small leak. More than likely, this wouldn’t be the only leak in the system so it wouldn’t take long for the cost to quickly add up for several leaks of this size.

If you’d like to discuss how EXAIR products can help identify and locate costly leaks in your compressed air system, please contact one of our application engineers at 800-903-9247.

Justin Nicholl
Application Engineer






Air Amplifiers – What is an Amplification Ratio?

On Friday my colleague, Russ, blogged about the Super Air Amplifier (see that BLOG here, including a video demo)  In discussing the Air Amplifiers, the topic of amplification was mentioned. Today, I’d like to expand a bit further the amplification aspect of the Air Amplifier performance.

As the name of the device implies, the compressed air used by the Air Amplifier is added to, and thus ‘amplified’, the total output flow of the unit. Depending on the size and type of Air Amplifier, the amplification ratio starts at 12:1 and goes up to 25:1, with the ratio being the output flow to the compressed air usage.


Super Air Amplifier and Adjustable Air Amplifier

EXAIR offers (2) types- the Super Air Amplifier and the Adjustable Air Amplifier.  The Super Air Amplifier uses a patented shim technology to maintain a precise gap, which controls the compressed air flow and expansion through the unit.  As the expanded air flows along the Coanda profile, a low pressure area is created at the center which induces a high volume flow of surrounding air into the primary air-stream.  The combined flow of primary and surrounding air exhausts from the Air Amplifier in a high volume, high velocity flow.  The larger diameter units have a greater cross sectional area with larger low pressure areas, resulting in greater amplification ratios.

The Below table shows the amplification ratios.


The Adjustable Air Amplifier does not use a shim, but rather has an infinitely adjustable gap, allowing for fine adjustment of performance.  Force and flow is changed by turning the exhaust end to adjust the gap, and is then locked into place. The method of the amplification is the same as for the Super Air Amplifier, and the amplification ratios are similar and shown below.


The Super Air Amplifiers and Adjustable Air Amplifiers are ideal for use in applications and processes that require cooling, drying and/or cleaning of parts, or the ventilation of confined areas or weld smoke or the exhausting of tank fumes.

If you have questions regarding the Air Amplifier, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Video Blog: The Monetary Benefits of an Engineered Solution

This video highlights the value and benefits of an engineered blow off solution.  We take a homemade open pipe blowoff and replace it with an EXAIR model 1100 Super Air Nozzle.  This air nozzle is then controlled through our Electronic Flow Controller, allowing for intermittent On/Off of the compressed air flow.  And, these solutions are wirelessly monitored via Zigbee network using our Wireless Digital Flowmeter.  Implementing these solutions results in a compressed air reduction of over 90%!!!


Full calculations along with supporting flow values (pulled from the same data shown in the video above) are shown below.

Screengrab of the flow values shown in the video above. Click for larger image.

The open pipe:

The first compressed air flow values to show up on the EXAIR Logger are for the open pipe blow off.  At 1 BAR operating pressure, this “solution” consumes 22.3 SCFM of compressed air.  At a cost of $0.25 for every 1,000 cubic feet of compressed air, this nozzle will cost $695.76 to operate 8 hours per day, 5 days per week, 52 weeks per year.

The engineered EXAIR Super Air Nozzle

Model 1100 EXAIR Super Air Nozzles consumes 4.7 SCFM at an operating pressure of 1 BAR – a reduction of 79% compared to the open pipe.  These savings prove out in terms of operating cost as well – $146.64 per year, compared to $695.76.

The engineered EXAIR Super Air Nozzle with Electronic Flow Control (EFC)

By controlling the “ON” time for this application with an EFC, we are only blowing for 32% of the time for each minute of operation which changes the required compressed air flow from 4.7 SCFM to a peak value of 1.5 SCFM. This control saves an additional 68% of compressed air flow.  And, these savings are compounded by eliminating the need for constant compressed air flow.  Total annual operating cost for the EXAIR 1100 Super Air Nozzle with Electronic Flow Control is just $46.80.

Implementing an engineered solution can have a TREMENDOUS impact on energy costs and operating costs in your facility.  Compressed air is the most expensive utility to produce and consume, making the impact of proper solutions of high value to any business.  Let us help you utilize engineered compressed air solutions in your facility by contacting an EXAIR Application Engineer today.

Lee Evans
Application Engineer

What’s So “Super” About The Super Air Amplifier?

EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of free air from the surrounding environment.

“Free air” from the surrounding environment?  You might think it’s too good to be true, and if you think you’re getting something for nothing, you’re right.  If you consider, though, that it’s oftentimes preferable to work smarter, not harder, then the use of engineered compressed air products is too good NOT to be true.  Case in point: the Super Air Amplifier.

The Coanda Effect is the “work smarter, not harder” part of the Super Air Amplifier

Simple and low cost, (hey, “engineered” doesn’t necessarily mean “complex and expensive”) the EXAIR Super Air Amplifier uses a small amount of compressed air to generate a tremendous amount of air flow through entrainment.  How much do they pull in?  Depending on the model, they entrain air at rates of 12:1 (for the 3/4″ Model 120020) to 25:1 (4″ & 8″ Models 120024 & 120028, respectively.)  The larger diameters mean there’s more cross sectional area to entrain air, so there is indeed efficiency to scale, size-wise.  There are a couple of great visuals in this video, if you want to see the entrainment in action (1:50) or the difference that the entrainment makes (1:30):


Where can you use a Super Air Amplifier?  The easy answer is, anyplace you want a consistent, reliable air flow.  The pressure supply can be regulated from a “blast to a breeze,” depending on the needs of your application.  The patented shim can be replaced for even higher performance, while maintaining the efficiency that makes it so valuable.  The balanced flow makes for incredibly quiet operation…no more noisy fans, blowers, or open-end compressed air pipes.  The body (3/4″ to 4″ sizes) is cast with a 2-hole flange for ease of installation.

When can you use a Super Air Amplifier?  Another easy answer: anytime you want.  If you need a continuous air flow, there are no moving parts to wear or electrical components to burn out.  Supply them clean, dry air, and they’ll run darn near indefinitely, maintenance free.

Alternately, if you need intermittent air flow, starting & stopping operation is as simple as opening & closing a valve in the compressed air supply line.  They produce rated flow immediately, and cut it off just as fast.

Some of the more popular applications are ventilation/exhaust, cooling, drying, cleaning, and dust collection.  There are five distinct models to choose from, and they’re all in stock.  We’re also happy to discuss special requirements that might lead to a custom product too.  Our Application Engineers work with Design & Production all the time to meet specific needs of particular situations.

If you’d like to find out more about letting the Super Air Amplifier, or any of EXAIR’s Intelligent Compressed Air Products work smarter for you, give me a call.

Russ Bowman
Application Engineer
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EXAIR Super Air Nozzles: 38 Day ROI Saves Money

Blow off station

I received an email from an engineer that was looking at our Super Air Nozzles.  They currently were using four blow-off lines that were made from 6mm ID copper tubes.  (Reference picture)  The system was designed to blow out holes after machining.  The engineer was in charge of the task of optimizing 25 machining stations similar to this one.  He was familiar with EXAIR products from his previous employment, and he recognized the waste of compressed air by using open pipe.  He purchased four Nano Super Air Nozzle, model 1110SS, for a trial.  He was impressed with the performance, the low sound level, and the engineered design in safety.  But, for upper management in his company, he had to show a cost savings in order to change all the stations in the facility.  He asked me to help him in calculating the compressed air savings.

He gave me some additional details about their application.  He was using the compressed air about 30% of the time throughout an 8 hour day at a pressure of 80 PISG.  He wanted to present the savings per day, week, and year as well as the payback period in his evaluation.  I have performed many of these calculations for other customers and was happy to help.  It is sometimes easier to speak in terms of savings, as everyone can relate to money, especially management.  (The numbers below can be adjusted to match your application and blow-off devices).


Cost of compressed air: $0.25/1000 cubic feet of air (this is based on $0.08/Kwh of electrical cost)

Flow: 1110SS Nano Super Air Nozzle – 8.3 SCFM at 80 PSIG

Flow:  6mm ID copper tube – 42 SCFM at 80 PSIG


The difference in compressed air flows from a 6mm tube to the Nano Super Air Nozzle is (42 SCFM – 8.3 SCFM) = 33.7 SCFM.  At a 30% duty cycle, we get 33.7 SCFM * 0.3 = 10.2 SCFM (cubic feet/minute) of additional compressed air being used.

Per day, the additional amount of compressed air wasted is:

10.2 cubic feet/minute * 60 min/hr * 8 hr/day (one shift) = 4,896 cubic feet per day.

Per week, the additional amount of compressed air wasted is:

4,896 cubic feet/day * 5 days/week = 24,480 cubic feet per week.

Per year, the additional amount of compressed air wasted is:

4,896 cubic feet/day * 250 days/year = 1,224,000 cubic feet per year.


With the cost to make compressed air at $0.25/1000 cubic feet, we have the following:

4,896 cubic feet/day * $0.25/1000 cubic feet = $1.22 per day

24,480 cubic feet/week * $0.25/1000 cubic feet = $6.12 per week

1,224,000 cubic feet/year * $0.25/1000 cubic feet = $306.00 per year.

From these values, the payback for a model 1110SS Super Air Nozzle is just under 38 days.  Because the EXAIR Super Air Nozzles are so efficient, some utility companies will offer a rebate program to use them.  This will improve your ROI even more.  (We can check to see if your local electric company participates in these programs).  Just think, the remaining life of the Super Air Nozzle will be using less compressed air and saving much money for the company.

The calculations above are only for one nozzle.  As discussed above with the engineer, they had 4 tubes/station and 25 stations in their plant.  So, if you multiply each figure by 100, you can see the large amount of money that can be saved.   The engineer presented these figures to upper management, and it was an easy decision to replace all the copper tubes with EXAIR nozzles.

Nano Super Air Nozzle

Don’t be fooled by the initial cost of a tube, pipe, drilled holes, or a substandard nozzle.  You can see by the facts above, if you use any additional compressed air in your blow-off application, it will cost you a lot of money in the long run.  If you need any help in calculating how much money EXAIR products can save you, you can use our Air Savings Calculator from our website, or you contact an Application Engineer at EXAIR.  We will be happy to help you.

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

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