Critical Components of Your Compressed Air System

In any manufacturing environment, compressed air is critical to the operation of many processes. You will often hear compressed air referred to as a “4th utility” in a manufacturing environment. The makeup of a compressed air system is usually divided into two primary parts: the supply side and the demand side. The supply side consists of components before and including the pressure/flow controller. The demand side then consists of all the components after the pressure/flow controller.

The first primary component in the system is the air compressor itself. 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.

Still on the supply side, but installed after the compressor, are after coolers, and compressed air dryers. An after cooler is designed to cool the air down upon exiting from the compressor. During the compression, heat is generated that carries into the air supply. An after cooler uses a fan to blow ambient air across coils to lower the compressed air temperature.

When air leaves the after cooler, it is typically saturated since atmospheric air contains moisture. In higher temperatures, the air is capable of holding even more moisture. When this air is then cooled, it can no longer contain all of that moisture and is lost as condensation. The temperature at which the moisture can no longer be held is referred to as the dewpoint. Dryers are installed in the system to remove unwanted moisture from the air supply. Types of dryers available include: refrigerant dryers, desiccant dryers, and membrane dryers.

Also downstream of the compressor are filters used to remove particulate, condensate, and lubricant. Desiccant and deliquescent-type dryers require a pre-filter to protect the drying media from contamination that can quickly render it useless. A refrigerant-type dryer may not require a filter before/after, but any processes or components downstream can be impacted by contaminants in the compressed air system.

Moving on to the demand side, we have the distribution system made up of a network of compressed air piping, receiver tanks when necessary, and point of use filters/regulators. Compressed air piping is commonly available as schedule 40 steel pipe, copper pipe, and aluminum pipe. Some composite plastics are available as well, however PVC should NEVER be used for compressed air as some lubricants present in the air can act as a solvent and degrade the pipe over time.

Receiver tanks are installed in the distribution system to provide a source of compressed air close to the point of use, rather than relying on the output of the compressor. The receiver tank acts as a “battery” for the system, storing compressed air energy to be used in periods of peak demand. This helps to maintain a stable compressed air pressure. It improves the overall performance of the system and helps to prevent pressure drop.

Finally, we move on to the point-of-use. While particulate and oil removal filters may be installed at the compressor output, it is still often required to install secondary filtration immediately at the point-of-use to remove any residual debris, particulate, and oil. Receiver tanks and old piping are both notorious for delivering contaminants downstream, after the initial filters.

Regulator and filter

In any application necessitating the use of compressed air, pressure should be controlled to minimize the air consumption at the point of use. Pressure regulators are available to control the air pressure within the system and throttle the appropriate supply of air to any pneumatic device. While one advantage of a pressure regulator is certainly maintaining consistent pressure to your compressed air devices, using them to minimize your pressure can result in dramatic savings to your costs of compressed air. As pressure and flow are directly related, lowering the pressure supplied results in less compressed air usage.

EXAIR manufactures a wide variety of products utilizing this compressed air to help you with your process problems. If you’d like to discuss your compressed air system, or have an application that necessitates an Intelligent Compressed Air Product, give us a call.

Tyler Daniel, CCASS

Application Engineer
Twitter: @EXAIR_TD

Compressor Image courtesy of Tampere Hacklab via Creative Commons License

Installing a Secondary Receiver Tank

Picture by Clker-Free-Vector licensed by Pixabay

We often run into situations where a customer does not have enough compressed air volume to implement a solution. This leaves three possible options. 1) Abandon the project all together and continue to feel the pain the problem creates. 2) Install a larger compressor, with associated expense. 3) Install a secondary, or “point of use” receiver tank to store the compressed air volume local to the application, to be available immediately without having to rely on the distribution system for storage capability. This 3rd option is a cost-effective solution customers often use to mitigate the impact of installing a new compressed air consuming product onto the system.

Large demand events on a compressed air system can leave the system short on air. This can result in a system pressure drop which is undesirable. Utilizing a secondary receiver tank to mitigate the impact of larger volume consuming events is a common and useful strategy that many compressed air professionals will recommend and pursue. In this kind of scenario, the receiver tank acts much like a capacitor in a camera flash. A camera battery charges a capacitor which then dumps its charge into the flash bulb when you take a photo for a notably bright flash which is what one generally wants from their camera flash.

In this same way, a receiver tank acts like the capacitor to “dump” the air volume needed to make a compressed air device work at its design pressure and flow for some prescribed period of time. In situations like this, the high demand does need to be an intermittent one so that the tank can then re-charge from the compressor system and be ready for the next air use event. This means that certain calculations need to be made to ensure that the receiver tank is sized properly to provide the desired effect.

How do you size a receiver tank? Here’s the calculation to determine the proper size:

Let’s consider an example of an Air Amplifier solution. A customer wants to blow on hot metal parts coming out of an oven to cool them down as an “air quench”. We evaluate the application and determine that (2) 2″ Super Air Amplifiers will provide the right amount of flow. Those units are going to operate at 60 PSIG to provide the desired effect. (2) 2″ Super Air Amplifiers will consume 24.5 SCFM @ 60 PSIG. Each batch of parts comes out of the oven at a rate of one batch every 5 minutes. They want to provide the necessary cooling for a total of 30 seconds to have the air quench effect. So, every 5 minutes, the Air Amplifiers will be blowing for 1/2 minute. Each “on” event consumes 12.25 Standard Cubic Feet of air. We then have 4 minutes, 30 seconds left to re-plenish the tank.

The last piece of information we need to know is the system pressure for the compressed air header feeding the tank. The system pressure is 120 PSIG. And so, our calculation looks like this:

V = 0.5 min. x 24.5 rate of flow x (60 PSIG + 14.5 PSIA)

V = 913

V = 15.2 ft.3

There are 7.48 gallons to a cubic foot, so our receiver tank in this example would be
15.2 ft.3 x 7.48 = 114 gallons.

Given the fact that receiver tanks are made in certain, standard sizes, a 120 gallon tank or two, 60 gallon tanks piped in upstream of the compressed air load would be appropriate for this application.

As a further note to the example, the refill rate to the tank(s) would need to be a minimum of 2.72 SCFM to get the volume replenished in time for the next event. This is less than 1 HP of industrial air compressor to maintain such a flow rate to refill the tank.

With some reasonably simple math to determine tank size, and a willingness to pursue this kind of air delivery solution, you can implement that compressed air solution at a fraction of the cost compared to a new compressor.

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Cover Photo by dkeissling and licensed by Pixabay

Secondary Receiver Tanks: Why Use Them and How to Size Them

Secondary receiver tanks can be strategically placed throughout the plant to improve the “ebbs and flows” of pneumatic demands.  The primary receiver tanks help to protect the supply side when demands are high, and the secondary receiver tanks help pneumatic systems on the demand side.  The purpose of secondary air storage is for dedicated end-use systems or for additional capacity at the end of distribution lines.  Essentially, it is easier and more efficient for compressed air to travel from a nearby source rather than traveling through long lengths of pipe.  With any high-demand events, it is beneficial to have additional storage.

As a comparison, I would like to relate a pneumatic system to an electrical system.  The receiver tanks would be like capacitors.  They store pressurized air like a capacitor stores energy from an electrical source.  If you have ever seen an electrical circuit board, you will notice many capacitors of different sizes throughout the circuit board.  The reason for this is to have a ready source of energy to increase efficiency and speeds with the ebbs and flows of electrical signals.  The same can be said for a pneumatic system with secondary receiver tanks.

To cover a current application, I had a customer that was looking at a model 1122108; 108” (2,743mm) Gen4 Super Ion Air Knife Kit.  The application was to remove static and debris from insulated panels for large refrigerated trailers.  They were worried about how much compressed air that it would use; and they were considering a blower-type system.  I went through the negative aspects of blower-type systems like loud noise levels, capital expense, high maintenance cost, large footprint, and ineffectiveness with turbulent air flows.  But, when you are limited to the amount of compressed air, it may seem difficult to get the best product for your application.  In looking at it another way, I asked him if the process was intermittent; and it was.  The cycle rate was 2 minutes on and 10 minutes off.  I was able to recommend a secondary tank to help ease the high demand for their compressed air system.

To calculate the volume size for your secondary receiver tank, we can use Equation 1 below.  It is the same for sizing a primary receiver tank, but the scalars are slightly different.  The supply line to this tank will typically come from a header pipe that supplies the entire facility.  Generally, it is smaller in diameter, so we have to look at the air supply that it can feed into the tank.  For example, a 1” NPT Schedule 40 pipe at 100 PSIG (7 bar) can supply a maximum of 150 SCFM (255 M3/hr) of air flow.  This value is used for Cap below.  The C value is the largest air demand for the machine or equipment that will be using the tank.  If the C value is less than the Cap value, then a secondary tank is not needed.  If the Cap is below the C value, then we can calculate the smallest tank volume that would be needed.  The other value in the equation is the minimum tank pressure.  In most cases, a regulator is used to set the air pressure for the machine or area.  If the specification is 80 PSIG (5.5 bar), then you would use this value as P2P1 is the header pressure that will be coming into the secondary tank.  With this collection of information, you can use Equation 1 to calculate the minimum tank volume

Equation 1:

V = T * (C – Cap) * (Pa) / (P1-P2)


V – Volume of receiver tank – Imperial (ft3) or SI (M3)

T – Time interval (minutes)

C – Air demand for system – Imperial (SCFM) or SI (M3/min)

Cap – Supply value of inlet pipe – Imperial (SCFM) or SI (M3/min)

Pa – Absolute atmospheric pressure – Imperial (PSIA) or SI (Bar)

P1 – Header Pressure – Imperial (PSIG) or SI (Bar)

P2 – Regulated Pressure – Imperial (PSIG) or SI (Bar)

For this customer above, I am still getting more details about their system.  But we went from a “we don’t have enough compressed air” to a “we can use a better solution with the Super Ion Air Knife”.  If you find that your compressed air system needs a boost for your pneumatic process, we may be able to recommend a secondary receiver for your system.  EXAIR does offer 60 gallon tanks, model 9500-60, to add to those specific areas.  If you have any questions about using a receiver tank in your application, you can contact an Application Engineer at EXAIR.  We will be happy to help.

John Ball
Application Engineer
Twitter: @EXAIR_jb

Intelligent Compressed Air®: Compressor Motors And Controls

Use of compressed air has gone hand in hand with manufacturing for centuries. From manually operated bellows devices that stoked fires to generate the high temperatures needed for forging metals in ancient times, to the massive steam or oil driven compressors used in the 1800’s on projects like the Mont Cenis Tunnel drills, to the sophisticated electric-powered compressors used widely across modern industry, compressed air has actually been “the fourth utility” longer than the other three (electricity, gas, and water) have been in existence.

Diesel & gas powered compressors offer advantages like higher power ratings, portability, and freedom from reliance on local electric power grids, but most air compressors in industrial use are powered by electric motors. They’re plentiful, reliable, and easily adaptable to a range of control schemes that offer efficient operation across a wide variety of operations.

Which control method is right for you will depend on a number of factors specific to your operation. Here’s a brief run-down that may help you narrow down the selection:

  • Compressors in smaller facilities that supply intermittent loads like air guns, paint sprayers, tire inflators, etc. (like the one shown on the right) are oftentimes controlled via Start/Stop. This turns the compressor motor on and off, in response to a pressure signal. This is the simplest, least expensive method, and is just fine for smaller reciprocating compressors that aren’t adversely affected by cycling on & off.
  • Some compressors ARE adversely affected by Start/Stop control…like rotary screw models. These take a finite amount of time to start back up, which could allow header pressure to drop below usable levels. If they cycle too often, heat from the starting current can build up & overheat the motor. If that’s not bad enough, the screw elements & bearings of the compressor itself are oil lubricated…every time they start up, there’s a finite amount of time where metal-to-metal contact occurs before the oil flow is providing rated lubrication. With Load/Unload control, the motor turns continuously, while a valve on the intake of the compressor is cycled by the compressor discharge pressure: it opens (loads) to build or maintain pressure, and closes (unloads) when rated pressure is achieved. When unloaded, the motor uses about 1/3 of the energy it uses while loaded.
  • While turning down energy use to 1/3 of full load is a great way to cut operating cost while maintaining operational integrity of your compressed air system, and physical integrity of your compressor, it doesn’t necessarily make sense when demand may be low enough to be serviced by existing system storage over long periods of time. That’s where Dual/Auto Dual control comes in. It allows you to select between Start/Stop and Load /Unload control modes.  Automatic Dual Control incorporates an over-run timer, so that the motor is stopped after a certain period of time without a demand. This method is most often used in facilities where different shifts have substantially different compressed air load requirements.

When any of the above control schemes are used, they will necessarily rely on having an adequate storage capacity…the compressor’s receiver, and intermediate storage (like EXAIR’s Model 9500-60 60 Gallon Receiver Tank, shown on right) must be adequately sized (and strategically located) to ensure adequate point-of-use pressures are maintained while the compressor’s motor or intake valve cycle. Other methods use variable controls to “tighten up” the cycle bands…these don’t rely on as much storage volume, and in some (but not all) cases, result in higher energy efficiency:

  • A variation of Load/Unload control, called Modulation, throttles the intake valve instead of opening & closing it, to maintain a specific system pressure. This method is limited in range from 100% to 40% of rated capacity, though, so it’s fairly inefficient in many cases.
  • Slide, spiral, or turn valves are built in to certain compressor designs to control output by a method called Variable Displacement, which (as advertised) changes the physical displacement volume of the air end. When header pressure rises, it sends a signal which repositions the valve progressively, reducing the working length of the rotors. This allows some bypass at the inlet, limiting the volume of air that’s being compressed with each turn of the rotor. Since the inlet pressure & compression ratio remain constant, the power draw from the partial load is considerably lower…so it costs less to operate. The normal operating range for this method is from 100% to 40% of rated capacity, but when used in conjunction with inlet valve Modulation, it’s effective & efficient down to 20% of rated capacity.
  • Of course, the most significant advance in efficient control of rotating industrial equipment since Nikola Tesla invented 3-phase AC is the Variable Speed Drive. When the frequency of the AC power supplied to an electric motor is changed, the speed at which it rotates changes in direct proportion. By applying this type of control to an air compressor, the motor’s speed is continuously controlled to match the air demand. Energy costs can be greatly reduced, as this method allows efficient turn down to as low as 20% of rated capacity.

As mentioned a couple times above, multiple control schemes can be applied, depending on user specific needs. Adding accessories, of course, adds cost to your capital purchase, but discussions with your air compressor dealer will lay out the pros, cons, and return on investment. While we don’t sell, service, or even recommend specific air compressors, EXAIR Corporation is in the business of helping you get the most out of your compressed air system. If you’d like to talk more about it, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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