Consider these Variables When Choosing Compressed Air Pipe Size

Here on the EXAIR blog we discuss pressure drops, correct plumbing, pipe sizing, and friction losses within your piping system from time to time.   We will generally even give recommendations on what size piping to use.  These are the variables that you will want to consider when selecting a piping size that will suit your need and give the ability to expand if needed.

The variables to know for a new piping run are as follows.

  • Flow Rate (SCFM) of demand side (products needing the supplied compressed air)
  • System Pressure (psig) – Safe operating pressure that will account for pressure drops.
  • Minimum Operating Pressure Allowed (psig) – Lowest pressure permitted by any demand side point of use product.
  • Total Length of Piping System (feet)
  • Piping Cost ($)
  • Installation Cost ($)
  • Operational Hours ( hr.)
  • Electical Costs ($/kwh)
  • Project Life (years) – Is there a planned expansion?

An equation can be used to calculate the diameter of pipe required for a known flow rate and allowable pressure drop.   The equation is shown below.

A = (144 x Q x Pa) / (V x 60 x (Pd + Pa)
A = Cross-Sectional are of the pipe bore. (sq. in.).
Q = Flow rate (cubic ft. / min of free air)
Pa = Prevailing atmospheric absolute pressure (psia)
Pd  = Compressor discharge gauge pressure (psig)
V = Design pipe velocity ( ft/sec)

If all of these variables are not known, there are also reference charts which will eliminate the variables needed to total flow rate required for the system, as well as the total length of the piping. The chart shown below was taken from EXAIR’s Knowledge Base.


Airflow Through 1/4″ Shed. 40 Pipe

Once the piping size is selected to meet the needs of the system the future potential of expansion should be taken into account and anticipated for.   If no expansion is planned, simply take your length of pipe and start looking at your cost per foot and installation costs.    If expansions are planned and known, consider supplying the equipment now and accounting for it if the additional capital expenditure is acceptable at this point.

The benefits to having properly sized compressed air lines for the entire facility and for the long term expansion goals makes life easier.   When production is increased, or when new machinery is added there is not a need to re-engineer the entire system in order to get enough capacity to that last machine.   If the main compressed air system is undersized then optimal performance for the facility will never be achieved.   By not taking the above variables into consideration or just using what is cheapest is simply setting the system up for failure and inefficiencies.   All of these considerations lead to an optimized compressed air system which leads to a sustainable utility.

Brian Farno
Application Engineer Manager

The Compressor Whisperer

(Whisperer, Whisperer, Whisperer…)

Professor Penurious is determined to break into television…we hope you enjoy the following trailer for his latest attempt.

Russ Bowman
Application Engineer
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Need More Capacity? Start By Finding it in House or Renting

I field a decent number of calls from companies that are trying to expand to new lines or venture into an area of production that they have not crossed into before.  Maybe it is bringing a process in-house that they traditionally outsourced, or altering a process that now requires a large scale blow off operation. In many cases, as these companies grow and succeed, their compressed air systems grow with them. Some of them need to find out find out how much air they will need if when they make decisions to bring processes in house or expand a current process.

One of the first options when needing more capacity from your current compressed air system is to take a look at the existing demand side and determine if we can free up enough supply to meet the requirements of this new option.   Let’s say for instance a new 60″ Super Air Knife is needed.   To test that unit at 80 psig inlet pressure we would need to free up 174 SCFM of compressed air. In all the years we have been around it is still surprising to consult with customers who are using large numbers of open blow-offs, homemade air knives, coolant hoses and nozzles for compressed air etc. These companies can find that extra capacity in their current systems by retrofitting engineered solutions on to the aforementioned poor solutions for keeping compressed air efficient. IF you are using some of those solutions, call EXAIR today to find out how much air our products may save you.

In the event that is not possible to find the necessary new volume of compressed air by streamlining your current system, it means looking at adding compressor capacity.  Some companies think they have to go out to buy a new compressor immediately, simply to test this new process.   That is more often than not, false.   The best recommendation I have is to look into renting a compressor, much like the one shown below.

A Rental Tow Behind Air Compressor

A Rental Tow Behind Air Compressor

The compressor distribution piping.

The compressor distribution piping.

I saw this unit while I was jogging, well attempting to jog, on my lunch break.  This was outside a local company that apparently, going through a very similar scenario like I mentioned above.  When I looked a little closer, I noticed the unit included around a 75-100′ of hose that did not use the dreaded quick disconnect fittings everyone sees.  Instead it utilized what I know as a Chicago style air fitting which does not restrict the air flow nearly as much as a quick disconnect and permits you to utilize the largest volume of compressed air from the compressor – remember folks: properly sized compressed air lines and fittings are extremely important when needing to keep volume and pressure of compressed air at high levels.

A Chicago Style Air Fitting

A Chicago Style Air Fitting


Once I looked up the statistics on the compressor I found that it will generate up to 375 CFM at 150 psig.  This is more than enough to test or run a 60″ Super Air Knife and validate whether additional compressors are needed, as well as if the Super Air Knife will perform to meet your needs.   Then, when you are done with the test, you can simply return the air compressor. Based on the results of this test, this could be another point to decide if you could save the needed air from your current system or if you would require a new compressor.

The EXAIR Guarantee

The EXAIR Guarantee

The moral that I am trying to instill in this blog is simple.  If you have a need for more compressed air to validate a new or improved process, don’t hesitate to think outside of your existing system. Where there is a will and a need, there is a way.  If it doesn’t work, take advantage of our 30 day unconditional trial.

Brian Farno
Application Engineer

Pressure Profile: Where to Measure Your Air Pressure

Generic Layout drawing of compressed air piping system.

In order to fully understand how efficient your compressed air system may be, you will need to generate a system pressure profile at some point.   This is a list or diagram of what pressures you have in your compressed air system at specific locations, as well as the pressure required by all the demand devices on your compressed air system.

One of the reasons for the pressure profile is that you may have an application that is far away from the compressor but also highly dependent on a specific operating pressure.   You may also find an application that, due to pressure losses within the system, causes an artificially high pressure demand.

The list below gives the critical points for measuring your compressed air system profile.

  1. At the air compressor discharge. (If using multiple compressors, measure at each.)
  2. If dryers of any type are being used after the compressor measure downstream from the dryer.
  3. Downstream of each filter. (If a particulate filter and oil removal filter are being used it is best to measure downstream of each individual device.   This is to tell when you have more than a 5 psig pressure drop or a clogged filter.)
  4. After each intermediate storage device, such as receiver tanks.
  5. At the point just before the main line from your compressor room branches off to distribution.
  6. The furthest point of each header line you have installed.
  7. On both sides of every filter/regulator units that are at high pressure point of use applications.

To give you an idea of why it is so important to measure these locations, take a look at the blogs we have posted on pressure drop. (Link Here)  As you can tell by the list of blogs that comes up, pressure drop through piping can really cause a lot of wasted energy in your compressed air system.   If you can get a good base line measurement by utilizing a pressure profile then you can start the process to optimizing your compressed air system.

6 steps

The EXAIR Six Steps To Optimizing Your Compressed Air System.


If you would like to discuss this or any of the other 6 steps to compressed air optimization, feel free to contact us.

Brian Farno
Application Engineer

A For Ingenuity, F For Performance

Over the past month or so, I have had several customers taking advantage of the EXAIR Efficiency Lab.  This one that came in really stood out to me though.  This is a 48″ long Steel pipe that was custom designed and made by the customer.  The unit has slots that we believe were EDM’d into the pipe.


The customer was using this to blow debris off sheets of steel.   Once we got the pipe hooked up and set to run we were only able to generate 3.5 psig inlet pressure to the pipe.   The measured consumption was 176.55 SCFM at 3.5 psig inlet pressure.  They were utilizing 80 psig inlet pressure, needless to say it was slightly overkill for the application.    At 80 psig the pipe would consume over 1,400 SCFM of compressed air.

We were able to replace the pipe with a 48″ Super Air Knife Kit that still produced the necessary force to remove the debris from the steel, and only consumed 139.2 SCFM at 80 psig.   The customer was able to save 1,252.8 SCFM and reduced the noise level drastically.   The amount of air saved is equivalent to a little more than a 300 HP compressor.   The amount of air saved is equivalent to 31.3 cents per minute of operation.

We get surprised (still) every now and then at the amount of compressed air customers are willing to use for applications. This example was a surprising one. But, now we have a customer who knows that EXAIR knows how to save compressed air and keep the plant running…while staying OSHA compliant…while reducing noise levels.

These guys took some time and spent some money to make this custom homemade blow off pipe. Needless to say, something that costs more and is custom, isn’t always better.  If you have a compressed air application in house and would like to see how you can optimize it, contact us.

Brian Farno
Application Engineer

Air Compressor Throughput Control

Throughput Control

At the end of my last blog, I mentioned the slide valve operation on a screw compressor.  A slide valve is the basis of throughput control for a screw compressor.  Throughput control is a term used to describe the process of controlling the energy input to the compressor in order to reach the control objective (output pressure and/or flow).  No matter the type of compressor, throughput control is achieved by using speed control, suction throttling, discharge throttling, or recycle control.  There are a few other methods of controlling throughput, but these four are the most common, and throughput control is a common practice used to dial in the needs of a compressed air system/application.

The first, speed control, is the most common and most efficient method.  Essentially, the output flow and pressure are regulated by adjusting the speed of the motor driving the compressor unit.  Increasing the speed of the motor driving the compressor will result in an increased output flow at a constant pressure, or an increased output pressure at a constant flow.  Speed control can also be coupled with other control methods to fine tune the throughput of the compressor.

Suction valve throttling is exactly what it sounds like.  The incoming air flow and pressure are restricted by installing a control valve immediately upstream of the compressor inlet, and the valve’s position is controlled as a function of the exhaust discharge pressure and/or flow.  When the valve is activated and the suction is “throttled” or restricted, the output flow will decrease (because there is less air taken in by the compressor), and the output pressure will subsequently increase.

Discharge valve throttling restricts the pressure from the compressor to match the process requirements at a constant flow.  As a result of this setup, the compressor must work harder than the process requires and this control scheme is extremely inefficient.

Recycle control uses a valve to return compressor discharge flow back to the suction port of the compressor.  As many people know, compressing a gas can generate a good amount of heat, and this heat is often transferred into the compressed air.  Because of this, a cooler is usually (and should be) installed in the line between the recycle control and the suction valves.  The recycle valve can modulate from fully open to fully closed, which gives a full range of control over the discharge flow and can help with loading/unloading of the compressor.

These control methods are all fairly straightforward and on their surface aren’t too intimidating.  They remind me of rudimentary PID controllers, which can be dialed in to a tee.   Think of the way an elevator car reaches the intended floor without slamming to a stop or jolting when it starts moving.  That’s achieved though PID control, and similar methodology is applied to compressor load and unload as well as operation.  But if I get under the surface of compressor control and see PID diagrams, I’m getting the professor!

Lee Evans
Application Engineer

Screw Compressors

Screw Compressor

A short time ago I picked up a book about the principles and operation theory of air compressors.  We have a wealth of knowledge floating around the department and company as a whole, so I thought this book may provide an opportunity for me to contribute.  As I read through, I find myself “geeking out” over the level of technicality with which compressors are designed.  Perhaps I’m biased based on experience and familiarity, but my compressor preference tends to lean toward a screw compressor.  This isn’t to say these are the best or most suitable compressor for every application (they most suitably aren’t), only that they sit with me the best.

A screw compressor, like a reciprocating compressor, is technically a positive displacement device (unlike an axial or centrifugal compressor which is classified as dynamic device).  A volume of gas becomes trapped in an enclosed space and then that volume is reduced resulting in an increase in pressure.  Within a screw compressor there are two screws with mating profiles which we can refer to as screw “A” and screw “B”.  Of these screws, screw “A” has concave inlets, and screw “B” has convex inlets.  These screws rotate in opposite directions and as screw “A” receives power from the outside source (motor), it transmits power through to screw “B” through a set of synchronization gears.  (Think of the way air is forced into an engine through a supercharger…)

As the screws rotate, gas is drawn into the inlet/suction port and compressed by rotary motion.  This gas is moved axially from the suction to the discharge port.  The location of a discharge port determines when compression is complete, and this location can be changed to regulate the discharge pressure.

The efficiency of such a setup is dependent on the clearance between the screws and the quality of the seal surrounding the air as it travels through this process.   To aid with efficiency and to increase seal quality, oil is sometimes injected into the inlet cavity, and is later separated for reuse.  (Aging components can result in oil contamination within the compressed air, which is why we recommend an oil removal filter when in doubt.)

One of my favorite things about screw compressors is the ability to control output through a slide valve.  As the valve is adjusted to shorten the working length of the rotor (screw), less horsepower is required to maintain operation.  This type of control is unique to screw compressor design and can yield significant reduction in operating cost, which we tend to like at EXAIR.

If you have compressed air or application related questions, give us a call.

Lee Evans
Application Engineer

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