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Perfectly Picking Your Compressed Air Pipes

Compressed Air Pipe

Perfectly Picking Your Compressed Air Pipes

No matter what it is, if you want something to be able to go from point A to point B then it needs to have a means of travel. If the object or substance you want to move does not have a path to travel, then it will not make it to the destination. This applies to compressed air and compressed air piping as well. If you do not have a system in place that will get the air you need to the point of use. 

The main objective of compressed air piping is to deliver the compressed air to the point of use without losing pressure or adding contaminants. The material that you use and the sizing of the piping can affect the pressure and velocity of the air traveling through the piping. So a lot goes into determining how to size these pipes properly. But that’s why you’re here, right?

In order to be able to pick out the proper sized piping, you need to understand how it works first. By understanding the why behind the pipes instead of just what they are. With a broader understanding, it will benefit you as the customer and as the individual using the equipment. The better you understand the equipment, the easier it will be for you to design and lay out your pipes.

When you have properly designed your compressed air distribution system, there are three demands you can expect:

  • Low-pressure drop between the compressor and the point of consumption
  • Minimum leakage from distribution piping
  • Efficient condensate separation

If your compressed air distribution system is inadequate, you can expect high energy bills, low productivity, and poor performance from your air tools. Just like with a sprinkler, if the flow is not strong enough or at the right pressure, it will cause problems with the actual usage of the water, just like compressed air.

 

Consider This First

Before we get into the sizing formulas and all of the nitty gritty details of the process. Let’s cover some basic additional information you may need to consider before you size and put your compressed air delivery system in place.

When you are building a compressed air system, knowing the maximum CFM requirements is incredibly important as these measurements dictate the sizing of your entire system. This measurement reflects the volume of air, in cubic feet per minute, that is moving through the system in, you guessed it, one minute. 

Alongside CFM, you are going to need to know the required operating pressure for your compressed air system. You want your system to keep in line with this operating pressure because every 2PSI that you stray above your operating pressure wastes 1 percent of energy. By going over all you are doing is costing yourself more money.

Not only does going over your operation pressure cost you, undersizing your pipes or equipment can be detrimental to production as well. Sometimes a drop as small as 1 PSI can cause problems over long stretches. The pipes in your system must have a surface area that is large enough to transport the necessary volume of airflow.

In addition to PSI and CFM, another characteristic to keep track of is the air velocity. If the air is moving faster than 9m/s it can transport debris and water vapor as well. This makes the ideal pipeline velocity in the range of 6-7m/s and to never exceed that 9m/s mark. This will prevent additional condensate and debris from being transported with the compressed air.

By taking these factors into consideration, you may be able to install a loop type compressed air distribution system. In these systems, a portion of the pipe is looped back on itself to increase the CFM of the system by a multiplier of 1.5. In other words, if you have pipe rated for 400 CFM at 125 PSI and you incorporate the loop system, the piping will be able to achieve 600 CFM at the desired 125 PSI.

When choosing the right sized pipes, some additional components you need to consider are:

  • Type of Air Compressor
  • Operating PSI
  • Maximum CFM
  • Estimated or Exact Length of Piping
  • Bends and Connections

Right now you probably are wondering how you ensure that your pipes are properly sized to these specific components so that problems do not arise. So let’s break down the formulas that will help you in determining the correct pipe size for your demands.

Below is a graph of ideal pipe size for respective CFM’s. Anything in green is acceptable and your sweet spot is right in between the green and orange, in the light orange/tan color. Never go into the orange as it will only cause problems for you.

 

Table 1

 

The Great Compressed Air Piping Formula

When it comes to finding the diameter of the pipe you need, it is a simple formula that you need to follow. The formula will be listed below along with a key to the variables and what they mean.

  • A
    • Area in square inches of a cross-section of the pipe
      • This is the size of the space in the pipe
  • Q
    • Flow Rate
    • CFM
  • Pa
    • Current absolute pressure
    • PSI
  • Pd
    • Compressor Gauge pressure
    • Excluding absolute pressure
  • V
    • Pipe Velocity
    • Feet per second

 

This formula will help you to determine the size of the pipe that you need, but it does not give you any inclination to how much pipe you are going to need. That is because before you figure out how much pipe you need, you need to know what size of pipe will work for your system. Now that you have figured out what size pipe you need, we can move onto the next step.

Unfortunately, when it comes to determining the square footage of piping there is no quick formula to figuring it out, instead you are going to need to make a scale diagram. In this pipe diagram, you are going to need to do a few things to ensure that you are getting all of your proper measurements.

Your diagram should not only be to scale, but also have pipe diameters, connections, regulators, and bends included as well. This will help you account for everything that you are going to need for your air distribution system. You’ll want to measure all of the short paths and add them together as well as the dimensions of all the connections, outlets, joints, and curves. 

The longer your piping is, the bigger it will need to be to avoid excess pressure loss, remember every 2% increase over that 100PSI mark increases your energy costs by 1%. Another thing you will want to keep in mind when sizing and measuring your pipes is including equivalent lengths in your calculations for fittings and bends. 

If you have a new system and are not quite sure how many bends, joints, couplings, and other miscellaneous components will be present, there is a basic rule of thumb that you should follow; Take your estimated meters of this equipment and then multiply it by 1.7 for your pressure drop calculations. Table 2 will help illustrate some of the typical sizes for these components.

 

Table 2

 

With piping, if it is too small then pressure drop is inevitable because the air will be stifled. A common mistake that causes this is sizing piping based on the compressor discharge port rather than being determined by PSI, CFM, and distance. Although it may cost more, upsizing your pipes by 1 can reduce or eliminate pressure drop and result in you saving more money.

Pressure drop is an unavoidable part of transporting compressed air. Drops occur due to the friction between the internal lining of the pipe and the air itself and unfortunately frictionless pipe is only a reality in our imaginations. The key is to focus on minimizing the pressure drop as much as possible.

For most applications, the base formula and the yardage of piping should be all that you need to figure out what type of pipe works best for your system. And if you don’t feel comfortable with just those, don’t be afraid to go look at Table 1 and Table 2. If you are worried this won’t be enough, then we have another formula you will be able to use.

 

This formula determines the flow coefficient of the piping, this is used to determine the pipes ability to allow things to pass or flow through it. The formula is:

  • Q is the rate of flow (expressed in US gallons per minute),
  • SG is the specific gravity of the fluid (for air = 1)
  • ΔP is the pressure drop across the valve (expressed in psi)

 

Picking The Right Type of Compressed Air Pipe

When it comes to your compressed air pipes choosing the right type of piping matters. The material can have a direct effect on efficiency and longevity in your system. It is important to consider your options and application before you decide on which piping you want to go with.

First things first, you should never, ever use PVC for your compressed air distribution. Not only does this material violate OSHA Regulations, but the readily available nature of it makes it easier for people to get their hands on. Just like many plastics, PVC becomes brittle and weak over time. This can crack, break, or even shatter and send shrapnel flying.

Not only is the plastic not up to the task of transporting compressed air, but it also degrades faster due to the presence of oil and heat in the line. This basically guarantees that if you use PVC, it will crack, break, or potentially send razor sharp shrapnel flying, which if you didn’t know, can be fatal.

Picking your pipes gives you four valid options, that all have their individual pros and cons of using, but most importantly they all stand up to OSHA Regulations. Let’s break down these different materials and how they can benefit your system if you were to use it.

 

Copper Pipe

With copper pipes, you get the combination of corrosion-free and adaptability due to the ease of cutting and welding it. These pipes are lightweight and have a range of fittings available to fit your compressed air system. These pipes have a solid laminar flow as well which gives them another advantage.

The big problem occurs with future changes to your system if you plan on using copper. If you need to add a new line it is going to require a reconfiguration of the piping with more welding and cutting to make sure everything lines up.

 

Aluminum Pipe

Aluminum piping is our preference. It is the current best option due to the flexibility and consistency of these pipes. They have anti-corrosive properties alongside being lightweight and fittings that are easy to use and can be changed out.

Unlike the other types of pipes, aluminum pipes can be changed around after they have been put in place with little change needed. Rather than needing to re-size and reweld the piping, you can change the joint out to allow for the new piping to be connected or switch out specific sections if it is causing problems.

 

Stainless Steel Pipe

Stainless-steel has a reputation for its consistency and no risk of degradation or corrosion. Although it has these great benefits, it is still incredibly heavy. Fitting and placing stainless-steel can be a difficult task to accomplish, not to mention it has a high material cost.

Due to the mix of high cost and difficulty to fit, these pipes are uncommon in the compressed air industry and are not the first choice for many people.

 

Black Steel Pipe

When it comes to black steel pipes, they are commonly used in compressed air systems. They are made of strong and durable material, but are time-consuming to put up. Unfortunately, these pipes are heavy and susceptible to corrosion. Not only are they a risk for corrosion, the threaded connections can slip and cause leaks.

These pipes are difficult to place due to their heavy nature, and even more difficult to change the piping layout if you have any changes in the future. By going with these pipes you lock yourself into that system until you have the time to upgrade or have no other choice but to change your piping.

 

If you have any other questions please refer to Table 3 below.

 

Table 3

 

Don’t Forget About The Future of Your Compressed Air Pipes

Now that you know the basics of air piping, let’s wrap the process together to make it as easy to understand the process as possible. You also want to keep your plans for the future in mind while you are doing this as well, you can always fit your air into the bigger pipes, but if your system gets bigger and you have pipes that are too small then you’re going to have a problem on your hands.

To start everything off, you are going to need to determine the maximum CFM of your compressor. This will be your baseline for the rest of your system. If the pipes don’t fit the compressor, the air is not going to move as it should.

After you have your CFM, you will need to draw a piping schematic that includes everything. Show all pipe fittings, valves, joints, etc in your drawing to ensure you have accurate measurements of everything. Once you have this drawn out then you can total the length of all the straight pipe that you will need.

Now you will want to use our handy dandy formula to help calculate your compressed air pipe size. This will give you the size necessary for your set up, as long as you are using variables from your setup that is. If the calculation is too daunting for you, there are charts available to help you determine that.

Once you have all this information, you will want to go back to the schematic to make sure you have all of the distance the air needs to travel. Then go back through one last time adding all of the length together to get your total piping, and then double check on Table 1. After you have done that you will be good to go on the necessary information for buying your pipe. 

All that is left is deciding your material and you will be ready to order your pipes. The process is a lot more daunting in concept than in actuality when you break it down into pieces.

 

Before You Buy

Although it can be an intimidating process, sizing your pipes is easier than you’d expect. It takes time and attention but not much more beyond that. Now that you have the tools at your disposal you can go out and get your own air distribution system, just don’t forget the basics.

Make sure that you have accounted for all of the pressure drop in your system, not just that which may be caused by the pipes. You’ll also want to regularly maintain your equipment so that it does not affect the integrity of your compressed air pipes. Any time that you can it is smart to reduce the distance the air has to travel to reduce the likelihood of pressure drop. 

Air piping is susceptible to the same problems as the rest of your compressed air equipment. Moisture and particulates can cause internal problems, problems downstream, or even completely shutdown your system. So take care of your components. Now go take control of your compressed air system.

 

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