Purchasing SPF Trailers: Is Your Air Pressure Equipment Sized for Optimal Performance?

When choosing your spray foam rig, your compressor needs to be large enough to provide sufficient air to all your equipment. When making this decision, you’ll need to consider whether you plan on using low-pressure or high-pressure spray foam machines. You’ll also want to understand the capacity needed to power your SPF guns, pump and your breathing equipment.

Let’s look at the two main considerations when sizing your compressor:

  • Spray foam air compressor volume: This is measured in cubic ft. per minute (CFM)
  • Spray foam air compressor pressure: This is measured in pounds per square inch (PSI)

The three most common items in your spray foam rig that need air are the gun and two transfer pumps. I always use the 5,5,5, rule:

  • 5 CFM for gun
  • 5 CFM for each transfer pump
  • 15-20 CFM of air at 120 PSI, at the bare minimum

Pressure and Volume Considerations for Your Spray Foam Rig

After you choose your spray foam insulation air compressor, you should consider the other pneumatic tools you may need. To answer this question, ask yourself whether you’ll be spraying open or closed cell foam.

If you are spraying open-cell foam, you will need a mixer. You’ll also need to determine whether you’ll be spraying a premixed product or a continuous mix product. Air-driven motorized mixers can take up a lot of CFM, so make sure your compressor can handle everything you have on the rig.

Let’s say you have 15 CFM available at 125 PSI. This will be plenty for most mixers if it’s a premixed material. Now, add 15 CFM more if you need to continuously mix AND power your gun and transfer pumps. You’d need 30 CFM to run all components in this system. If you overwork the compressor, you start losing pressure, and, unfortunately, a lack of pressure or volume can cost you money.

Here are some examples:

  • Lack of air pressure to your transfer pumps can reduce the feed capacity to your proportioner, causing off-ratio situations and reduced yield.
  • Lack of air volume to your mixer can reduce yield by improperly mixing material in the drum.
  • Lack of air to your gun can cause a trigger lag and reduced cleanoff ability. This increases downtime since your crew will be cleaning the tip more often and the potential for crossover by lagging trigger speed.

High-Pressure Breathing Air Systems: Are They Necessary?

Another component to consider is a high-pressure breathing air system that runs off the compressor. These fresh air systems take a minimum of 15 CFM. This number can go up depending on how many workers you need to supply air to and also by how much additional air usage is required for cooling devices. By keeping your installers comfortable, cooling devices can reduce the hours spent on site, cutting labor costs substantially.


Choosing the right air compressor for your spray foam rig is very important, as an improperly sized compressor could cost you a ton of money.

How? If sized incorrectly, your components will starve for air and you will end up having to invest in a larger air compressor and/or generator. Replacing this equipment could cost you tens of thousands of dollars.

Understanding the Types of Insulation Machines and How They Affect Your Compressor Size

Another thing to take into consideration with compressor sizing is the type of machine you are buying. There are a few types of spray foam machines; the most common machines for trailers are electric-driven, but hydraulic and pneumatic options are popular as well.

An electric-driven machine might not demand a large air compressor. However, being air-driven, pneumatic machines require a much larger air compressor with higher CFM ratings. So, be sure your supplier understands the sizing of the compressors and the components you are running in your rig.

Managing Air Quality & Moisture Concerns in Humid Climates

Now that you’ve sized your compressor appropriately, let’s move on to managing the air quality. Three common contaminants could wreak havoc on your rig, crew and foam: liquid water, water vapor and oil. To prevent damage caused by these elements, make sure your rig is outfitted with this equipment:

  • Water separators to manage moisture concerns
  • Air drying equipment to mitigate water vapor and overheating
  • Oil coalescing filters keep oil in a compressor from harming the air dryer

Without the proper management of all three contaminants of compressed air, you may be throwing money down the drain.

Some questions you need to ask before buying a rig:

  • Does the spray rig have an air dryer?
  • What is the maximum inlet temperature?
  • Is this air dryer sized appropriately for my compressor?
  • Is the air dryer sized appropriately for my climate area? Critical for work in hot climates. Air dryers remove harmful water vapor from the air.

Water Vapor Concerns & Solutions

Remember, an air dryer only manages water vapor and has little defense against liquid bulk water, which is why a bulk water separator must be used in tandem with an air dryer.

Without the right bulk water separator and air dryer, your rig will be left prone to significant moisture-related damage.

Moisture causes problems with isocyanates, decreases yield and causes air-driven equipment failures. Make sure the dryer is equipped to handle the CFM of the compressor you’re pairing it with, as well as the inlet air temperature.

Many inexpensive dryers are rated for 125-160°F inlet air. This is an issue, because without proper time to cool, air temperature in a foam rig may exceed 200°F, which requires a dryer rated for higher inlet temperatures.

Foam rigs should also have a water separator installed before the air dryer for removing liquid water. Remember, air dryers remove water vapor, and water separators remove liquid water.

Having an air dryer on your rig, especially in humid climates, is critical. Replacing your pumps, lines, guns, etc is extremely expensive if you get moisture in your A-side lines. Don’t cut costs — get the air dryer!

Oil Filtration Concerns & Solutions

Oil is introduced into almost any form of compressed air, which is why oil levels go down on most compressors! Oil is good in some instances, but not so much in the SPF industry.

Oil-saturated air introduced into most all air dryers is problematic. Whether you’re using a desiccant or refrigerated-style dryer, oil can contaminate or coat the internal cooling vanes in a refrigerated dryer.

Unless you want to spend money on replacing your dryer, you should install an oil coalescing filter.

How You Can Gain an Edge on Your Competitors and Save Money With Your Rig:

  1. Install a Water Separator
    • Reduce bulk water content in your system.
    • Encourage greater foam adhesion by limiting water in the air.
    • Minimize the chance for corrosion.
  2. Install an Oil Coalescer
    • Avoid replacing your air dryer.
    • Increase the service life of breathing air filters.
    • Encourage greater foam adhesion by limiting oil in the air.

Other options to consider include compressor auto tank drains and a continuous-run function to reduce the amount of current being used during electric motor startup. These two options need to be done right to increase spray foam system uptime. When done wrong, it can not only cause unwanted downtime but it can result in costly repairs.

Remember, improperly sized air compressors and poor air quality are frequent killers of SPF rigs — causing moisture and equipment issues that could cost you more than you can handle.

Considering an SPF Rig but Not Sure How to Get Started?

In short, make sure your rig builder is someone you trust and are completely comfortable with. Avoid going for the easy and cheap options, and invest in a rig that will keep your business growing for many years to come.

A spray foam rig or trailer is a lifelong investment, and cutting corners usually ends up costing you more money in the long run. Work with the pros — contact your local IDI Distributor’s expert team to get started!

By: Ken Allison, Director of Business Development

Ken specializes in business development and building science. You can find him at any of our training events around the country helping local contractors grow their business. Contact your local rep about the next training event near you to hear Ken’s advice first-hand.

Read the Full Series:

Read our full rig series to determine what type of rig you should invest in to get the most ROI. Learn about the important factors that should go into your rig purchase decision — and how they could affect your rig’s performance on the job … and your profitability!

  1. Introducing Our Mini-Series (what you should know about owning a spray foam rig)
  2. Important SPF Rig Weight & Capacity Considerations
  3. How to Choose the Right Air Filtration System
  4. Choosing SPF Equipment With the Best ROI
  5. Choosing Power and Auxiliary Equipment
  6. Other Cost-Saving Considerations


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