Wondering how to choose the right air compressor for your facility? In this guide, we’ll cover all the basics, including how air compressors work, the types of air compressors, and air compressor specifications and features to look for.
How to Choose the Right Air Compressor
Choosing the right air compressor for industrial and commercial applications can be complicated. The right choice depends on several factors:
- How much air (CFM) is required by your applications?
- What air pressure is needed?
- Are your air requirements continuous or sporadic?
- Where will the air compressor be used?
Applications for Industrial Air Compressors
An air compressor acts like a battery in the shop, manufacturing facility or job site. Compressed air is used to power a lot of different industrial and commercial applications. Some of the most common include:
- Powering hand-held pneumatic tools such as nail guns, air hammers, grinders, caulking guns, hydraulic riveters, impact wrenches, and ratchets.
- Paint spray, for both hand-held airbrushing and painting tools and industrial spray booths.
- Powering pneumatic manufacturing lines, including conveyor systems and automated hydraulic machinery
- Many metal working machines such as CNC’s, Laser cutting and blow guns.
The best air compressor will depend on the application it is being used for. Understanding how air compressors work and the different types of commercial and industrial air compressors will help you make the right choice.
How Does an Air Compressor Work?
Air compressors work by taking in air from the environment and squeezing it, reducing the size of each cubic foot. As air is compressed, it is pressurized: the smaller the volume that the air is forced into, the more pressure it exerts. This is known as Boyle’s Law and is expressed mathematically like this: P1 x V1 = P2 x P2
It is this pressurization that gives compressed air the ability to do work. In essence, as you compress air into a smaller space, you are storing energy that can be used later to power different applications. The compressed air can be used immediately to power various tools and machines. More commonly, it goes into an air receiver tank, which stores the compressed air for later use and ensures a consistent supply of ready-to-use air.
Air compressors achieve compression in one of two ways.
- Positive air displacement: Air is forced into a chamber, where it is compressed using mechanical means into a smaller volume. Pistons, screws or rotary vanes may be used to achieve mechanical compression. This is the most common method of air compression used in both home and commercial air compressors. Rotary screw, rotary vane and reciprocating air compressors all rely on positive displacement.
- Dynamic displacement: Rotating fan blades powered by an engine create airflow. As air moves through the space, it is gradually constricted into a smaller volume. Axial air compressors and centrifugal air compressors rely on dynamic air displacement. These types of air compressors are generally only used for very high-volume industrial applications, such as large air separation plants.
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Types of Air Compressors
What type of air compressor should you use? There are several types of air compressors to consider. As explained above, most air compressors use a form of positive displacement to generate compression. These range from small portable units used by small shops, home hobbyists and DIYers to large industrial air compressors used to power entire factories. The right type of air compressor depends on your application and how much, how often and how consistently you are using air.
A reciprocating (or piston-style) air compressor uses pistons driven by a crankshaft to compress air. They are best for applications that require short bursts of air intermittently, such as manual air-powered tools, blow-off and cleaning, tire inflation, airbrushing and sandblasting. They can be safely run with occasional, inconsistent use and at less than maximum capacity. A reciprocating air compressor is a great choice for smaller shops with lots of manual processes or with horsepower requirements of 10 HP or less.
Rotary Screw Air Compressors
Rotary screw air compressors use two meshing helical screws (or rotors) to compress air. Rotary screw air compressors are best for applications that require continuous air, such as robotic manufacturing equipment and conveyor systems. They produce a consistent, nonstop supply of clean air, making them the best choice for paint line, food processing, packaging and other applications where air quality is a consideration. They also tend to have quieter operation than a comparable rotary vane model, so they may be a good choice if noise is a concern. They are recommended for applications with duty cycles of 30-100%. They are not recommended if your air requirements are occasional or intermittent; they do not perform well with downtime.
Rotary screw air compressors come in both fixed-speed and variable-speed models. A fixed-speed rotary screw always is operating at maximum capacity. A variable speed drive allows the air compressor to ramp capacity up and down based on actual use. If your demand for air varies (but does not drop to zero), a VSD rotary screw compressor is an excellent choice.
Rotary Vane Air Compressors
A rotary vane air compressor is similar to a rotary screw compressor, but uses a rotor with individual sliding vanes to compress air instead of the helical screw mechanism. As the rotor turns, the vanes are pushed towards the wall of the chamber via centrifugal force, forming a seal. The trapped air is compressed into a smaller space during the revolution. Like rotary screw compressors, rotary vane compressors are designed for continuous use and come in both fixed-speed and variable-speed models. They typically have the same ambient temperature requirements and preventive maintenance frequencies as their rotary screw cousins.
Because the mechanism is very simple, rotary vane air compressors may offer benefits in terms of energy efficiency, service life and maintenance costs. Older models had a reputation for requiring more time to complete a PM compared to a rotary screw compressor, but modern models (with better oil filtration and separation) have largely eliminated this concern. However, if the rotary vane mechanism needs to be rebuilt, it may be harder to find a facility capable of completing the rebuild than it would be for a rotary screw compressor. Larger vane compressors over 50 HP are usually less efficient than rotary screws.
Portable Air Compressors
Most portable air compressors use reciprocating, or piston-style, technology. Portable air compressors range from small hand-held units with 1–5 CFM capacity to larger truck-mounted units with capacities of up to 100 CFM. Smaller portables come in “pancake” and “hotdog” styles, named for the shape of their integrated tank. These units are great for hobbyists, DIYers, small shops, roadside service and other applications requiring small, intermittent bursts of air.
Air Compressor Specifications
In addition to selecting the right type of air compressor for your application, it is also important to size the air compressor appropriately for your needs. There are three main specifications to consider when selecting an industrial air compressor, and they are all related.
- PSI (Pounds per Square Inch) is a measure of air pressure, or the amount of force the air exerts on the surrounding materials. PSI translates to the amount of energy stored in your compressed air system and the amount of work it can perform.
- CFM (Cubic Feet per Minute) is a measure of how much air the compressor can produce each minute. PSI and CFM are interrelated: your CFM rating is always for a specific pressure rating (e.g., 100 CFM at 90 PSI).
- Horsepower (HP) measures the amount of work that a motor can perform. The HP rating on your air compressor tells you the size of the motor it has.
Air Compressor PSI
Air compressors are rated for a maximum PSI. A typical industrial air compressor may have a maximum PSI of 125, which is more than adequate for most manufacturing, auto shop or fabrication applications. Some applications, such as sandblasting and certain laboratory applications, may require a higher PSI. Remember that PSI and CFM always go hand-in-hand; see more on CFM below.
Maintaining the right PSI is critical for both safety and productivity. If the PSI for your system is too low, tools and machinery may not work properly or stop working entirely. If pressure is too high, it may damage tools and equipment or create safety concerns.
The first step to calculating air compressor specifications is determining the PSI requirements of the tools and machines the compressor will power. Different tools have different PSI ratings. Most pneumatic hand tools (such as air hammers, staple guns, nail guns, ratchets, air brushes and impact wrenches) require around 90 PSI. CNC machines and other hydraulic machinery may be rated for up to 100 – 110 PSI.
The PSI for your compressed air system should be set to ensure that pressure will not drop below the minimum PSI for the tools and machines the system is powering. Because pressure drops as it moves through piping and connectors, you will need to set your system a little above your minimum required PSI to ensure that machines at the end of the run don’t lose pressure.
Aire Tip: Many facilities have PSI set higher than is necessary for their equipment. A 2 PSI reduction in plant pressure will save ~1% in energy costs for your compressed air system. Read more: Reduce Plant Pressure to Save Money and Energy
Air Compressor CFM
CFM is the easiest way to measure and compare the capacity of an air compressor. At a given PSI, an air compressor with a rating of 100 CFM can perform a lot more work than one rated for 50 CFM. Remember, the CFM rating for your air compressor is given at a particular PSI (typically 90 – 100 PSI). CFM is the amount of airflow that the air compressor can deliver to maintain that PSI.
You may see air compressors rated in SCFM. This stands for “Standard Cubic Feet per Minute.” This is the air compressor’s rating at standard atmospheric conditions (14.5 PSI atmospheric pressure, or sea level, and 70°F with relative humidity of 0%). Your actual delivered CFM will vary slightly depending on your elevation, temperature and humidity; rating units in SCFM allows accurate comparison between machines without worrying about these variables.
Your CFM requirements will depend on how many tools and machines are using air in your system and the PSI that needs to be maintained for them to run properly. There are several methods for determining your overall CFM demand, including direct calculation, Pump-Up Tests, and Draw-Down Tests.
Aire Tip: A Pump-Up Test can help you calculate your CFM demand. Read more: How to Calculate Air Compressor CFM Output and Production Requirements
Air Compressor Horsepower and Voltage
You may think that the HP rating of your air compressor’s motor is the most important indicator of the amount of power it can deliver. However, HP may actually be the least important rating for your air compressor. While more HP is generally correlated with higher CFM output, CFM is the more important number.
The amount of horsepower required to generate airflow at a given CFM will vary depending on the efficiency of the air compressor. The more efficient the compressor, the more airflow per HP it is able to generate. The efficiency will depend on the type and design of the air compressor. In general, rotary screw air compressors are more efficient than piston air compressors and require less HP to generate the same CFM.
In addition to HP, you’ll also want to pay attention to the air compressor voltage. Industrial air compressors have two voltage options: 208-230V and 460V. Make sure the model you choose has the right voltage for your facility. If you have both voltages available in your plant, it is more energy- and cost-efficient to go with the high-voltage option.
Air Compressor Features
What features should you look for in a commercial air compressor? Once you have determined the type and size of air compressor you need for your operations, you can start comparing the feature sets for different compressors. Here are some things you should look for.
If you are purchasing a commercial air compressor, ASME Certification is something that should be considered a must. The American Society of Mechanical Engineers, or ASME, is an organization that sets engineering codes and manufacturing standards for a variety of machines, parts and system components. ASME acts as an independent quality assurance organization to ensure the safety and quality of manufactured items. An ASME certification stamp means that the manufacturer has met all safety and engineering standards for their product.
Smaller air compressors sold by big-box stores for home use may not be ASME rated. If your HP and CFM requirements are low, you may be tempted to purchase one of these off-the-shelf consumer models. However, these units are not designed for daily use in a commercial or industrial environment. Look for the ASME rating to ensure that your air compressor can safely meet your usage demands.
Variable Speed Drive
Rotary screw and rotary vane air compressors come in both fixed-speed and variable-speed models. A variable speed drive (VSD) motor controls the frequency supplied to the drive motor in response to real-time demand on the system. If your demand for air is variable, a VSD drive can save significant energy and money.
Aire Tip: A VSD motor can help slash energy bills for your compressed air system by up to 70%. In some cases, your energy company will help you pay for the upgrade. Read more: Why Choose or Upgrade to a Variable Speed Drive Air Compressor?
The compressor should come with an internal cooling system to keep the pumping mechanism and motor cool. The cooling system will extend the life of your compressor.
- An air-cooling system uses a fan to cool the pump and vents excess heat from the system into the ambient air.
- A closed-loop dry cooling system acts similarly to the radiator of a car or the coils of an air conditioner. Liquid (typically a coolant such as glycol) continually moves through a series of closed coils, carrying heat away from the compressor pump and motor. Excess heat radiates off the coils to re-cool the liquid for the next cycle.
- An open-loop evaporative cooling system uses fresh water and moving air to cool the compressor. A fan blows air across the water, which provides natural cooling to the compressor motor.
Thermal Overload Switch
Air compression generates a lot of excess heat. An industrial air compressor should come with a thermal overload switch, which will shut off the motor if the compressor starts to overheat. This will greatly reduce the risk of burning out the motor.
Standard vs. Oil-free Pumps
Reciprocating (piston-style) air compressors have two options when it comes to the air compressor pump: oil-lubricated and oil-free. Oil-free units have piston rings coated with a non-stick material that provides the lubrication for the piston motion. An oil-free pump minimizes contaminants in the airstream.
Single-Stage vs. Multi-Stage
Reciprocating air compressors come in both single-stage and dual- or multi-stage versions. Small compressors and portables are single-stage. Most industrial and commercial air compressors are dual-stage. This means that air goes through a second stage of compression before going into the air receiver tank. Dual-stage air compressors are capable of producing more air at a higher PSI. They are a better choice for continuous operation, facilities with multiple air-powered tools and machines, and applications requiring pressures greater than 100 PSI.
Air Compressor Accessories: What Else Do You Need?
What kinds of accessories do you need for your industrial air compression system? An industrial air compressor is usually paired with several other elements to create a complete system. These include air dryers, air receiver tanks, drain valves, oil/water separators, compressed air piping, hoses and couplers.
An air dryer removes excess moisture from compressed air. When air is compressed, moisture present in each cubic foot is increased and the air is heated therefore able to hold more moisture. The air dryer removes excess moisture from the airstream and ensures a supply of clean, dry air. An air dryer is important to prevent the buildup of condensation in compressed air piping, equipment and tools, which can lead to corrosion.
There are two basic types of air dryers for compressed air systems: refrigerated and desiccant.
- Refrigerated air dryers chill the air until water vapor condenses and drops out. They dry air down to a dew point of 38°F. This is adequate for most industrial compressed air applications.
- Desiccant air dryers use desiccating beads to adsorb and remove water vapor from the air. They produce ultra-dry air at a dew point of -40 to -100°F. Desiccant air dryers may be needed for specialty applications including laboratory, food processing, outdoor use in winter and pharmaceutical production.
A heat exchanger captures the excess heat produced by air compression. The heat exchanger not only removes excess heat from your compressed air system, but actually captures it so it can be used for other purposes. Waste heat from the air compressor can be used to heat parts of your facility, provide heat for production processes, or to heat hot water. The heat exchanger will pay for itself over time as it reduces your energy bills by putting waste heat to use.
Air Receiver Tanks
The air receiver tank (sometimes called an air compressor tank or compressed air storage tank) is a tank that receives and stores compressed air after it exits the air compressor. This gives you a reserve of compressed air that you can draw on without running your air compressor. An air reserve allows you to meet sudden, sharp demands for compressed air and ensures a steady supply of air to compressor controls, eliminating short-cycling of your compressor motor and over-pressurization of your system. The air receiver tank also acts as a secondary heat exchanger, allowing compressed air to cool before it is used in your processes.
Aire Tip: A good rule of thumb is to have three to five gallons of air storage capacity per air compressor CFM output. Read more: Air Receiver Tank Full Guidelines
A drain valve is a requirement for your air compressor, air receiver tank and refrigerated dryer. Drain valves allow excess condensation to be easily drained away. This condensation must be drained daily, or more often for high-production facilities. There are a few types to choose from.
- Manual drain valves, as the name implies, must be opened manually by maintenance staff. They are likely to come standard with your compressed air equipment. Typically, a little compressed air is lost along with the water each time the drain is opened.
- Zero-loss drain valve uses a float system to open the drain automatically when enough water accumulates. Because they are only open for the amount of time needed to drain the condensate, they prevent compressed air waste. They also eliminate a maintenance task, making your compressed air system easier to care for.
- Electric drain valves can be programmed to open for a few seconds at set times to drain the system, automating drain valve maintenance. Unlike a zero-loss system, the valve will open whether or not condensate is present, which means some compressed air may be lost if it is set to open too long or too frequently. An electric drain valve can be a great choice if your system needs to be drained frequently (as often as every minute) and produces a predictable amount of condensate.
If you are not using an oil-free compressor model, an oil-water separator is highly recommended. An oil-water separator (sometimes called a condensate separator) is a device that separates oils and lubricants from liquid water. The oil-water separator collects condensate from your air compressor, tank, filters and dryer and removes the oil so it can be disposed of properly rather than put down the drain with the water. A separator may be required to keep your facility in compliance with EPA and local regulations.
An inline air compressor filter captures contaminants (such as oils and particulates from the compressor and microorganisms) before the compressed air goes into the air dryer, air receiver tank or piping. This ensures that the air that is used to power your machines and processes is as clean as possible. There are three types of inline filters:
- Standard particulate filters capture solid dry particulate, typically down to 1 micron in size.
- Coalescing filters remove aerosolized oil mists from compressed air as well as dry particulate.
- Activated carbon filters remove oil mists, vapors and gases. They should be used in combination with a coalescing filter for maximum efficiency. A 2-in-1 inline filter provides both types of filtration.
Compressed Air Piping
The compressed air piping system delivers air from the compressor or air receiver tank to the rest of the facility where it is used. Piping must be strong enough to withstand the pressures of compressed air delivery. Black iron pipe is the most common material, but galvanized steel, stainless steel, copper and aluminum can also be used. Some plastics are acceptable, but PVC pipe should never be used.
Aire Tip: Aluminum piping is lightweight, does not corrode, and offers excellent leak resistance and ease of installation. Read more: What Is the Best Piping Material for Compressed Air Systems?
Hoses and Couplers
Hoses and couplers are used to connect equipment and machines to the compressed air piping system. Quick couplings are designed for easy change-out of air-powered tools; they are a great option for stations where several different manual pneumatic tools may be used.
Aire Tip: Hoses and couplings are often sources of compressed air leaks if they are not properly used and maintained. Use piping to connect to stationary equipment wherever possible, and reserve hoses and quick couplings for applications where quick change-out or mobility is required. Read more: How to Detect and Fix Compressed Air Leaks
The Best Industrial Air Compressors
The best industrial air compressor for you depends on your application. Fluid-Aire Dynamics sells, installs and maintains best-in-class industrial air compressors and accessories from Pneutech, Ingersoll Rand, CompAir, Saylor Beall, Mattei and Hydrovane.
Not sure which air compressor is right for you? Our experienced compressed air system engineers can help you select the best air compressor for your facility. We will help you:
- Calculate your CFM and PSI requirements for your compressed air system.
- Choose between rotary screw, reciprocating and rotary vane air compressor models.
- Determine whether a VSD air compressor drive is right for you.
- Put together a package of air compressor features and accessories tailored to your application, goals and budget.