If you’ve shopped around for an air compressor, you’ve probably seen the term “duty cycle” come up a time or two. The duty cycle rating is an important factor in terms of your compressor’s longevity and what you intend to use it for. But there’s a fair amount of confusion surrounding just what a duty cycle is and what difference it actually makes. So in this article, I’ll lay out everything you need to know about air compressor duty cycles – in plain English.
What Is an Air Compressor Duty Cycle?
An air compressor duty cycle is the portion of time a compressor pump runs relative to the compressor’s total cycle time. The total cycle time is how long it takes to reach cut-out pressure, turn off, and reach cut-in pressure during use. The duty cycle is usually represented as a percentage.
Some manufacturers also define “duty cycle” as the amount of time a compressor can provide air at a given output (CFM) at a given pressure (PSI). This is the cause of considerable confusion among consumers since it doesn’t necessarily correlate with the actual run time of the compressor pump. Manufacturers can use either definition depending on how they want to advertise their product. But we’ll get into that a little later.
As far as we’re concerned, from a practical standpoint, we can view the duty cycle rating as the percentage of time our compressor pump should be running in a given period of use. For example, if our compressor’s duty cycle is 50%, the pump shouldn’t be running for any longer than 30 minutes in 1 hour.
Why Does Duty Cycle Matter?
An air compressor’s duty cycle matters because it gives you an idea of what kinds of applications that compressor is good for. But it’s even more important for preserving your compressor’s longevity. Exceeding the recommended duty cycle can prematurely wear out or damage the pump components.
Duty cycle ratings are mainly used in reference to reciprocating piston compressors (the most common type found outside of industrial settings). It’s less important when referring to rotary screw and rotary scroll compressors, which are generally designed to run continuously without wear or damage due to overheating.
Piston air compressors typically feature a pressure switch, which tells the pump to turn on or off when the storage tank reaches certain pressure limits. When the tank reaches cut-out pressure (typically just below the max tank pressure) the pump turns off. When the tank reaches cut-in pressure (typically around 30 PSI below cut-out pressure), the pump turns back on. The difference between the two pressure limits is called the pressure band.
While you’re using the stored air within the pressure band, the compressor pump will be off, allowing it to cool. This cooling period is vital for reciprocating piston compressors, which don’t have the built-in cooling systems that rotary screw or scroll compressors do. Depriving your compressor of the necessary cooling period is a sure way to wear out the pump components faster and shorten your compressor’s lifespan.
Luckily, in most cases, the time it takes for the tank pressure to drop from cut-out to cut-in (while still using the air) is enough to provide adequate cooling – in other words, the duty cycle takes care of itself. The main risk is if you’re using tools or performing tasks that demand a higher CFM than the pump can provide – this will cause the pump to run longer to keep up with the demand, and you’ll exceed your duty cycle.
Now, let’s explore a few of the most common duty cycle ratings for air compressors.
Duty Cycle Percentages Compared
If it’s not advertised on the packaging or marketing materials, most air compressor manufacturers list a recommended duty cycle in the product manual. In most cases, this is a general recommendation to preserve the life of the product.
25% Duty Cycle
If your compressor has a 25% duty cycle, this essentially means that the pump can run roughly one-quarter of the total cycle. So if your compressor’s total cycle takes 1 minute (60 seconds), you shouldn’t exceed 15 seconds of pump run time for every minute of use. On a slightly more macro scale, this means your pump shouldn’t be allowed to run more than 2.5 minutes in a 10-minute period.
This isn’t a very common duty cycle rating, but you may find it on some smaller air compressors designed for very light use, such as inflating small tires or sports equipment.
50% Duty Cycle
A 50% duty cycle rating is much more common and can be found on compressors of various sizes and capabilities. This rating means that you can run your compressor pump for 30 seconds of every minute (5 minutes for every 10-minute period). Naturally, this is much more practical as it will allow for somewhat more continuous operation.
This is a great duty cycle for most light-to-medium duty applications that don’t require long periods of continuous use – nailing, stapling, cutting, inflating, cleaning, drilling, automotive repair (impact wrench), and even some small paint jobs.
75% Duty Cycle
As you can imagine, a 75% duty cycle is even more desirable. These compressors require a very short cooling/rest period – you can run the pump for 45 seconds out of every minute, 7.5 minutes for every 10-minute period, or 45 minutes out of every hour.
You’ll most often find this kind of duty cycle on larger compressors, such as those used in automotive or woodworking shops, where minimal downtime is the goal.
100% Duty Cycle
With the above examples in mind, a 100% duty cycle must mean that the compressor can run nonstop, right? Well, here’s where that other definition comes in and things get a little dicey.
Many rotary screw/scroll compressors can run continuously for long periods, meaning they have a 100% duty cycle (or more accurately, a “continuous duty cycle”). But reciprocating piston compressors don’t have the cooling power to run 100% of the time – well, they could do it, but it wouldn’t take long for the pump to overheat and fail or simply wear out rapidly.
So if you see a piston compressor that claims to have a 100% duty cycle, this means that it can continuously provide a given CFM output and pressure (PSI) for 100% of the total cycle.
In other words, you’ll be able to work continuously because you’ll be drawing air power from the storage tank while the pump cools and the tank will fill faster than you’re using air when the pump is on (provided that your application doesn’t demand a higher CFM/PSI than the compressor can supply). It does not mean that you can run the pump continuously.
For example, let’s say your piston compressor promises an output of 5 CFM @ 90 PSI with a 100% duty cycle. So you kick it on and start using it with a tool that requires that exact output. Let’s say the pump runs for 60 seconds before it reaches cut-out pressure and turns off. Now you’re drawing from the air inside the receiver tank and it takes another 60 seconds to reach the cut-in pressure, which turns the pump back on.
In this scenario, the actual duty cycle was 50% (1 minute on, 1 minute off) but you had a continuous supply of air at the promised CFM/PSI for the total cycle. So the compressor does technically fulfill the manufacturer’s definition of a 100% duty cycle.
Intermittent Vs. Continuous Duty Cycles
It can be helpful to divide duty cycles into two main categories – intermittent and continuous.
Intermittent Duty Cycles
Naturally, any compressor with a duty cycle rating lower than 100% can be considered intermittent. The vast majority of piston compressors fall into this category. Intermittent duty compressors are more than adequate for most homeowners, general contractors, and even auto mechanics.
Most basic applications can be performed with intermittent air power since you only use air in relatively short bursts. These include:
- Inflating tires or sports equipment
- Powering impact wrenches
- Cleaning (air blower)
- Light-duty craft painting
Here’s an example of a versatile and powerful intermittent use compressor with a 50% duty cycle – Craftsman 20 Gallon 1.8 HP Air Compressor.
Continuous Duty Cycles
Most compressors rated for continuous duty are of the rotary screw variety. These are most often used in industrial/factory settings where continuous operation is a necessity. Some piston compressors may also be able to provide continuous use (as described above) if not true continuous duty.
These compressors are the best option for applications that require long-term continuous operation. These include:
- Painting (automotive/large surfaces)
- Manufacturing applications
How To Identify the Duty Cycle of Your Air Compressor
The best way to identify your air compressor’s duty cycle rating is to look in the user manual – it should be listed with the other specifications. If you can’t find it there, your best bet is to contact the manufacturer.
If you haven’t yet purchased an air compressor but you want to find out its duty cycle rating, the packaging or online product page may or may not list it in the specs. If not, you may be able to download the user manual from the manufacturer’s website. If all else fails, reach out to the manufacturer directly.
I hope this article has helped clear up the subject of air compressor duty cycles. As you can see, there’s more to a compressor’s duty cycle rating than meets the eye. But if you want to find a compressor that meets your needs – and avoid burning out your compressor pump – it’s an important rating to know. Thanks for reading!