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Air Compressor Duty Cycle – What Is It, How It Works

Published Categorized as Air Compressor Theory, Notebook 5 Comments on Air Compressor Duty Cycle – What Is It, How It Works

The compressor Duty Cycle is quite an important piece of information to have when you are sizing an air compressor for your home or business workshop. The majority of air compressor models are not designed to run continuously. If you plan on using your air compressor for extended periods, then the duty cycle of that make and model is something you need to know.

This article will provide you with all the relevant information on the air compressor duty cycle!

Table of Contents

What is an Air Compressor Duty Cycle?

Some compressors need to have a rest period of a certain percentage of their operating time, to give the compressor time to cool down. You want this to happen, to prevent breakdowns and to prolong the life of your compressor. Air compressor duty cycles are relatively straightforward to understand but can often be quite difficult to read because there are no universal characters that represent the values amongst various compressor manufacturers.

Usually, the duty cycle is expressed as a percentage of a certain time frame, often a 10-minute segment. But other times it may be an exact value of time. In the latter case, you can take the number of seconds or minutes that the percentage represents and subtract that from the total cycle time.

Sweaty person on extended duty cycle
Overheating when working too hard happens to compressors too!

In the case of the former, when listed as a percentage, the duty cycle is equal to the compressor’s run time divided by the total cycle time. The percentage equates to the amount of time you can keep the compressor working, plus the corresponding time it cools down. So for example, a compressor with a duty cycle of 50% for a particular brand and model of the compressor would mean that this particular unit could run steadily for 10 minutes, and then it must have a 10 minute rest period before it kicks into compress more air for a 20 minute operating period.

The problem with the duty cycle of an air compressor is that, unlike many other standards in the compressed air industry, there is not an official definition for the duty cycle of an air compressor. And because of this, a lot of confusion is created, and operators end up purchasing expensive compressors that don’t necessarily meet their expectations. Compressors that claim to have a 100% duty cycle, aren’t guaranteed to be able to run continuously, like a lot of people assume they are. But, more on this later!

It is often the home shop DIY that gets caught in the compressor duty cycle trap, not knowing what the duty cycle of their compressor is and burning it out through too prolonged use during one session. This is why it’s so important to know and understand your compressor’s duty cycle rating.

Air Compressor Duty Cycle Examples

Let’s take a look at some examples of common duty cycle ratings that most compressors have so you can better understand their work and rest time periods.

25% Duty Cycle

When an air compressor’s duty cycle rating is 25%, this means that the run time for the compressor is one-quarter of the total cycle time. If the compressor has a cycle time of one hour, then the run time would be 15 minutes. Therefore, for every 15 minutes of operation, the compressor would need 45 minutes rest period.

A compressor with such a low run time is suited to small applications that require only intermittent power, such as portable compressors used for DIY home projects.

30% Duty Cycle

If an air compressor specifies having a 30% duty cycle, the compressor would run for approximately one-third of the total cycle time. So, with an hour cycle time, the compressor would have a run time of 20 minutes. Therefore, for every 20 minutes of operating, the compressor would need 40 minutes rest period.

These types of compressors are can be used for moderate applications where the tools are used relatively frequently but not continuously, in places like a car garage where motor parts need to be fastened and unfastened every few minutes or so.

50% Duty Cycle

A 50% duty cycle on air compressors is very common and easy to understand. The compressor can provide power for half of its overall cycle time. So, with a compressor cycle of one hour, the compressor will allow you to draw pressurized air for a total of 30 minutes. Before having to wait another 30 minutes to use it again.

Air compressors with a 50% duty cycle rating are typically used for medium-scaled operations that only require intermittent air power. In many cases, workplaces that do not want to invest in larger air compressors will make do with 50% rated compressors.

75% Duty Cycle

Air compressors with 75% duty cycle ratings will run for three-quarters of their total cycle time. So, in terms of an hour cycle time, the compressor will run for 45 minutes before needing a 15 minute rest time.

You will find these compressors in places like repair garages powering pneumatic screws, hammers, nailers, and wrenches for seconds at a time. Since these tools do not require constant airflow, they can have a brief moment of rest.

100% Duty Cycle

Air compressors with 100% duty cycle ratings are able to deliver pressurized air for its whole cycle time. These compressors are suitable for processes that require constant airflow for minutes or even hours on end. Some tools like pneumatic sanders and spray painters are perfect examples.

A compressed air system with a 100% duty cycle will need a cooling component equipped to ensure that the engine doesn’t overheat if it is being used for a long period. Factory settings will typically be the home for air compressors with a 100% duty cycle.

It’s extremely common that air compressors with a 100% duty cycle will operate at 100 PSI at a moderate temperature around 72 degrees Fahrenheit as any deviation from these specifications can affect the compressor’s cycle time.

How Often Should an Air Compressor Cycle?

You must check carefully for your compressor’s duty cycle rating. A compressor that shows ample flow capacity for your air grinder might run well beyond its duty cycle when it is being used on a big job at home. This will inevitably lead to maintenance issues which are avoided by being sure of the duty cycle before you buy and when you use your air compressor.

The number of times an air compressor cycles will significantly impact the system’s efficiency. If you allow your compressor to cycle more often than the recommended duty cycles from the manufacturer, you serious risk of causing premature wear and tear.

The cycle time of an air compressor is the length of time it takes for the system to load and unload compressed air. If a compressor is cycling quickly, it is going to consume more energy. Therefore, it’s better to have a longer cycle time with fewer cycles per hour to get the most life out of your air compressor.

There are a few additional measures you can take to lengthen your air compressor cycle time and make it more efficient:

  • use a larger tank receiver
  • try a wider pressure band
  • drop the pressure between the tank receiver and the compressor

The manual that comes with your compressor should indicate the duty cycle. However, mine did not. That is inexcusable, in my view. If you are not sure about the duty cycle of your air compressor, and you plan to use your compressor for long periods of time, see if you can get the manufacturer’s name from the store and email them to ask about the duty cycle for the model you are contemplating buying or using.

Intermittent or Continuous Duty Cycle: Which to Choose

A lot of people make the mistake of thinking that the closer you have to 100% duty cycle, the better. Of course, in situations like factory plants where 0% downtime is a goal then yes, they are ideal. But, for tools that don’t need to run for more than a few minutes at a time, intermittent air power is certainly efficient.

Intermittent Duty Cycle Compressors

More often than not, intermittent duty cycles will provide you with enough compressed air to complete the task at hand without losing productivity. For example, here are a few tasks that can easily be completed with intermittent duty cycles:

  • Completing DIY projects at home
  • Filling tires or other inflatables
  • Powering mechanical tools like nailers and wrenches that only need power for a few seconds at a time every few minutes

Typically, the compressors used for intermittent uses are smaller than those used for continuous. This allows them to be portable! They will tend to be single-stage piston compressors, where the air is drawn into a cylinder and pressurized once with a crankshaft-driven piston. In two-stage piston compressors, the air is sent to a second cylinder and stroked yet again by a smaller piston to reach pressures as high as 175 PSI. For more information on 2 Stage Air Compressor Vs Single Stage visit our guide!

Single-stage piston compressors lack the necessary cooling components for continuous use. And so, a piston air compressor is generally limited to duty cycles between 25% to 50%. Here’s an example of a portable air compressor that boasts a 50% intermittent duty cycle according to its manual.

Continuous Duty Cycle Compressors

On the other hand, continuous duty cycles allow you to provide constant compressed air to tools and machinery without the need for downtime. For example, here are a few tasks that can easily be completed with continuous duty cycles:

  • Lifting heavy in-process works in automobile manufacturing facilities
  • Operating conveyor belt systems in bottling plants
  • Powering tools used to manufacture electronics

Centrifugal and rotary screw air compressors are typically the types of compressors that are able to offer the maximum duty cycle. These compressors are equipped with cooling systems that allow them to run continuously without any damage to the motor due to overheating.

Rotary screw compressors allow air to pass through the rotors of two counter-rotating helical screws, here the rotors are filled with lubricant to create an air-tight seal as each generation of compressed air is passed through the compressor.

Rotary screw compressors are typically very large units that are suitable for industrial use like in manufacturing factories. And so, most rotary screw compressors offer a 100% duty cycle allowing users to power their machines and tools continuously. Below is an example of a rotary screw compressor that boasts a 100% continuous-use duty cycle.

One thing with continuous duty cycles is making sure it actually is! In recent years, there has been a trend toward manufacturers offering air compressors that claim 100% duty cycle. If those models are not industrial-designed compressors, be careful.

For those models, this statement does not mean that you can run the compressor all day without harm. For these compressors, it is better to take their claim for a 100% duty cycle and interpret it to mean that this particular compressor is suitable for limited extended use, but NOT for running all day, flat out.

Furthermore, if the compressor manual says that a model is a 100% duty cycle and it’s smaller, a do-it-yourself type air compressor, you better read the fine print. My bet is that it will not be a true 100% duty cycle, as in you can run the compressor for long periods without damage.

A 100% duty cycle simply means that the compressor will deliver a consistent CFM and PSI the whole time the compressor is in use, which is very different from being able to run continuously. Piston air compressors can generate upwards of 150 PSI of compressed air and have a larger storage tank per horsepower when compared with a rotary screw compressor (note: rotary screw compressors are made for continuous use, so they do not need a large storage tank).

The piston compressor will fill the storage tank with highly pressurized air that depletes over time, and so the compressor will eventually kick back in when the pressure drops to its cut-in pressure and refill the tank.

A piston compressor with a high duty cycle rating of 100% does not mean it can run continuously but instead can provide air at a specific pressure and flow 100% of the time with the help of its storage tank. The piston compressor will eventually need to stop and cool down. The stop and cool down, is essential for compressors that are not rated as continuous run, and will prevent premature wear and tear.

Takeaway: A 100% duty cycle does not mean you can continuously run your air compressor. You must ensure that the compressor is rated as continuous run in order to run it continuously without the need to stop and let it cool down. Compressors rated as continuous run only idle down when they’re not in use.

Air Compressor Duty Cycle Relationship With CFM

CFM ratings on air compressors are another very important rating to look for when selecting an air compressor, along with the duty cycle. CFM ratings tend to be based on the output of the air compressor pump, and it’s even more important to understand the relationship between the duty cycle and CFM.

In order to understand the compressor’s CFM capabilities to deliver continuously as opposed to intermittently, you must multiply the CFM rating of the compressor by the duty cycle percentage. I’ll provide you with a number of examples of the common duty cycles I provided earlier. Let’s say we have an air compressor with a 20 CFM rating.

25% Duty Cycle

For a 20 CFM air compressor with a 25% duty cycle, you would be able to continuously deliver:

20 CFM * 25% = 5 CFM

Therefore, this type of compressor would be suited to any tools that require 5 CFM or less – if you require continuous use. If you only need to power your tools intermittently (say 50% of the time) then you will be able to power tools up to 10 CFM:

10 CFM (tool rating) * 50% (intermittent tool use) = 5 CFM

30% Duty Cycle

For an air compressor with a 30% duty cycle and CFM rating of 20, you would be able to continuously deliver:

20 CFM * 30% = 6.67 CFM

This type of air compressor would, therefore, be suited to tools that are rated below 6.67 CFM in order to operate continuously. For intermittent use, this compressor will power tools up to 13.34 CFM during the operation of the compressor:

13.34 CFM (tool rating) * 50% (intermittent tool use) = 6.67 CFM

50% Duty Cycle

For a 50% duty cycle, a 20 CFM compressor would be able to continuously deliver:

20 CFM * 50% = 10 CFM

If your air tool, requires less than 10 CFM then sure, you can provide continuous air to the tool within the compressor’s duty cycle. However, if the tool exceeded 10 CFM, you will only be able to use this tool intermittently as the compressor would not be able to keep up with the demand. On that note, you could power tools up to 20 CFM if they were used intermittently:

20 CFM (tool rating) * 50% (intermittent tool use) = 10 CFM

75% Duty Cycle

A 20 CFM rated compressor with a 75% duty cycle rating would be able to continuously deliver:

20 CFM * 75% = 15 CFM

This compressor would therefore be capable of powering tools up to 15 CFM continuously, whether that is 1 x 15 CFM tool, or 3 x 5 CFM tools. The compressor would also be able to power tools up to 30 CFM if they were used intermittently:

30 CFM (tool rating) * 50% (intermittent tool use) = 15 CFM

100% Duty Cycle

If the compressor has a 100% duty cycle rating and was specified as continuous use, then you could provide the full 20 CFM to your air tool, or even multiple air tools throughout the whole compressor cycle period.

20 CFM * 100% = 20 CFM

Air compressors like this will be able to provide multiple tools continuously, or even more tools intermittently, hence they’re typically used in factories or workshops where multiple jobs are taking place at once. For a compressor of this rating, it would enable you to power devices up to 40 CFM intermittently:

40 CFM (tool rating) * 50% (intermittent tool use) = 20 CFM

Hopefully, you now understand how an air compressor’s duty cycle and CFM ratings relate to one another and are ever so important to consider when buying a new air compressor. We have a number of pages available on this site that act as guides for what size air compressor you need; visit them here:

Breaking In a New Compressor

I thought it would be worth briefly mentioning breaking in a new compressor. Some compressors need a 30-minute continuous run, with the receiver drain wide open to the atmosphere to break in when you first purchase them. Others may need 15 or 20 minutes. Your compressor manual will tell you the break-in period.

People, therefore, assume (maybe a mistake…we’ll see?) that the duty cycle on the unit would be 30 minutes, and take pains to ensure that if it ever runs for 30 minutes at a stretch, to shut it down and let it cool for that same amount of time. This can, of course, work, but it’s important to look up your duty cycle in your manual or contact the manufacturer directly if you have any doubts.

Industrial compressor users are normally purchasing compressors through an industrial supplier or from the manufacturer, and the salespeople for those firms are professionals. They should make sure that the buyer gets the right unit. Industrial compressors frequently have a continuous run 100% duty cycle, meaning they can run continuously without a cool-down period, a feature that is necessary for high-production compressed air use.

FAQs (Frequently Asked Questions)

What is a duty cycle on an air compressor?

The duty cycle is often represented as a percentage that is equal to the compressor’s run time divided by the total cycle time. This percentage rating manufacturers provide you with equates to the amount of time you can keep the compressor working, plus the corresponding time it needs to cool down. For example, let’s look at a 50% duty cycle: if the cycle time of the compressor is 30 minutes, then the compressor needs 15 minutes rest for every 15 minutes of work.

What is a good duty cycle for a compressor?

A good duty cycle for an air compressor typically depends on the jobs you are carrying out. If you are simply conducting DIY jobs at home and are using tools once every few minutes then a 50% duty cycle will suffice. If you are aiming to complete spray painting or sanding jobs then you’ll need a 100% continuous run duty cycle in order to not have to stop-start.

How do I know the duty cycle of my air compressor?

The best way to know or find out your compressor duty cycle is to look inside your user manual, it should be specified here. If not, I will recommend contacting your manufacturer directly to find out. It’s important you know your rating, as you do not want to exceed it and cause the premature wear and tear of your compressor.

What is a 100% duty cycle?

100% duty cycle is when compressors are able to deliver compressed air throughout their whole cycle time. But, it is important to note that this doesn’t necessarily mean they’re capable of continuous use unless it’s specified. A compressor with a 100% duty cycle rating but not specified as being continuous use, will still need rest time otherwise you risk premature wear. On the other hand, a compressor with a 100% duty cycle rating and specified as being continuous use, can be used continuously without premature wear and will only rest when not in use.

If you have any questions regarding the air compressor duty cycle, please leave a comment below, with a photo if applicable so that someone can help you!

By Bill Wade

About Air Compressors has been helping folks with their Air Compressor Problems since 2002 online. We're a community of DIY and Compressed Air professionals who are keen to support everyone across the globe with their air compressor issues and troubleshooting. Whether you're trying to identify an old air compressor, or troubleshoot an error code on a sophisticated new industrial air compressor - the community at About-Air-Compressors.com is here to help you

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