What Is Duty Cycle

An air compressor’s duty cycle refers to the amount of time it takes the pump to fill up its tank. Another way to view this is the amount of time a compressor will consistently deliver pressurized air within a total cycle time. While metrics to measure duty cycle may vary, you will commonly see it denoted as a percentage. This percentage is meant to help define the amount of time a compressor will spend cycling on and off while operating at a consistent PSI (pressure) and CFM (flow). Duty cycle is most commonly used when discussing reciprocating, or piston, compressors, but it can be applied to other air compressors that load/unload as well.

How to Calculate Duty Cycle

To find this percentage you take the compressor’s time running and divide it by the total cycle time. Total cycle time can be defined as the compressor’s run time plus its cool down time.

For example: if a compressor’s total cycle time is 10 minutes, but it only ran for 8 minutes of this time, it would have an 80% duty cycle. This means, those remaining 2 minutes were used as cool down time until the next cycle.

In the above example, the 80% duty cycle is dictating that the compressor will deliver pressurized air for a combined 8 minutes and must be off for 2 minutes before it can run again.

Why Does Duty Cycle Matter

While most compressors have automatic shutoffs, it is important to pay attention to your compressor’s duty cycle to ensure it is not being overworked and received the proper amount of rest time necessary to deliver optimal performance.

Air Compressor Duty Cycle Ratings Explained

25% Duty Cycle

An air compressor with a 25% duty cycle runs for ¼ of the entire cycle time. Because of this, small, light-duty operations that need occasional air power are best suited for compressors with 25% duty cycle. These generally are in-home or small shop units, not ones used in large manufacturing facilities.

30% Duty Cycle

Compressors with 30% duty cycle will run for 1/3 the total cycle time, meaning it spends more time resting or cooling down, than it does providing air. These compressors are used in situations where air is required frequently, but not continuously.

50% Duty Cycle

An air compressor with 50% duty cycle means that it will operate half the cycle-time while cooling down and resting the other half of the cycle-time. These types of compressors are generally used for medium-grade applications that require only occasional air power such as pneumatic hand tools.

75% Duty Cycle

75% duty cycle means the air compressor will be running ¾ of the total cycle time. A compressor running at 75% duty cycle is best suited for jobs where applications require brief intervals of run time. An example would be auto bodies or repair shops that use pneumatic hand tools such as nailers, drills, or wrenches. These types of tools don’t require continuous air supply, but they have brief resting periods between uses.

100% Duty Cycle

Air compressors with 100% duty cycle means they can run continuously without needing to rest and cool down. They will deliver pressurized air throughout their entire cycle time. Because of this, compressors with 100% duty cycle are best used in processes that require continuous airflow for long periods of time such as conveying systems or pneumatic sanders. A risk for air compressors running at 100% duty cycle is the engine overheating. These compressors should have a cooling component to mitigate this risk.

Can An Air Compressor Have Multiple Duty Cycles?

Duty cycle also refers to the PSI (pressure) and CFM (flow) provided for that percentage of total cycle time. Because of this, a compressor advertised at a 100% duty cycle could provide 125 PSI and 25 CFM for the entire cycle time. But that same compressor could also be advertised at a 50% duty cycle by providing a higher PSI at a lower CFM. Duty cycle depends completely upon the applications and the PSI and CFM necessary to complete them.

How Often Should a Compressor Cycle

A compressor’s efficiency is largely dependent on the number of times it cycles. The quicker a compressor cycles, the more energy it consumes. Because of this, it is better to have longer cycle times that occur fewer times per hour. This preserves energy and thus the compressor’s lifespan. Using a larger storage tank, trying a wider pressure band, and dropping the pressure between the main storage tank and the compressor are three ways to lengthen your cycle time.

Preventing Over-Cycling

Over-cycling happens when a unit cycles too much in a given time period. This can happen due to plant demand changing over time. Consult a Zorn Compressor & Equipment expert to ensure your facility receives the proper air compressor for your unique applications.

Intermittent vs. Continuous Duty Cycle Air Compressors

Intermittent Duty Cycles

Intermittent duty cycle means that the compressor needs to cool down regularly to prevent overheating and maximize efficiency. Many reciprocating air compressors operate with

intermittent duty cycles. Some examples of applications that are a good fit for intermittent duty cycles include:

• Filling automobile tires up with air
• Powering hand tools such as pneumatic wrenches
• Blowing off surfaces for cleaning

Continuous Duty Cycles

Continuous duty cycle air compressors can run for long periods of time without regular breaks to cool down. Most of these compressors have cooling systems that help to prevent overheating and allow the compressor to continuously run without a cool down period. The most common compressor type that can run with a continuous duty cycle is a rotary screw. Most centrifugal units are also fit for continuous duty cycles. A few examples of applications that are a good fit for continuous duty cycles include:

• Lifting heavy car parts I automobile manufacturing facilities
• Operating conveyor belts in packaging factories
• Painting large areas

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Our compressed air experts look forward to meeting you to discuss your equipment and support needs. Please contact us directly at (262) 695-7000 with any questions or to schedule service for your system moving forward.

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