What is Compressor Duty Cycle and How is it Calculated?

When we discuss compressors, PSI and CFM typically receive the most attention. 

But there’s a metric that is far more important when it comes to performance and reliability: 

Duty cycle. 

If you’ve been in the air business long enough, chances are you’ve paid insufficient attention to compressor duty cycles at some point, and suffered the consequences: failures that come too soon, skyrocketing energy costs, and expensive downtime.

Understanding duty cycle is the first step in making the shift from playing catch-up to intelligently managing your compressed air system, cutting long-term costs. 

In this guide, we cover what a compressor duty cycle is, why it’s essential and how to calculate it. 

What is Compressor Duty Cycle and How is it Calculated?

The duty cycle shows how much of a set period a compressor spends actually doing work – compressing air – before it needs to rest.

During the remaining time, the machine cycles off to cool down. This helps prevent overheating and wear. Most manufacturers – including Atlas Copco – base this rating on a 10-minute window, following IEC motor duty standards.

The Duty Cycle Formula

Calculating your compressor’s actual duty cycle is a straightforward process. You only need a stopwatch and a typical operating period.

The universal formula is:

Duty Cycle (%) = (Run Time / (Run Time + Rest Time)) x 100

• Run Time (Loaded Time): The time the compressor motor is ON and compressing air.
• Rest Time (Unloaded/Off Time): The time the compressor is OFF and cooling down.
• Total Cycle Time: Run Time + Rest Time

Example: Say a compressor runs for seven and a half minutes. It then pauses for two and a half. That makes it – in total – a ten-minute cycle.

7.5 divided by 10, multiplied by 100, gives a 75 % duty cycle.

Understanding that figure helps you notice inefficiencies sooner. It also helps to avoid overloading the machine, and keep components in good shape – before small faults become expensive repairs.

The Real-World Impact of a Duty Cycle Mismatch

Running a compressor past its rated duty cycle – known as over-cycling – can trigger a series of problems. The compressor builds heat faster than the cooling system can handle, and over time that excess heat can cause major damage.

• Skyrocketing Energy Costs: Energy consumption can account for up to 80% of a compressor’s lifecycle cost (Atlas Copco data). An overworked, inefficient machine running constantly will dramatically inflate your utility bills.
• Premature Component Failure: When temperatures climb too high, the oil can’t protect the moving parts as it should. Friction builds, and pieces like piston rings, bearings, and valves start wearing out early. Over time, this adds directly to your air compressor maintenance costs – one of the main reasons proactive service plans matter so much.
• Increased Moisture and Contamination: When the air heats up, it traps more water vapour. If the compressor is under strain, that extra moisture moves through the system. It later condenses, leading to rust in the pipework – and problems with air tools or final products.
• Costly Production Downtime: The cumulative effect of this strain is unplanned equipment failure, which brings production to a halt.

Conversely, a grossly oversized compressor will “short-cycle” by starting and stopping too frequently. 

This puts extra stress on the motor. It creates a level of friction that wears the components out sooner – and allows moisture to build up in the oil sump.

Keeping within the proper duty cycle stops that from happening and helps lower long-term costs. It also ensures compressors operate safely within design limits—a key part of any compressed air efficiency strategy.

How Compressor Type Dictates Duty Cycle Capability

The duty cycle is not an arbitrary limit; it is determined by the compressor’s core technology and its ability to manage heat. The two most common different types of air compressors and their uses have vastly different capabilities.

Reciprocating (Piston) Compressors: For Intermittent Use

Piston compressors create a lot of heat and depend on simple air-cooling – mainly through fins and a fan built into the flywheel.

This method has a limited capacity to dissipate heat, which is why most piston models have an intermittent duty cycle, typically ranging from 50% to 75%. They are designed for applications with fluctuating air demand, such as workshops and service centres. Consider Atlas Copco’s Automan and LE/LT series. 

The Automan line is suited for general workshop use, while the LE/LT series are oil-lubricated, multi-stage designs for higher pressures and continuous performance.

Rotary Screw Compressors: Built for Continuous Duty

Rotary screw compressors are engineered for 100% continuous duty. 

They use a highly efficient internal cooling system where injected oil lubricates, seals, and – most importantly – absorbs the heat of compression. This oil is continuously circulated through a cooler, typically an air-cooled circuit with a thermostatic bypass, allowing the machine to run non-stop without risk of overheating. 

They are the workhorses of industry, ideal for manufacturing and processing facilities that require a constant supply of compressed air. 

The Atlas Copco GA and GX ranges are recognised across the industry for their ability to run continuously under full load.

Decoding the “100% Duty Cycle” Misconception

A common point of confusion is the “100% duty cycle” rating sometimes applied to piston compressors. 

Often, this refers to the system’s ability to deliver continuous air from a large storage tank, rather than the compressor pump’s ability to run continuously. The pump still cycles on and off to fill the tank.

That is very different from a true continuous-duty rotary screw compressor which is mechanically and thermally designed to run continuously. 

An exception exists in high-end, industrial-grade piston models, like Atlas Copco’s LE Series, which use S1-rated continuous duty motors and advanced cooling to achieve true 100% duty cycle performance.

What is Compressor Duty Cycle and How is it Calculated

Is Your Compressor Overworked? Warning Signs and Solutions

Spotting a mismatch between a compressor and its duty cycle is vital. It can help you to avoid some serious potential damage.

7 Warning Signs to Watch For

1. Constant Running: The compressor keeps running without a break – even when demand drops.
2. Overheating: The unit feels excessively hot. Or it keeps tripping the thermal overload.
3. Tripped Breakers: Too much current from the motor causes breakers to trip.
4. Unusual Noises: Sounds like grinding, squealing, or knocking – which often point to heavy internal wear.
5. Pressure Drops: Tools lack power because the system cannot maintain pressure.
6. Moisture in Air Lines: Water is not separating from the air because the compressor is running too hot.
7. Spiking Energy Bills: Running more power through your system doesn’t make you more efficient.

A Strategic Approach to Optimisation

If you’re experiencing any of these symptoms, it’s time to act. 

Better ventilation and a leak audit can help in the short term, but the real fix is making sure your compressor matches the air demand of your site.

For facilities where demand rises and falls, a Variable Speed Drive (VSD) air compressor is the most efficient option.

VSD technology automatically adjusts motor speed to meet actual air use in real time, cutting out start–stop cycles and wasted energy. The Atlas Copco GA VSD+ range is a proven choice for reliable, energy-efficient operation.

The most reliable way to diagnose a mismatch is with professional analysis. The expert engineers at Search Air use data logging equipment to perform a detailed air compressor energy audit. This assessment identifies inefficiencies and provides the precise data needed to ensure your compressor matches your real-world demand profile. 

A comprehensive air compressor sizing guide can also help in understanding the requirements.

Meeting UK Compliance and Efficiency Standards

Properly managing your compressor’s duty cycle is not just about saving money; it is also about compliance. 

An efficient compressed air system helps your business align with UK energy regulations. 

This covers the Energy Savings Opportunity Scheme (ESOS), Streamlined Energy and Carbon Reporting (SECR), and compliance with safety rules under the Pressure Systems Safety Regulations 2000 (PSSR).

Duty cycle management also goes hand in hand with ISO 8573-1 air quality standards. It ensures a consistent supply of clean air whilst optimising your operational efficiency.

Expert Support for Your Compressed Air System

Choosing the right duty cycle for your compressor is vital for keeping performance high, reliability steady, and efficiency consistent.

By matching the compressor design to your site’s duty profile, you can manage costs more effectively – and also reduce the risk of unexpected downtime.

Search Air, as an Atlas Copco Premier Distributor, can design, install, and maintain your system to ensure it is running as efficiently as possible and in full compliance. 

With depots in Leeds, Sheffield, and Nottingham, we’re well placed to provide support – reaching customers throughout Yorkshire and the East Midlands quickly and efficiently.

Book an Air Compressor Energy Audit to cut inefficiency and boost performance, and speak with our engineers to identify the ideal duty cycle for your operation.

Request your free airCHECK visual inspection to identify no-cost/low-cost efficiency gains.

Common Questions About Compressor Duty Cycle

What does 100% duty cycle mean?

It means the compressor can run continuously – without stopping to cool down. Rotary screw models are designed for this level of performance. This makes them ideal for heavy, industrial applications.

How can I measure my compressor’s duty cycle?

Track how long the compressor runs. As well as how long it rests during a normal 10-minute period. 

Then apply the following formula:

(Run Time ÷ (Run Time + Rest Time)) × 100.

What happens if I exceed my compressor’s duty cycle?

The compressor will overheat. This overheating causes the lubricating oil to break down. It also causes other components to wear out much faster – and can significantly shorten the life of your compressor.