Understanding Air Compressor Duty Cycle to Optimize Performance
Choosing the right air compressor is key to maximizing productivity and preventing costly downtime. Along with PSI and CFM ratings, duty cycle is a critical specification that is often misunderstood. This blog will clearly explain duty cycle, how to ensure your compressed air system meets the specifications of your application and why it matters.
What Does Air Compressor Duty Cycle Mean?
The simple definition of duty cycle, which is also referred to as run/rest time, is the amount of time an air compressor can make air compared to the amount of time it must rest or cool down within a complete cycle.
Technically speaking, duty cycle is the percentage of time within a complete cycle that a compressor can provide its rated, consistent pressure (pounds per square inch; PSI) and flow (cubic feet per minute; CFM). A complete cycle includes both the running and resting time.
Think of duty cycle as a HIIT (high intensity interval training) workout where the athlete has a period of intense exercise, then a period of rest before beginning the intense exercise/rest cycle again.
Common Duty Cycle Ratings Explained
Air compressors are rated for a variety of duty cycles. Here, we will explain the most common.
What does a 100% duty cycle mean?
An air compressor with a 100% duty cycle has a continuous duty cycle, which means it runs 100% of the time at its rated PSI and CFM without a rest period. Continuous duty cycle compressors are used in industrial facilities where a continuous air demand is needed to operate manufacturing equipment. Rotary screw and centrifugal compressors typically provide a continuous duty cycle.
What does intermittent duty cycle (70%, 60%, etc.) mean?
Often compressors specify a percentage for their duty cycle, such as 70% duty cycle. This means the compressor runs for a specified percentage of time and then cools down or rests for the remaining time of the complete cycle.
For example:
- A 70%, or 70/30, duty cycle means the compressor can run for 7 minutes and then must cool down for 3 minutes of its complete 10-minute cycle.
- A 60%, or 60/40, duty cycle means an air compressor will run for 6 minutes and rest for 4 minutes of a complete 10-minute cycle.
- A 50%, or 50/50, duty cycle air compressor provides equal run and rest time, so 5 minutes on and 5 minutes off in its 10-minute cycle.
Reciprocating compressors typically offer intermittent duty cycles and are used in intermittent applications, such as powering pneumatic tools in an automotive shop.
What is a normal duty cycle?
There is no “normal” duty cycle. The right duty cycle is dependent upon your facility’s air demand. For a small shop, a 25% duty cycle might be normal, while in a large manufacturing facility, 100% is the standard.
How to Calculate Your Air Compressor Duty Cycle Requirement
The first step to calculating your required duty cycle is to determine your facility’s actual air demand by logging tool and equipment use during both average and peak demand periods, noting whether demand is continuous or intermittent.
Then, use the following calculation:
(Compressor Run Time in Minutes) / (Run + Rest Time in Minutes) x 100 = Duty Cycle %
For example, if your compressor runs for 4 minutes to build pressure and then rests for 6 minutes before starting again, the cycle time is 10 minutes. The calculation for this air compressor duty cycle would be:
(4 minutes run time) / (4 minutes run time + 6 minutes rest time) x 100 = 40% duty cycle.
The Duty Cycle Rule: Matching the Compressor to Your Application
To ensure reliability and a long service life, the air compressor’s duty cycle rating must adequately meet the demands of your application.
What happens if you exceed your compressor’s duty cycle?
By forcing your compressor to run longer than the time for which it was designed, you are exceeding your compressor’s rated duty cycle, which can cause overheating, excessive component wear and, ultimately, premature failure.
A reciprocating compressor with a 50% duty cycle will quickly experience mechanical issues if forced to run 100% of the time to maintain pressure, whereas a rotary screw compressor designed for continuous operation will perform well in the application and experience a long service life.
How often should a compressor cycle?
Your compressor’s cycling frequency aligns with its duty cycle rating and compressed air storage capacity. If a compressor is cycling too often and running for longer periods than it is rated for, it is a clear sign that the compressor system isn’t sized properly for the demands of the application. This will result in premature compressor failure and excessive energy consumption.
Your Partner in Compressed Air System Optimization
Don’t guess on your investment. Selecting a compressor with the right duty cycle is essential for system performance, reliability and efficiency. As a solution provider, JHFOSTER doesn’t just sell equipment, our experts evaluate, design, integrate and support your compressed air system. Contact the experts at JHFOSTER for a complete system evaluation to ensure your compressor meets the needs of your application. Get a quote or a system evaluation today to find the most effective and reliable compressed air solution for your facility.
