Understanding Your Compressor’s Duty Cycle

Compressed air is the fourth essential utility in any industrial building, following electricity, gas, and water, but a lack of understanding of one crucial performance metric is leaving thousands of pounds of energy, high maintenance costs, and plant failure on UK factory floors.

The duty cycle of a compressor is more than just a technical specification buried in data sheets, it’s the key performance indicator of how long a compressor can last and its ability to do its job. Choosing one that’s unsuited to your application not only wastes energy, but is likely to lead to premature equipment failure. 

Anglian Compressors guides companies across East Anglia and the Midlands through getting the most out of their investment, improving their productivity, and staying compliant.

Compressor Duty Cycles Explained

The duty cycle on a compressor is the percentage of time that the machine can safely run within a given time period, generally 10 minutes, without overheating. This directly relates to the cooling ability of the compressor.

The formula is straightforward:

Compressor Time On/(Time On+Time Off) ​×100 = Duty Cycle Percentage

Example: If your compressor is on for 6 minutes, and off for 4 minutes, your compressor has a duty cycle of 60%.

• 50% Duty Cycle: Your compressor can run for 5 minutes, but then needs to cool down for 5 minutes. 50% is suitable for intermittent use, such as in a small garage, but will not cope with more continuous demand.
• 75% Duty Cycle: Your air compressor can run for 7.5 minutes out of a total of 10 minutes. A 75% duty cycle is suitable for a busy automotive repair shop, where tools are used frequently but not required to be operated continuously.
• 100% Duty Cycle: 100% duty cycle compressors are designed to run indefinitely without a cool-down period, which is essential for demanding industrial applications.

The Duty Cycle Distinction Between Piston and Rotary Screw

The most significant determiner of your compressor’s duty cycle and capabilities is which type of compressor you own. The choice between the two most common types, piston and rotary screw, will dictate your system’s performance and reliability.

Reciprocating (Piston) Compressors for Intermittent Use

Piston compressors are the workhorses of facilities with intermittent demand; due to their simpler cooling design, they have lower duty cycle ratings, typically ranging from 50% to 75%, and require these essential rest periods to dissipate heat.

Rotary Screw Compressors Engineered for 100% Continuous Duty

Continuous-duty air compressors, such as rotary screw air compressors, are designed for a 100% duty cycle; their advanced oil-flooded mechanism actively cools their internal components, meaning they can operate 24/7 without suffering any damage. It’s this continuity and reliability that make them the industry benchmark in manufacturing and production-critical applications. 

For a true 100% duty cycle compressor your UK business can rely on, the choice is almost always one of the Different Types of Air Compressors in the rotary screw category.

The “100% Duty Cycle” Piston Compressor Misconception

Do not take a “100% duty cycle” rating on a piston compressor to mean it can run continuously for an 8-hour shift; it means the machine can run continuously within a limited cycle (such as 10 minutes), then must be shut down for a lengthy cool-down cycle. Expecting 100% duty cycle piston compressors to run like a rotary screw is a costly mistake.

The Consequences of Mismatching Your Duty Cycle

Forcing your compressor to operate beyond its intended duty cycle, known as over-cycling, is a common cause of premature failure; it starts a predictable chain of events beginning with dangerous overheating, and ending with costly operational shutdowns and equipment degradation that is best avoided.

The Warning Signs Your Air Compressor is Overworked

• Frequent Circuit Breaker Trips: When the motors operating your air compressor overheat, they draw too much current, which will cause your circuit breaker, or fuse, to trip. This is a clear sign of severe mechanical strain caused by overworking.
• Excessive Heat: If your entire unit is hot to the touch or it frequently experiences thermal overload shutdowns, your compressor is overworking.
• Unusual Noises: Rattling, grinding, or chattering sounds most likely indicate there are  loose or failed internal components in your system.
• Moisture in Air Lines: Overheating compressors are not able to effectively separate the water vapour from the compressed air, which will cause rusting, corrosion, and downstream contamination.

Financial and Operational Consequences

• Accelerated Wear: The high temperatures caused by overworking your air compressor will break down lubricating oil and increase the friction and wear on critical components in your system, like piston rings, bearings, and valves.
• More Frequent Maintenance: All that accelerated wear means more frequent repairs and expensive component replacements.
• Higher Energy Costs:  Overworked compressors are inefficient as they are forced to operate for more extended periods to meet demands, using more electricity and driving up your energy costs.
• Unplanned Downtime: Component failures mean more unplanned production stoppages, lost revenue, and demoralising emergency call-out charges.

Duty Cycles Across UK Industries

Here are some use cases to help you gain a better practical understanding of air compressor duty cycles in your specific setting:

• Automotive Workshops: compressed air demand in car workshops is often random or intermittent, but can experience intense peaks, like when powering impact wrenches. A heavy-duty, two-stage reciprocating compressor can offer a 75% duty cycle, perfect for this application, for a great value.
• Manufacturing Plants: Production lines most often operate 24/7 and expect a completely stable and uninterrupted supply of air. A 100% duty cycle rotary screw compressor is the only viable option in these circumstances.
• Paint & Body Shops: There is demand for a continuous, high volume of clean, dry air in body shops. A 100% duty cycle rotary screw is crucial for preventing moisture contamination and ensuring a flawless finish.
• Food & Beverage: With a non-negotiable need for air purity and continuous operation for processes such as packaging and bottling, the food and beverage industry standard is a 100% duty cycle oil-free compressor.

How to Optimise Your System for the Correct Duty Cycle

Achieving the optimal match between machine and purposes requires intelligent system design and management.

The Crucial First Step of Right-Sizing

Getting your air compressor size correct is fundamental to operating a reliable and efficient system; If it’s undersized, your compressor will over-cycle and eventually fail, but if it’s oversized, your compressor will use more energy by cycling more frequently than necessary.

A professional air audit will equip you with the data you need to select a compressor of the  correct size for your facility, as well as identifying any other possible efficiency gains. Anglian Compressors can arrange a comprehensive AIRScan air audit for your facility to ensure your system is the best option available.

The Power of VSD Technology

For any facility with fluctuating air demand, Variable Speed Drive (VSD) air compressors are by far the most efficient choice. The Atlas Copco GA VSD⁺ compressor, for example, continuously varies its motor speed to match its air production to your facility’s actual demand at any given moment, helping you reduce your energy costs by up to 60% and eliminate energy waste.

Advanced Monitoring and Maintenance

Your compressor’s duty cycle also determines how often it needs to be serviced, and over-cycled compressors require the most frequent maintenance. By using real-time performance monitoring, such as SMARTLINK, your compressor’s service schedule can transition from calendar-based to a proactive and predictive one, as detailed in our maintenance and service agreements. This data-focussed approach to maintenance decreases the likelihood of unforeseen breakdowns, as well as reducing the total life-cycle cost of ownership.

UK Compliance and Best Practices

Running a compressed air system in the UK requires compliance with several prescriptive regulations and standards of good practice.

• PSSR 2000: The Pressure Systems Safety Regulations 2000 require most industrial systems to be supported by a Written Scheme of Examination and to have periodic statutory inspections by a ‘competent person’.
• BCAS Guidance: The British Compressed Air Society (BCAS) has published a series of best practice guidance notes covering system installation, pipework, filtration, drying, and air purity.
• Carbon Trust Findings: Research by The Carbon Trust has identified areas where additional savings can be made; a simple 10% reduction in system pressure can lead to a 5% energy saving, while a single 3mm air leak can cost over £700 per year in wasted electricity.

Your Next Step to an Optimised System

Understanding your compressor’s duty cycle is crucial to maintaining your system’s health and optimising your bottom line, and a firm grasp of the difference between intermittent-duty piston models and 100% duty cycle Rotary Screw Compressors is the first step toward a sound investment. Embracing technology like VSD and predictive monitoring is a straight shot to reducing your energy costs, and all of this can be estimated using a Compressor Running Cost Calculator. 

Your compressed air system is one of your most valuable assets, and keeping it correctly specified and professionally maintained is one of the best investments you can make for the health of your business. 

We provide dedicated support to businesses across East Anglia and the Midlands from our base in Peterborough, so why not contact Anglian Compressors for expert advice, a comprehensive system audit, or a speedy response service?