PET Air Compressor Sizing - How To Choose The Best

PET Air Compressor Sizing – How To Choose The Best

Proper PET compressor sizing is a crucial decision that can significantly impact your operation’s efficiency and overall costs. The best size of compressed air equipment for your needs depends on various factors, including air usage, duty cycle, and future needs.

Discover everything you need to know with Control Gear’s guide to PET Air Compressor sizing.

The Critical Role of Air Compressors in PET Bottle Production

High-performance air compressors play a pivotal role in PET bottle production, powering a vast range of pneumatic tools and machinery throughout the manufacturing process. The PET industry primarily depends on efficient air compressors to ensure the seamless functioning of operations, from the initial stages of preform production, to the final steps of bottle blowing and shaping.

The PET bottle manufacturing process involves two key stages:

  • Injection moulding PET preforms
  • Blow moulding the preforms into bottles

An effective and efficient PET compressor system is essential during the blow moulding stage, where high-pressure air inflates the preform inside a mould to its final bottle shape. A stable and reliable air supply is crucial here, as any fluctuations in pressure might result in defective bottles.

Selecting the right air compressor size for your PET bottle manufacturing directly affects the efficiency, cost-effectiveness, and overall success of your operations. Incorrect sizing, such as choosing a run-of-the-mill low-pressure air compressor for PET bottle manufacturing, can have serious consequences, leading to inefficiencies, increased costs, and potential equipment damage.

Understanding the Basics

PET (Polyethylene Terephthalate): A Critical Player in Packaging

Polyethylene Terephthalate, commonly known as PET, is a type of plastic that has gained significant importance in the packaging sector, especially in food and beverage containers. This thermoplastic polymer resin is renowned for its strength, transparency, and ability to serve as a barrier against moisture, thus ensuring that the contents within the container remain fresh, and uncontaminated, over an extended period.

Air Compressors In PET

Air compressors play an integral role in PET production, specifically in the blow moulding process used to shape bottles. This process begins when PET is heated and moulded into a preform, a tube-like piece with a moulded screw top. The preform is then placed inside the blow mould, and the air compressor is put into action.

High-pressure air, usually between 20-40 Bar, is pumped into the preform, inflating it to take the shape of the mould, thus forming the bottle. The compressor’s role is critical here as the air pressure must be precise and maintained consistently.

For this reason, choosing a high-quality, reliable air compressor, such as those by Atlas Copco, is essential. Notably, Atlas Copco’s ZR/ZT compressors are ISO-certified for 100% oil-free air, ensuring contamination-free, high-pressure air supply for the blow moulding process.

Key Considerations for Sizing

Know Your Requirements

  • Air Demand: The first step in determining your compressor size is to calculate your total air demand. This demand is based on the quantity of air required by all the equipment that will be run simultaneously. It’s crucial to remember that the compressor must be capable of supplying the peak air demand, not just the average.
  • Current Tools: Consider the tools, machinery, or equipment you are currently using. Each tool has a specific air consumption rate, typically expressed in cubic feet per minute (CFM). Compressor size should be chosen based on the cumulative CFM of all tools running concurrently, with some additional capacity to accommodate potential future needs.
  • Power: The compressor’s power, usually measured in kilowatts (KW), is another crucial factor. The power requirement of a compressor is directly linked to the air demand and the pressure necessary to operate your equipment. If your equipment requires high pressure, you’ll need a compressor with a higher kilowatt rating.
  • Pressure: Knowing the pressure requirements of your operation is vital when selecting a compressor. This is typically measured in pounds per square inch (PSI) or Bar. Remember, your compressor must be capable of delivering enough high-pressure air for all of your tools or machines. Atlas Copco’s P37 – P275 compressors, for instance, can provide a pressure range of 25-40 Bar, making them suitable for high-pressure applications, such as PET blow moulding.
  • Wastage and Leakages: An additional factor to consider when sizing your PET air compressor is the potential for wastage and leakages. Air can be lost through leaks in the air distribution system, inefficient use of air by machinery, and even through the natural dissipation of compressed air. Consequently, it’s important to factor in a buffer for these losses when sizing your compressed air system.

Duty Cycle

The concept of the duty cycle is one of the pivotal factors that influence the performance and lifespan of a PET air compressor. It reflects the compressor’s operational time in relation to a complete on/off cycle. A higher duty cycle indicates that the compressor is continuously running and working with minimal pauses.

The calculation formula for duty cycle is straightforward:

Duty cycle % = Compressor on time / (Compressor on time + Compressor off time).

Monitor the duty cycle closely as consistently pushing the compressor beyond its maximum capacity can lead to premature wear and potential system failure. For example, if a PET air compressor operates for 40 minutes in an hour and rests for 20 minutes, the duty cycle would be 66.67% (40 / (40+20)). This means the compressor is working two-thirds of the time and resting for one-third.

Compressor selection must consider the anticipated duty cycle. Atlas Copco offers a range of PET air compressors designed to handle varying duty cycles, allowing businesses to achieve their production targets without compromising on the compressor’s longevity.

Measure the Area

Sufficient space ensures that the compressor fits comfortably, and there is enough room for maintenance and repair work.

Start by taking the dimensions of your available space: length, width, and height. Bear in mind that the compressor shouldn’t occupy the entire space; adequate room should be left for ventilation, as air compressors generate a lot of heat, and poor ventilation can lead to overheating.

Future expansions or modifications in the setup should also be factored into the space considerations. Your business may grow, or operational changes might necessitate the addition of other machinery and equipment in the future.

Calculate Air Demand

To ensure the optimal operation of your PET air compressor, accurately calculating air demand is crucial.

  • Focus on the air consumption of each machine: Every piece of machinery in your facility has a specific air consumption rate, expressed in CFM (Cubic Feet per Minute). For example, the Atlas Copco GA VSD S series offers flow rates ranging from 14  to 272 CFM, enabling you to meet your specific air needs.
  • Account for leakages, loading, and wastage of air: It’s important to consider these important factors as these can significantly affect your compressor’s efficiency. Atlas Copco’s SMARTLINK data monitoring solution can help identify such anomalies for timely maintenance or upgrades.
  • Use CFM (Cubic Feet per Minute) as the standard measurement: CFM is the universal measurement for air flow. While compressor manufacturers may provide you with various metrics, always bring them back to CFM to make coherent comparisons.

Calculating air demand is not just about the immediate requirements of machines. It’s also about anticipating future needs, accounting for air wastage, and ensuring room for growth. A correctly sized air compressor can significantly boost your operational efficiency and reduce costs.

Understanding Pressure Requirements

Pressure, distinct from airflow or free air delivery, signifies the force needed per unit area in the operation of your PET air compressor. It must meet or exceed the highest pressure demand of any tool or application. Pressure is typically measured in pounds per square inch (PSI) or bar.

To correctly size your PET air compressor, you need to identify the application within your operations that requires the highest pressure. Then, select a compressor that can deliver this pressure consistently. Underestimating the pressure demands can lead to poor performance and potential damage to your tools or processes.

However, factors like long pipe runs, sharp bends, narrow pipes, or restrictions can cause a pressure drop between the compressor output and the point of use. So, it’s best to factor in an additional 1 bar (around 15 PSI) above your highest required pressure to compensate for potential pressure drop.

Remember, understanding your pressure requirements helps in selecting the most efficient and effective compressor, ultimately optimising your processes and minimising energy usage.

Advanced Considerations

Duty Cycle’s Role

The duty cycle, expressed as a percentage, refers to how long a tool is in operation compared to its rest time in a particular cycle. For example, if a tool operates for 30 minutes in an hour and rests for the remaining 30 minutes, it has a duty cycle of 50%.

Let’s take a closer look at how the duty cycle affects the total CFM required. First, calculate the CFM required by each tool or application during its operation, this is usually provided by the manufacturer. Then, add up the CFMs of all tools or applications that could be in use at the same time to get the total CFM. However, since not all tools will be in operation simultaneously, multiply this total CFM by the duty cycle (expressed as a decimal). This will give you an accurate estimation of the actual CFM needed for your operations.

For example, if your total calculated CFM is 100, but your average duty cycle is 60%, the actual CFM you require is 60 (100 CFM x 0.6). Opting for a compressor like Atlas Copco’s GA VSD S range, capable of providing this CFM, ensures your tools operate effectively without wasting energy.

Understanding Voltage Synchronisation

When selecting a PET AIR compressor, it’s imperative to match the compressor’s voltage requirements with the available voltage in your facility. Voltage mismatch can lead to inefficient compressor performance or even equipment failure. Compressors typically come in single, double, or three-phase power configurations.

Single-phase power is generally used for smaller compressors, while larger, industrial-scale compressors usually require three-phase power. Double-phase power is less common and is typically specific to certain regions or types of machinery.

Determining the Right Tank Size

Choosing the appropriate tank size for your PET AIR Compressor is a crucial step that should be based primarily on the compressor’s CFM (Cubic Feet per Minute) requirements. This value represents the volume of air that the compressor can supply over a minute, directly influencing its performance and efficiency.

Typically, standard tank sizes are available and can meet a broad range of needs. However, for specialised applications or unique operational conditions, customisation might be necessary.

For instance, Atlas Copco’s range of PET compressors offers varying tank sizes and custom configurations, ensuring a perfect fit for your operation.

Regulated Speed Models

Regulated Speed Models, also known as Variable Speed Drive (VSD) compressors, have a significant advantage in their ability to provide energy efficiency. These models can match the speed of the compressor to the air demand, thereby reducing energy output when the demand is low or non-existent. This adaptability results in considerable energy savings and minimises wear and tear on the compressor, increasing its lifespan.

The Benefits of Correct Sizing

Energy Efficiency

An appropriately sized PET air compressor from Atlas Copco is designed to operate at peak efficiency, reducing power consumption. A correctly sized compressor that matches your operational needs can result in substantial cost savings over the life of the equipment, making it not only an environmentally responsible choice but a financially sound one as well.

Equipment Lifespan

The right compressor size can mitigate unnecessary wear and tear on your equipment. An oversized compressor can lead to frequent stop-start cycles, putting undue stress on the motor and other components. Conversely, an undersized one may be forced to operate beyond its limits, increasing wear and reducing its lifespan.

Maintenance Costs

Maintenance costs can spiral out of control with an incorrectly sized compressor. Overworking or under-utilising a compressor can lead to frequent breakdowns and higher servicing costs. The correct compressor size not only operates efficiently but reduces the frequency of maintenance intervals and the likelihood of unexpected and costly repairs.


A correctly sized compressor is essential in ensuring optimal performance. It ensures that the compressor can adequately meet the facility’s air demand without being overburdened or underutilised. Atlas Copco’s PET air compressors are designed to deliver consistent, high-quality compressed air that meets your facility’s unique requirements.

Common Mistakes to Avoid

Air Demand Estimations

Overestimating results in investing in a larger machine than necessary, leading to higher initial costs and inefficient power usage. On the other hand, underestimating air demand can result in the compressor running at full capacity continuously, leading to premature wear and tear.

Ignoring Duty Cycle

The duty cycle, the percentage of time a compressor can run without risking overheating, often goes overlooked, leading to inefficiencies and increased wear on the compressor. Running a compressor beyond its duty cycle can result in overworking the machine, leading to potential breakdowns and costly repairs.

Future Considerations

While sizing your compressor for current needs is important, it’s essential to consider potential future expansions or changes in production that could increase air demand. If you anticipate growth in your operations, opting for a compressor with a slightly higher capacity might be a smart investment. Atlas Copco’s ZH and ZH+ oil-free centrifugal compressors are designed for high-capacity needs, making them an excellent choice for future-proofing your operations.

Key Takeaways for PET Air Compressor Sizing

Careful sizing of PET air compressors is crucial for efficient operation and long-term performance. Overestimating or underestimating air demand can lead to cost inefficiencies and premature wear and tear. Products like the Atlas Copco GA 90+ to 160+ range are recommended due to their Variable Speed Drive (VSD) technology, which matches motor speed with air demand.

The duty cycle of your PET Air Compressor is equally important; Atlas Copco’s ZR/ZT compressors provide a 100% duty cycle, ensuring reliable operation over extended periods. 

Lastly, anticipate potential growth in operations when sizing your compressor. Atlas Copco’s ZH and ZH+ air-cooled oil-free compressors are designed for high-capacity needs, making them an excellent choice for future-proofing your operations.

Always remember that the importance of correct sizing cannot be overstated, and the long-term benefits of making an informed decision are significant.

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