Selecting compressed air dryers: Beyond the basics

COMPRESSED AIR dryers are designed to remove water vapour from compressed air across a range of industrial processes. They are essential where moisture, rust, or contamination in the air supply can compromise equipment and product quality. Industrial applications that use compressed air and require a defined level of air purity and dryness, classified according to ISO 8573-1 (particles, water, oil) and achieved through compressed air treatment systems tested per ISO 12500, rely on these dryers. The goal is to provide clean, dry air to support the reliability and efficiency of processes.

Different types of dryers (heated desiccant, heatless desiccant, refrigerated) use different technologies to reduce overall moisture by lowering the ‘pressure dew point’ and preventing condensation downstream. However, when sizing and selecting the right drying technology, it is not uncommon for a limited number of parameters to be considered, including flow rate, pressure, inlet temperature, and the required dew point. That said, there are other equally important factors that can impact performance, compliance, and filter lifecycle costs.

A fresh look at selection criteria

Understanding the precise installation environment of the compressed air dryer is crucial. For example, simply knowing a compressed air dryer will be located "outside" is insufficient because the specific external location introduces a unique set of challenges that can impact the dryer's performance and lifespan. The considerations for a roof installation compared to a ground installation are dramatically different due to environmental extremes and structural issues. Placing a dryer on a roof introduces additional challenges. These include those related to thermal stress, weather exposure and accessibility, as well as freezing risks such as ice formation in refrigerated dryer heat exchangers and in condensate management systems. 

The acoustic profile of a compressed air dryer is an often-overlooked environmental factor that can present operational concerns. Some air dryer designs may generate noise levels that approach the threshold for hearing protection. In the UK, the Control of Noise at Work Regulations 2005 sets action levels at 80 and 85 dB, while the EU’s Directive 2003/10/EC sets lower exposure action value at 80 dB and upper exposure action value at 85 dBA. Sophisticated silencers included in dryers can help to address this issue.

Maintenance access and serviceability

While initial cost and performance ratings may often dominate the buying decision, the ease and speed of maintenance are significant contributors to long-term operating costs and production reliability. A compressed air dryer is an integral part of the manufacturing process. When it goes offline for servicing, the production line may be interrupted, often requiring a bypass line or a standby dryer in critical installations.

In many industrial facilities, dryers are often placed in tight, inconvenient spaces, yet access is paramount. For maintenance tasks, such as a simple filter check or complex valve replacement, technicians require adequate room. A compact design might mean that essential service points are pressed against a wall or obscured by piping. Filter accessibility or cartridge replacement time are therefore key considerations so that filters can be replaced without extensive disassembly and essential components like cartridges can be swapped out. If a unit requires significant disassembly or the use of specialised lifting gear just to access a component, the service time increases, which can lead to higher labour costs and greater risk of accidental damage.

Compliance and certification considerations

It is important to verify that the pressure-containing components comply with applicable regulatory requirements. In Europe, this mainly includes PED compliance and CE marking; internationally, ASME may be required. Depending on the application, ATEX compliance may also be necessary.

In addition, material certification according to EN 10204 (e.g., 3.1 or 3.2) is often required for pressure-containing components, and local laws and regulatory interpretations should always be considered.

The system should also be designed for low pressure drop, as unnecessary restrictions force compressors to run at higher discharge pressures, increasing energy consumption and operating costs. Tracking pressure drop, flow rates, dew points, and power consumption per cycle can help identify inefficiencies and optimise performance. Data-driven maintenance can also help extend service intervals and avoid unexpected downtime.

Looking beyond moisture and oil​

Compressed air carries more than just moisture and traditional contaminants such as oil and particles; it also contains gaseous components like oxygen, carbon dioxide, and other naturally occurring or process-related gases. In most compressed air applications, oxygen is simply part of air composition, but in nitrogen generation it is an impurity that must be removed, while in breathing-air systems its concentration must be tightly controlled. Carbon dioxide can also be critical in applications such as breathing air and specific laser processes.

When selecting a compressed air dryer, it’s vital to look beyond basic parameters to include more extensive environmental, operational, compliance, and lifecycle factors. This more effectively supports the selection of a reliable system that delivers long-term performance and efficiency.

Louis Cottaz is product manager at Donaldson

For more information: 

www.donaldson.com

Tel: +44 1 16 269 6161