Moisture is an unavoidable byproduct of compression. The right dryer depends on the pressure dewpoint your application requires and the ambient conditions your system operates in. Refrigerant dryers cover general industrial use; desiccant dryers are required when sub-zero dewpoints are critical; membrane dryers suit low-flow, point-of-use applications. Specifying the wrong type — or undersizing for your environment — creates reliability problems that compound over time.
Why is moisture a problem in compressed air systems?
Atmospheric air contains water vapour. Compression increases vapour concentration, and as the air cools downstream, that vapour condenses into liquid water. A 75 kW compressor operating in Perth during summer can generate 50–100 litres of liquid water per day in the distribution system.
Pipe corrosion is the most common consequence. Moisture reacts with carbon steel pipework to form iron oxide, progressively reducing bore diameter and contaminating downstream air. In systems operating without adequate drying for years, internal corrosion can remove 20–30% of pipe flow capacity.
Pneumatic instrument and valve failure is the most operationally costly outcome. Control valves, positioners, and solenoids rely on dry air to function within specification. Water in instrument air lines causes stiction, erratic response, and seal degradation — a failed control valve in a process plant can trigger a production shutdown.
Product contamination in food processing and pharmaceutical applications is a regulatory failure risk. Liquid water entrained in compressed air can contact product or product-contact surfaces, triggering HACCP non-conformances. This is why ISO 8573-1 moisture classes exist — to formalise the dewpoint requirement by application.
Frozen lines are relevant in refrigerated processing areas and outdoor distribution pipework. Water present above zero dewpoint can freeze at valves, actuators, and fittings in cold ambient conditions, causing blockages and mechanical damage.
How does a refrigerant dryer work?
A refrigerant dryer cools the compressed air to approximately 3°C using a refrigeration circuit. At that temperature, water vapour condenses into liquid, collects in a separator, and drains automatically. The dried air re-warms against the incoming wet air through a heat exchanger, preventing condensation on downstream pipework.
The result is a pressure dewpoint (PDP) of approximately +3°C — adequate for most general industrial distribution systems operating indoors.
Refrigerant dryers are the correct choice for:
- General manufacturing and workshop compressed air
- Pneumatic tools and actuators in climate-controlled environments
- Plant air where ISO 8573-1 Class 4 or Class 5 moisture quality is acceptable
Limitations in the Western Australian context: Refrigerant dryers are rated at 35°C inlet air and 25°C ambient. In Perth, summer ambient temperatures regularly reach 35–42°C; in the Pilbara, 45°C+ is common. Operating above rated conditions — routine in WA compressor rooms and on mine sites — increases moisture load and degrades actual dewpoint performance. Dryers must be sized for worst-case inlet conditions, not nameplate ratings.
How does a desiccant dryer work?
A desiccant dryer uses a hygroscopic material — typically activated alumina or silica gel — to adsorb moisture from compressed air. Desiccant dryers operate on a twin-tower cycle: one tower dries the incoming air while the other regenerates. Two regeneration methods are available:
Heatless (pressure swing) desiccant dryers use a portion of the dried air — typically 15–20% of rated flow — as purge air to regenerate the spent tower. The design is simple and reliable, but the purge loss is a permanent operating cost. At scale, this represents significant wasted compressor energy.
Heated desiccant dryers use electric heaters to regenerate the desiccant, reducing purge air consumption to 3–5%. Capital cost and complexity are higher, but operating cost is lower at high flow rates and continuous-duty applications.
Both types deliver pressure dewpoints of −40°C to −70°C — well below any practical condensation risk in Australian operating environments.
Desiccant dryers are the correct choice for:
- Instrument air systems (control valves, positioners, analysers)
- Food and pharmaceutical process air requiring ISO 8573-1 Class 2 or Class 1 moisture quality
- Outdoor distribution pipework exposed to cold ambient conditions
- Applications where downstream equipment cannot tolerate any risk of liquid water
For detail on ISO 8573-1 oil and particle limits alongside moisture, see our guide to ISO 8573-1 air purity classes.
How does a membrane dryer work?
A membrane dryer uses a bundle of semi-permeable hollow-fibre membranes. Water vapour passes through the membrane walls from the high-pressure bore side to the low-pressure shell side, swept away by a small purge flow. The dried air exits at near-full pressure.
Membrane dryers have no moving parts, require no electrical supply, and are low-maintenance. The primary maintenance task is replacing the inlet coalescing filter that protects the membrane from liquid water and oil.
Membrane dryers are the correct choice for:
- Point-of-use applications requiring low dewpoints at low flow rates
- Remote or portable applications where power supply is limited
- Hazardous area installations where electrical equipment requires additional certification
- Systems where maintenance simplicity outweighs operating cost
Limitations: Membrane dryers are flow-limited — practical for flows up to approximately 100 l/min, suitable for instruments and control panels, but not plant-wide distribution. Performance is sensitive to inlet temperature and oil contamination. They are not a substitute for refrigerant or desiccant dryers in central plant applications.
Compressed air dryer comparison
| Type | Pressure dewpoint | Capital cost | Energy use | Maintenance | Best application |
|---|---|---|---|---|---|
| Refrigerant | +3°C PDP | Lowest | Moderate (compressor motor) | Low — refrigerant circuit servicing | General industrial, workshop, plant air |
| Desiccant (heatless) | −40°C to −70°C PDP | Moderate | High (15–20% purge air loss) | Low — desiccant replacement every 3–5 years | Instrument air, food/pharma, cold environments |
| Desiccant (heated) | −40°C to −70°C PDP | Higher | Moderate (heat + minimal purge) | Medium — heater elements, controls | High-flow instrument air, continuous duty |
| Membrane | −20°C to −40°C PDP (typical) | Low–moderate (unit cost) | Low–moderate (purge loss, no power) | Very low — inlet filter replacement only | Point-of-use, remote, portable, hazardous area |
What ISO 8573-1 moisture class do you need?
ISO 8573-1 classifies compressed air moisture quality by pressure dewpoint:
| Class | Maximum pressure dewpoint | Typical application |
|---|---|---|
| Class 1 | −70°C PDP | Instrument air (critical), pharmaceutical process air |
| Class 2 | −40°C PDP | Instrument air (standard), food contact air, cold-climate distribution |
| Class 3 | −20°C PDP | General manufacturing, pneumatic controls indoors |
| Class 4 | +3°C PDP | General plant air, most workshop applications |
| Class 5 | +7°C PDP | Non-critical applications — rarely specified |
| Class 6 | Up to +10°C PDP | Non-critical; essentially undried air |
Class 4 (+3°C PDP) is delivered by a refrigerant dryer and covers most general industrial applications. Classes 1 and 2 require desiccant drying. If your class is unclear, start by confirming your compressed air flow and pressure requirements — moisture class specification follows from that baseline.
How does Perth’s climate affect dryer selection?
Dryer performance is a function of inlet air conditions, not nameplate rating. Manufacturers publish performance data at reference conditions — typically 35°C inlet air and 25°C ambient. In Western Australia, both are routinely exceeded.
Perth metropolitan area: Summer ambient temperatures of 35–42°C are normal from December through March; poorly ventilated compressor rooms regularly exceed 45°C. Under these conditions, a refrigerant dryer sized to nameplate capacity may deliver +7°C to +10°C dewpoint rather than the rated +3°C — a shift from ISO 8573-1 Class 4 to Class 5 or 6 that matters in any application dependent on dry air.
Pilbara and regional WA: Ambient temperatures above 45°C are documented across the Pilbara during heatwaves. For mining and resources applications in regional WA, desiccant dryers are often the more reliable specification — they maintain consistent dewpoint performance regardless of ambient temperature.
Sizing rule: Size for worst-case summer ambient, not annual average. Actual inlet air temperature, operating pressure, and flow rate determine the dryer requirement — not nameplate compressor output. We apply these conditions to every dryer specification we provide.
Frequently Asked Questions
Does every compressed air system need a dryer?
In practice, yes — for any system serving industrial equipment, controls, or product-contact processes. For any system with distribution pipework, pneumatic controls, or process applications, a dryer is a basic requirement, not an optional upgrade.
When should I choose a desiccant dryer over a refrigerant dryer?
Choose a desiccant dryer when your application requires a dewpoint below 0°C (instrument air, food process air, outdoor pipework), when ambient conditions degrade refrigerant dryer performance, or when your process requires ISO 8573-1 Class 2 or better. The higher operating cost is justified by consistent, deep drying regardless of ambient temperature.
What does it cost to run a desiccant dryer?
The dominant cost is purge air — 15–20% of rated flow, added directly to compressor energy consumption. For a 75 kW compressor running 4,000 hours per year, this is approximately $8,000–$12,000 AUD per year at typical WA industrial tariffs. Heated units reduce purge to 3–5%, paying back the additional capital cost within a few years at high utilisation.
What are the limitations of membrane dryers?
Membrane dryers are unsuitable for central plant use above approximately 100 l/min. They are highly sensitive to oil contamination — a failed inlet coalescing filter can foul the membrane permanently. Dewpoint degrades at flows above the rated capacity. They are a point-of-use or specialised tool, not a substitute for refrigerant or desiccant dryers in plant-wide applications.
Specify the right dryer for your operating conditions
The correct dryer type is determined by your required pressure dewpoint, your actual operating conditions, and the consequences of moisture in your process. Our team works with mining operations, food manufacturers, and general industrial customers across Perth, WA and Victoria to assess dryer requirements and size equipment for worst-case summer conditions — not nameplate ratings.
If you are commissioning a new system, upgrading an existing installation, or experiencing downstream moisture problems, contact us to discuss the right dryer specification for your application.
Speak to our team about the right compressed air dryer for your application.
Compressor Systems Australia is an industrial compressed air specialist with operations across Western Australia and Victoria. Our technical team has over 100 years of collective industry experience servicing mining, manufacturing, food processing, and automotive customers.