Compressed Air Quality ISO 8573-1 — Choosing Dryers and Filters for Factories in Thailand

Compressed air is called a factory's "fourth utility" after power, water, and gas — driving air tools, valves, cylinders, paint spraying, and processes. But "dirty" compressed air (water, oil, particles) is the silent cause of sticking valves, broken tools, rust in piping, and product defects.

In humid Thailand, this is especially severe. This article explains the ISO 8573-1 air-quality standard and how to choose a dryer + filter to suit the job.

1. ISO 8573-1 — Three Contaminants to Control

The standard classifies contaminants into three types, each with a "purity class" (lower = cleaner):

1. Solid particles — dust, rust
2. Water — measured by pressure dew point (PDP)
3. Oil — liquid + aerosol + vapor combined

The designation is 3 digits, e.g. 1.2.1 = [particles 1].[water 2].[oil 1]

2. Dryer — Refrigerated vs Desiccant

flowchart TD
  A[Air from compressor
hot + saturated] --> B{How dry must it be?}
  B -->|General work
piping > 0C| C[Refrigerated Dryer
PDP +3C, Class 4
economical]
  B -->|Food/pharma/electronics
cold/outdoor lines| D[Desiccant Dryer
PDP -40 to -70C
Class 1-2]
  C --> E[Next-stage filter]
  D --> E
  E --> F{Need oil Class 1?}
  F -->|Yes| G[Coalescing + Activated Carbon]
  F -->|No| H[Coalescing + Particulate]
  G --> I[Air to ISO 8573-1 spec]
  H --> I

• Refrigerated dryer — cools the air so vapor condenses out, reaching PDP ~+3°C (Class 4), removing ~98% of moisture. Economical, general use, but cannot serve piping below 0°C
• Desiccant dryer — air passes through activated alumina/silica gel that adsorbs moisture, reaching PDP -40°C to -70°C (Class 1-2). For applications needing very dry air

3. Filtration — Multiple Stages by Required Class

• Particulate filter — removes dust/rust
• Coalescing filter — merges oil aerosol + water mist into draining droplets
• Activated carbon filter — adsorbs oil vapor (required for oil Class 1, food/pharma)

The filter test standard is ISO 12500. Food/pharma may require an oil-free compressor for air in direct product contact.

4. The Thailand Context — Humidity Means Taking Drying Seriously

Thailand's high relative humidity means compressed air carries more vapor than in dry climates. Plants that skip the dryer commonly see:

• Rust in air piping → particles enter the tools
• Water in valves/solenoids → frequent sticking/failure
• Paint/food work ruined by water/oil contamination

= repair and scrap costs many times higher than the dryer + filter.

5. Compressed-Air System Checklist

1. State the required class (e.g. 1.4.1 general, 1.2.1 food/pharma)
2. Choose the dryer by dew point: refrigerated (general) / desiccant (very dry)
3. Stage the filters by oil/particle class
4. Use automatic drains to remove condensate
5. Measure for real (dew point + oil) to confirm the class — don't assume

Clean compressed air goes hand in hand with the right-grade compressor oil — we supply industrial compressor oils for rotary screw and reciprocating units across ISO 6743-3 grades, with guidance on selecting by compressor type and operating temperature to keep your air system clean, long-lasting, and with less condensate.

Talk to our engineering team to set a clean compressed-air system to spec — call 02-096-2118 or LINE OA @sahawatt1988.

Summary

• ISO 8573-1 controls three contaminants: particles · water (dew point) · oil — coded e.g. 1.2.1
• Refrigerated dryer (PDP +3°C, Class 4) for general work · Desiccant (-40 to -70°C, Class 1-2) for food/pharma/cold
• Oil Class 1 (≤0.01 mg/m³) requires coalescing + activated carbon
• Humid Thailand = take drying seriously, or rust + water damage the whole system
• State the class + measure for real (dew point/oil) in the spec

Clean air to the right class = durable tools, non-sticking valves, fewer defects — far cheaper than the dryer cost.