How to Check Compressed Air Quality

The specific process of checking compressed air quality largely depends on the contaminant you’re testing for. Different methods are outlined in the ISO 8573 standard, which suggests the most effective practices.

In this guide, we’ll go over different testing methodologies to help you choose the right ones. We’ll then cover the importance of a regular testing schedule and the general benefits of ongoing testing.

Understanding Compressed Air Contaminants

Compressed air quality issues stem from three main contaminants:

1. Water
2. Oil
3. Particulate matter

Each of these poses unique risks to your operations and requires specific testing methods.

Water is perhaps the most common and problematic contaminant. It enters the system through ambient air and can cause issues like:

• Corrosion
• Freezing in lines
• Microbial growth

Oil contamination typically comes from the compressor itself. Even “oil-free” compressors can introduce hydrocarbons into the system from intake air or downstream components.

Particulate matter includes:

• Dust
• Rust
• Pipe scale
• Other solid contaminants

These particles can clog valves, damage sensitive equipment, and contaminate end products.

Understanding these contaminants is the first step to developing an effective testing regimen that protects your equipment and ensures compliance with industry standards.

The ISO 8573 Standard for Air Quality

The ISO 8573 standard provides the definitive framework for testing and classifying compressed air quality. It’s an internationally recognized standard that helps manufacturers maintain consistent air quality across their operations.

ISO 8573 categorizes air quality into classes ranging from 0 (most stringent) to 9 (least stringent) for each contaminant type. The classification determines the maximum allowable levels of particles, water, and oil in your compressed air system.

For example, Class 1 particulate air allows no more than 20,000 particles sized 0.1-0.5 microns per cubic meter, while Class 1 water content requires a pressure dew point of -70°C or below.

Different industries have different requirements. For example, food and beverage operations typically require Class 2 air, while pharmaceutical manufacturing might need Class 1 or even Class 0 for certain applications.

Knowing your industry’s requirements under ISO 8573 provides the baseline for your testing protocol.

Testing for Water Content

There are several ways to measure water content in compressed air systems, most notably:

• Dew point measurement: this is the most common approach that uses hygrometers to measure the temperature at which moisture begins to condense out of the air, providing an accurate indication of water vapor content.
• Electronic sensors: electronic sensors offer continuous monitoring capabilities. These devices can be installed at critical points in your system to provide real-time data on moisture levels.
• Detection tubes: for periodic testing, detection tubes provide a simple, cost-effective solution. These disposable tubes contain chemicals that change color when exposed to moisture, giving a quick visual indication of water content.
• Spectroscopic analysis: this method offers the highest precision for critical applications. This laboratory technique identifies the exact water content by measuring how the moisture absorbs specific wavelengths of light.

Your chosen method depends on your industry requirements and the sensitivity needed. Pharmaceutical and medical applications typically require continuous monitoring with high-precision instruments, while general manufacturing might need only periodic testing.

Oil Content Measurement Techniques

Testing compressed air for oil requires specialized techniques suited to different forms of oil contamination. The most common methods include:

• Aerosolized oil testing: utilizes specialized membranes that capture oil droplets from a measured volume of air. After collection, the membrane is analyzed to determine the concentration of oil aerosols.
• Gas chromatography: the gold standard for oil vapor testing. This laboratory technique separates and identifies volatile hydrocarbons present in the air sample with exceptional accuracy.
• Colorimetric testing: offers a simpler approach for routine monitoring. These tests use chemicals that change color in the presence of oil, providing a quick indication of contamination levels.
• Online monitors: provide continuous measurement of oil content. These devices use various technologies such as infrared absorption or flame ionization to detect hydrocarbon contamination in real-time.

The ISO 12500 standard establishes testing methodologies for oil removal equipment. This standard ensures that manufacturers consistently test and rate compressed air filters under controlled conditions (typically 101.5 psig pressure and 68°F temperature).

Particle Testing Methodologies

Particulate contamination can be tested using two methods:

1. Microscopic filter collection: involves passing a measured volume of air through a membrane filter. The collected particles are then counted and sized under a microscope to determine contamination levels.
2. Laser particle counters: provide more immediate results than microscopic collection. These devices detect and count particles by measuring the light scattered when particles pass through a laser beam.

On-site testing with portable laser counters is particularly valuable for troubleshooting. They allow technicians to identify contamination sources by testing at various points throughout the system.

The particle size ranges typically measured are 0.1-0.5 microns, 0.5-1.0 microns, and 1.0-5.0 microns. Different ISO classes specify maximum allowable counts for each size range.

Regular particle testing helps identify:

• Filter failures
• System leaks
• Upstream contamination 

This preventive approach saves on maintenance costs and extends equipment life.

Developing a Testing Schedule

The frequency of compressed air quality testing depends on three key factors:

1. Your industry
2. Regulatory requirements
3. Criticality of your applications

A well-planned schedule ensures compliance while optimizing resources.

Critical applications like breathing air require the most frequent testing. OSHA standards typically recommend quarterly testing for breathing air systems to ensure worker safety.

Regulated industries such as pharmaceutical manufacturing, medical device production, and food processing should conduct comprehensive testing at least annually. Some operations may require more frequent monitoring based on risk assessment.

General manufacturing facilities should establish a baseline with comprehensive testing, and then implement regular monitoring based on their specific needs and the stability of their systems.

It’s best to combine continuous monitoring with critical parameters and periodic comprehensive testing. This approach provides both immediate alerts to problems and thorough documentation for compliance purposes.

Don’t forget to document all testing results carefully. These records are essential for demonstrating regulatory compliance and for tracking system performance over time to identify trends before they become problems.

Benefits of Regular Compressed Air Testing

Regular testing of compressed air quality delivers numerous benefits beyond basic compliance with standards, such as:

• Preventing equipment damage: clean, dry air extends the life of pneumatic tools, valves, cylinders, and other components that rely on compressed air.
• Product quality improvements: for industries like food processing, pharmaceuticals, and electronics, air quality directly affects end product quality.
• Energy efficiency gains: contamination can increase pressure drop across filters and tools, forcing compressors to work harder and consume more energy.
• Reduced maintenance costs: clean air means less wear on system components, fewer emergency repairs, and longer intervals between scheduled maintenance.

Conclusion

Checking compressed air quality is not merely a regulatory requirement but a fundamental practice for ensuring operational efficiency and product quality. The methods outlined here provide a comprehensive approach to monitoring all three primary contaminants.

Regular testing according to ISO 8573 standards helps identify potential issues before they cause damage or contamination, so implement a structured testing schedule based on your industry’s requirements.

The investment in proper testing equipment and procedures pays dividends through extended equipment life, reduced maintenance costs, and consistent product quality.