What Is Dew Point and Why Does It Matter in Compressed Air Systems?

Moisture is one of the biggest threats to compressed air system performance, product quality and equipment reliability. Yet many facilities overlook one of the most important indicators of air quality: dew point.

Whether you operate a manufacturing plant, food processing facility, pharmaceutical production line or industrial workshop, understanding dew point is essential for maintaining compressed air quality and protecting critical equipment.

In this guide, we explain what dew point is, why it matters, how it relates to ISO 8573 air quality standards, and how dew point monitoring can help reduce costs while improving system reliability.

What Is Dew Point?

Dew point is the temperature at which water vapour in the air begins to condense into liquid water.

Every volume of air contains some amount of moisture. As air cools, its ability to hold water vapour decreases. When the temperature reaches the dew point, excess moisture condenses into liquid droplets.

In compressed air systems, this moisture can create significant operational problems if it is not properly controlled.

Simply put:

The lower the dew point, the drier the compressed air.

For example:

Dew Point Air Quality
+10°C Relatively moist
+3°C Typical refrigerated dryer performance
-20°C Dry compressed air
-40°C High-quality industrial air
-70°C Extremely dry air for critical applications

Understanding dew point allows engineers to determine whether compressed air is sufficiently dry for a specific process or application.

Why Is Moisture a Problem in Compressed Air Systems?

Atmospheric air naturally contains water vapour.

When air is compressed, the concentration of moisture increases dramatically. Without effective drying and monitoring, water can accumulate throughout the compressed air network.

This can lead to:

Corrosion

Moisture promotes corrosion inside:

  • Pipework
  • Valves
  • Air receivers
  • Pneumatic equipment

Over time, corrosion can cause leaks, contamination and costly equipment failures.

Product Contamination

In industries such as food, beverage, pharmaceutical and electronics manufacturing, even small amounts of moisture can damage products or compromise quality standards.

Equipment Damage

Excess moisture can:

  • Wash away lubricants
  • Damage pneumatic cylinders
  • Cause valves to stick
  • Accelerate wear

Freezing Risks

In colder environments, condensed moisture may freeze inside pipework and control systems, causing blockages and equipment failures.

Increased Maintenance Costs

Moisture-related failures often result in:

  • Unplanned downtime
  • Component replacement
  • Production interruptions
  • Higher maintenance expenditure

This is why compressed air drying and dew point monitoring are critical parts of any modern compressed air system.

How Is Dew Point Measured?

Dew point is measured using specialised dew point sensors designed for compressed air applications.

These sensors continuously monitor moisture levels and calculate the temperature at which condensation would occur.

Modern sensors provide:

  • Continuous real-time monitoring
  • Alarm functions
  • Digital outputs
  • Data logging
  • Remote monitoring capability

Continuous monitoring allows operators to detect dryer failures before moisture begins affecting production processes.

Pressure Dew Point vs Atmospheric Dew Point

A common source of confusion is the difference between atmospheric dew point and pressure dew point.

Atmospheric Dew Point

Measured at normal atmospheric pressure.

Pressure Dew Point

Measured under the operating pressure of the compressed air system.

Because compressed air systems operate under pressure, pressure dew point (PDP) is the value most commonly used in industrial applications.

When discussing compressed air quality, engineers almost always refer to pressure dew point.

What Is a Good Dew Point for Compressed Air?

The ideal dew point depends on the application.

General Industrial Use

Most facilities using refrigerated dryers operate at approximately:

+3°C Pressure Dew Point

This is sufficient for many general manufacturing environments.

Industrial Process Applications

Facilities requiring improved air quality often target:

-20°C to -40°C Pressure Dew Point

These levels are typically achieved using desiccant dryers.

Critical Applications

Industries such as:

  • Pharmaceuticals
  • Electronics manufacturing
  • Medical gas production

may require:

-70°C Pressure Dew Point or lower

The drier the air required, the more important accurate dew point monitoring becomes.

Dew Point and ISO 8573 Standards

One of the most common reasons companies monitor dew point is to comply with ISO 8573 compressed air quality standards.

ISO 8573 is the internationally recognised standard for compressed air quality.

The standard classifies compressed air based on:

  • Solid particles
  • Water content
  • Oil contamination

For moisture content, the standard defines specific pressure dew point classes.

ISO 8573 Water Classes

Water Class Pressure Dew Point
Class 1 ≤ -70°C
Class 2 ≤ -40°C
Class 3 ≤ -20°C
Class 4 ≤ +3°C
Class 5 ≤ +7°C
Class 6 ≤ +10°C

Many industries specify a required ISO 8573 class as part of quality management procedures.

Without dew point monitoring, it is difficult to demonstrate ongoing compliance.

The Role of Compressed Air Dryers

Dryers are responsible for removing moisture from compressed air.

Different dryer technologies achieve different dew point levels.

Refrigerated Dryers

Refrigerated dryers typically achieve:

+3°C Pressure Dew Point

Advantages include:

  • Low operating costs
  • Simple maintenance
  • Suitable for general industrial use

Desiccant Dryers

Desiccant dryers typically achieve:

-40°C to -70°C Pressure Dew Point

Advantages include:

  • Extremely dry air
  • Suitable for critical applications
  • Consistent performance

Membrane Dryers

Membrane dryers are often used where:

  • Low flow rates are required
  • Electrical power is unavailable
  • Compact installation is important

Regardless of dryer type, monitoring dew point remains essential to verify performance.

Why Dew Point Monitoring Is Essential

Many facilities assume that if a dryer is operating, air quality is acceptable.

Unfortunately, dryers can fail without obvious warning signs.

Common causes of dew point problems include:

  • Saturated desiccant material
  • Refrigeration system faults
  • Blocked drains
  • Contaminated filters
  • Sensor failures
  • Incorrect operating conditions

Continuous monitoring allows maintenance teams to identify these issues before they affect production.

Benefits of Continuous Dew Point Monitoring

Early Fault Detection

Monitoring provides immediate visibility into dryer performance.

Rising dew point levels often indicate developing problems long before production is affected.

Reduced Downtime

Early intervention prevents moisture-related equipment failures.

Improved Product Quality

Maintaining a stable dew point helps ensure consistent product quality and process performance.

ISO 8573 Compliance

Continuous monitoring provides documented evidence of air quality compliance.

Lower Maintenance Costs

Preventing moisture damage reduces maintenance requirements and extends equipment life.

Choosing a Dew Point Sensor

When selecting a dew point sensor, engineers should consider:

Measurement Range

The sensor must cover the expected operating range.

Accuracy

Higher accuracy improves confidence in air quality measurements.

Response Time

Fast response times allow rapid detection of dryer issues.

Connectivity

Modern sensors may offer:

  • 4-20mA outputs
  • Modbus communications
  • Alarm relays
  • Ethernet connectivity

Data Logging

Recording long-term trends supports maintenance planning and compliance reporting.

Dew Point Monitoring Solutions

For permanent installations, the FA500 Dew Point Sensor provides continuous compressed air moisture monitoring with integrated display and alarm functionality.

For demanding industrial applications requiring reliable long-term monitoring, the FA550 Dew Point Sensor delivers highly accurate dew point measurement across a wide operating range.

For portable audits and verification testing, the DP500 Portable Dew Point Meter allows engineers to perform spot checks, system surveys and compressed air quality assessments with integrated data logging capabilities.

These solutions help facilities maintain air quality, optimise dryer performance and support ISO 8573 compliance programmes.

Common Dew Point Monitoring Mistakes

Avoid these common errors:

Installing Sensors in the Wrong Location

Sensors should be installed downstream of dryers and filters where air quality can be accurately assessed.

Ignoring Trend Data

A gradual increase in dew point often indicates a developing issue that requires attention.

Calibrating Too Infrequently

Regular calibration ensures measurement accuracy.

Monitoring Only During Commissioning

Air quality should be monitored continuously rather than checked only during initial installation.

How Often Should Dew Point Be Checked?

Critical applications should monitor dew point continuously.

For less demanding systems, regular spot checks may be sufficient.

However, continuous monitoring generally provides the greatest protection against unexpected dryer failures and moisture-related issues.

The cost of monitoring is typically far lower than the cost of product contamination, downtime or equipment damage.

Conclusion

Dew point is one of the most important indicators of compressed air quality.

By understanding and monitoring dew point, organisations can prevent moisture-related failures, improve equipment reliability, maintain product quality and comply with ISO 8573 air quality standards.

Whether your facility uses refrigerated dryers, desiccant dryers or membrane dryers, continuous dew point monitoring provides valuable insight into system performance and helps ensure compressed air remains fit for purpose.

Investing in reliable dew point monitoring equipment such as the FA500, FA550 or DP500 can help protect both your compressed air system and your bottom line.

 

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