What is a pressure dew point?

You're probably wondering how exactly water and compressed air go together. Water, or technically correct condensation, is a natural by-product of compressed air generation. How much water is actually produced during compressed air generation depends on various factors: air temperature, humidity, compressor size and the required pressure determine the water content of your compressed air. In any case, the water content of the compressed air must be kept as low as possible to avoid negative effects on your compressed air system.

High moisture levels can damage compressed air systems, leading to corrosion, contamination, and equipment malfunction.

Atmospheric Dew Point (ADP): The temperature at which water vapor in air begins to condense into liquid at atmospheric pressure (typically 1 bar or 14.7 psi).

Pressure Dew Point (PDP): The temperature at which water vapor condenses at elevated pressure, such as in compressed air systems.

Here are some most common questions regarding atmospheric dew point (ADP) and presure dew point (PDP):

The ability of the air to carry water in vapor form depends on the temperature. The warmer the air, the more water it can carry. It is therefore important to know that the atmospheric dew point (ADP) must not be compared with the pressure dew point (PDP).

Maintaining the correct pressure dew point (PDP) is crucial to prevent damage and ensure efficiency in your compressed air system. Excess moisture can cause serious problems both to the system itself and to the quality of manufactured products.

Negative effects on the compressed air system:

• Corrosion of pipelines and equipment (e.g., CNC machines)

• Damage to pneumatic controls, leading to costly shutdowns

• Rust and increased wear due to lubricant washout

• Freezing in cold weather, damaging control lines

• Excessive maintenance of the air compressor and a shorter system lifespan

   

Impact on manufactured products:

• Quality problems caused by contamination, such as discoloration and reduced adhesion of paints or coatings

• Risk of bacterial and fungal growth, especially problematic in food processing and pharmaceutical industries

Lowering the PDP reduces moisture and helps prevent microorganism growth, ensuring both system reliability and product quality.

The ideal pressure dew point (PDP) varies across industries. For example, the pharmaceutical industry demands exceptionally low dew points to ensure product quality, while other industries may require less stringent standards. Lowering the PDP beyond what is necessary increases costs, so it is important to choose the appropriate PDP according to the specified requirements.

Companies often follow ISO class standards to determine the optimal dew point for their applications:

Note: The required dewpoint will also depend on the ambient temperature, for example:

• A PDP of +8˚C will prevent any condensation in the compressed air pipe if exposed to an ambient temperature of +25 ˚C
• The same PDP of +8 ˚C will condensate in the compressed air pipe if exposed to an ambient temperature of +5 ˚C

Accurate dew point measurement is essential for maintaining the quality of compressed air in industrial applications. Here’s an overview of the most common methods:

• Capacitive type dew point sensors: Ideal for continuous monitoring of dew point in compressed air, these sensors detect changes in capacitance due to moisture. They offer real-time data, helping maintain optimal drying conditions and achieving energy savings, especially when used with a compressed air dew point transmitter.

• Chilled mirror: Known for high accuracy, these dew point meters for compressed air cool a mirror until condensation forms, determining the dew point. Despite their precision, they are expensive, require maintenance, and are less suited for continuous industrial use.

• Moisture Indicators: Cost-effective and easy to install, these indicators visually show rising moisture levels. While not a precise dew point measurement tool, they provide quick insights when placed downstream from an air dryer.

Choosing the right dew point sensor for compressed air ensures reliable industrial dew point measurement, optimizing system performance and energy efficiency.

Achieving a low PDP requires proper moisture management within the compressed air system:

• Use an aftercooler or moisture separator to remove a large percentage of vaporized water.

• Utilize a wet tank to reduce water content, but ensure daily draining to prevent corrosion.

• Apply refrigerated air dryers for moderate dew points or desiccant dryers for extremely low PDPs.

It's important to understand that the lower the required PDP, the higher the cost and complexity of the equipment needed. While filters are essential for removing solid particles and liquid droplets, they cannot remove moisture in its gaseous form.

To effectively reduce moisture vapor, dryers are necessary. The type of dryer you choose depends on the PDP your application demands. Other methods, like over-compression or cooling, can also assist in moisture removal.

Choosing the right drying solution is an important step to protect your compressed air system and maintain product quality.

Do you want to optimize your air quality without overpaying? Selecting the appropriate drying method depends on your application’s quality control needs. Over-drying compressed air can be costly. Get the right balance with advice from our experts.