Moisture: The Hidden Enemy of Compressed Air Systems

Most users assume the air delivered through pipelines is clean and dry, but this is seldom the case. Apart from dust and debris, moisture is a commonly underestimated hazard. It compromises the performance and service life of compressed air equipment, as well as associated production processes and pneumatic components. Therefore, proper control and precise monitoring of moisture with dew point sensors are far more essential than many people think.

Moisture inside compressed air systems can freeze, causing rust and pitting on pipes and components. It also flushes away lubricants, accelerates tool wear, and damages valves and cylinders. Damp air breeds bacteria. This is particularly risky for the food and pharmaceutical industries, often resulting in defective products and costly production downtime. It is surprising that many enterprises only track basic parameters such as pressure, flow rate and power consumption. In fact, dew point monitoring is an effective way to avoid numerous operational troubles and unnecessary expenses.

• Moisture Content and Dew Point

Dew point, usually measured in degrees Fahrenheit, indicates the amount of water vapor contained in compressed air or other gases. We primarily focus on the pressure dew point for compressed air, since measurements are taken at a pressure 6 to 8 times higher than standard atmospheric pressure. Gas pressure directly affects dew point: the lower the pressure, the lower the dew point. When the temperature drops, moisture in compressed air condenses, leaving several liters of water accumulating in the system every week.

• Causes of Excessive Moisture

Moisture issues arise from a variety of factors. A frequent culprit is faulty oil-water separators or combined oil and water separators installed after compressors, typically caused by mechanical malfunctions such as stuck floats. If the problem goes unnoticed, water will flow freely into the system and collect in air receivers. For this reason, investing in float drains, timer drains or electronic condensate drain systems is well worthwhile.

Other contributing factors include clogged cooling elements in aftercoolers and oil coolers, and inadequate knowledge of how refrigerated dryers operate under varying ambient temperatures. When selecting dryers and setting target pressure dew points, enterprises must take average ambient temperature into consideration, in addition to the air quality requirements of production processes.

• Dew Point Meter Installation

Three types of dew point sensors are widely used in the industry: chilled mirror sensors, capacitive metal oxide sensors and polymeric sensors. Among them, capacitive polymeric sensors deliver outstanding resistance to dust and contamination, remain unaffected by condensation, and feature excellent long-term stability and cost performance. They measure dew point by detecting changes in capacitance, with readings available in either degrees Celsius or Fahrenheit.

It is vital to determine the quantity and installation positions of sensors to ensure accurate and reliable measurements. For basic monitoring, install one dew point sensor downstream of the dryer and upstream of the air receiver to keep track of dryer operation. Mounting the sensor after the receiver will lead to delayed readings.

If two or more dryers work in parallel, fit a sensor at the outlet of each unit. If only one sensor is installed on the main pipeline leading to air receivers, technicians cannot quickly locate the faulty dryer when abnormal readings occur.

• System Optimization

Continuous monitoring lays the foundation for a stable, efficient and cost-effective compressed air system. It requires integrating dew point measurement with the monitoring of flow rate, pressure, temperature and power consumption.

Specialized monitoring systems like those developed by Deman compile all data on a unified interface, enabling 24/7 real-time monitoring and analysis all year round.

Fluctuating air demand, varying dew point, overheating compressors and other anomalies are displayed visually, with instant alerts triggered once faults are detected. The collected data also provides valuable references for maintenance optimization, expansion planning and overall system improvement. Continuous monitoring helps extend equipment lifespan, cut maintenance and energy costs, and prevent product waste and unplanned production shutdowns.