3 Key Steps for Moisture Removal in Compressed Air Systems

Understanding Humidity in Air Compressors

“Humidity” refers to the moisture content in the air. Air compressors do not produce water themselves but act as carriers of water during the compression process. As air is compressed or cooled, it becomes saturated and, when oversaturated, water precipitates from the air. This change is from a gas to a liquid, which is how water is created.

The Cooling Process in Air Compressors

Air compressors work by compressing air, and cooling starts immediately during the compression process. The compressor head temperature rises significantly—about 100°C—because the air is compressed, releasing heat. Moisture in the natural air will form water vapor during compression and be discharged along with the compressed air.

To mitigate this, air compressors often include an air cooler. The cooler reduces the temperature of the compressed air, promoting the condensation of water. This helps remove some of the moisture. However, if the compressor lacks efficient cooling, compressed air and water may flow into the pipeline system.

The Role of Compressed Air and Water in the System

Even if the air compressor is properly draining moisture, the compressed air exiting the unit remains saturated. With cooling, some liquid water will still condense.

In the compressed air system, several pipes, filters, and air tanks are connected to the compressor outlet. These components are usually cooler than the compressed air. This temperature difference leads to condensation, especially in air tanks. The high-speed airflow inside the tank causes the temperature to drop quickly, and water vapor condenses into liquid water.

In humid weather or cold environments, more condensation forms. This is why drainage in air tanks is critical. Most air compressor manufacturers emphasize proper drainage to prevent liquid water from traveling downstream with the air. The “bottom-in and top-out” method of pipe installation in air tanks helps prevent this.

How to Remove Water from Compressed Air

Complete removal of water from compressed air is neither possible nor necessary. The goal is to reach the desired level of dryness for the specific application.

For most general uses, such as powering cylinders, blowing, or operating pneumatic tools, it is sufficient to ensure that the air does not contain liquid water at the current ambient temperature.

For specialized applications, like spraying, textiles, electronics, or food and medicine, moisture removal is more critical. These applications each have specific moisture requirements. There are generally three levels of moisture removal in compressed air systems:

1. Air Compressor Body

The air compressor should have an air-water separation device to remove as much water as possible from the compressed air. Smaller or simpler air compressors may lack this feature. If absent or malfunctioning, the back-end equipment will need to handle the water removal, which can lead to overload.

2. Air Compressor Pipelines and Tanks

The air tank, filter, and pipeline outlets are critical drainage points. The air tank plays a key role in removing water. Today, both manual ball valves and automatic drainage devices are commonly used. Regardless of the drainage system, regular maintenance and inspection are essential.

3. Special Water Removal Equipment

For more advanced water removal, the system can include pipeline gas-water separators, refrigerated dryers, adsorption dryers, and precision filters. These devices should be selected based on the specific needs of the application.

When to Drain the Air Compressor

Drainage frequency depends on factors like the environment and operating conditions. For manual ball valve drainage systems, the condensed water should be drained regularly. For automatic drainers, the self-draining function should be inspected frequently.

The frequency of drainage largely depends on the humidity of the air and the temperature of the compressed air. During humid seasons or high-temperature conditions, more frequent drainage and inspections are necessary.

Air Compressor with Dryer: The Ultimate Solution for Clean, Dry Compressed Air

4 Reasons for changes in the exhaust volume of screw compressors