Problems with compressed air condensation

Water condensation is a natural occurrence and byproduct of compressing air. The amount of water produced by an air compressor is largely dependent on the inlet condition, ambient air quality, and pressure.

In simpler terms, air temperature, humidity, compressor size, and required pressure determine the amount of water coming from a unit. This moisture affects the whole system, including piping. Since hot, humid air has a higher moisture content than cold air, water vapor is created within the compressor.

This water can be separated using accessories, including aftercoolers, condensation separators, refrigerant dryers and adsorption dryers. 

A compressor working with 7 bar(e) overpressure compresses air to 7/8 of its volume. This also reduces the air's ability to hold water vapor by 7/8.

These factors determine which combination of coolers and dryers are suitable.

To further explain compressed air moisture, let's evaluate ambient temperature, flow rate (size of compressor), inlet pressure, inlet temperature, and pressure dew point (PDP).

• Flow Rate or Compressor Size. Applications requiring higher flow rates (CFM or l/w) will produce greater system water content levels.
• Ambient Temperature / Humidity Content. Compressors operating in higher ambient temperatures and humidity levels produce larger amounts of water vapor within the system.
• Inlet Air Temperature. The higher the inlet temperature going into a compressor, the more water content is present in the compressed air.
• Pressure. Unlike flow, temperature, or humidity, high pressure levels generate low moisture levels. As an example, if you squeeze a water filled sponge hard, the water is pushed out.
• Pressure Dew Point (PDP). Pressure dew point is a common way to measure the water content in compressed air. PDP refers to the temperature at which air or gas is saturated with water and begins to turn into a liquid state through condensation. PDP is also the point at which air is not able to hold any more water vapor.

To minimize water content in compressed air, a lower PDP level is required. This is important since higher PDP values refer to greater amounts of water vapor in the system. The type and size of the dryer determines PDP and condensation levels in compressed air.

A lower pressure dew point in drying systems means higher energy costs because it requires more effort to remove moisture. To keep costs low, it's important to avoid using an excessively powerful drying solution that goes beyond your actual needs. Instead, choose a drying system that matches your specific requirements to maintain efficiency and control expenses.

When conducting a compressed air test, it's important to understand the different types of dew point sensors available:

• Capacitive type dew point sensors: These are ideal for continuous monitoring of the dew point in compressed air systems. They measure changes in capacitance due to moisture levels, providing real-time data. This helps in maintaining optimal drying conditions and can lead to energy savings when used with appropriate dryer controls.

• Chilled mirror: This technology offers the most accurate dew point measurement by cooling a mirror until condensation forms. The temperature at which this occurs is the dew point. However, chilled mirror devices are expensive, require frequent cleaning, a trained operator, and periodic calibration, making them less suitable for continuous monitoring.

• Moisture indicator: A cost-effective tool that changes color to indicate moisture levels. It can be installed anywhere in the system downstream from an air dryer. While it provides a quick visual indication of rising moisture levels, it is not an accurate measurement tool.

Understanding these tools can greatly enhance the effectiveness of your compressed air testing process.

Untreated compressed air condensation can damage and cause problems to pneumatic systems, air motors, and valves. In addition, any components or machines connected to the system can be impacted, resulting in potential contamination of the end product.

Here is a list that further explains the adverse effects of moisture:

• Corrosion of piping system and equipment (i.e. CNC and other manufacturing machines).
• Damaging of pneumatic controls which can result in expensive shutdowns.
• Rusting and increased wear for production equipment due to washing away of lubricant.
• Quality issues due to risk of discoloration, lowered quality and adherence of paint.
• In cold weather operations, freezing can occur, causing damage to control lines.
• Excessive maintenance to the air compressor and shorter life of equipment.

Furthermore, compressed air moisture can have many damaging effects on plant air, instrument air, valves and cylinders, as well as air powered tools. To avoid unnecessary, excessive maintenance costs and potential downtime, it is recommended to be proactive. Properly implementing the necessary steps to keep compressed air dry, clean, and suitable for your application is highly recommended.

Selecting the proper drying method for compressed air largely depends on the specific requirements needed to meet quality control standards for your application.

1. One of the first steps to remove compressed air moisture inside the compressor. This is important as a moisture separator or aftercooler is capable of removing 40-60% of vaporized water.
2. After the compressed air leaves the aftercooler it remains saturated with water and can have damaging effects on the overall system if left untreated.
3. Since an air compressor's tank is much cooler than incoming hot compressed air, utilizing an air receiver can aid in reducing water content. It is important to keep in mind that a wet tank collects excess moisture, and needs to be drained daily. This is important to avoid corrosion and wear.
4. If your application calls for further moisture removal, it's necessary to introduce an external or internal (integrated) dryer. 

• With a refrigerated air dryer, the air temperature is lowered to 3 degrees Celsius (37 degrees Fahrenheit). This process causes water vapor to condensate out of compressed air. If a refrigerated dryer's dew point is not sufficient, a desiccant air dryer should be used.
• A desiccant dryer reduces the dew point to at least -40 degrees Celsius, resulting in bone dry air. Such levels are essential for spray-painting operations, printing, and other pneumatic tool applications.