How to Prevent and Remove Moisture in Air Compressors

Mar 23, 2021 by Brad Taylor

Table of contents

Water can damage air compressor systems and contaminate the products and jobs you need to complete. Though preventive maintenance is the best step to avoid these situations, knowing how to remove excess water is equally important. Discover how to get water out of air compressor systems and the harm caused by moisture in our comprehensive guide. 

What Causes Moisture in Compressed Air?

To understand how to keep water out of air compressor lines, you must first know what causes moisture to enter these systems. Air compressors work by squeezing air into a smaller volume under high pressure. This process compresses the air to about eight times the normal atmospheric pressure, making it unable to hold as much water. As the temperature lowers and the pressure rises, water vapor condenses into a liquid needing somewhere to go. The result is condensation inside the system. 

Though moisture is an inevitable byproduct of compressed air, the amount in the system relates to several factors. The quantity of compressed air and its humidity level directly affect how much moisture is in your system. Additionally, moisture buildup could be due to these factors.

  • Equipment failure: As its internal parts wear out, an air compressor becomes more moisture-prone. It’s even worse if the system hasn’t received proper maintenance. Over time, the system loses the power and efficiency to extract water. At the same time, the compressor heats up more rapidly, allowing more moisture to build up.
  • Environmental factors: All air carries moisture, and humid air has considerably more. If your compressor takes in that extra moisture, there will be additional condensation within the machine. You can prevent this in several ways. First, move your compressors to a less humid area. If you have conditioned indoor spaces, take your compressors inside. You can also use a refrigerated air dryer to reduce moisture. If you need a steam-free work environment, try a desiccant air dryer.
  • An undersized unit: If you’re straining your air compressor beyond its capacity, it will heat up more rapidly. This problem is more significant with piston compressors, which generate more heat when used for longer periods. You can combat this issue by investing in a larger air compressor or a separation system. A desiccant separator will remove the water from your compressed air.

    Problems Caused by Moisture in Compressed Air Systems

    Moisture in air compressor systems can cause an array of problems. Water damage can be costly and corrosive. Allowing condensation to accumulate for extended periods can dry the surfaces and cause rust on various system components. As a result, your system could drag or overheat. Other problems you could encounter include the following.

    • Corrosion: Rust is one of the most significant issues you could face when water builds in your compressor. A clean and dry system prevents damage to critical components and avoids blockages. 
    • Pneumatic control damage: You can experience scale buildup, clogged orifices and rust in pneumatic devices if condensation builds inside your system. High moisture levels will reduce productivity and lead to costly downtime while you resolve the issue. 
    • Production equipment wear: Liquid can wash away lubrication inside your compressor. When water removes these lubricants and oils, you can experience premature wear and tear in metal components. 
    • Piping corrosion: Metal components do not perform well with blends of water and oxygen. The result can be corrosion and rust inside pipes and the machine. You may also experience hammer events, which are knocking sounds coming from inside the piping. 
    • Contamination: Industries needing to follow strict guidelines may ruin a job or products by allowing water to accumulate in air compressor systems. For example, if you’re using an air-powered spray painter, water in the compressed air supply will mix with the paint and compromise the job. Anything from food products to lubricants to solvents could experience contamination. 
    • Filter and circuit damage: Moisture can cause pressure drops in filters over time, making them less efficient while requiring you to spend more money. 
    • Ice buildup: Ice can form when temperatures drop too low, clogging air lines and damaging your equipment. 
    • Valve and cylinder system damage: Condensation can cause debris to accumulate in the system, and the water will combine with solid impurities such as oils and dirt to cause narrow airflow tracts and slow production speeds. This issue can also cause rubber component damages that result in stiffening or ruptures. 

    How to Prevent Water in Air Compressor Systems

    One way to reduce excess moisture in your compressed air is to decrease the humidity of air going into the compressor, placing it where ambient temperatures are lower. When intake air is drier, the drying systems have less work to do to get air down to the required dewpoint. Air compressor maintenance is also critical to keep moisture out of the compressor.

    Compressor Room Environment

    If the compressor is outdoors, there may not be much you can do to reduce the humidity of intake air, unless you can avoid working when the weather is damp. If the compressor is indoors, you will have more control over the intake air quality. Keeping the compressor room cool, well-ventilated and dry will reduce the burden on air-drying equipment. Some steps you can take: 

    • Ensure the compressor room has plenty of ventilation to keep temperatures down, reduce moisture buildup and prevent compressor overheating. 
    • Consider insulating your compressor room for better temperature control. 
    • Add a dehumidifier to the compressor room. 
    • Fix leaks, and don’t allow water to pool on the floor near the compressor.

    Air Compressor Maintenance

    Proper preventive maintenance will also help avoid moisture problems in your compressed air system. Prevention is often the best tactic to keep your systems in working condition. Schedule regular maintenance sessions, and be sure to monitor your system’s progress over time. If you ever notice a problem with your system, address it immediately to avoid future costly damages. Steps to take include:

    • Drain the system as needed or maintain automatic drain valves.
    • Maintain all filtration systems and replace the intake and inline filters as needed.
    • Maintain the oil/water separator.
    • Perform all required air dryer maintenance and ensure components work correctly. For instance, check refrigerant in refrigerated dryers and recharge desiccant dryers on schedule.
    • Ensure the after-cooling system is clean and working correctly. 

    Additional Water Prevention Ideas

    You can invest in several other tools or steps to prevent water from accumulating in your system. For example, an air dryer can remove moisture from the air before it can enter your system. You can connect these devices to your compressor for efficient water prevention. 

    Inline filters are also effective at keeping out water. These devices filter impurities from the air before it goes into your system, capturing moisture before it can cause damage. 

    Water traps are an affordable option for catching moisture before it can enter your system. You can attach these devices to your air compressor system with a hose or pipe through the inlet. However, if your system doesn’t have an inlet, you can find water traps that connect directly to your system. Avoid water traps that reduce airflow by connecting to the outlet, as this can cause overheating in your system.

    How to Remove Moisture From Air Compressors

    Preventing all moisture from entering your system is impossible, but you can remove most of the accumulated fluid. You will need to address the situation by using various tools and components, which could include a combination of refrigerated or desiccant air dryers and mechanical moisture separation. 

    Draining the Water

    The first step in your moisture control plan is to regularly drain excess water from the compressed air system. Draining the air compressor will not remove water still held as vapor in the air, but it will prevent excess liquid from building up within the tank and air supply lines. The most straightforward way to accomplish this is with a condensate drain valve, a small device that opens to channel excess liquid out of the system. You should install them at each place where liquid accumulates, including: 

    • Compressor intercoolers and after-coolers — compressors should have a water separator in good working order at the discharge port that takes out 70% of the moisture from compressing the air.
    • Air receiver tanks
    • Air dryers 
    • Low points in the piping distribution system

    There are three basic types of drain valves.

    • Manual drain valves: The maintenance team opens these valves manually to drain liquid water. You should empty water at least once daily if you drain the tank manually.
    • Automatic timer drain valves: Automatic timer-based drain valves and float drains eliminate the need to remember to drain the collection points. An auto drain valve will regularly open to release excess liquid, which can be a valuable benefit if your maintenance staff is too busy or the item is not in an easily accessible location. 
    • Zero-loss drain valves: A zero-loss drain valve is another automated solution. It uses a float mechanism to detect when liquid water has accumulated and opens just long enough to release it. A zero-loss drain can save money by reducing the loss of air along with liquid water.

    Addressing Other Components

    You'll need to tackle various components throughout your system with different tools and devices. Learn more about these processes below.

    • After-coolers: The after-cooler system is where water vapor first condenses back into a liquid. After-coolers bring temperatures close to ambient air temperatures. In rotary-screw air compressors, around 70% of excess water falls out in the after-cooler, which significantly increases the dryer's efficiency. 
    • Air receiver tank: You can use an air receiver tank as a secondary heat exchanger to cool air as it sits in the tank. As the temperature drops a degree, more water will fall out, making this device beneficial for removing additional moisture from compressed air. 
    • Water separate filter: These devices can remove up to 40 to 60% of water in the air with centrifugal force. 
    • Refrigerated air dryers: If you need additional moisture removal, a refrigerated air dryer can chill the air, forcing it to hold less moisture. After cooling, the excess vapor condenses to a liquid, and the water trap removes it through an automatic drain valve. 
    • Desiccant air dryers: A desiccant air dryer is an excellent option if you need very dry air. These work by using a chemical process to remove liquid from the air. These dryers remove nearly all vapor from air streams by compressing air to a minus 40 to minus 100 degree Fahrenheit dewpoint.
    • Piping system air drying: Drip legs plumb water from air pipping as the air cools in the distribution system. These systems rely on gravity to collect condensation as it forms. The system could have several drop points with a water trap or drain at each. 
    • Absorption drying: These systems are less common than others, but can be more cost-effective. However, some residue may remain, and you may need to replace materials frequently. 

    How Dry Does Compressed Air Need to Be?

    Some applications — such as painting, printing and some kinds of air-powered instruments — are highly sensitive to moisture in the compressed air stream. For these, you may need a multi-stage solution that removes as much water as possible from the air.

    For other tasks, such as tire fill, the air's moisture content may be less critical. Regularly draining excess water out of the receiver tank and lines, and perhaps adding a mechanical separator, might be enough. 

    It is critical to understand your application's dewpoint requirements and design the air drying system accordingly. Discover the dewpoint of various applications below:

    • For most applications, such as powering pneumatic tools and equipment, a refrigerated air dryer is adequate for reducing the dewpoint to 38 to 40 degrees Fahrenheit.
    • For sensitive uses such as pharmaceutical production, food manufacturing or medical air, a desiccant dryer is likely to be necessary to get the dewpoint down to minus 40 to minus 100 degrees Fahrenheit. 

    ISO standards for air quality may govern some processes. ISO 8573 lays out purity classes for air, including moisture content.

    • Class 9: ≤10 g water/m3 air
    • Class 8: ≤ 5 g water/m3 air
    • Class 7: ≤ 0.5 g water/m3 air
    • Class 6: ≤ 50 degrees Fahrenheit vapor pressure dewpoint
    • Class 5: ≤ 45 degrees Fahrenheit vapor pressure dewpoint
    • Class 4: ≤ 37 degrees Fahrenheit vapor pressure dewpoint
    • Class 3: ≤ minus 4 degrees Fahrenheit vapor pressure dewpoint
    • Class 2: ≤ minus 40 degrees Fahrenheit vapor pressure dewpoint
    • Class 1: ≤ minus 94 degrees Fahrenheit vapor pressure dewpoint
    • Class 0: process specific 

    Protect Your Air Compressor From Moisture With Fluid-Aire Dynamics

    There is no one-size-fits-all answer to designing a system to remove water from compressed air. The ideal solution for you will depend on several variables, including your system usage, your local atmospheric and environmental conditions and the indoor environment in which you use your system. Most importantly, it depends on your air's dewpoint and purity requirements. Understanding these is the first step to compressed air system design. If you’re unsure if your current system meets your needs, compressed air testing can determine how much moisture, oil and particulate is in your air. 

    Fluid-Aire Dynamics can help you design a compressed air system that fulfills your dewpoint and air purity requirements. Contact us about your moisture control concerns. 

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