How to Drain Your Compressed Air System

Dec 24, 2021 by Brad Taylor

Table of contents

Draining excess water from your compressed air system is very important to maintain the longevity of your system and keep moisture out of your compressed air supply. Fortunately, draining condensate from your compressed air system is easy with either manual or automatic drain valves. Learn why draining your air compressor, air dryers, receiver tanks and other components of your compressed air system is important, what kind of drains you need, and how often to drain your air system components. And for repairing compressed air systems, give us a call at any time!

Why do I need to drain water from my compressed air system?

Draining the condensate that builds up inside your compressed air system is very important. Moisture is an inevitable byproduct of air compression. It comes from the humidity in the intake air. As air is compressed into a smaller volume, it is also heated and thus able to hold more moisture. As the air cools, water vapor condenses back into a liquid and enters the compressed air stream. Further condensation happens as the air cools because warmer air holds more water vapor than cooler air. This results in condensation forming at various points in the system, including the compressor, air dryers, air receiver tanks, and the compressed air piping.

This condensate is bad news for your compressed air system. Moisture buildup inside the tank, pipes, or compressor will cause corrosion over time. Corrosion weakens the structural integrity of pipes, tanks, and other metal components, reducing their lifespan. It also creates contaminants that can get into the air supply or create blockages in your distribution system.

Additionally, excess moisture will end up in the compressed air supply. As air the airstream cools, dropping the temperature by 20 to 25 degrees, it creates water inside items using compressed air. This can damage tools and equipment that rely on clean, dry air. Moisture may also cause quality problems for products, such as corrosion of metallic products, spoilage of dry goods, damage to air tools and cylinders, and poor finish quality for paints and coatings

What is an air compressor drain valve?

A drain valve is simply a device that allows excess moisture to be drained from the compressed air system. It is used at low points in the system where water collects. The valve mechanism can be opened to allow water to drain out via gravity and closed to prevent air from escaping once the water has drained. Drain valves may be found on compressors, air dryers, air receiver tanks, inline filters, and at low points in the compressed air piping. They should be used anywhere moisture may collect in the compressed air system.

How do I drain water from my air compressor?

The air inside the compressor itself is very hot. This keeps most of the moisture in the air while it is inside the compressor. The air quickly cools once it leaves the compressor, and this is where moisture will fall out as condensation. This is why water collects in your air receiver tank, air dryers, and distribution system. If you have an after-cooler on your air compressor, this is the first place where water will collect. The after-cooler will have a drain valve at the bottom, which may be manual or automatic. If it is a manual drain valve, it should be opened on a regular basis to drain excess liquid. Automatic drain valves will open on a timer or use a float mechanism to drain liquid as required.

How do I drain water from my air dryers and receiver tanks?

Most of the moisture in compressed air falls out of the airstream after it leaves the compressor. As the airstream cools, water vapor condenses back into a liquid. This liquid will collect in your air receiver tanks and your air dryers. These components should be equipped with a drain valve to drain the collected water.

Draining the air receiver tank is easy. The valve will be installed at the bottom of the tank where water collects. If the drain is manual, just open the valve and let the water run out. This process should only take a few seconds. Close the valve promptly when water stops draining to reduce air loss. Automatic drain valves can be used to reduce manual air compressor maintenance requirements.

Refrigerated air dryers drop the temperature to 38-40°F and need to be drained on a continuous basis with an automatic drain. These dryers work by chilling air to allow additional moisture to fall out of the airstream. This liquid collects in a water trap, which is drained with the automatic drain valve.

Desiccant air dryers work differently. Instead of chilling the air to form a condensate, they use desiccant (usually activated alumina, silica gel, or a molecular sieve) that bonds with the water vapor chemically to remove it from the air. Once the desiccant material becomes fully saturated, it is regenerated to remove the collected liquid and allow the desiccant to be used again. These dryers need filtration before the dryer to remove any oil and water and protect the desiccant from contamination. Automatic drains are used here to remove the oil and water.

Do I need drains for my compressed air piping system? 

If air is properly dried before entering the distribution system, there should be little excess water in the pipes themselves. However, on warm days, if the dryer is not oversized for the temperature, it is possible for condensation to happen in the pipes as the air cools. This condensate will collect at low points in the distribution system. These low points should be equipped with either a drip leg or a drain valve. Drip legs are a passive system that simply allows accumulated water to drip out of the piping system on its own. Drain valves will need to be opened periodically to allow water to drain.

How often do I need to drain my air compressor or receiver tank?

Drainage requirements will depend on factors such as your usage patterns for your air compressor, the humidity of air going into the compressor, and the type of air drying system you are using. You can reduce maintenance with an automatic drain valve.

What kind of drain valves should I use in my compressed air system? 

Manual drain valves are simple, but they can create a high maintenance burden to keep water out of the system. Most operations relying on compressed air for industrial applications will benefit from an automatic drain valve. Automatic drain valves can be used anywhere that a drain valve is placed.

  • Electric drain valves open on a timer to drain water. They can be set to open for a few seconds at a time on a regular schedule, such as once a minute or once an hour.
  • A zero-loss drain valve uses a float mechanism to trigger the valve opening. This reduces air loss because the drain valve is only open when needed.

If you’re seeing excess moisture in your compressed air system, or have questions about drain valves, contact us for help. 

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