Moisture in Your Compressed Air is a Bad Deal

Mar 23, 2021 by Brad Taylor


Have you ever dusted yourself off with compressed air and ended up getting power washed with water instead?! Where did that water come from and does it belong there?

As we learned in science class, the air we breathe contains water in a gaseous state. The compressed air industry expresses the amount of water in a system by dewpoint and relative humidity. The warmer the air, the more water the compressed air can hold. This is why we see so much more water in our compressed air on a hot summer day after it has rained. When we compress the air to 100 PSI (pounds per square inch), the volume is reduced to eight times the original volume. This is known as compression ratio, and is like squeezing a sponge. As this squeezing action takes place, the gaseous humidity changes to a liquid state. As the gas was compressed, it met the saturation point or 100% relative humidity. It can no longer hold the water in suspension. That’s where the water that you washed yourself with, came from! 

Is dry compressed air important for me? Water is a corrosive. Not only does it rust pipes, but it accelerates wear on pneumatic valves and cylinders. It also lowers the quality of your finished product by:

  • Causing fish eyes or orange peel effect on paint finishing
  • Rusting of your finished machined metal products
  • Spoilage of raw product including dry goods, chemicals, etc.
  • Inconsistent operation of automated equipment due to worn air valves and cylinders

Are you having a problem with wet compressed air? Call now so it doesn’t get worse! 877.927.2551

How can I prevent this corrosive water from entering my compressed air system? The simplest way is through drip legs, water traps, after-coolers, and coalescing filters. Though these devices remove liquid contaminants from the compressed air, the relative humidity is still 100%. This means that once more cooling occurs, more water will condense and be visible at use points throughout the system. Examples of this include:

  • Additional cooling as the compressed air travels through the pipes
  • Pipes on a cold outside wall in the winter months
  • Compressed air going through a cooler/refrigerated air

Some of our customers still see water at some air nozzles, air tools, and ventures and this baffles them. This water is created from the Joule-Thomson Effect. As compressed air rapidly expands, a cooling effect takes place. Condensation will occur if the temperature of the cooling effect is lower than the dew point of the compressed air. The only way to completely eliminate the moisture from the compressed air is to reduce the dew point to the appropriate level. This can be accomplished through additional mechanical means. Read on…

The types of dryers you can buy that are used to to lower the dew point or relative humidity of compressed air:

Buying Refrigerated Air Dryers

This type of drying provides around a 38° dew point by refrigerating the compressed air. It condenses the moisture and then coalesces those water droplets to form bigger heavier droplets. It is like the water that forms on the outside of a cold beer mug. Then gravity does its job by pulling the cooled condensed moisture down into an integrated moisture trap. This moisture is then removed through an automated drain. Refrigerated Dryers are used in 95% of compressed air installations. They are very common in the manufacturing, sandblasting, and automotive industries.

Buying Regenerative Desiccant Air Dryers

This is an adsorption type dryer which provides down to a negative -100° dew point. Desiccant Dryers are commonly used in labs, hospitals, powder coating, and in electronic manufacturing. They are used in approximately 5% of compressed air installations. This type of dryer will use up to 20% of its capacity to regenerate the dryer media. This solution is employed many times as a point-of-use application because of this additional demand on the system.

Membrane-Type Air Dryers

These devices use a permeable microtube technology. They are commonly used in low-flow applications like dental labs, lab environments and critical, point-of-use applications.

Benefits of Clean Dry Compressed Air

  • Lessens wear on equipment
  • Improves equipment efficiency
  • Improves your end product quality

Do I need dry air on my system? YES! Unless you are doing water blasting!

Contact us if you need help with a moisture issue that you need to get under control. Call 877.927.2551 or visit us at to check out our other products and services.

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