Date:
By: Anina Diener

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?

spray-gunHow did it get there? As learnt in science class, the air we breathe contains water in a gaseous state. The amount of water is measured in the compressed air industry by dew point and relative humidity. The hotter the air, the more water the compressed air can hold which is why we see so much more water in our compressed air on a hot summer day after it just rained. When we compress the air to 100 PSI (pounds per square inch), it’s volume is reduced to eight times its original volume (known a compression ratio) which is like squeezing a sponge. As this squeezing action takes place, the gaseous humidity goes through a phase transformation to a liquid state. This is because as the gas was compressed, it met its saturation point or 100% relative humidity, and no longer could hold the water in suspension. This is where the water that you just washed yourself with, came from!

Is dry compressed air important for me? Water is a corrosive. It not only rusts pipes, but 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 includes dryer good, chemicals, etc.
  • Inconsistent operation of automated equipment due to poor air valves and cylinders

Are you having a problem with wet compressed air? Call now so it doesn’t get worse! 847.678.8388!

How can I prevent this corrosive water from entering my compressed air system? Simplest way is through drip legs, water traps, after-coolers, and coalescing filters. While this removes liquid contaminants from the compressed air, the relative humidity is still 100%. This means that once additional cooling occurs, more water will condense and will be seen 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.
  • One that often baffles users is those that do have compressed air dryers, but still see water at some air nozzles, air tools and ventures. This water is created from what is known as the Joule-Thomson Effect. As compressed air rapidly expands, a cooling effect takes place. If the temperature of the cooling effect is lower than the dew point of the compressed air, condensing will take place again. The only way to eliminate the moisture from the compressed air completely is to reduce the dew point to the appropriate level through additional mechanical means. Read on….

To lower the dew point or relative humidity of the compressed air you can use…

  • Refrigerated air dryers – This type of drying provides around a 38 degree dew point by refrigerating the compressed air, condensing moisture (just like the water that forms on the outside of a cold beer mug), and then coalescing those water droplets to form bigger heavier droplets so that gravity can do its job by pulling the cooled condensed moisture down into its integrated moisture trap. This moisture is emptied by an automated drain. This type of dryer method is generally used in manufacturing, sandblasting, and automotive industries. These are used in probably 95% of compressed air installations.
  • Regenerative desiccant air dryer – This is an absorption type dryer which can provide down to a negative (-) 100 degree dew point. Desiccant dryers are often found in labs, hospitals, powder coating, and electronic manufacturing industries. These are used in probably 5% of compressed air installations. This dryer will use up to 20% of its capacity to regenerate the dryer media and is sometimes only considered at point of use application because of this additional demand on the system.
  • Membrane type Air Dryers – This is a permeable microtube technology. Commonly used in low flow applications including dental labs, lab environments and point of use applications.

Benefits of Clean Dry Compressed Air

  • Lessens wear on equipment
  • Improves equipment efficiency
  • Improves your end product quality
  • You don’t get pressure washed when you simply wanted dust yourself off after a long day!!

So, do I need dry air on my system? In short, YES, unless you are doing water blasting!

Feel free to contact us if you need help with a moisture issue that you need to get under control!
Call 847.678.8388
Or visit us at www.fluidairedynamics.com to check out our other products and services.