What’s the difference between a compressed air moisture separator and a compressed air dryer

Not sure? You’re not alone.

Many manufacturers, offer both moisture separators and dryers. Yet these two types of equipment have very different characteristics. It’s important to understand the difference when presenting air treatment options to a customer.

A moisture separator comes in many shapes and sizes, from a small cylindrical vessel to a big vertical pressure vessel. Sometimes called a moisture trap, a separator removes only liquid water from compressed air lines. Within a separator there are usually impingement baffles, wire mesh, cyclonic devices, or filter elements. These features force liquid to fall to a low point in the container. Here the liquid can be drained.

Point to Remember: A liquid separator only removes liquid. It does not remove humidity from the compressed air.

Only a dryer removes humidity from the air line. Think of humidity as the water that hasn’t yet turned into liquid. An air dryer typically uses a desiccant media to extract water vapor from the air. Blast Pak air dryers, for example, use Dry-O-Lite desiccant tablets to absorb humidity. Extracting humidity is desirable because this prevents the formation of new liquid. Compressed air cools as it travels through hoses to the blast pot. Cooling causes condensation, or liquid formation. This is why an operator can end up with wet abrasive, even when using a good moisture separator after the compressor. The water has formed in the hose that runs from the separator to the pot.

Point to Remember: A dryer extracts humidity and prevents new liquid from forming.

Use moisture separators in non-critical applications, where modest amounts of liquid can be tolerated at the point of use. Use a dryer in applications where the operator will accept no liquid whatsoever in the pot, nozzle, or respirator.

(reference Tech Tips - Van Air Systems)