Dryers and Filters

Why use a Dryer in a Compressed Air System?

Water vapour (humidity-moisture) enters the air system through the air compressor inlet air filter. The air compressor sucks in approximately 7 cubic feet of atmospheric air at 0 psig, and that volume of air is compressed into 1 cubic feet of air at 100 psig. The water vapour (humidity-moisture) that was in the 7 cubic feet of atmospheric air is now compressed into 1 cubic feet of compressed air.


There are 3 forms of water in compressed air:

Liquid water.

Aerosol (mist).

Vapour (gas).

Liquid water is easily removed by general purpose line filters. They remove 98% of the liquid water and less than 10% water mist & 0% vapour.


Water in Aerosol or Vapour form requires the use of a Compressed Air Dryer.


For every 10°C drop in compressed air temperature, the moisture holding capacity of air is reduced by 50%.


Drying prevents liquid water forming downstream where it can contaminate or damage the system causing operating problems, costly maintenance, and repairs.

Air Dryer

Types of Compressed Air Dryer

Compressed Air Filtration & Dryers - Air Compressor Line Filters

Fridge Dryers

Refrigerated Air Dryers can help solve the problem of harmful moisture in a compressed air system. Excess moisture in a system can harm equipment and ruin processes or product, costing time and money. This method of drying is very popular as it produces dewpoints, which are adequate for most applications using well proven technologies that encounter few problems if properly sized, installed and maintained.


How a Fridge Dryer Works:  

The refrigerated air dryer cools the incoming compressed air first in an air-to-air heat exchanger where the outgoing cool dry air pre-cools the hot incoming air and condenses some moisture out.

Then the incoming air enters an air-to-refrigerant heat exchanger where the air is cooled to 3º c by the liquid refrigerant. This process causes the moisture to condense into liquid water and it is drained away. The outgoing air then enters the air-to-air heat exchanger and is warmed up to keep the outside of pipes from sweating.

Compressed Air Filtration & Dryers - Air Compressor Line Filters

Desiccant Dryers

A desiccant air dryer uses a special material, called desiccant to dry the compressed air. This desiccant is made of a material that attracts water, the water sticks to the surface of the desiccant. Every once in a while, the desiccant needs to be dried, or ‘regenerated’, to remove the water again.


A desiccant dryer is used where a higher quality (i.e. of that of a Fridge Dryer) of dry air is required.


How a Desiccant Dryer Works:

A desiccant dryer usually has two identical towers, filled with desiccant. One tower is used to dry the compressed air, while the other tower is regenerated.

Every once in a while (controlled by a central control unit) the dryer switches towers. The compressed air is now dried by the second tower, while the first tower, filled with wet, saturated desiccant is dried.

On most dryers, there is a small sight-glass. Behind the glass are small beads. This is not the drying-desiccant, but an indicator. It will change colour when the air the is too wet.

When the desiccant has done its job for some time, it has absorbed all the water from the compressed air and is saturated with water. It cannot hold any more water. In order to re-use the desiccant, the water needs to be elimated. This is called regeneration.

The regeneration process is done in one of the two towers of the air dryer, the one that is not operational. There are two ways the desiccant can be regenerated: by hot air or by dried compressed air.

With the hot air method, a separate system consisting of a fan with an electric heater is used to blow hot air through the desiccant to dry it. This is just normal air drawn from the compressor room.

Why use Line Filters in a Compressed Air System?

Liquid water and contaminants can damage the inside of pipes and other pneumatic components. Many pneumatic valves and cylinders contain small orifices that can easily get plugged with contamination.Matching the level of filtration used in the system to the quality of air required is the most cost effective and energy efficient option.

Three types of Compressor Line Filtration commonly used are:-

Particulate or General Purpose Filter

Help remove harmful liquid oil, water condensate, pipe scale, dirt and rust from a compressed air system.

Coalescing Filter / Oil Removal Filter

A Coalescing Filter aids remove of harmful oil aerosols by coalescing action.

Adsorber Filter / Vapour Removal Filter

This type of filter removes oil vapours, oily odours and solid particulates. Designed specifically for those application that will not tolerate the presence of oil vapours and associated odours.


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