Refrigerated Air Dryers
Refrigerated dryers cool the compressed air to 4 °C. If you go lower than 4°C, the water condensate will freeze inside the pipes and block the flow. It takes much more cooling capacity to cool water than compressed air. This is why you put a cyclonic inline filter with an automatic moisture drain before the refrigerated dryer. This is to get rid of all the condensate before it enters the dryer.
The dryer cools the compressed air to 4°C and put it through its built-in cyclonic inline filter with an automatic drain. The dew point of the compressed air after this filter will be 4°C under the specific pressure, through the dryer. It is normal practice to put an after filter after the dryer as a safety element, to take odors from the compressed air.
Desiccant Air Dryers or Heatless Dryers
Desiccant dryers or heatless dryers work on the principle where desiccant crystals absorb the moisture. These crystals always want to adapt to their environment. If the environment is wet, it absorbs moisture to also become wet. If the environment is dry, the crystals give off moisture and also become dry. These dryers consist of two chambers.
One chamber is absorbing the moisture under pressure while it purges approximately 15 % to 20 % of its dry air, through the other chamber. This second chamber is without pressure and the air is purging out the bottom with the moisture. After the second chamber is dried, it switches chambers and the process starts from the beginning again. These absorption dryers also work with pre and after filters for the same reasons as the refrigerated dryers.
Absorption dryers can dry compressed air to a dew point of less than -60 °C under pressure.
What is the function of an Air Dryer?
When atmospheric air is compressed, the dew point goes up. The higher the pressure the less water the air can carry and water start to condense from the air. Once you cool this air, more water will condense from it.
Water is non-compressable. The pneumatic valves and cylinders work on the elasticity of the compressed air. If water enters the valves and cylinders, it reacts like a solid non-forgiving obstacle and just break the seals and other parts.
In-line Cyclonic filter/ Water trap:
If you put an inline cyclonic filter in the compressed airline, it will take most of the water droplets from the compressed air, but the air will still be saturated, at that pressure and temperature, after the filter. The moment this air cools further, more condensation will take place.
Please note, if you only feed a stream of water to the cyclonic filter, this filter cannot create air to send down the line and the water will run straight through this filter. This type of filter can only take out small droplets of water. This is why your airlines must always run with a slope, to prevent water to build up in the lower parts of the airline and form a pocket of water down your airline.
Why you should buy the correct air dryer for your application.
When air is compressed, the dew point becomes higher and water starts to condense in the system. Water is non-compressible and causes damage to most pneumatic systems. It is very important to get this water out of your compressed air.
How do you select the correct Air Dryer?
The air dryer must be sized correctly. If the air dryer is too small, you may flood the dryer and water moisture will still go through to your application. You can install an energy-efficient air dryer for one application in your factory or you can install it to dry all the compressed air being used in the factory.
If you size it for the one application, you must know the air consumption of this application. Go to Tools on this web site and calculate the air consumption (litre/min). If you want to dry all the compressed air of the factory, you must know the air compressor’s output. Go to Tools on this web site and calculate the air delivery of the compressor(s). Airpower can calculate it from the total compressor kW.
All dryers must have a pre-filter with an automatic drain. The water drained before the compressed air enters the air dryer reduces the load on the dryer. Air Dryers, such as membrane air dryers, are designed to have a maximum air inlet temperature of 40 °C. If you can keep your hand indefinitely on the inlet pipe, the temperature is fine. If not, you will need an aftercooler between your compressor and your dryer.
Refrigerated air dryers from 750 liters/min up to 6500 liter/min ex-stock. Larger ex overseas. Dew point 4°C under pressure. Automatic drain pre and manual drain after filters.
Screw compressors have no valves or other mechanical forces to cause imbalances unlike piston compressors.
Airpower keeps universal spare parts for compressors. Pressure switches, non return valves and safety valves are universal to all compressors. Bottom entry filters/ regulators, electric motors and starters can be used for many makes of compressors.