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Maintenance for air treatment components, part 1: Refrigerated Dryers

Compressed air dryers are indispensable in most commercial and industrial compressed air systems, as they remove moisture that can increase maintenance and downtime in production equipment and possibly ruin products.

In the first part of this two-part blog post we’ll take a look at maintenance components in Refrigerated Dryers. In part 2 we will look at Desiccant Dryers.​

Refrigerated dryers are the most commonly used dryer type. They remove water from compressed air by cooling it so that the water vapor condenses and can be easily separated. They are fairly simple and very reliable, with relatively few service points. A refrigerated dryer consists of heat exchangers, a refrigeration system, a separator/drain, and a control system.

 

Heat exchangers

Heat exchangers, like the condenser and evaporator of the refrigeration circuit, can have reduced heat transfer capacity if they are contaminated. When contaminated, the condenser gets clogged causing less efficient cooling of the refrigerant, while a clogged evaporator may cause excessive pressure drop across the dryer.

  • For the condenser, when it operates less efficiently, the refrigerant doesn’t get cooled as much and will cause higher refrigerant temperatures, and thus lower evaporator temperatures and higher compressed air dew point. To prevent this, periodically clean the fins with compressed air or a bristle brush. If using compressed air, be sure to direct the air stream in a way that blows it out rather than deeper into the cooling fins. If using a brush, make sure it is soft enough not to bend or damage the fins of the heat exchanger.
  • Evaporator contamination may be more difficult to spot since a visual check can’t really be done. Checking the differential pressure across the dryer would help indicate this. If the pressure drop is abnormally high, then that may mean there’s a blockage in the evaporator. Cleaning the blockage is difficult, but it does show that a filter before the dryer will be needed.

Refrigerant

  • Check the dryer temperature. There’s usually a green/red or green/yellow/red indicator. If in yellow/red, it's telling you that the evaporator temperature and thus the dew point of the compressed air is elevated, and indicates: 1) there is a problem in the refrigeration circuit, 2) the room temperature or compressed air temperature is too high, 3) the flow through the dryer exceeds its designed operating conditions, or 4) a combination of these. Regardless of the reason, the dryer is not drying the air to specification. 
  • Checking the refrigerant circuit requires the services of a qualified technician certified to work with refrigerants, but before calling them in, you can check 2 and 3 yourself. Hang a thermometer in the room or use an infrared thermometer. The infrared device can also be used on the piping to check the compressed air temperature going into the dryer (the temperature of the air in the pipe could be hotter than the pipe surface temperature).  Also check your compressor specs to see how much volume is going into the dryer.  If the room temperature is 100°F or less and the dryer is not being overfed, call for a service technician. 
  • Another maintenance checkpoint would be to spot leaks in the refrigeration circuit. This is usually done by a soap bubble test, or by using ultrasonic and infrared leak detectors. Leaks can appear very small at first and won’t affect the refrigeration system, but over time, when the system loses more refrigerant, operational problems will arise. 

Separator/drain

Because refrigerated dryers chill and condense water vapor into liquid water, it is vital that the drain valve is working properly to remove the condensate from the separator.  Otherwise, it may simply be carried downstream with compressed air. On average a 100-cfm dryer generates about 6 gallons of condensate during a 3-shift operation, so it’s important to discharge it reliably. Drains should be checked periodically and serviced at least annually.  

  • Check separator and drain function regularly by testing the drain for condensate removal. There are several types of drain mechanisms and some are more vulnerable to clogging than others.  Some drains have test buttons to help check their function. Though mostly water, condensate may have oils and particulates that can build up and interfere with the drain mechanism.
  • If there is a strainer to trap debris, it should be opened and cleaned out. If they are heavily contaminated, it could indicate that the drain mechanism needs attention.
  • The drain supplier can provide a maintenance kit to replace the serviceable parts of the drain. This is usually a simple task.   

Controls

For most refrigerated dryers the controls are very reliable and typically do not need much attention; however, it would be worthwhile to periodically check that the controller readings, settings, setpoints, and alarms are correct. 

 

Choose HPC KAESER for your compressed air needs

HPC and its Authorised Distributors are experienced and qualified to design, install, and tailor the compressed air system to meet your individual requirements while maximising efficiency. Peace of mind is also provided that all work will be in accordance with HPC guidelines and current legislation.

HPC and its Authorised Distributors are also able to offer a variety of service plan options tailored to your needs. Get in touch to speak to an experienced and knowledgeable HPC KAESER trained engineer about your compressed air needs. 

 

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