By Ron Marshall
Recently, a reader wrote in with this question …
I’m the sole maintenance technician for a distribution facility. We have a compressed air system that involves two reciprocating compressors (20 years old), alternated in use every three months, with the other kept in reserve for emergency backup. Both are connected to a refrigerated dryer that uses a separation bowl with a float valve for draining the moisture. They are shut down properly each night and I start them up each morning.
Recently the dryer’s drain suddenly started venting considerable air and spitting ice. I’ve replaced the float valve assembly (twice), bowl and all the internal parts and gaskets. Still, the drain keeps venting air after about 4-5 hours into operation. I’ve shut off the air to the dryer and drained the system — and sometimes the valve will shut and sometimes not. At this time, the loss of air is a hindrance to operations and production so I can’t do it often or for long.
We’ve had the dryer refrigeration checked and it was found to be 11-lb low on freon, which they filled and checked the rest. We’ve added our dryer to their PM list. I’ve been told the problem could be caused by a freon leak which will be checked next PM date.
What would cause an issue with the drain?
So, it looks like you have a problem with the air dryer and/or drain. The temperature at any point should not be getting low enough to form ice anywhere. Because you had to refill your dryer refrigerant, there is likely a refrigeration leak. Low refrigerant pressure can cause icing. Systems with reciprocating compressors are hard on air dryers, due to the pulsations produced and the high temperatures involved — so don’t expect very long life.
Your condensate drains should not be blasting excessively; if it is a float drain, then minimal air should be released. It sounds like a replacement is needed.
It might be time for a new dryer. If so, be sure to install one that is compatible with reciprocating compressors (usually a high temperature variety) and ensure it is sized large enough for worst case temperatures and flows. If you are located in a hot and humid environment, then oversizing may be required to ensure good dew point, or the installation of secondary coolers to reduce inlet air temperature. The lower the temperature, the less moisture needs to be removed by the dryer. Dryer manufacturers can help with selecting new equipment.
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