The Importance of Prefilter Maintenance and Drainage

When it comes to proper desiccant dryer performance one of the most common culprits resulting in poor dew point performance, is lack of prefilter maintenance and/or faulty prefilter drain operation. Most oil coalescing prefilter elements should be replaced at 2000 hours of service. Without a disciplined PM schedule to replace these elements and to confirm proper prefilter bowl drain operation, you run the risk of contaminating the desiccant bed.

Manual drain valves on the bottom of these filters are often problematic when not drained in a timely fashion, allowing oil to re-entrain into the airstream, causing oil to enter the desiccant chamber. Float type drains (internal or external) must be checked for correct operation as they may become fouled with oil/water emulsion and fail to operate properly. Electronic solenoid auto drains complete with off/on settable timers are most favorable when used with a strainer, as they allow periodic draining to disperse oil/water into a dedicated collection container, keeping the element cleaner and extending its’ life period.

Zero loss drain systems are often oversold as an energy savings feature. These devices use collection pots to accumulate, then isolate and disperse liquids with no loss of compressed air. Often these drains are improperly sized for the application and still allow water to re-entrain into the air stream. Although they may have acceptable performance when used with refrigerant dryer systems, desiccant drying systems requiring very low dew points may be adversely affected by their installation. APPL does not recommend their use with desiccant air dryer installations..