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What Causes the Dewpoint to Spike on your Air Compressor?

The simple answer, dewpoint is the temperature at which condensation begins to form. The longer answer is dewpoint is the temperature at which water vapor in your compressed air is no longer vapor, and changes to a liquid form (condensation). As your compressor is compressing air, the stored air can become very warm, meaning that it contains a lot of water vapor. As the air cools down, that vapor will turn to condensation. If enough condensation forms, you now have free-flowing water through your air lines. Having water in your compressed air is never a good thing, and depending on the application, it can become catastrophic.

What Causes Dewpoint to Spike?

Dewpoint readings can help diagnose several problems, so monitor the drying-air dewpoint throughout an entire dryer cycle.

Below are a few reasons to consider when your dryers' dewpoint spikes:

- Dirty Heat Exchanger

- Failed Cooling Fan

- Overloading the dryer either by high inlet temperature, high ambient temperature or low pressure

- Faulty drain valve

- Failed pre-filters

- Ambient air is leaking into the closed-loop circuit and causing premature loading of the desiccant.

- Totally inactive regeneration circuit or badly contaminated desiccant (or loss of refrigerant)

- Operate the dryer in a clean, temperature controlled, dry indoor area with minimum outlet piping to avoid back pressure on the purge line.

Dewpoint Demand Control (DPD)

The Dewpoint Demand control is an energy saver that can extend the drying cycle without purging, during periods of lower moisture loads. The Dewpoint Demand system offers, in one compact package, the utmost in flexibility and accuracy sensing the actual dewpoint of the outlet air. The hygrometer senses the dewpoint at the outlet of the dryer at the end of the drying cycle, and extends the drying cycle until the preset adjustable dewpoint setpoint is reached. During this extended drying cycle, the purge valves are closed and the opposite tower is pressurized and prepared for the drying cycle. The dewpoint demand option reduces purge loss and extends valve life. This option consists of the following:

• Digital Dewpoint Display • Adjustable Setpoints • High Humidity Alarm Light with Dry Contact

Calibration:To maintain accuracy, the probe should be recalibrated annually. Recalibrated probes are available through your local distributor.

Probe Replacement: Isolate and depressurize the probe chamber. Disconnect the sensor cable from the sensor. Remove, and replace the probe. Pressurize the probe chamber and connect the sensor cable. A small amount of sample air (approximately 2-10 SCFH) should expel out the chamber needle valve.

Jim Phillis

You ask, we answer. Visit our Expert Corner for every #CPTechThursday to find answers to common industry questions and highlights of CP's high-quality compressors. We love providing our customers with answers to their technical questions.

Jim Phillis , Technical Support Chicago Pneumatic

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