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DHD Trouble Shooting Guide
Click-on a symptom from the chart and you will be moved to information on suspect items or components and recommended solutions. Solutions to process drying problems are presented in each column below as a "most likely” cause. These are ranked by numeral; the lowest being the most likely cause.
For example: under the Column - Low Air Flow, the Blower Rotation isindicated as the most likely cause.

Problem
Valves Blower Rotation Process Blower Amps Regeneration Blower Amps Cooling Coil High Return Temperature Regeneration Filter Process Filter Regeneration Air Flow Desiccant Air Leaks Pressure at Hopper Air Oulet Vacuum at Hopper Air Inlet Plugged Hopper Regeneration Heater Amps Process Heater Amps Process Air Damper Dewpoint Instrument

High Dewpoint 3Low Air Flow 6 1 4

High Air Flow

Over Temp 6 1

Under Temp

Solution
1

8 5 4 7 2 6 9 2 10 9 7 9 3 8 5 3 1 2 3 4 1 8 3 2 7 2 5

Dewpoint Instrument | Back to Selection Chart The Dewpoint Instrument uses air flow from the dryer to detect the dewpoint of the air leaving the drying system. A reading of -40ºF is typically considered optimum. Over time the sensor in the dewpointinstrument may become contaminated or connections may loosen. Operation should be checked against another instrument to confirm actual dewpoint

If the instrument is faulty you should test to determine the cause: faulty mechanical connection, faulty or contaminated sensor, faulty cable or faulty dewpoint board. All of these tests are simple to perform. To perform a dewpoint instrument test: 1. Checksample cell for positive air flow. If no positive air flow check the lines going to the instrument. 2. Test sensor by placing in ambient and view readings - should climb to 0º or higher. 3. Test cable by unplugging from sensor and view reading - should drop to -40ºF or lower. 4. Test dewpoint board by removing cable from board and view reading - should drop to -40ºF or lower. Repair or replacecomponents are required.

Air Leaks | Back to Selection Chart Leaks must be detected and repaired or hoses replaced as these leaks allow ambient (wet) air into the drying system, having a significant impact on drying efficiency. Some of the problems associated with air leaks are High Dewpoints, Low Air Flow through the drying system and Low Process Temperatures detected at the hopper. Some systemscan be hard piped to eliminate the chance of flexible hose leakage. Over time flexible dryer hose may develop pin hole air leaks. Also mechanical connections may loosen with vibration over time. Check mechanical fasteners. Tighten as required and then check hose for physical leaks. If leaks are detected the hose should be replaced.

Valves | Back to Selection Chart Four-way valves channel theprocess and reactivation air flows to the appropriate desiccant beds. If the air flow is not directed to the appropriate bed the drying system can be adversely affected. Some of the problems associated with misaligned valves are: - High Dewpoints as moist regeneration air enters the process air system. - Low Air Flow through the system as the process air fights against the regeneration air. - HighProcess Temperatures at the hopper as regeneration air at 600ºF is misdirected into the process air stream Wiper blades should cover the duct ports inside the valve housing and position themselves on the valve seats at the end of the valve motor stroke. The two valves are controlled by the single valve actuator motor which simultaneously positions the wipers in positions parallel to one another. Toperform DHD valve leakage test. 1. Set dryer control to 32ºF. 2. Note position of valve. Approximate position of wiper blades on the shafts is indicated by notches in one

end of each valve shaft. 3. Cycle the dryer to point where the Regeneration Blower is off. Check at the regeneration outlet for either positive air flow or vacuum. Either indicates leakage past the valve wipers. 4. If you...
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