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Why Air Dryers are Obsolete

Air Dryer Problems

Loadcraft (8 axle) Mobile Oil Rig Utilizing ClearDrain
(Fully Extended to Its 110' Height)

In a typical engineered air brake system the wet tank is sized to provide 75-78% efficiency (water removal with manual draining once per day) based upon anticipated air usage and external environmental conditions.  This anticipated usage is based on compressor size and an average number of brake applications with approximately 36% relative humidity & approximately 76 degrees F.  When compressors run longer periods of time (i.e. solid-waste vehicles, dump trucks, buses, etc.) they will pump more moisture with the air.  Wet tanks work on the law of physics known as the ideal gas laws.  Simply stated, when compressed air is allowed to expand it will drop in pressure.  This pressure drop will result in a commensurate drop in temperature, thereby condensation will occur.  Excessive brake application, short cycle times and wet tank being too small are among the primary reasons leading to too much residual moisture.  Consider also that the airflow from an air dryer will always be considerably warmer than the cooler environment of the wet tank where air constantly circulating over its outer metal surface creates ideal conditions for oil and water vapor to expand and thereby recondense into droplets, which will then accumulate.

  
Questions about Air Dryers

Questions:

Why does oil get beyond the air dryer and into brake valves?
Why do the air tanks have water in them even with an air dryer installed?
Why do air dryer purge valves constantly leak air?
Why must I frequently replace desiccant canisters?
Why does build-up to maximum air pressure take longer than usual?
What causes premature air compressor break down?
What causes carbon build-up in the discharge line of air compressor?
How can an air dryer malfunction cause a vehicle breakdown?

Answers:

Why does oil get beyond the air dryer and into brake valves?
When the discharge temperature of the air compressor becomes excessive the lubricating oil from the compressor breaks down molecularly into a vapor.  This vapor floats on the air stream, can coat the desiccant pellets and is not filtered out of the air stream by the dryer.  When the temperature of the compressed air cools, the gaseous vapor reverts to droplets of oil.  These droplets can contaminate the sensitive air valves downstream of the dryer.  Some oil additives cannot be absorbed by desiccant and when mixed with moisture, high air temperature and pressure can become caustic acids in the brake system.  Also, most valves are lubricated by the manufacturer with specific lubricants that provide longevity to the valves.  Oil from the compressor tends to wash these lubricants from the valves sending the lubricants through the air system where they pick up additional contaminants.  These contaminants ultimately get deposited into seals and seating surfaces, which reduce the life of the component.  In some instances the lubricant washed out by the compressor oil is essential for the proper operation of the valve(s) affected.

The ClearDrain System avoids most, if not all, of these problems.

Excessive High Temperatures Can Be Caused By the Following:

  • Desiccant saturated by carbon and oil which results in flow restriction and the air compressor's becoming overworked.
  • Discharge volume from the air compressor is too small for the vehicle’s application.
  • Purge valve of air dryer leaking due to carbon and oil contamination.
  • Leaks within the air brake system.
  • Faulty governor valve due to carbon and oil contamination.
  • Leaking intake valve from the air compressor.
  • Other air system leaks.

All of the above listed items can cause an air compressor to overwork its specific duty cycle by 25-30% (loaded) and 70-75% (unloaded).  Overworking an air compressor results in costly maintenance and vehicle downtime.
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Why do the air tanks have water in them even with an air dryer installed?


In due course of operation the desiccant beads in the dryer become coated and/or saturated with carbon and oil contaminates thereby preventing the desiccant from absorbing water vapor and moisture.

Additional Causes For Water To Become Present In Air Tanks

  • Discharge temperature of the air compressor is too high.
  • Discharge volume from the air compressor is too small for the vehicle’s application thus causing high temperatures and extended load times.
  • Capacity of the air dryer is too small for the vehicle’s application.
  • Purge valve of air dryer leaking due to carbon and oil contamination.
  • Purge cycle of air dryer is cut short due to high air consumption of vehicle.
  • Warm air recondenses in the cooler environment of the wet tank.

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Why do air dryer purge valves constantly leak air?

Contaminated purge valves leak due to carbon and oil particles.  The carbon particles can prevent the correct sealing of the purge valve.

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Why must I frequently replace desiccant canisters?

Desiccant canisters are usually replaced when significant amounts of water are found to be in the air tanks.  Desiccant is coated with oil and carbon.  Desiccant longevity is determined by the amount of contamination filtered from the air system.
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Why does build-up to maximum air pressure take longer than usual?


Desiccant saturated with carbon and oil causes a restriction, thereby resulting in longer periods to build to maximum air pressure.

Additional Causes of  Delayed Air Pressure Build-Up Time

  • Discharge air line of compressor blocked by carbon deposits.
  • Purge valve leaking.
  • Leaking intake valve from the air compressor.
  • Governor valve is faulty.
  • Air compressor discharge volume is limited by the air dryer’s capacity.  When the compressor discharge volume is much larger for the dryer it generates an increased pressure drop or restriction.

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What causes premature air compressor break down?

A dryer saturated with contamination causes a restriction thereby creating a greater demand and workload for the compressor ultimately resulting in premature break down.

Additional Contributions To Air Compressor Failure

  • An air compressor that becomes over-worked.
  • Excessive discharge temperature from the air compressor.
  • Purge valve leaking on dryer.
  • Discharge volume of compressor too small for vehicle application.
  • Discharge air line from compressor blocked by carbon deposits.

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What causes carbon build-up in the discharge line of air compressor?

High air temperature and pressure turns oil vapor and droplets into carbon deposits.  The combination of carbon particles and oil droplets saturate the desiccant in the dryer causing restricted airflow.  The greater the build-up the greater the restriction in the discharge line of the air compressor.
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How can an air dryer malfunction cause a vehicle breakdown?

Carbon deposits in the purge valve of the dryer could cause the purge valve to constantly vent to the atmosphere.  A jammed purge valve can cause air starvation to the brake system thereby triggering activation of the spring brakes and the vehicle becomes inoperable.
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 The ClearDrain System avoids most, if not all, of these problems.

  
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