Compressor Oil Contamination - Part II - 2012-04

Compressor Oil Contamination Part II - Prevention   

 

In Part I we noted two ways compressor lubrication failure can occur: Oil contamination and oil breakdown. Either of these can result in compressor failure even though the Net Oil Pressure of the system appears good. Here in Part II we will list steps you can take to help avoid these problems. 

Foreign Particles

Due to handling. 

Foreign material, solids, liquids, or gasses can be introduced when adding lubricant to the compressor or charging the refrigerant loop. Refrigerants are excellent degreasers and as such any contaminant in the refrigerant will eventually migrate to the compressor oil.

    • Fill the compressor crankcase from a known-good source of lubricant. Always use an oil specified by your service manual.
    • Use clean rags and fill from clean containers when adding lubricants.
    • Always use an oil pump to replace the oil, using good techniques such as making sure there is a solid hose of oil (no bubbles) from the pump.
    • Charge your refrigerant loop from a known-good source of gas.
    • If a refrigerant or lubricating loop must be opened, be sure it is protected from contamination and is clean when re-sealed.


Due to operation. 

No matter how well lubricated, it is a fact of life that moving parts wear and wear generates foreign particles. Periodic service, oil and filter changes, insure that the contaminants are removed before they can build up to a point of causing damage.

Common causes of contamination:

    • Chips from broken reed valves
    • Dirt from the casting process used for the compressor body, heads, and other cast iron components.
    • Moisture from the atmosphere.
    • Acid from chemicals in the atmosphere.
    • Air- Oxygen (oxidizer) and Nitrogen (non-condensable).


Due to sludge. 

Sludge is caused by chemical breakdown of the oil. Frequently this breakdown is due to operating temperatures which are higher than the oil rating, usually above 300 degrees F internal.

High temperature can be caused by:

    • High discharge temperatures
    • High compression ratio
    • Damaged reeds on the valve plate
    • Suction leaks
    • Reduced lubrication
    • Clearances which are less than the manufacturer's recommended tolerances.

Another source of sludge is moisture in the oil. Moisture can be from three sources: Contaminated oil or contamination during handling, suction leaks introducing air, or cooling loop leaks into either the refrigerant loop or the compressor crankcase.

To limit the creation of sludge:

    • Always use clean oil and fill carefully.
    • Continuously monitor for suction leaks.
    • Periodically sample your oil and check for moisture.

Chemical Breakdown

Caused by acids.

Acid formation is a significant cause of lubrication failure. There are two strong acids which may form when there is a refrigerant leak: Hydrochloric acid or hydrofluoric acid, depending upon the composition of the refrigerant. Suction leaks introduce air and the oxygen in the air reacts with the refrigerant under high temperature and high heat to form the acid. The acid attacks the copper piping of the refrigerant system causing corrosion and producing particulates of copper salts.

The copper particulates plate out onto the connecting rod bearing surfaces and also form sludge in the oil channels of the crank shaft. The sludge restricts the flow of oil while the copper plating on the bearing surfaces decreases clearances, and operating temperatures rise. Once this cycle begins it is an ever-accelerating breakdown of the oil due to high temperature.

Prevent this by continuously monitoring for refrigerant leaks.

 

Caused by moisture. 

As noted above, moisture has three primary sources and can be prevented by careful handling when filling the compressor crankcase, prevention of suction leaks, and maintaining a leak-free refrigerant cooling loop.

 

Caused by excessive temperatures. 
Too high an operating temperature can cause oil breakdown as well as sludge. The prevention is the same as noted above: Maintain correct clearances and always operate within the manufacturer's stated parameters.

 

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Tech Tips Home

These technical tips are for use by qualified maintenance personnel who are familiar with their specific freeze drying equipment. These tips are intended only as general guidelines. Lyophilization equipment is frequently custom configured and some tips may not be appropriate for all freeze dryers. Always read and follow the directions of your equipment's maintenance manual. If you would like to discuss one of our tech tips, please contact Dave Clayton at 215-672-7800 ext-1376.


 

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