What is cloud point and pour point

When oil cooled slowly, the temperature at which it appears hazy or cloudy is known as cloud point. The temperature at which oil stops flowing even after tilting the glass containing the oil under test to a horizontal position for 5 seconds is known as pour point.

Determination of cloud and pour point cloud pour points determined by pour point apparatus. the lubricating oil sample is filled (to a height of 2’’ to 2) in a flat bottom glass tube of 30 mm in diameter and 120mm in height. The tube is covered tightly by cork stopper. The glass tube is enclosed by air jacket the whole assembly is dipped in a freezing mixture. The freezing mixture depends on the working temperature range of the apparatus.

As the cooling takes place via air jacket the oil temperature falls. At every degree fall in temperature, the glass tube is momentarily removed from the air jacket and checked for any haziness and replaced immediately. The temperature at which haziness or cloudiness is noticed is reported as cloud point.
If the sample is cooled further, at particular temperature oil stops flowing even after tilting the jar to horizontal for 5seconds. This temperature is reported as pour point.

The significance of cloud and pour points

  • Cloud point is of more significance for fuel oils than lubricating oils.
  • Pour point is important for the lubricants used in low temperature.
  • If the high pour point of lubricant is used at low temperature then it would freeze jamming the machine parts.
  • The fluid film mechanism of lubrication will also fail.
  • Pour point is generally lower using depressants like polymethacrylates.

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