Temperature affects air compressor oil as well as performance!

When ambient air is compressed to do work for you, considerable heat of compression is released and this temperature affects air compressor oil as well as compressor performance. As an illustration, the heat of compression released from a 100 horsepower air compressor could heat 4 homes in the worst of winter. If not handled properly in the summer, this heat can become a killer.

What are the temperature affects on air compressor oil.

Excessive heat has a severe impact on most compressor oils. It is a well accepted rule
of thumb that oil life expectancy is reduced by half for every 10 degree rise above normal operating temperature.

The common physical characteristics of lubricants that are affected by temperature include viscosity, viscosity index, pour point and the base oil.

The viscosity of an oil is singularly the most important consideration when selecting a lubricant. And also the characteristic that temperature affects the most in air compressor oil performance.

When an oil film forms between a bearing and a shaft, some of the oil's molecules are attracted to the surface of the shaft, while other oil molecules are attracted to the bearing surface. This is called the shear rate and is directly affected by the oil's viscosity and operating temperatures.

Since oil with a lower viscosity and high potential shear rate must still maintain a sufficient oil film, it is quite apparent that as temperatures rise the temperature affects on the air compressor oil may become apparent and the oil film may fail and metal-to-metal contact may occur. If the oil's viscosity is too high with a low potential shear rate, the internal resistance to flow will increase the temperature dramatically, causing an overheated condition, which can also cause a breakdown of the oil film and may cause oxidation of the oil. Therefore, it is critical that oils be selected by always taking the operating temperature affects on the air compressor oil into account.

Going hand in hand with the viscosity of the oil, when considering the temperature affects on air compressor oil, is the viscosity index. Viscosity Index The viscosity index (VI) is the term used to describe the oil's "resistance to viscosity change as the temperature changes." For example, an oil that thins out significantly as its temperature increases is said to have a low VI. An oil whose viscosity does not change significantly as it is heated up is said to have a high VI.

This temperature/viscosity relationship is the most critical and important consideration when considering the temperature affects on air compressor oil that will be operated in temperatures that change dramatically.

Synthetic oils have particularly good performance across a wide range of operating temperatures, making them particularly good in controlling the temperature affects on air compressor oil. However, to protect from high acid numbers, loss of lubricity and increased viscosity, long oil change intervals must be monitored with frequent lube analysis, particularly when exposed to high ambient temperatures.

The base oil also has a major part to play in determining the performance of the oil under extreme temperature. Base Oil Mineral-based (non-synthetic) oils have various bases depending upon their molecular and chemical structure. Base oils can be paraffinic, naphthenic or aromatic, and the selection process should take into account the type of base oil.

For example, naphthenic base oils have low natural VIs and may be selected for equipment where extreme temperatures do not affect operation. On the other hand, paraffinic base oils have natural VIs that are considerably higher than naphthenic types, making them desirable base stocks for lubricants used in outdoor applications.

For extreme operating temperatures it is highly recommended that a synthetic oil be used; such as one chosen from Habot Synthetic Lubricants’ compressor oil range. These synthetic oils have low friction and good thermal conductivity therefore reducing operating temperatures by up to 20°C compared to traditional air compressor oil.

But it’s not only extremely high temperatures that affects air compressor oil; in extremely low temperature operation, the pour point is critical. Pour Point The pour point of is defined as the lowest temperature at which a lubricant will flow. It is frequently and erroneously used as the oil viscosity selection criteria.

For example, let's say an oil has a pour point of minus 30 degrees C. Most people assume that this means that the oil will flow to the bearings of the equipment even when the ambient temperature is at minus 30 degrees C. This is a fallacy. At best, this oil with a pour point of minus 30 degrees C and operating in an ambient temperature of minus 30 degrees C will merely churn at the oil pump until the churning causes an increase in the oil's temperature. This in turn allows the oil's viscosity to thin sufficiently so that it slowly begins to flow through the oil passages to the lubricated components.

These low temperature affects on air compressor oil can be disastrous!

To summarise the temperature affects on air compressor oil.

The affects of extreme temperatures on air compressor oil is pretty similar to those of any other oil:

• Change in viscosity – decreasing with an increase in temperature. 
• Oxidation of the oil under high temperature conditions. 
• Accelerated depletion of the additive package at high temperatures. 

All of these temperature affects on air compressor oil can be minimised by choosing a good synthetic air compressor lubricant.