Oil is used as lubrication, helping to reduce the friction between the components in the pump of an air compressor. It seals the compressor from gas leaks and helps manage temperature during operation. Less heat from friction means less energy is consumed and a longer machine life is achieved. Monitoring and managing lubricant viscosity can prevent costly breakdowns and plays a role in energy efficiency.

What is oil viscosity?

Viscosity refers to an oil’s resistance to flow/shear. It decreases (thins) with increasing temperature and increases (thickens) with decreasing temperature. An oil’s viscosity is determined by measuring the time (in seconds) required for a fixed volume to flow a known distance (by gravity) through a capillary within a calibrated viscometer (an instrument for measuring the viscosity of liquids) at a closely controlled temperature. Viscosity is reported in a unit called the centistoke (cSt). The viscosity of an oil is the first and most important consideration when selecting an oil for a specific application. The viscosity must conform to the speed, load and temperature conditions of the lubricated parts.

What is the viscosity index?

Some oils contain the ability to resist changes in viscosity due to a change in temperature. This property is referred to as the oil’s viscosity index or VI. The higher the VI, the less the oil’s viscosity is altered by temperature changes and the better the protection provided at higher temperatures. The lower the VI, the greater the change of viscosity of the oil with temperature fluctuations. 

Why is oil viscosity important?

  • when oil viscosity goes out of spec, compressor bearings begin to fail, causing wear on the rotor assembly
  • loss of proper lubrication leads to production downtime/loss of revenue
  • loss of proper lubrication leads to high repair costs
  • proper oil viscosity reduces energy use
  • viscosity governs the sealing effects of oils and the rate of oil consumption
  • oil viscosity determines the ease with which machines are started and/or operated under varying temperature conditions
  • proper oil viscosity increases the life of a compressor


What factors affect oil viscosity?

Many factors affect oil viscosity:

  • Oxidation occurs when churning oil foams, exposing more oil to surface air and causing oxidation. This lowers viscosity and threatens useful lubricant life.
  • Dilution results when lubricant oil is diluted with gas (such as methane) decreasing viscosity.
  • Bubbles form as foaming oil churns against the screws or vanes of the compressor, dropping the viscosity of the oil.
  • Contamination occurs when hydrocarbon vapours in the process mix with the oil.
  • Significant temperature changes (typically at start-up) affect the viscosity of the oil 


How can you protect your compressor and ensure good performance?

Monitoring and managing lubricant viscosity can prevent costly breakdowns due to bearing failure. Refineries commonly perform monthly lab checks but these checks are insufficient to prevent bearing failure and subsequent plant downtime. Protect your compressor(s) by adding in-line oil viscometers to all new and existing units. In-line viscosity monitoring provides plant operations with real-time data on the lubricant viscosity. This saves lab and technician time and reduces the chance of damaging equipment. 

While the goal is a lubricant with a long and useful life, harsh environments, contaminants and even humidity in a refinery’s external environment can greatly reduce lube oil’s useable lifespan. Monitoring lube oil viscosity is the best way to prevent bearing wear and compressor failure. 


Experiencing wear and tear on your compressor? Gaspro’s qualified service technicians inspect and service all our compressor units. We offer “Same Day Service” to ensure optimum run time and efficiency for all our clients. Our fully stocked service trucks handle all our client’s needs and our focused team takes pride in their work. We strive to provide dependable products and prompt service to all clients. We’re continually improving and innovating our products to meet changing industry demands. Gaspro is a leading provider of compressor packages in Canada. Contact us to request a proposal. Call 403-443-8886 or email us at clint.praski@gaspro.ca.