What to know about hydraulic lubricants

What criteria is typically used to select a hydraulic lubricant for use?

The choice of a hydraulic lubricant should take into account the following parameters:

• OEM requirements

• Appropriate viscosity

• Is a high VI required?

• Anti-wear properties (FZG level should be indicated)

• In service fluid behavioral needs: shear stability, foaming properties, demulsibility.

What additional properties could be important for hydraulic oil in specific environments?

For some specific applications, the hydraulic oil must have certain additional properties.

• Low flammability. In order to limit the risk of fire, certain applications (steelworks, mines, etc.) require the use of fire resistant fluids.

• Suitability for incidental food contact. For the food and pharmaceutical industrial oils “suitable for incidental food contact” may be required.

• Biodegradability. For applications in which the oil may be in contact with the environment, biodegradable lubricants can be proposed, in order to limit the impact on the environment.

What are the important characteristics for hydraulic lubricants in service?

• Viscosity Index (VI)

• The influence of air and water on the hydraulic oil properties Shear stability: Addition of a viscosity index improver (VII) enables a widening of the functioning temperature ranges of hydraulic fluids by altering the viscosity at higher temperatures. However, there is a variety of VIIs which have different shear stabilities. VIIs are polymers (long carbon chains) which may be cut into smaller chains when subjected to shear. When this occurs to significant levels, the viscosity index is reduced and the operating viscosity may no longer be suitable for the operation. The use of VIIs with good shear stability is required for optimal performance in use.

Fluid behavior when subjected to air and water: Air and water acts as pollutants for hydraulic fluids. Their presence increases the fluid’s compressibility, which leads to reduced precision in the transmission of the force and/or movement. In addition, they may cause breakdowns in the oil film and reduce the duty life of the operating oil. The properties enabling separation of the oil with these pollutants are crucial. Foaming and Air release properties are important indicators of interaction with air. Demulsibility indicates the degree of interaction with water.

SOURCE | SHUTTERSTOCK / EZIU

What is the right viscosity for a hydraulic lubricant?

Viscosity of hydraulic oil is one of the most critical properties. The right viscosity: Hydraulic equipment functions in a defined viscosity range. It is therefore important to supply a hydraulic oil of the right viscosity in order to guarantee optimum functioning of the installation.

Insufficient viscosity leads to breakdowns in the oil film, and therefore, wearing on the moving parts. Consequently, losses are increased. On the other hand, an excessive viscosity has a negative impact on efficiency, heat exchanges and may lead to cavitations phenomena in pumps.Note: the impact of pressure on viscosity should not be forgotten (viscosity increases with experienced pressure).

High viscosity index - for applications over a wide temperature range: For the application in various climatic conditions, it is important to guarantee an appropriate viscosity over the whole temperature range, hence the importance of the viscosity index for these applications.

The higher the viscosity index, the lower the variation in viscosity in relation to temperature. A high viscosity index enables proper functioning over a much wider temperature range. .

These questions were provided by TotalEnergies Marketing South Africa.