1. Monograde or Multigrade
The most important factor one should consider when choosing a hydraulic fluid is the viscosity. If the grade of the viscosity does not match the temperature range of the operating hydraulic system then other properties, no matter how good, are useless. In this case, the maximum life of the component will not be reached. Here are some of the variables that needs to be considered when determining the correct viscosity of the hydraulic fluid:
- Determine the starting viscosity given the ambient temperature is at minimum
- The maximum operating temperature to be expected considering the maximum ambient temperature
- Determine the permissible and optimum range of the component’s viscosity
Multigrade oil is used when the system needs a constant velocity within a wide range of operating temperature. It will be most likely used if the hydraulic system needs to operate in winter where the temperature is freezing and during summer season.
The optimum range is around 25 to 36 centistokes. If the viscosity of the fluid can be maintained at such level then the hydraulic systems’ overall efficiency is maximized, meaning input power lost to heat is reduced. In this case, multigrade oil can benefit the hydraulic system by reducing its power consumption. When used in mobile hydraulic equipment, this could mean fuel consumption will be reduced.
There are negative effects on the air separation properties when using the multigrade fluid which is not good especially for mobile hydraulic systems because they have a small reservoir.
It is not ideal to use multigrade oil if the hydraulic system is operating in a narrow temperature range. If it is able to achieve optimum fluid viscosity with monograde then it should use monograde rather than multigrade to avoid any negative effects.
2. Detergent or No Detergent
There are some types of antiwear hydraulic fluids that has detergents and dispersants in the component, These types are approved by components manufacturers for hydraulic systems.
Detergent oils have the ability to suspend and disperse contaminants which means the components are free from debris. The downside is that these contaminants need to be filtered out. Use of detergent oils is ideal for mobile hydraulic systems because of the small volume it contains.
3. Antiwear or No Antiwear
Antiwear are mostly used when constant lubrication is desired. The problem with antiwear additives is that it breaks down metal chemically and reduces the filtering property. There are some antiwear additives that have overcome this negative effect which makes antiwear an essential additive especially to hydraulic systems that require high pressure and performance.
If unsure, it is safe to use the hydraulic oil recommended by the hydraulic systems’ manufacturer. Though there are cases where in some specific application, choosing another type of hydraulic fluid can result to an increase in performance and reliability of the hydraulic system.