In hydraulic circuits, experts use fluids as power transmission elements that also serve to lubricate, cool and seal clearances between elements. The lubrication and cooling capacity of hydraulic fluids such as oil are the most important characteristics for avoid wear between moving parts.
Index
Viscosity in hydraulic oils
Another of the most important characteristics when selecting the hydraulic fluid is the viscosity, which should always be interpreted in relation to the temperature and pressure of the application. Low viscosity oils are used in high speed and low temperature applications. High viscosity oils, on the other hand, are suitable for low speed and high temperature applications.
The viscosity index (IV) is a parameter calculated from the change in viscosity versus temperature. The higher the index, the smaller the change in viscosity versus temperature. If the viscosity is strongly altered by sudden changes in temperature, it can cause problems in the operation of the system.
In the following table, we show the viscosity behavior with respect to temperature of different hydraulic oils.
Types of hydraulic oils
Hydraulic oils are divided into three main groups according to Tables 2 and 3. mineral oils the use of pressure fluids is becoming more and more common. “anti-pollutants” o biodegradable, which in turn are classified into vegetable oil-based pressure fluids (HETG), polyglycol liquids (HEPG), and synthetic ester liquids (HEEG).
- Mineral oil-based hydraulic fluids
- Hardly flammable liquids
Precautions with the use of hydraulic oils
- Impurities in the hydraulic circuits: Hydraulic oils can be contaminated with particles such as sand, metallic particles and even products resulting from the oxidation of the oil itself due to aging. It is essential to include a filter in the hydraulic circuit to remove impurities and avoid alterations in the operation of the seal and the rest of the system elements. As soon as particles appear below the sealing edge, the seal will fail.
- Presence of air inside the oil: All hydraulic fluids contain dissolved air. It is only when the pressure drops that the air dissolved in the fluid is released, causing bubbles that could accumulate in the free spaces not occupied by the seals. With a sudden increase in pressure, the oil-air mixture overheats, which could lead to ignition by compression. If this effect, called “Diesel”, is repeated with a certain frequency, it leads to the destruction of the seal.
We are experts in hydraulic systems and we will advise you on the compatibility of the elastomer seal with any hydraulic fluid. In addition, we provide you with a link to our compatibility or chemical inertness table that will allow you to check the compatibility of elastomers at a generic level. However, please note that this table should be taken as a general selection. Only a test in real working conditions can give the certainty of the good behavior of a given compound or formulation.
In case of doubt, you can contact us for any clarification and we will advise you accordingly. Consult our chemical inertia tables.