Several demands are placed on hydraulic fluids systems and these demands continuously change as the hydraulic industry is constantly evolving. The industry requires higher efficiency and speed to operate in extreme pressure and temperature. Hydraulic fluids selection would primarily require a good understanding of the characteristics of the fluid. The characteristics of an ideal fluid are as follows:
- hydrolytic stability
- long life
- thermal stability
- constant viscosity despite the differences in temperature
- high anti-wear ability
- water proof
- low chemical corrosiveness
- comparatively low cost
- Type of pumps that will be used
- degree of operating temperatures in the system
- operating pressures
- loads to be encountered by different components
- operating cycle
- characteristic of control and power valves
- The fluid’s viscosity requirements are being determined by the minimum and the maximum temperatures in the hydraulic system. The system’s load is also considered in the equation. The hydraulic fluid should be able to maintain a level of viscosity at a very high temperature. One must also be careful that the hydraulic fluid should not be so viscous when the temperature is very low because the fluid may not anymore be pumped.
- Foams should be eliminated in hydraulic systems since this will corrupt the performance of the system. Foam will be prevented by getting rid of air leaks in the system. Despite measures to prevent air leaks, there are still two general types of foam that frequently occur. Surface foam which usually happens on the surface of a reservoir. Among the types of foam, the surface foam is easier to eliminate. This can be done through defoaming additives and at the same time thru a proper sump design in order for the foam to enter the sump and will be dissipated.
- Entrained air. Entrained air is a more complicated problem in that the foam is already drawn towards the system. In extreme cases, the problem will lead to cavitation which is a hammering action that will destroy hydraulic parts. This type of foaming is prevented by selecting the proper additives and the most efficient base oil. A reminder that needs to be taken into account is that there are some anti-foam agents that when used at very high concentration in order to reduce surface foam will back fire and instead increase entrained air.